Patent Publication Number: US-2023136710-A1

Title: Systems and methods for harvesting images for vehicle navigation

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority of U.S. Provisional Application No. 63/274,194, filed Nov. 1, 2021. The foregoing application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates generally to vehicle navigation. 
     Background Information 
     As technology continues to advance, the goal of a fully autonomous vehicle that is capable of navigating on roadways is on the horizon. Autonomous vehicles may need to take into account a variety of factors and make appropriate decisions based on those factors to safely and accurately reach an intended destination. For example, an autonomous vehicle may need to process and interpret visual information (e.g., information captured from a camera) and may also use information obtained from other sources (e.g., from a GPS device, a speed sensor, an accelerometer, a suspension sensor, etc.). At the same time, in order to navigate to a destination, an autonomous vehicle may also need to identify its location within a particular roadway (e.g., a specific lane within a multi-lane road), navigate alongside other vehicles, avoid obstacles and pedestrians, observe traffic signals and signs, and travel from one road to another road at appropriate intersections or interchanges. Harnessing and interpreting vast volumes of information collected by an autonomous vehicle as the vehicle travels to its destination poses a multitude of design challenges. The sheer quantity of data (e.g., captured image data, map data, GPS data, sensor data, etc.) that an autonomous vehicle may need to analyze, access, and/or store poses challenges that can in fact limit or even adversely affect autonomous navigation. Furthermore, if an autonomous vehicle relies on traditional mapping technology to navigate, the sheer volume of data needed to store and update the map poses daunting challenges. 
     SUMMARY 
     Embodiments consistent with the present disclosure provide systems and methods for vehicle navigation. 
     In an embodiment, a system for enriching a navigational map using previously captured images may include at least one processor. The at least one processor may be programmed to receive at least one image, the at least one image having been captured by a camera of a vehicle from an environment of the vehicle during a first time period; during a second time period after the first time period: use a first object model to identify a representation of a first object in the at least one image and localize the at least one image relative to a map database based on the representation of the first object; and store the at least one image in the map database based on the localization; and during a third time period after the second time period, use a second object model to identify a representation of a second object in the at least one image, wherein the second object model was not available to the system during the second time period. 
     In an embodiment, a method for enriching a navigational map using previously captured images may include receiving at least one image, the at least one image having been captured by a camera of a vehicle from an environment of the vehicle during a first time period; during a second time period after the first time period: using a first object model to identify a representation of a first object in the at least one image and localizing the at least one image relative to a map database based on the representation of the first object; and storing the at least one image in the map database based on the localization; and during a third time period after the second time period, using a second object model to identify a representation of a second object in the at least one image, wherein the second object model was not available to the system during the second time period. 
     In an embodiment, a system for selectively collecting images to enrich a navigational map may include at least one processor. The at least one processor may be programmed to identify a geographical region associated with a map database; receive from a plurality of vehicles indications of locations of the plurality of vehicles; determine, based on the indications of locations of the plurality of vehicles, a subset of the plurality of vehicles; select at least one vehicle of the subset of the plurality of vehicles: transmit to the selected at least one vehicle a request for image data collected from the geographical region; receive image data from the at least one vehicle, the image data including metadata identifying a location associated with the collection of the image data within the geographical region, wherein the metadata does not include information identifying the at least one vehicle; and store the received image data in the map database. 
     Consistent with other disclosed embodiments, non-transitory computer readable storage media may store program instructions, which are executed by at least one processor and perform any of the methods described herein. 
     The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate various disclosed embodiments. In the drawings: 
         FIG.  1    is a diagrammatic representation of an exemplary system consistent with the disclosed embodiments. 
         FIG.  2 A  is a diagrammatic side view representation of an exemplary vehicle including a system consistent with the disclosed embodiments. 
         FIG.  2 B  is a diagrammatic top view representation of the vehicle and system shown in  FIG.  2 A  consistent with the disclosed embodiments. 
         FIG.  2 C  is a diagrammatic top view representation of another embodiment of a vehicle including a system consistent with the disclosed embodiments. 
         FIG.  2 D  is a diagrammatic top view representation of yet another embodiment of a vehicle including a system consistent with the disclosed embodiments. 
         FIG.  2 E  is a diagrammatic top view representation of yet another embodiment of a vehicle including a system consistent with the disclosed embodiments. 
         FIG.  2 F  is a diagrammatic representation of exemplary vehicle control systems consistent with the disclosed embodiments. 
         FIG.  3 A  is a diagrammatic representation of an interior of a vehicle including a rearview mirror and a user interface for a vehicle imaging system consistent with the disclosed embodiments. 
         FIG.  3 B  is an illustration of an example of a camera mount that is configured to be positioned behind a rearview mirror and against a vehicle windshield consistent with the disclosed embodiments. 
         FIG.  3 C  is an illustration of the camera mount shown in  FIG.  3 B  from a different perspective consistent with the disclosed embodiments. 
         FIG.  3 D  is an illustration of an example of a camera mount that is configured to be positioned behind a rearview mirror and against a vehicle windshield consistent with the disclosed embodiments. 
         FIG.  4    is an exemplary block diagram of a memory configured to store instructions for performing one or more operations consistent with the disclosed embodiments. 
         FIG.  5 A  is a flowchart showing an exemplary process for causing one or more navigational responses based on monocular image analysis consistent with disclosed embodiments. 
         FIG.  5 B  is a flowchart showing an exemplary process for detecting one or more vehicles and/or pedestrians in a set of images consistent with the disclosed embodiments. 
         FIG.  5 C  is a flowchart showing an exemplary process for detecting road marks and/or lane geometry information in a set of images consistent with the disclosed embodiments. 
         FIG.  5 D  is a flowchart showing an exemplary process for detecting traffic lights in a set of images consistent with the disclosed embodiments. 
         FIG.  5 E  is a flowchart showing an exemplary process for causing one or more navigational responses based on a vehicle path consistent with the disclosed embodiments. 
         FIG.  5 F  is a flowchart showing an exemplary process for determining whether a leading vehicle is changing lanes consistent with the disclosed embodiments. 
         FIG.  6    is a flowchart showing an exemplary process for causing one or more navigational responses based on stereo image analysis consistent with the disclosed embodiments. 
         FIG.  7    is a flowchart showing an exemplary process for causing one or more navigational responses based on an analysis of three sets of images consistent with the disclosed embodiments. 
         FIG.  8    shows a sparse map for providing autonomous vehicle navigation, consistent with the disclosed embodiments. 
         FIG.  9 A  illustrates a polynomial representation of a portions of a road segment consistent with the disclosed embodiments. 
         FIG.  9 B  illustrates a curve in three-dimensional space representing a target trajectory of a vehicle, for a particular road segment, included in a sparse map consistent with the disclosed embodiments. 
         FIG.  10    illustrates example landmarks that may be included in sparse map consistent with the disclosed embodiments. 
         FIG.  11 A  shows polynomial representations of trajectories consistent with the disclosed embodiments. 
         FIGS.  11 B and  11 C  show target trajectories along a multi-lane road consistent with disclosed embodiments. 
         FIG.  11 D  shows an example road signature profile consistent with disclosed embodiments. 
         FIG.  12    is a schematic illustration of a system that uses crowd sourcing data received from a plurality of vehicles for autonomous vehicle navigation, consistent with the disclosed embodiments. 
         FIG.  13    illustrates an example autonomous vehicle road navigation model represented by a plurality of three-dimensional splines, consistent with the disclosed embodiments. 
         FIG.  14    shows a map skeleton generated from combining location information from many drives, consistent with the disclosed embodiments. 
         FIG.  15    shows an example of a longitudinal alignment of two drives with example signs as landmarks, consistent with the disclosed embodiments. 
         FIG.  16    shows an example of a longitudinal alignment of many drives with an example sign as a landmark, consistent with the disclosed embodiments. 
         FIG.  17    is a schematic illustration of a system for generating drive data using a camera, a vehicle, and a server, consistent with the disclosed embodiments. 
         FIG.  18    is a schematic illustration of a system for crowdsourcing a sparse map, consistent with the disclosed embodiments. 
         FIG.  19    is a flowchart showing an exemplary process for generating a sparse map for autonomous vehicle navigation along a road segment, consistent with the disclosed embodiments. 
         FIG.  20    illustrates a block diagram of a server consistent with the disclosed embodiments. 
         FIG.  21    illustrates a block diagram of a memory consistent with the disclosed embodiments. 
         FIG.  22    illustrates a process of clustering vehicle trajectories associated with vehicles, consistent with the disclosed embodiments. 
         FIG.  23    illustrates a navigation system for a vehicle, which may be used for autonomous navigation, consistent with the disclosed embodiments. 
         FIGS.  24 A,  24 B,  24 C, and  24 D  illustrate exemplary lane marks that may be detected consistent with the disclosed embodiments. 
         FIG.  24 E  shows exemplary mapped lane marks consistent with the disclosed embodiments. 
         FIG.  24 F  shows an exemplary anomaly associated with detecting a lane mark consistent with the disclosed embodiments. 
         FIG.  25 A  shows an exemplary image of a vehicle&#39;s surrounding environment for navigation based on the mapped lane marks consistent with the disclosed embodiments. 
         FIG.  25 B  illustrates a lateral localization correction of a vehicle based on mapped lane marks in a road navigation model consistent with the disclosed embodiments. 
         FIG.  26 A  is a flowchart showing an exemplary process for mapping a lane mark for use in autonomous vehicle navigation consistent with disclosed embodiments. 
         FIG.  26 B  is a flowchart showing an exemplary process for autonomously navigating a host vehicle along a road segment using mapped lane marks consistent with disclosed embodiments. 
         FIG.  27    illustrates an exemplary system for providing one or more map segments to one or more vehicles, consistent with the disclosed embodiments. 
         FIGS.  28 A,  28 B,  28 C, and  28 D  illustrate exemplary potential travel envelopes for a vehicle, consistent with disclosed embodiments. 
         FIGS.  28 E,  28 F,  28 G, and  28 H  illustrates exemplary map tiles associated with potential travel envelopes for a vehicle, consistent with disclosed embodiments. 
         FIGS.  29 A and  29 B  illustrate exemplary map tiles, consistent with disclosed embodiments. 
         FIG.  30    illustrates an exemplary process for retrieving map tiles, consistent with disclosed embodiments. 
         FIGS.  31 A,  31 B,  31 C, and  31 D  illustrate an exemplary process for decoding map tiles, consistent with disclosed embodiments. 
         FIG.  32    is a flowchart showing an exemplary process for providing one or more map segments to one or more vehicles, consistent with the disclosed embodiments. 
         FIG.  33    illustrates an exemplary system for automatically generating a navigational map relative to one or more road segments, consistent with the disclosed embodiments. 
         FIGS.  34 A,  34 B, and  34 C  illustrate an exemplary process for collecting navigational information, consistent with disclosed embodiments. 
         FIG.  35    is a flowchart showing an exemplary process for automatically generating a navigational map relative to one or more road segments, consistent with the disclosed embodiments. 
         FIG.  36    is an illustration of an example system for harvesting images for vehicle navigation, consistent with the disclosed embodiments. 
         FIG.  37    is an illustration of an example a process for anonymizing harvested images, consistent with the disclosed embodiments. 
         FIG.  38    illustrates an example process for anonymous on demand data harvesting, consistent with the disclosed embodiments. 
         FIG.  39    is a diagrammatic illustration of an example validation performed through image harvesting, consistent with the disclosed embodiments. 
         FIG.  40    is a flowchart showing an example process for enriching a navigational map using previously captured images, consistent with the disclosed embodiments. 
         FIG.  41    is a flowchart showing an example process for selectively collecting images to enrich a navigational map, consistent with the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. While several illustrative embodiments are described herein, modifications, adaptations and other implementations are possible. For example, substitutions, additions or modifications may be made to the components illustrated in the drawings, and the illustrative methods described herein may be modified by substituting, reordering, removing, or adding steps to the disclosed methods. Accordingly, the following detailed description is not limited to the disclosed embodiments and examples. Instead, the proper scope is defined by the appended claims. 
     Autonomous Vehicle Overview 
     As used throughout this disclosure, the term “autonomous vehicle” refers to a vehicle capable of implementing at least one navigational change without driver input. A “navigational change” refers to a change in one or more of steering, braking, or acceleration of the vehicle. To be autonomous, a vehicle need not be fully automatic (e.g., fully operation without a driver or without driver input). Rather, an autonomous vehicle includes those that can operate under driver control during certain time periods and without driver control during other time periods. Autonomous vehicles may also include vehicles that control only some aspects of vehicle navigation, such as steering (e.g., to maintain a vehicle course between vehicle lane constraints), but may leave other aspects to the driver (e.g., braking). In some cases, autonomous vehicles may handle some or all aspects of braking, speed control, and/or steering of the vehicle. 
     As human drivers typically rely on visual cues and observations to control a vehicle, transportation infrastructures are built accordingly, with lane markings, traffic signs, and traffic lights are all designed to provide visual information to drivers. In view of these design characteristics of transportation infrastructures, an autonomous vehicle may include a camera and a processing unit that analyzes visual information captured from the environment of the vehicle. The visual information may include, for example, components of the transportation infrastructure (e.g., lane markings, trafic signs, traffic lights, etc.) that are observable by drivers and other obstacles (e.g., other vehicles, pedestrians, debris, etc.). Additionally, an autonomous vehicle may also use stored information, such as information that provides a model of the vehicle&#39;s environment when navigating. For example, the vehicle may use GPS data, sensor data (e.g., from an accelerometer, a speed sensor, a suspension sensor, etc.), and/or other map data to provide information related to its environment while the vehicle is traveling, and the vehicle (as well as other vehicles) may use the information to localize itself on the model. 
     In some embodiments in this disclosure, an autonomous vehicle may use information obtained while navigating (e.g., from a camera, GPS device, an accelerometer, a speed sensor, a suspension sensor, etc.). In other embodiments, an autonomous vehicle may use information obtained from past navigations by the vehicle (or by other vehicles) while navigating. In yet other embodiments, an autonomous vehicle may use a combination of information obtained while navigating and information obtained from past navigations. The following sections provide an overview of a system consistent with the disclosed embodiments, followed by an overview of a forward-facing imaging system and methods consistent with the system. The sections that follow disclose systems and methods for constructing, using, and updating a sparse map for autonomous vehicle navigation. 
     System Overview 
       FIG.  1    is a block diagram representation of a system  100  consistent with the exemplary disclosed embodiments. System  100  may include various components depending on the requirements of a particular implementation. In some embodiments, system  100  may include a processing unit  110 , an image acquisition unit  120 , a position sensor  130 , one or more memory units  140 ,  150 , a map database  160 , a user interface  170 , and a wireless transceiver  172 . Processing unit  110  may include one or more processing devices. In some embodiments, processing unit  110  may include an applications processor  180 , an image processor  190 , or any other suitable processing device. Similarly, image acquisition unit  120  may include any number of image acquisition devices and components depending on the requirements of a particular application. In some embodiments, image acquisition unit  120  may include one or more image capture devices (e.g., cameras), such as image capture device  122 , image capture device  124 , and image capture device  126 . System  100  may also include a data interface  128  communicatively connecting processing device  110  to image acquisition device  120 . For example, data interface  128  may include any wired and/or wireless link or links for transmitting image data acquired by image accusation device  120  to processing unit  110 . 
     Wireless transceiver  172  may include one or more devices configured to exchange transmissions over an air interface to one or more networks (e.g., cellular, the Internet, etc.) by use of a radio frequency, infrared frequency, magnetic field, or an electric field. Wireless transceiver  172  may use any known standard to transmit and/or receive data (e.g., Wi-Fi, Bluetooth®, Bluetooth Smart, 802.15.4, ZigBee, etc.). Such transmissions can include communications from the host vehicle to one or more remotely located servers. Such transmissions may also include communications (one-way or two-way) between the host vehicle and one or more target vehicles in an environment of the host vehicle (e.g., to facilitate coordination of navigation of the host vehicle in view of or together with target vehicles in the environment of the host vehicle), or even a broadcast transmission to unspecified recipients in a vicinity of the transmitting vehicle. 
     Both applications processor  180  and image processor  190  may include various types of processing devices. For example, either or both of applications processor  180  and image processor  190  may include a microprocessor, preprocessors (such as an image preprocessor), a graphics processing unit (GPU), a central processing unit (CPU), support circuits, digital signal processors, integrated circuits, memory, or any other types of devices suitable for running applications and for image processing and analysis. In some embodiments, applications processor  180  and/or image processor  190  may include any type of single or multi-core processor, mobile device microcontroller, central processing unit, etc. Various processing devices may be used, including, for example, processors available from manufacturers such as Intel®, AMD®, etc., or GPUs available from manufacturers such as NVIDIA®, ATI®, etc, and may include various architectures (e.g., x86 processor, ARM®, etc.). 
     In some embodiments, applications processor  180  and/or image processor  190  may include any of the EyeQ series of processor chips available from Mobileye®. These processor designs each include multiple processing units with local memory and instruction sets. Such processors may include video inputs for receiving image data from multiple image sensors and may also include video out capabilities. In one example, the EyeQ2® uses 90 nm-micron technology operating at 332 Mhz. The EyeQ2® architecture consists of two floating point, hyper-thread 32-bit RISC CPUs (MIPS32® 34K® cores), five Vision Computing Engines (VCE), three Vector Microcode Processors (VMP®), Denali 64-bit Mobile DDR Controller, 128-bit internal Sonics Interconnect, dual 16-bit Video input and 18-bit Video output controllers, 16 channels DMA and several peripherals. The MIPS34K CPU manages the five VCEs, three VMP™ and the DMA, the second MIPS34K CPU and the multi-channel DMA as well as the other peripherals. The five VCEs, three VMP® and the MIPS34K CPU can perform intensive vision computations required by multi-function bundle applications. In another example, the EyeQ3®, which is a third generation processor and is six times more powerful that the EyeQ2®, may be used in the disclosed embodiments. In other examples, the EyeQ4® and/or the EyeQ5® may be used in the disclosed embodiments. Of course, any newer or future EyeQ processing devices may also be used together with the disclosed embodiments. 
     Any of the processing devices disclosed herein may be configured to perform certain functions. Configuring a processing device, such as any of the described EyeQ processors or other controller or microprocessor, to perform certain functions may include programming of computer executable instructions and making those instructions available to the processing device for execution during operation of the processing device. In some embodiments, configuring a processing device may include programming the processing device directly with architectural instructions. For example, processing devices such as field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and the like may be configured using, for example, one or more hardware description languages (HDLs). 
     In other embodiments, configuring a processing device may include storing executable instructions on a memory that is accessible to the processing device during operation. For example, the processing device may access the memory to obtain and execute the stored instructions during operation. In either case, the processing device configured to perform the sensing, image analysis, and/or navigational functions disclosed herein represents a specialized hardware-based system in control of multiple hardware based components of a host vehicle. 
     While  FIG.  1    depicts two separate processing devices included in processing unit  110 , more or fewer processing devices may be used. For example, in some embodiments, a single processing device may be used to accomplish the tasks of applications processor  180  and image processor  190 . In other embodiments, these tasks may be performed by more than two processing devices. Further, in some embodiments, system  100  may include one or more of processing unit  110  without including other components, such as image acquisition unit  120 . 
     Processing unit  110  may comprise various types of devices. For example, processing unit  110  may include various devices, such as a controller, an image preprocessor, a central processing unit (CPU), a graphics processing unit (GPU), support circuits, digital signal processors, integrated circuits, memory, or any other types of devices for image processing and analysis. The image preprocessor may include a video processor for capturing, digitizing and processing the imagery from the image sensors. The CPU may comprise any number of microcontrollers or microprocessors. The GPU may also comprise any number of microcontrollers or microprocessors. The support circuits may be any number of circuits generally well known in the art, including cache, power supply, clock and input-output circuits. The memory may store software that, when executed by the processor, controls the operation of the system. The memory may include databases and image processing software. The memory may comprise any number of random access memories, read only memories, flash memories, disk drives, optical storage, tape storage, removable storage and other types of storage. In one instance, the memory may be separate from the processing unit  110 . In another instance, the memory may be integrated into the processing unit  110 . 
     Each memory  140 ,  150  may include software instructions that when executed by a processor (e.g., applications processor  180  and/or image processor  190 ), may control operation of various aspects of system  100 . These memory units may include various databases and image processing software, as well as a trained system, such as a neural network, or a deep neural network, for example. The memory units may include random access memory (RAM), read only memory (ROM), flash memory, disk drives, optical storage, tape storage, removable storage and/or any other types of storage. In some embodiments, memory units  140 ,  150  may be separate from the applications processor  180  and/or image processor  190 . In other embodiments, these memory units may be integrated into applications processor  180  and/or image processor  190 . 
     Position sensor  130  may include any type of device suitable for determining a location associated with at least one component of system  100 . In some embodiments, position sensor  130  may include a GPS receiver. Such receivers can determine a user position and velocity by processing signals broadcasted by global positioning system satellites. Position information from position sensor  130  may be made available to applications processor  180  and/or image processor  190 . 
     In some embodiments, system  100  may include components such as a speed sensor (e.g., a tachometer, a speedometer) for measuring a speed of vehicle  200  and/or an accelerometer (either single axis or multiaxis) for measuring acceleration of vehicle  200 . 
     User interface  170  may include any device suitable for providing information to or for receiving inputs from one or more users of system  100 . In some embodiments, user interface  170  may include user input devices, including, for example, a touchscreen, microphone, keyboard, pointer devices, track wheels, cameras, knobs, buttons, etc. With such input devices, a user may be able to provide information inputs or commands to system  100  by typing instructions or information, providing voice commands, selecting menu options on a screen using buttons, pointers, or eye-tracking capabilities, or through any other suitable techniques for communicating information to system  100 . 
     User interface  170  may be equipped with one or more processing devices configured to provide and receive information to or from a user and process that information for use by, for example, applications processor  180 . In some embodiments, such processing devices may execute instructions for recognizing and tracking eye movements, receiving and interpreting voice commands, recognizing and interpreting touches and/or gestures made on a touchscreen, responding to keyboard entries or menu selections, etc. In some embodiments, user interface  170  may include a display, speaker, tactile device, and/or any other devices for providing output information to a user. 
     Map database  160  may include any type of database for storing map data useful to system  100 . In some embodiments, map database  160  may include data relating to the position, in a reference coordinate system, of various items, including roads, water features, geographic features, businesses, points of interest, restaurants, gas stations, etc. Map database  160  may store not only the locations of such items, but also descriptors relating to those items, including, for example, names associated with any of the stored features. In some embodiments, map database  160  may be physically located with other components of system  100 . Alternatively or additionally, map database  160  or a portion thereof may be located remotely with respect to other components of system  100  (e.g., processing unit  110 ). In such embodiments, information from map database  160  may be downloaded over a wired or wireless data connection to a network (e.g., over a cellular network and/or the Internet, etc.). In some cases, map database  160  may store a sparse data model including polynomial representations of certain road features (e.g., lane markings) or target trajectories for the host vehicle. Systems and methods of generating such a map are discussed below with references to  FIGS.  8 - 19   . 
     Image capture devices  122 ,  124 , and  126  may each include any type of device suitable for capturing at least one image from an environment. Moreover, any number of image capture devices may be used to acquire images for input to the image processor. Some embodiments may include only a single image capture device, while other embodiments may include two, three, or even four or more image capture devices. Image capture devices  122 ,  124 , and  126  will be further described with reference to  FIGS.  2 B- 2 E , below. 
     System  100 , or various components thereof, may be incorporated into various different platforms. In some embodiments, system  100  may be included on a vehicle  20 ), as shown in  FIG.  2 A . For example, vehicle  200  may be equipped with a processing unit  110  and any of the other components of system  100 , as described above relative to  FIG.  1   . While in some embodiments vehicle  200  may be equipped with only a single image capture device (e.g., camera), in other embodiments, such as those discussed in connection with  FIGS.  2 B- 2 E , multiple image capture devices may be used. For example, either of image capture devices  122  and  124  of vehicle  200 , as shown in  FIG.  2 A , may be part of an ADAS (Advanced Driver Assistance Systems) imaging set. 
     The image capture devices included on vehicle  200  as part of the image acquisition unit  120  may be positioned at any suitable location. In some embodiments, as shown in  FIGS.  2 A- 2 E and  3 A- 3 C , image capture device  122  may be located in the vicinity of the rearview mirror. This position may provide a line of sight similar to that of the driver of vehicle  200 , which may aid in determining what is and is not visible to the driver. Image capture device  122  may be positioned at any location near the rearview mirror, but placing image capture device  122  on the driver side of the mirror may further aid in obtaining images representative of the driver&#39;s field of view and/or line of sight. 
     Other locations for the image capture devices of image acquisition unit  120  may also be used. For example, image capture device  124  may be located on or in a bumper of vehicle  200 . Such a location may be especially suitable for image capture devices having a wide field of view. The line of sight of bumper-located image capture devices can be different from that of the driver and, therefore, the bumper image capture device and driver may not always see the same objects. The image capture devices (e.g., image capture devices  122 ,  124 , and  126 ) may also be located in other locations. For example, the image capture devices may be located on or in one or both of the side mirrors of vehicle  200 , on the roof of vehicle  200 , on the hood of vehicle  200 , on the trunk of vehicle  200 , on the sides of vehicle  200 , mounted on, positioned behind, or positioned in front of any of the windows of vehicle  200 , and mounted in or near light figures on the front and/or back of vehicle  200 , etc. 
     In addition to image capture devices, vehicle  200  may include various other components of system  100 . For example, processing unit  110  may be included on vehicle  200  either integrated with or separate from an engine control unit (ECU) of the vehicle. Vehicle  200  may also be equipped with a position sensor  130 , such as a GPS receiver and may also include a map database  160  and memory units  140  and  150 . 
     As discussed earlier, wireless transceiver  172  may and/or receive data over one or more networks (e.g., cellular networks, the Internet, etc.). For example, wireless transceiver  172  may upload data collected by system  100  to one or more servers, and download data from the one or more servers. Via wireless transceiver  172 , system  100  may receive, for example, periodic or on demand updates to data stored in map database  160 , memory  140 , and/or memory  150 . Similarly, wireless transceiver  172  may upload any data (e.g., images captured by image acquisition unit  120 , data received by position sensor  130  or other sensors, vehicle control systems, etc.) from by system  100  and/or any data processed by processing unit  110  to the one or more servers. 
     System  100  may upload data to a server (e.g., to the cloud) based on a privacy level setting. For example, system  100  may implement privacy level settings to regulate or limit the types of data (including metadata) sent to the server that may uniquely identify a vehicle and or driver/owner of a vehicle. Such settings may be set by user via, for example, wireless transceiver  172 , be initialized by factory default settings, or by data received by wireless transceiver  172 . 
     In some embodiments, system  100  may upload data according to a “high” privacy level, and under setting a setting, system  100  may transmit data (e.g., location information related to a route, captured images, etc.) without any details about the specific vehicle and/or driver/owner. For example, when uploading data according to a “high” privacy setting, system  100  may not include a vehicle identification number (VIN) or a name of a driver or owner of the vehicle, and may instead of transmit data, such as captured images and/or limited location information related to a route. 
     Other privacy levels are contemplated. For example, system  100  may transmit data to a server according to an “intermediate” privacy level and include additional information not included under a “high” privacy level, such as a make and/or model of a vehicle and/or a vehicle type (e.g., a passenger vehicle, sport utility vehicle, truck, etc.). In some embodiments, system  100  may upload data according to a “low” privacy level. Under a “low” privacy level setting, system  100  may upload data and include information sufficient to uniquely identify a specific vehicle, owner/driver, and/or a portion or entirely of a route traveled by the vehicle. Such “low” privacy level data may include one or more of, for example, a VIN, a driver/owner name, an origination point of a vehicle prior to departure, an intended destination of the vehicle, a make and/or model of the vehicle, a type of the vehicle, etc. 
       FIG.  2 A  is a diagrammatic side view representation of an exemplary vehicle imaging system consistent with the disclosed embodiments.  FIG.  2 B  is a diagrammatic top view illustration of the embodiment shown in  FIG.  2 A . As illustrated in  FIG.  2 B , the disclosed embodiments may include a vehicle  200  including in its body a system  100  with a first image capture device  122  positioned in the vicinity of the rearview mirror and/or near the driver of vehicle  200 , a second image capture device  124  positioned on or in a bumper region (e.g., one of bumper regions  210 ) of vehicle  200 , and a processing unit  110 . 
     As illustrated in  FIG.  2 C , image capture devices  122  and  124  may both be positioned in the vicinity of the rearview mirror and/or near the driver of vehicle  200 . Additionally, while two image capture devices  122  and  124  are shown in  FIGS.  2 B and  2 C , it should be understood that other embodiments may include more than two image capture devices. For example, in the embodiments shown in  FIGS.  2 D and  2 E , first, second, and third image capture devices  122 ,  124 , and  126 , are included in the system  100  of vehicle  200 . 
     As illustrated in  FIG.  2 D , image capture device  122  may be positioned in the vicinity of the rearview mirror and/or near the driver of vehicle  200 , and image capture devices  124  and  126  may be positioned on or in a bumper region (e.g., one of bumper regions  210 ) of vehicle  200 . And as shown in  FIG.  2 E , image capture devices  122 ,  124 , and  126  may be positioned in the vicinity of the rearview mirror and/or near the driver seat of vehicle  200 . The disclosed embodiments are not limited to any particular number and configuration of the image capture devices, and the image capture devices may be positioned in any appropriate location within and/or on vehicle  200 . 
     It is to be understood that the disclosed embodiments are not limited to vehicles and could be applied in other contexts. It is also to be understood that disclosed embodiments are not limited to a particular type of vehicle  200  and may be applicable to all types of vehicles including automobiles, trucks, trailers, and other types of vehicles. 
     The first image capture device  122  may include any suitable type of image capture device. Image capture device  122  may include an optical axis. In one instance, the image capture device  122  may include an Aptina M9V024 WVGA sensor with a global shutter. In other embodiments, image capture device  122  may provide a resolution of 1280×960 pixels and may include a rolling shutter. Image capture device  122  may include various optical elements. In some embodiments one or more lenses may be included, for example, to provide a desired focal length and field of view for the image capture device. In some embodiments, image capture device  122  may be associated with a 6 mm lens or a 12 mm lens. In some embodiments, image capture device  122  may be configured to capture images having a desired field-of-view (FOV)  202 , as illustrated in  FIG.  2 D . For example, image capture device  122  may be configured to have a regular FOV, such as within a range of 40 degrees to 56 degrees, including a 46 degree FOV, 50 degree FOV, 52 degree FOV, or greater. Alternatively, image capture device  122  may be configured to have a narrow FOV in the range of 23 to 40 degrees, such as a 28 degree FOV or 36 degree FOV. In addition, image capture device  122  may be configured to have a wide FOV in the range of 100 to 180 degrees. In some embodiments, image capture device  122  may include a wide angle bumper camera or one with up to a 180 degree FOV. In some embodiments, image capture device  122  may be a 7.2M pixel image capture device with an aspect ratio of about 2:1 (e.g., H×V=3800×1900 pixels) with about 100 degree horizontal FOV. Such an image capture device may be used in place of a three image capture device configuration. Due to significant lens distortion, the vertical FOV of such an image capture device may be significantly less than 50 degrees in implementations in which the image capture device uses a radially symmetric lens. For example, such a lens may not be radially symmetric which would allow for a vertical FOV greater than 50 degrees with 100 degree horizontal FOV. 
     The first image capture device  122  may acquire a plurality of first images relative to a scene associated with the vehicle  200 . Each of the plurality of first images may be acquired as a series of image scan lines, which may be captured using a rolling shutter. Each scan line may include a plurality of pixels. 
     The first image capture device  122  may have a scan rate associated with acquisition of each of the first series of image scan lines. The scan rate may refer to a rate at which an image sensor can acquire image data associated with each pixel included in a particular scan line. 
     Image capture devices  122 ,  124 , and  126  may contain any suitable type and number of image sensors, including CCD sensors or CMOS sensors, for example. In one embodiment, a CMOS image sensor may be employed along with a rolling shutter, such that each pixel in a row is read one at a time, and scanning of the rows proceeds on a row-by-row basis until an entire image frame has been captured. In some embodiments, the rows may be captured sequentially from top to bottom relative to the frame. 
     In some embodiments, one or more of the image capture devices (e.g., image capture devices  122 ,  124 , and  126 ) disclosed herein may constitute a high resolution imager and may have a resolution greater than 5M pixel, 7M pixel, 10M pixel, or greater. 
     The use of a rolling shutter may result in pixels in different rows being exposed and captured at different times, which may cause skew and other image artifacts in the captured image frame. On the other hand, when the image capture device  122  is configured to operate with a global or synchronous shutter, all of the pixels may be exposed for the same amount of time and during a common exposure period. As a result, the image data in a frame collected from a system employing a global shutter represents a snapshot of the entire FOV (such as FOV  202 ) at a particular time. In contrast, in a rolling shutter application, each row in a frame is exposed and data is capture at different times. Thus, moving objects may appear distorted in an image capture device having a rolling shutter. This phenomenon will be described in greater detail below. 
     The second image capture device  124  and the third image capturing device  126  may be any type of image capture device. Like the first image capture device  122 , each of image capture devices  124  and  126  may include an optical axis. In one embodiment, each of image capture devices  124  and  126  may include an Aptina M9V024 WVGA sensor with a global shutter. Alternatively, each of image capture devices  124  and  126  may include a rolling shutter. Like image capture device  122 , image capture devices  124  and  126  may be configured to include various lenses and optical elements. In some embodiments, lenses associated with image capture devices  124  and  126  may provide FOVs (such as FOVs  204  and  206 ) that are the same as, or narrower than, a FOV (such as FOV  202 ) associated with image capture device  122 . For example, image capture devices  124  and  126  may have FOVs of 40 degrees, 30 degrees, 26 degrees, 23 degrees, 20 degrees, or less. 
     Image capture devices  124  and  126  may acquire a plurality of second and third images relative to a scene associated with the vehicle  200 . Each of the plurality of second and third images may be acquired as a second and third series of image scan lines, which may be captured using a rolling shutter. Each scan line or row may have a plurality of pixels. Image capture devices  124  and  126  may have second and third scan rates associated with acquisition of each of image scan lines included in the second and third series. 
     Each image capture device  122 ,  124 , and  126  may be positioned at any suitable position and orientation relative to vehicle  200 . The relative positioning of the image capture devices  122 ,  124 , and  126  may be selected to aid in fusing together the information acquired from the image capture devices. For example, in some embodiments, a FOV (such as FOV  204 ) associated with image capture device  124  may overlap partially or fully with a FOV (such as FOV  202 ) associated with image capture device  122  and a FOV (such as FOV  206 ) associated with image capture device  126 . 
     Image capture devices  122 ,  124 , and  126  may be located on vehicle  200  at any suitable relative heights. In one instance, there may be a height difference between the image capture devices  122 ,  124 , and  126 , which may provide sufficient parallax information to enable stereo analysis. For example, as shown in  FIG.  2 A , the two image capture devices  122  and  124  are at different heights. There may also be a lateral displacement difference between image capture devices  122 ,  124 , and  126 , giving additional parallax information for stereo analysis by processing unit  110 , for example. The difference in the lateral displacement may be denoted by dx, as shown in  FIGS.  2 C and  2 D . In some embodiments, fore or aft displacement (e.g., range displacement) may exist between image capture devices  122 ,  124 , and  126 . For example, image capture device  122  may be located 0.5 to 2 meters or more behind image capture device  124  and/or image capture device  126 . This type of displacement may enable one of the image capture devices to cover potential blind spots of the other image capture device(s). 
     Image capture devices  122  may have any suitable resolution capability (e.g., number of pixels associated with the image sensor), and the resolution of the image sensor(s) associated with the image capture device  122  may be higher, lower, or the same as the resolution of the image sensor(s) associated with image capture devices  124  and  126 . In some embodiments, the image sensor(s) associated with image capture device  122  and/or image capture devices  124  and  126  may have a resolution of 640×480, 1024×768, 1280×960, or any other suitable resolution. 
     The frame rate (e.g., the rate at which an image capture device acquires a set of pixel data of one image frame before moving on to capture pixel data associated with the next image frame) may be controllable. The frame rate associated with image capture device  122  may be higher, lower, or the same as the frame rate associated with image capture devices  124  and  126 . The frame rate associated with image capture devices  122 ,  124 , and  126  may depend on a variety of factors that may affect the timing of the frame rate. For example, one or more of image capture devices  122 ,  124 , and  126  may include a selectable pixel delay period imposed before or after acquisition of image data associated with one or more pixels of an image sensor in image capture device  122 ,  124 , and/or  126 . Generally, image data corresponding to each pixel may be acquired according to a clock rate for the device (e.g., one pixel per clock cycle). Additionally, in embodiments including a rolling shutter, one or more of image capture devices  122 ,  124 , and  126  may include a selectable horizontal blanking period imposed before or after acquisition of image data associated with a row of pixels of an image sensor in image capture device  122 ,  124 , and/or  126 . Further, one or more of image capture devices  122 ,  124 , and/or  126  may include a selectable vertical blanking period imposed before or after acquisition of image data associated with an image frame of image capture device  122 ,  124 , and  126 . 
     These timing controls may enable synchronization of frame rates associated with image capture devices  122 ,  124 , and  126 , even where the line scan rates of each are different. Additionally, as will be discussed in greater detail below, these selectable timing controls, among other factors (e.g., image sensor resolution, maximum line scan rates, etc.) may enable synchronization of image capture from an area where the FOV of image capture device  122  overlaps with one or more FOVs of image capture devices  124  and  126 , even where the field of view of image capture device  122  is different from the FOVs of image capture devices  124  and  126 . 
     Frame rate timing in image capture device  122 ,  124 , and  126  may depend on the resolution of the associated image sensors. For example, assuming similar line scan rates for both devices, if one device includes an image sensor having a resolution of 640×480 and another device includes an image sensor with a resolution of 1280×960, then more time will be required to acquire a frame of image data from the sensor having the higher resolution. 
     Another factor that may affect the timing of image data acquisition in image capture devices  122 ,  124 , and  126  is the maximum line scan rate. For example, acquisition of a row of image data from an image sensor included in image capture device  122 ,  124 , and  126  will require some minimum amount of time. Assuming no pixel delay periods are added, this minimum amount of time for acquisition of a row of image data will be related to the maximum line scan rate for a particular device. Devices that offer higher maximum line scan rates have the potential to provide higher frame rates than devices with lower maximum line scan rates. In some embodiments, one or more of image capture devices  124  and  126  may have a maximum line scan rate that is higher than a maximum line scan rate associated with image capture device  122 . In some embodiments, the maximum line scan rate of image capture device  124  and/or  126  may be 1.25, 1.5, 1.75, or 2 times or more than a maximum line scan rate of image capture device  122 . 
     In another embodiment, image capture devices  122 ,  124 , and  126  may have the same maximum line scan rate, but image capture device  122  may be operated at a scan rate less than or equal to its maximum scan rate. The system may be configured such that one or more of image capture devices  124  and  126  operate at a line scan rate that is equal to the line scan rate of image capture device  122 . In other instances, the system may be configured such that the line scan rate of image capture device  124  and/or image capture device  126  may be 1.25, 1.5, 1.75, or 2 times or more than the line scan rate of image capture device  122 . 
     In some embodiments, image capture devices  122 ,  124 , and  126  may be asymmetric. That is, they may include cameras having different fields of view (FOV) and focal lengths. The fields of view of image capture devices  122 ,  124 , and  126  may include any desired area relative to an environment of vehicle  200 , for example. In some embodiments, one or more of image capture devices  122 ,  124 , and  126  may be configured to acquire image data from an environment in front of vehicle  200 , behind vehicle  200 , to the sides of vehicle  200 , or combinations thereof. 
     Further, the focal length associated with each image capture device  122 ,  124 , and/or  126  may be selectable (e.g., by inclusion of appropriate lenses etc.) such that each device acquires images of objects at a desired distance range relative to vehicle  200 . For example, in some embodiments image capture devices  122 ,  124 , and  126  may acquire images of close-up objects within a few meters from the vehicle. Image capture devices  122 ,  124 , and  126  may also be configured to acquire images of objects at ranges more distant from the vehicle (e.g., 25 m, 50 m, 100 m, 150 m, or more). Further, the focal lengths of image capture devices  122 ,  124 , and  126  may be selected such that one image capture device (e.g., image capture device  122 ) can acquire images of objects relatively close to the vehicle (e.g., within 10 m or within 20 m) while the other image capture devices (e.g., image capture devices  124  and  126 ) can acquire images of more distant objects (e.g., greater than 20 m, 50 m, 100 m, 150 m, etc.) from vehicle  200 . 
     According to some embodiments, the FOV of one or more image capture devices  122 ,  124 , and  126  may have a wide angle. For example, it may be advantageous to have a FOV of 140 degrees, especially for image capture devices  122 ,  124 , and  126  that may be used to capture images of the area in the vicinity of vehicle  200 . For example, image capture device  122  may be used to capture images of the area to the right or left of vehicle  200  and, in such embodiments, it may be desirable for image capture device  122  to have a wide FOV (e.g., at least 140 degrees). 
     The field of view associated with each of image capture devices  122 ,  124 , and  126  may depend on the respective focal lengths. For example, as the focal length increases, the corresponding field of view decreases. 
     Image capture devices  122 ,  124 , and  126  may be configured to have any suitable fields of view. In one particular example, image capture device  122  may have a horizontal FOV of 46 degrees, image capture device  124  may have a horizontal FOV of 23 degrees, and image capture device  126  may have a horizontal FOV in between 23 and 46 degrees. In another instance, image capture device  122  may have a horizontal FOV of 52 degrees, image capture device  124  may have a horizontal FOV of 26 degrees, and image capture device  126  may have a horizontal FOV in between 26 and 52 degrees. In some embodiments, a ratio of the FOV of image capture device  122  to the FOVs of image capture device  124  and/or image capture device  126  may vary from 1.5 to 2.0. In other embodiments, this ratio may vary between 1.25 and 2.25. 
     System  100  may be configured so that a field of view of image capture device  122  overlaps, at least partially or fully, with a field of view of image capture device  124  and/or image capture device  126 . In some embodiments, system  100  may be configured such that the fields of view of image capture devices  124  and  126 , for example, fall within (e.g., are narrower than) and share a common center with the field of view of image capture device  122 . In other embodiments, the image capture devices  122 ,  124 , and  126  may capture adjacent FOVs or may have partial overlap in their FOVs. In some embodiments, the fields of view of image capture devices  122 ,  124 , and  126  may be aligned such that a center of the narrower FOV image capture devices  124  and/or  126  may be located in a lower half of the field of view of the wider FOV device  122 . 
       FIG.  2 F  is a diagrammatic representation of exemplary vehicle control systems, consistent with the disclosed embodiments. As indicated in  FIG.  2 F , vehicle  200  may include throttling system  220 , braking system  230 , and steering system  240 . System  100  may provide inputs (e.g., control signals) to one or more of throttling system  220 , braking system  230 , and steering system  240  over one or more data links (e.g., any wired and/or wireless link or links for transmitting data). For example, based on analysis of images acquired by image capture devices  122 ,  124 , and/or  126 , system  100  may provide control signals to one or more of throttling system  220 , braking system  230 , and steering system  240  to navigate vehicle  200  (e.g., by causing an acceleration, a turn, a lane shift, etc.). Further, system  100  may receive inputs from one or more of throttling system  220 , braking system  230 , and steering system  24  indicating operating conditions of vehicle  200  (e.g., speed, whether vehicle  200  is braking and/or turning, etc.). Further details are provided in connection with  FIGS.  4 - 7   , below. 
     As shown in  FIG.  3 A , vehicle  200  may also include a user interface  170  for interacting with a driver or a passenger of vehicle  200 . For example, user interface  170  in a vehicle application may include a touch screen  320 , knobs  330 , buttons  340 , and a microphone  350 . A driver or passenger of vehicle  200  may also use handles (e.g., located on or near the steering column of vehicle  200  including, for example, turn signal handles), buttons (e.g., located on the steering wheel of vehicle  200 ), and the like, to interact with system  100 . In some embodiments, microphone  350  may be positioned adjacent to a rearview mirror  310 . Similarly, in some embodiments, image capture device  122  may be located near rearview mirror  310 . In some embodiments, user interface  170  may also include one or more speakers  360  (e.g., speakers of a vehicle audio system). For example, system  100  may provide various notifications (e.g., alerts) via speakers  360 . 
       FIGS.  3 B- 3 D  are illustrations of an exemplary camera mount  370  configured to be positioned behind a rearview mirror (e.g., rearview mirror  310 ) and against a vehicle windshield, consistent with disclosed embodiments. As shown in  FIG.  3 B , camera mount  370  may include image capture devices  122 ,  124 , and  126 . Image capture devices  124  and  126  may be positioned behind a glare shield  380 , which may be flush against the vehicle windshield and include a composition of film and/or anti-reflective materials. For example, glare shield  380  may be positioned such that the shield aligns against a vehicle windshield having a matching slope. In some embodiments, each of image capture devices  122 ,  124 , and  126  may be positioned behind glare shield  380 , as depicted, for example, in  FIG.  3 D . The disclosed embodiments are not limited to any particular configuration of image capture devices  122 ,  124 , and  126 , camera mount  370 , and glare shield  380 .  FIG.  3 C  is an illustration of camera mount  370  shown in  FIG.  3 B  from a front perspective. 
     As will be appreciated by a person skilled in the art having the benefit of this disclosure, numerous variations and/or modifications may be made to the foregoing disclosed embodiments. For example, not all components are essential for the operation of system  100 . Further, any component may be located in any appropriate part of system  100  and the components may be rearranged into a variety of configurations while providing the functionality of the disclosed embodiments. Therefore, the foregoing configurations are examples and, regardless of the configurations discussed above, system  100  can provide a wide range of functionality to analyze the surroundings of vehicle  200  and navigate vehicle  200  in response to the analysis. 
     As discussed below in further detail and consistent with various disclosed embodiments, system  100  may provide a variety of features related to autonomous driving and/or driver assist technology. For example, system  100  may analyze image data, position data (e.g., GPS location information), map data, speed data, and/or data from sensors included in vehicle  200 . System  100  may collect the data for analysis from, for example, image acquisition unit  120 , position sensor  130 , and other sensors. Further, system  100  may analyze the collected data to determine whether or not vehicle  200  should take a certain action, and then automatically take the determined action without human intervention. For example, when vehicle  200  navigates without human intervention, system  100  may automatically control the braking, acceleration, and/or steering of vehicle  200  (e.g., by sending control signals to one or more of throttling system  220 , braking system  230 , and steering system  240 ). Further, system  100  may analyze the collected data and issue warnings and/or alerts to vehicle occupants based on the analysis of the collected data. Additional details regarding the various embodiments that are provided by system  100  are provided below. 
     Forward-Facing Multi-Imaging System 
     As discussed above, system  100  may provide drive assist functionality that uses a multi-camera system. The multi-camera system may use one or more cameras facing in the forward direction of a vehicle. In other embodiments, the multi-camera system may include one or more cameras facing to the side of a vehicle or to the rear of the vehicle. In one embodiment, for example, system  100  may use a two-camera imaging system, where a first camera and a second camera (e.g., image capture devices  122  and  124 ) may be positioned at the front and/or the sides of a vehicle (e.g., vehicle  200 ). The first camera may have a field of view that is greater than, less than, or partially overlapping with, the field of view of the second camera. In addition, the first camera may be connected to a first image processor to perform monocular image analysis of images provided by the first camera, and the second camera may, be connected to a second image processor to perform monocular image analysis of images provided by the second camera. The outputs (e.g., processed information) of the first and second image processors may be combined. In some embodiments, the second image processor may receive images from both the first camera and second camera to perform stereo analysis. In another embodiment, system  100  may use a three-camera imaging system where each of the cameras has a different field of view. Such a system may, therefore, make decisions based on information derived from objects located at varying distances both forward and to the sides of the vehicle. References to monocular image analysis may refer to instances where image analysis is performed based on images captured from a single point of view (e.g., from a single camera). Stereo image analysis may refer to instances where image analysis is performed based on two or more images captured with one or more variations of an image capture parameter. For example, captured images suitable for performing stereo image analysis may include images captured: from two or more different positions, from different fields of view, using different focal lengths, along with parallax information, etc. 
     For example, in one embodiment, system  100  may implement a three camera configuration using image capture devices  122 ,  124 , and  126 . In such a configuration, image capture device  122  may provide a narrow field of view (e.g., 34 degrees, or other values selected from a range of about 20 to 45 degrees, etc.), image capture device  124  may provide a wide field of view (e.g., 150 degrees or other values selected from a range of about 100 to about 180 degrees), and image capture device  126  may provide an intermediate field of view (e.g., 46 degrees or other values selected from a range of about 35 to about 60 degrees). In some embodiments, image capture device  126  may act as a main or primary camera. Image capture devices  122 ,  124 , and  126  may be positioned behind rearview mirror  310  and positioned substantially side-by-side (e.g., 6 cm apart). Further, in some embodiments, as discussed above, one or more of image capture devices  122 ,  124 , and  126  may be mounted behind glare shield  380  that is flush with the windshield of vehicle  200 . Such shielding may act to minimize the impact of any reflections from inside the car on image capture devices  122 ,  124 , and  126 . 
     In another embodiment, as discussed above in connection with  FIGS.  3 B and  3 C , the wide field of view camera (e.g., image capture device  124  in the above example) may be mounted lower than the narrow and main field of view cameras (e.g., image devices  122  and  126  in the above example). This configuration may provide a free line of sight from the wide field of view camera. To reduce reflections, the cameras may be mounted close to the windshield of vehicle  200 , and may include polarizers on the cameras to damp reflected light. 
     A three camera system may provide certain performance characteristics. For example, some embodiments may include an ability to validate the detection of objects by one camera based on detection results from another camera. In the three camera configuration discussed above, processing unit  110  may include, for example, three processing devices (e.g., three EyeQ series of processor chips, as discussed above), with each processing device dedicated to processing images captured by one or more of image capture devices  122 ,  124 , and  126 . 
     In a three camera system, a first processing device may receive images from both the main camera and the narrow field of view camera, and perform vision processing of the narrow FOV camera to, for example, detect other vehicles, pedestrians, lane marks, traffic signs, traffic lights, and other road objects. Further, the first processing device may calculate a disparity of pixels between the images from the main camera and the narrow camera and create a 3D reconstruction of the environment of vehicle  200 . The first processing device may then combine the 3D reconstruction with 3D map data or with 3D information calculated based on information from another camera. 
     The second processing device may receive images from main camera and perform vision processing to detect other vehicles, pedestrians, lane marks, traffic signs, traffic lights, and other road objects. Additionally, the second processing device may calculate a camera displacement and, based on the displacement, calculate a disparity of pixels between successive images and create a 3D reconstruction of the scene (e.g., a structure from motion). The second processing device may send the structure from motion based 3D reconstruction to the first processing device to be combined with the stereo 3D images. 
     The third processing device may receive images from the wide FOV camera and process the images to detect vehicles, pedestrians, lane marks, traffic signs, traffic lights, and other road objects. The third processing device may further execute additional processing instructions to analyze images to identify objects moving in the image, such as vehicles changing lanes, pedestrians, etc. 
     In some embodiments, having streams of image-based information captured and processed independently may provide an opportunity for providing redundancy in the system. Such redundancy may include, for example, using a first image capture device and the images processed from that device to validate and/or supplement information obtained by capturing and processing image information from at least a second image capture device. 
     In some embodiments, system  100  may use two image capture devices (e.g., image capture devices  122  and  124 ) in providing navigation assistance for vehicle  200  and use a third image capture device (e.g., image capture device  126 ) to provide redundancy and validate the analysis of data received from the other two image capture devices. For example, in such a configuration, image capture devices  122  and  124  may provide images for stereo analysis by system  100  for navigating vehicle  200 , while image capture device  126  may provide images for monocular analysis by system  100  to provide redundancy and validation of information obtained based on images captured from image capture device  122  and/or image capture device  124 . That is, image capture device  126  (and a corresponding processing device) may be considered to provide a redundant sub-system for providing a check on the analysis derived from image capture devices  122  and  124  (e.g., to provide an automatic emergency braking (AEB) system). Furthermore, in some embodiments, redundancy and validation of received data may be supplemented based on information received from one more sensors (e.g., radar, lidar, acoustic sensors, information received from one or more transceivers outside of a vehicle, etc.). 
     One of skill in the art will recognize that the above camera configurations, camera placements, number of cameras, camera locations, etc., are examples only. These components and others described relative to the overall system may be assembled and used in a variety of different configurations without departing from the scope of the disclosed embodiments. Further details regarding usage of a multi-camera system to provide driver assist and/or autonomous vehicle functionality follow below. 
       FIG.  4    is an exemplary functional block diagram of memory  140  and/or  150 , which may be stored/programmed with instructions for performing one or more operations consistent with the disclosed embodiments. Although the following refers to memory  140 , one of skill in the art will recognize that instructions may be stored in memory  140  and/or  150 . 
     As shown in  FIG.  4   , memory  140  may store a monocular image analysis module  402 , a stereo image analysis module  404 , a velocity and acceleration module  406 , and a navigational response module  408 . The disclosed embodiments are not limited to any particular configuration of memory  140 . Further, application processor  180  and/or image processor  190  may execute the instructions stored in any of modules  402 ,  404 ,  406 , and  408  included in memory  140 . One of skill in the art will understand that references in the following discussions to processing unit  110  may refer to application processor  180  and image processor  190  individually or collectively. Accordingly, steps of any of the following processes may be performed by one or more processing devices. 
     In one embodiment, monocular image analysis module  402  may store instructions (such as computer vision software) which, when executed by processing unit  110 , performs monocular image analysis of a set of images acquired by one of image capture devices  122 ,  124 , and  126 . In some embodiments, processing unit  110  may combine information from a set of images with additional sensory information (e.g., information from radar, lidar, etc.) to perform the monocular image analysis. As described in connection with  FIGS.  5 A- 5 D  below, monocular image analysis module  402  may include instructions for detecting a set of features within the set of images, such as lane markings, vehicles, pedestrians, road signs, highway exit ramps, traffic lights, hazardous objects, and any other feature associated with an environment of a vehicle. Based on the analysis, system  100  (e.g., via processing unit  110 ) may cause one or more navigational responses in vehicle  200 , such as a turn, a lane shift, a change in acceleration, and the like, as discussed below in connection with navigational response module  408 . 
     In one embodiment, stereo image analysis module  404  may store instructions (such as computer vision software) which, when executed by processing unit  110 , performs stereo image analysis of first and second sets of images acquired by a combination of image capture devices selected from any of image capture devices  122 ,  124 , and  126 . In some embodiments, processing unit  110  may combine information from the first and second sets of images with additional sensory information (e.g., information from radar) to perform the stereo image analysis. For example, stereo image analysis module  404  may include instructions for performing stereo image analysis based on a first set of images acquired by image capture device  124  and a second set of images acquired by image capture device  126 . As described in connection with  FIG.  6    below, stereo image analysis module  404  may include instructions for detecting a set of features within the first and second sets of images, such as lane markings, vehicles, pedestrians, road signs, highway exit ramps, traffic lights, hazardous objects, and the like. Based on the analysis, processing unit  110  may cause one or more navigational responses in vehicle  200 , such as a turn, a lane shift, a change in acceleration, and the like, as discussed below in connection with navigational response module  408 . Furthermore, in some embodiments, stereo image analysis module  404  may implement techniques associated with a trained system (such as a neural network or a deep neural network) or an untrained system, such as a system that may be configured to use computer vision algorithms to detect and/or label objects in an environment from which sensory information was captured and processed. In one embodiment, stereo image analysis module  404  and/or other image processing modules may be configured to use a combination of a trained and untrained system. 
     In one embodiment, velocity and acceleration module  406  may store software configured to analyze data received from one or more computing and electromechanical devices in vehicle  200  that are configured to cause a change in velocity and/or acceleration of vehicle  200 . For example, processing unit  110  may execute instructions associated with velocity and acceleration module  406  to calculate a target speed for vehicle  200  based on data derived from execution of monocular image analysis module  402  and/or stereo image analysis module  404 . Such data may include, for example, a target position, velocity, and/or acceleration, the position and/or speed of vehicle  200  relative to a nearby vehicle, pedestrian, or road object, position information for vehicle  200  relative to lane markings of the road, and the like. In addition, processing unit  110  may calculate a target speed for vehicle  200  based on sensory input (e.g., information from radar) and input from other systems of vehicle  200 , such as throttling system  220 , braking system  230 , and/or steering system  240  of vehicle  200 . Based on the calculated target speed, processing unit  110  may transmit electronic signals to throttling system  220 , braking system  230 , and/or steering system  240  of vehicle  200  to trigger a change in velocity and/or acceleration by, for example, physically depressing the brake or easing up off the accelerator of vehicle  200 . 
     In one embodiment, navigational response module  408  may store software executable by processing unit  110  to determine a desired navigational response based on data derived from execution of monocular image analysis module  402  and/or stereo image analysis module  404 . Such data may include position and speed information associated with nearby vehicles, pedestrians, and road objects, target position information for vehicle  200 , and the like. Additionally, in some embodiments, the navigational response may be based (partially or fully) on map data, a predetermined position of vehicle  200 , and/or a relative velocity or a relative acceleration between vehicle  200  and one or more objects detected from execution of monocular image analysis module  402  and/or stereo image analysis module  404 . Navigational response module  408  may also be configured to determine a desired navigational response based on sensory input (e.g., information from radar) and inputs from other systems of vehicle  200 , such as throttling system  220 , braking system  230 , and steering system  240  of vehicle  200 . Based on the desired navigational response, processing unit  110  may transmit electronic signals to throttling system  220 , braking system  230 , and steering system  240  of vehicle  200  to trigger a desired navigational response by, for example, turning the steering wheel of vehicle  200  to achieve a rotation of a predetermined angle. In some embodiments, processing unit  110  may use the output of navigational response module  408  (e.g., the desired navigational response) as an input to execution of velocity and acceleration module  406  for calculating a change in speed of vehicle  200 . 
     Furthermore, any of the modules (e.g., modules  402 ,  404 , and  406 ) disclosed herein may implement techniques associated with a trained system (such as a neural network or a deep neural network) or an untrained system. 
       FIG.  5 A  is a flowchart showing an exemplary process  500 A for causing one or more navigational responses based on monocular image analysis, consistent with disclosed embodiments. At step  510 , processing unit  110  may receive a plurality of images via data interface  128  between processing unit  110  and image acquisition unit  120 . For instance, a camera included in image acquisition unit  120  (such as image capture device  122  having field of view  202 ) may capture a plurality of images of an area forward of vehicle  200  (or to the sides or rear of a vehicle, for example) and transmit them over a data connection (e.g., digital, wired, USB, wireless. Bluetooth, etc.) to processing unit  110 . Processing unit  110  may execute monocular image analysis module  402  to analyze the plurality of images at step  520 , as described in further detail in connection with  FIGS.  5 B- 5 D  below. By performing the analysis, processing unit  110  may detect a set of features within the set of images, such as lane markings, vehicles, pedestrians, road signs, highway exit ramps, traffic lights, and the like. 
     Processing unit  110  may also execute monocular image analysis module  402  to detect various road hazards at step  520 , such as, for example, parts of a truck tire, fallen road signs, loose cargo, small animals, and the like. Road hazards may vary in structure, shape, size, and color, which may make detection of such hazards more challenging. In some embodiments, processing unit  110  may execute monocular image analysis module  402  to perform multi-frame analysis on the plurality of images to detect road hazards. For example, processing unit  110  may estimate camera motion between consecutive image frames and calculate the disparities in pixels between the frames to construct a 3D-map of the road. Processing unit  110  may then use the 3D-map to detect the road surface, as well as hazards existing above the road surface. 
     At step  530 , processing unit  110  may execute navigational response module  408  to cause one or more navigational responses in vehicle  200  based on the analysis performed at step  520  and the techniques as described above in connection with  FIG.  4   . Navigational responses may include, for example, a turn, a lane shift, a change in acceleration, and the like. In some embodiments, processing unit  110  may use data derived from execution of velocity and acceleration module  406  to cause the one or more navigational responses. Additionally, multiple navigational responses may occur simultaneously, in sequence, or any combination thereof. For instance, processing unit  110  may cause vehicle  200  to shift one lane over and then accelerate by, for example, sequentially transmitting control signals to steering system  240  and throttling system  220  of vehicle  200 . Alternatively, processing unit  110  may cause vehicle  200  to brake while at the same time shifting lanes by, for example, simultaneously transmitting control signals to braking system  230  and steering system  240  of vehicle  200 . 
       FIG.  5 B  is a flowchart showing an exemplary process  500 B for detecting one or more vehicles and/or pedestrians in a set of images, consistent with disclosed embodiments. Processing unit  110  may execute monocular image analysis module  402  to implement process  500 B. At step  540 , processing unit  110  may determine a set of candidate objects representing possible vehicles and/or pedestrians. For example, processing unit  110  may scan one or more images, compare the images to one or more predetermined patterns, and identify within each image possible locations that may contain objects of interest (e.g., vehicles, pedestrians, or portions thereof). The predetermined patterns may be designed in such a way to achieve a high rate of “false hits” and a low rate of “misses.” For example, processing unit  110  may use a low threshold of similarity to predetermined patterns for identifying candidate objects as possible vehicles or pedestrians. Doing so may allow processing unit  110  to reduce the probability of missing (e.g., not identifying) a candidate object representing a vehicle or pedestrian. 
     At step  542 , processing unit  110  may filter the set of candidate objects to exclude certain candidates (e.g., irrelevant or less relevant objects) based on classification criteria. Such criteria may be derived from various properties associated with object types stored in a database (e.g., a database stored in memory  140 ). Properties may include object shape, dimensions, texture, position (e.g., relative to vehicle  200 ), and the like. Thus, processing unit  110  may use one or more sets of criteria to reject false candidates from the set of candidate objects. 
     At step  544 , processing unit  110  may analyze multiple frames of images to determine whether objects in the set of candidate objects represent vehicles and/or pedestrians. For example, processing unit  110  may track a detected candidate object across consecutive frames and accumulate frame-by-frame data associated with the detected object (e.g., size, position relative to vehicle  200 , etc.). Additionally, processing unit  110  may estimate parameters for the detected object and compare the object&#39;s frame-by-frame position data to a predicted position. 
     At step  546 , processing unit  110  may construct a set of measurements for the detected objects. Such measurements may include, for example, position, velocity, and acceleration values (relative to vehicle  200 ) associated with the detected objects. In some embodiments, processing unit  110  may construct the measurements based on estimation techniques using a series of time-based observations such as Kalman filters or linear quadratic estimation (LQE), and/or based on available modeling data for different object types (e.g., cars, trucks, pedestrians, bicycles, road signs, etc.). The Kalman filters may be based on a measurement of an object&#39;s scale, where the scale measurement is proportional to a time to collision (e.g., the amount of time for vehicle  200  to reach the object). Thus, by performing steps  540 - 546 , processing unit  110  may identify vehicles and pedestrians appearing within the set of captured images and derive information (e.g., position, speed, size) associated with the vehicles and pedestrians. Based on the identification and the derived information, processing unit  110  may cause one or more navigational responses in vehicle  200 , as described in connection with  FIG.  5 A , above. 
     At step  548 , processing unit  110  may perform an optical flow analysis of one or more images to reduce the probabilities of detecting a “false hit” and missing a candidate object that represents a vehicle or pedestrian. The optical flow analysis may refer to, for example, analyzing motion patterns relative to vehicle  200  in the one or more images associated with other vehicles and pedestrians, and that are distinct from road surface motion. Processing unit  110  may calculate the motion of candidate objects by observing the different positions of the objects across multiple image frames, which are captured at different times. Processing unit  110  may use the position and time values as inputs into mathematical models for calculating the motion of the candidate objects. Thus, optical flow analysis may provide another method of detecting vehicles and pedestrians that are nearby vehicle  200 . Processing unit  110  may perform optical flow analysis in combination with steps  540 - 546  to provide redundancy for detecting vehicles and pedestrians and increase the reliability of system  100 . 
       FIG.  5 C  is a flowchart showing an exemplary process  500 C for detecting road marks and/or lane geometry information in a set of images, consistent with disclosed embodiments. Processing unit  110  may execute monocular image analysis module  402  to implement process  500 C. At step  550 , processing unit  110  may detect a set of objects by scanning one or more images. To detect segments of lane markings, lane geometry information, and other pertinent road marks, processing unit  110  may filter the set of objects to exclude those determined to be irrelevant (e.g., minor potholes, small rocks, etc.). At step  552 , processing unit  110  may group together the segments detected in step  550  belonging to the same road mark or lane mark. Based on the grouping, processing unit  110  may develop a model to represent the detected segments, such as a mathematical model. 
     At step  554 , processing unit  110  may construct a set of measurements associated with the detected segments. In some embodiments, processing unit  110  may create a projection of the detected segments from the image plane onto the real-world plane. The projection may be characterized using a 3rd-degree polynomial having coefficients corresponding to physical properties such as the position, slope, curvature, and curvature derivative of the detected road. In generating the projection, processing unit  110  may take into account changes in the road surface, as well as pitch and roll rates associated with vehicle  200 . In addition, processing unit  110  may model the road elevation by analyzing position and motion cues present on the road surface. Further, processing unit  110  may estimate the pitch and roll rates associated with vehicle  200  by tracking a set of feature points in the one or more images. 
     At step  556 , processing unit  110  may perform multi-frame analysis by, for example, tracking the detected segments across consecutive image frames and accumulating frame-by-frame data associated with detected segments. As processing unit  110  performs multi-frame analysis, the set of measurements constructed at step  554  may become more reliable and associated with an increasingly higher confidence level. Thus, by performing steps  550 ,  552 ,  554 , and  556 , processing unit  110  may identify road marks appearing within the set of captured images and derive lane geometry information. Based on the identification and the derived information, processing unit  110  may cause one or more navigational responses in vehicle  200 , as described in connection with  FIG.  5 A , above. 
     At step  558 , processing unit  110  may consider additional sources of information to further develop a safety model for vehicle  200  in the context of its surroundings. Processing unit  110  may use the safety model to define a context in which system  100  may execute autonomous control of vehicle  200  in a safe manner. To develop the safety model, in some embodiments, processing unit  110  may consider the position and motion of other vehicles, the detected road edges and barriers, and/or general road shape descriptions extracted from map data (such as data from map database  160 ). By considering additional sources of information, processing unit  110  may provide redundancy for detecting road marks and lane geometry and increase the reliability of system  100 . 
       FIG.  5 D  is a flowchart showing an exemplary process  500 D for detecting traffic lights in a set of images, consistent with disclosed embodiments. Processing unit  110  may execute monocular image analysis module  402  to implement process  500 D. At step  560 , processing unit  110  may scan the set of images and identify objects appearing at locations in the images likely to contain traffic lights. For example, processing unit  110  may filter the identified objects to construct a set of candidate objects, excluding those objects unlikely to correspond to traffic lights. The filtering may be done based on various properties associated with traffic lights, such as shape, dimensions, texture, position (e.g., relative to vehicle  200 ), and the like. Such properties may be based on multiple examples of traffic lights and traffic control signals and stored in a database. In some embodiments, processing unit  110  may perform multi-frame analysis on the set of candidate objects reflecting possible traffic lights. For example, processing unit  110  may track the candidate objects across consecutive image frames, estimate the real-world position of the candidate objects, and filter out those objects that are moving (which are unlikely to be traffic lights). In some embodiments, processing unit  110  may perform color analysis on the candidate objects and identify the relative position of the detected colors appearing inside possible traffic lights. 
     At step  562 , processing unit  110  may analyze the geometry of a junction. The analysis may be based on any combination of: (i) the number of lanes detected on either side of vehicle  200 , (ii) markings (such as arrow marks) detected on the road, and (iii) descriptions of the junction extracted from map data (such as data from map database  160 ). Processing unit  110  may conduct the analysis using information derived from execution of monocular analysis module  402 . In addition, Processing unit  110  may determine a correspondence between the traffic lights detected at step  560  and the lanes appearing near vehicle  200 . 
     As vehicle  200  approaches the junction, at step  564 , processing unit  110  may update the confidence level associated with the analyzed junction geometry and the detected traffic lights. For instance, the number of traffic lights estimated to appear at the junction as compared with the number actually appearing at the junction may impact the confidence level. Thus, based on the confidence level, processing unit  110  may delegate control to the driver of vehicle  200  in order to improve safety conditions. By performing steps  560 ,  562 , and  564 , processing unit  110  may identify traffic lights appearing within the set of captured images and analyze junction geometry information. Based on the identification and the analysis, processing unit  110  may cause one or more navigational responses in vehicle  200 , as described in connection with  FIG.  5 A , above. 
       FIG.  5 E  is a flowchart showing an exemplary process  500 E for causing one or more navigational responses in vehicle  200  based on a vehicle path, consistent with the disclosed embodiments. At step  570 , processing unit  110  may construct an initial vehicle path associated with vehicle  200 . The vehicle path may be represented using a set of points expressed in coordinates (x, z), and the distance d i  between two points in the set of points may fall in the range of 1 to 5 meters. In one embodiment, processing unit  110  may construct the initial vehicle path using two polynomials, such as left and right road polynomials. Processing unit  110  may calculate the geometric midpoint between the two polynomials and offset each point included in the resultant vehicle path by a predetermined offset (e.g., a smart lane offset), if any (an offset of zero may correspond to travel in the middle of a lane). The offset may be in a direction perpendicular to a segment between any two points in the vehicle path. In another embodiment, processing unit  110  may use one polynomial and an estimated lane width to offset each point of the vehicle path by half the estimated lane width plus a predetermined offset (e.g., a smart lane offset). 
     At step  572 , processing unit  110  may update the vehicle path constructed at step  570 . Processing unit  110  may reconstruct the vehicle path constructed at step  570  using a higher resolution, such that the distance d k  between two points in the set of points representing the vehicle path is less than the distance d i  described above. For example, the distance d k  may fall in the range of 0.1 to 0.3 meters. Processing unit  110  may reconstruct the vehicle path using a parabolic spline algorithm, which may yield a cumulative distance vector S corresponding to the total length of the vehicle path (i.e., based on the set of points representing the vehicle path). 
     At step  574 , processing unit  110  may determine a look-ahead point (expressed in coordinates as (x l , z l )) based on the updated vehicle path constructed at step  572 . Processing unit  110  may extract the look-ahead point from the cumulative distance vector S, and the look-ahead point may be associated with a look-ahead distance and look-ahead time. The look-ahead distance, which may have a lower bound ranging from 10 to 20 meters, may be calculated as the product of the speed of vehicle  200  and the look-ahead time. For example, as the speed of vehicle  200  decreases, the look-ahead distance may also decrease (e.g., until it reaches the lower bound). The look-ahead time, which may range from 0.5 to 1.5 seconds, may be inversely proportional to the gain of one or more control loops associated with causing a navigational response in vehicle  200 , such as the heading error tracking control loop. For example, the gain of the heading error tracking control loop may depend on the bandwidth of a yaw rate loop, a steering actuator loop, car lateral dynamics, and the like. Thus, the higher the gain of the heading error tracking control loop, the lower the look-ahead time. 
     At step  576 , processing unit  110  may determine a heading error and yaw rate command based on the look-ahead point determined at step  574 . Processing unit  110  may determine the heading error by calculating the arctangent of the look-ahead point, e.g., arctan (x l /z l ). Processing unit  110  may determine the yaw rate command as the product of the heading error and a high-level control gain. The high-level control gain may be equal to: (2/look-ahead time), if the look-ahead distance is not at the lower bound. Otherwise, the high-level control gain may be equal to: (2*speed of vehicle  200 /look-ahead distance). 
       FIG.  5 F  is a flowchart showing an exemplary process  500 F for determining whether a leading vehicle is changing lanes, consistent with the disclosed embodiments. At step  580 , processing unit  110  may determine navigation information associated with a leading vehicle (e.g., a vehicle traveling ahead of vehicle  200 ). For example, processing unit  110  may determine the position, velocity (e.g., direction and speed), and/or acceleration of the leading vehicle, using the techniques described in connection with  FIGS.  5 A and  5 B , above. Processing unit  110  may also be configured to determine one or more road polynomials, a look-ahead point (associated with vehicle  200 ), and/or a snail trail (e.g., a set of points describing a path taken by the leading vehicle), using the techniques described in connection with  FIG.  5 E , above. 
     At step  582 , processing unit  110  may analyze the navigation information determined at step  580 . In one embodiment, processing unit  110  may calculate the distance between a snail trail and a road polynomial (e.g., along the trail). If the variance of this distance along the trail exceeds a predetermined threshold (for example, 0.1 to 0.2 meters on a straight road, 0.3 to 0.4 meters on a moderately curvy road, and 0.5 to 0.6 meters on a road with sharp curves), processing unit  110  may determine that the leading vehicle is likely changing lanes. In the case where multiple vehicles are detected traveling ahead of vehicle  200 , processing unit  110  may compare the snail trails associated with each vehicle. Based on the comparison, processing unit  110  may determine that a vehicle whose snail trail does not match with the snail trails of the other vehicles is likely changing lanes. Processing unit  110  may additionally compare the curvature of the snail trail (associated with the leading vehicle) with the expected curvature of the road segment in which the leading vehicle is traveling. The expected curvature may be extracted from map data (e.g., data from map database  160 ), from road polynomials, from other vehicles&#39; snail trails, from prior knowledge about the road, and the like. If the difference in curvature of the snail trail and the expected curvature of the road segment exceeds a predetermined threshold, processing unit  110  may determine that the leading vehicle is likely changing lanes. 
     In another embodiment, processing unit  110  may compare the leading vehicle&#39;s instantaneous position with the look-ahead point (associated with vehicle  200 ) over a specific period of time (e.g., 0.5 to 1.5 seconds). If the distance between the leading vehicle&#39;s instantaneous position and the look-ahead point varies during the specific period of time, and the cumulative sum of variation exceeds a predetermined threshold (for example, 0.3 to 0.4 meters on a straight road, 0.7 to 0.8 meters on a moderately curvy road, and 1.3 to 1.7 meters on a road with sharp curves), processing unit  110  may determine that the leading vehicle is likely changing lanes. In another embodiment, processing unit  110  may analyze the geometry of the snail trail by comparing the lateral distance traveled along the trail with the expected curvature of the snail trail. The expected radius of curvature may be determined according to the calculation: (δ z   2 +δ x   2 )/2/(δ x ), where δ x  represents the lateral distance traveled and &amp;, represents the longitudinal distance traveled. If the difference between the lateral distance traveled and the expected curvature exceeds a predetermined threshold (e.g., 500 to 700 meters), processing unit  110  may determine that the leading vehicle is likely changing lanes. In another embodiment, processing unit  110  may analyze the position of the leading vehicle. If the position of the leading vehicle obscures a road polynomial (e.g., the leading vehicle is overlaid on top of the road polynomial), then processing unit  110  may determine that the leading vehicle is likely changing lanes. In the case where the position of the leading vehicle is such that, another vehicle is detected ahead of the leading vehicle and the snail trails of the two vehicles are not parallel, processing unit  110  may determine that the (closer) leading vehicle is likely changing lanes. 
     At step  584 , processing unit  110  may determine whether or not leading vehicle  200  is changing lanes based on the analysis performed at step  582 . For example, processing unit  110  may make the determination based on a weighted average of the individual analyses performed at step  582 . Under such a scheme, for example, a decision by processing unit  110  that the leading vehicle is likely changing lanes based on a particular type of analysis may be assigned a value of “1” (and “0” to represent a determination that the leading vehicle is not likely changing lanes). Different analyses performed at step  582  may be assigned different weights, and the disclosed embodiments are not limited to any particular combination of analyses and weights. 
       FIG.  6    is a flowchart showing an exemplary process  600  for causing one or more navigational responses based on stereo image analysis, consistent with disclosed embodiments. At step  610 , processing unit  110  may receive a first and second plurality of images via data interface  128 . For example, cameras included in image acquisition unit  120  (such as image capture devices  122  and  124  having fields of view  202  and  204 ) may capture a first and second plurality of images of an area forward of vehicle  200  and transmit them over a digital connection (e.g., USB, wireless, Bluetooth, etc.) to processing unit  110 . In some embodiments, processing unit  110  may receive the first and second plurality of images via two or more data interfaces. The disclosed embodiments are not limited to any particular data interface configurations or protocols. 
     At step  620 , processing unit  110  may execute stereo image analysis module  404  to perform stereo image analysis of the first and second plurality of images to create a 3D map of the road in front of the vehicle and detect features within the images, such as lane markings, vehicles, pedestrians, road signs, highway exit ramps, traffic lights, road hazards, and the like. Stereo image analysis may be performed in a manner similar to the steps described in connection with FIGS. SA- 5 D, above. For example, processing unit  110  may execute stereo image analysis module  404  to detect candidate objects (e.g., vehicles, pedestrians, road marks, traffic lights, road hazards, etc.) within the first and second plurality of images, filter out a subset of the candidate objects based on various criteria, and perform multi-frame analysis, construct measurements, and determine a confidence level for the remaining candidate objects. In performing the steps above, processing unit  110  may consider information from both the first and second plurality of images, rather than information from one set of images alone. For example, processing unit  110  may analyze the differences in pixel-level data (or other data subsets from among the two streams of captured images) for a candidate object appearing in both the first and second plurality of images. As another example, processing unit  110  may estimate a position and/or velocity of a candidate object (e.g., relative to vehicle  200 ) by observing that the object appears in one of the plurality of images but not the other or relative to other differences that may exist relative to objects appearing if the two image streams. For example, position, velocity, and/or acceleration relative to vehicle  200  may be determined based on trajectories, positions, movement characteristics, etc. of features associated with an object appearing in one or both of the image streams. 
     At step  630 , processing unit  110  may execute navigational response module  408  to cause one or more navigational responses in vehicle  200  based on the analysis performed at step  620  and the techniques as described above in connection with  FIG.  4   . Navigational responses may include, for example, a turn, a lane shift, a change in acceleration, a change in velocity, braking, and the like. In some embodiments, processing unit  110  may use data derived from execution of velocity and acceleration module  406  to cause the one or more navigational responses. Additionally, multiple navigational responses may occur simultaneously, in sequence, or any combination thereof. 
       FIG.  7    is a flowchart showing an exemplary process  700  for causing one or more navigational responses based on an analysis of three sets of images, consistent with disclosed embodiments. At step  710 , processing unit  110  may receive a first, second, and third plurality of images via data interface  128 . For instance, cameras included in image acquisition unit  120  (such as image capture devices  122 ,  124 , and  126  having fields of view  202 ,  204 , and  206 ) may capture a first, second, and third plurality of images of an area forward and/or to the side of vehicle  200  and transmit them over a digital connection (e.g., USB, wireless, Bluetooth, etc.) to processing unit  110 . In some embodiments, processing unit  110  may receive the first, second, and third plurality of images via three or more data interfaces. For example, each of image capture devices  122 ,  124 ,  126  may have an associated data interface for communicating data to processing unit  110 . The disclosed embodiments are not limited to any particular data interface configurations or protocols. 
     At step  720 , processing unit  110  may analyze the first, second, and third plurality of images to detect features within the images, such as lane markings, vehicles, pedestrians, road signs, highway exit ramps, traffic lights, road hazards, and the like. The analysis may be performed in a manner similar to the steps described in connection with  FIGS.  5 A- 5 D and  6   , above. For instance, processing unit  110  may perform monocular image analysis (e.g., via execution of monocular image analysis module  402  and based on the steps described in connection with FIGS. SA- 5 D, above) on each of the first, second, and third plurality of images. Alternatively, processing unit  110  may perform stereo image analysis (e.g., via execution of stereo image analysis module  404  and based on the steps described in connection with  FIG.  6   , above) on the first and second plurality of images, the second and third plurality of images, and/or the first and third plurality of images. The processed information corresponding to the analysis of the first, second, and/or third plurality of images may be combined. In some embodiments, processing unit  110  may perform a combination of monocular and stereo image analyses. For example, processing unit  110  may perform monocular image analysis (e.g., via execution of monocular image analysis module  402 ) on the first plurality of images and stereo image analysis (e.g., via execution of stereo image analysis module  404 ) on the second and third plurality of images. The configuration of image capture devices  122 ,  124 , and  126 —including their respective locations and fields of view  202 ,  204 , and  206 —may influence the types of analyses conducted on the first, second, and third plurality of images. The disclosed embodiments are not limited to a particular configuration of image capture devices  122 ,  124 , and  126 , or the types of analyses conducted on the first, second, and third plurality of images. 
     In some embodiments, processing unit  110  may perform testing on system  100  based on the images acquired and analyzed at steps  710  and  720 . Such testing may provide an indicator of the overall performance of system  100  for certain configurations of image capture devices  122 ,  124 , and  126 . For example, processing unit  110  may determine the proportion of “false hits” (e.g., cases where system  100  incorrectly determined the presence of a vehicle or pedestrian) and “misses.” 
     At step  730 , processing unit  110  may cause one or more navigational responses in vehicle  200  based on information derived from two of the first, second, and third plurality of images. Selection of two of the first, second, and third plurality of images may depend on various factors, such as, for example, the number, types, and sizes of objects detected in each of the plurality of images. Processing unit  110  may also make the selection based on image quality and resolution, the effective field of view reflected in the images, the number of captured frames, the extent to which one or more objects of interest actually appear in the frames (e.g., the percentage of frames in which an object appears, the proportion of the object that appears in each such frame, etc.), and the like. 
     In some embodiments, processing unit  110  may select information derived from two of the first, second, and third plurality of images by determining the extent to which information derived from one image source is consistent with information derived from other image sources. For example, processing unit  110  may combine the processed information derived from each of image capture devices  122 ,  124 , and  126  (whether by monocular analysis, stereo analysis, or any combination of the two) and determine visual indicators (e.g., lane markings, a detected vehicle and its location and/or path, a detected traffic light, etc.) that are consistent across the images captured from each of image capture devices  122 ,  124 , and  126 . Processing unit  110  may also exclude information that is inconsistent across the captured images (e.g., a vehicle changing lanes, a lane model indicating a vehicle that is too close to vehicle  200 , etc.). Thus, processing unit  110  may select information derived from two of the first, second, and third plurality of images based on the determinations of consistent and inconsistent information. 
     Navigational responses may include, for example, a turn, a lane shift, a change in acceleration, and the like. Processing unit  110  may cause the one or more navigational responses based on the analysis performed at step  720  and the techniques as described above in connection with  FIG.  4   . Processing unit  110  may also use data derived from execution of velocity and acceleration module  406  to cause the one or more navigational responses. In some embodiments, processing unit  110  may cause the one or more navigational responses based on a relative position, relative velocity, and/or relative acceleration between vehicle  200  and an object detected within any of the first, second, and third plurality of images. Multiple navigational responses may occur simultaneously, in sequence, or any combination thereof. 
     Sparse Road Model for Autonomous Vehicle Navigation 
     In some embodiments, the disclosed systems and methods may use a sparse map for autonomous vehicle navigation. In particular, the sparse map may be for autonomous vehicle navigation along a road segment. For example, the sparse map may provide sufficient information for navigating an autonomous vehicle without storing and/or updating a large quantity of data. As discussed below in further detail, an autonomous vehicle may use the sparse map to navigate one or more roads based on one or more stored trajectories. 
     Sparse Map for Autonomous Vehicle Navigation 
     In some embodiments, the disclosed systems and methods may generate a sparse map for autonomous vehicle navigation. For example, the sparse map may provide sufficient information for navigation without requiring excessive data storage or data transfer rates. As discussed below in further detail, a vehicle (which may be an autonomous vehicle) may use the sparse map to navigate one or more roads. For example, in some embodiments, the sparse map may include data related to a road and potentially landmarks along the road that may be sufficient for vehicle navigation, but which also exhibit small data footprints. For example, the sparse data maps described in detail below may require significantly less storage space and data transfer bandwidth as compared with digital maps including detailed map information, such as image data collected along a road. 
     For example, rather than storing detailed representations of a road segment, the sparse data map may store three-dimensional polynomial representations of preferred vehicle paths along a road. These paths may require very little data storage space. Further, in the described sparse data maps, landmarks may be identified and included in the sparse map road model to aid in navigation. These landmarks may be located at any spacing suitable for enabling vehicle navigation, but in some cases, such landmarks need not be identified and included in the model at high densities and short spacings. Rather, in some cases, navigation may be possible based on landmarks that are spaced apart by at least 50 meters, at least 100 meters, at least 500 meters, at least 1 kilometer, or at least 2 kilometers. As will be discussed in more detail in other sections, the sparse map may be generated based on data collected or measured by vehicles equipped with various sensors and devices, such as image capture devices, Global Positioning System sensors, motion sensors, etc., as the vehicles travel along roadways. In some cases, the sparse map may be generated based on data collected during multiple drives of one or more vehicles along a particular roadway. Generating a sparse map using multiple drives of one or more vehicles may be referred to as “crowdsourcing” a sparse map. 
     Consistent with disclosed embodiments, an autonomous vehicle system may use a sparse map for navigation. For example, the disclosed systems and methods may distribute a sparse map for generating a road navigation model for an autonomous vehicle and may navigate an autonomous vehicle along a road segment using a sparse map and/or a generated road navigation model. Sparse maps consistent with the present disclosure may include one or more three-dimensional contours that may represent predetermined trajectories that autonomous vehicles may traverse as they move along associated road segments. 
     Sparse maps consistent with the present disclosure may also include data representing one or more road features. Such road features may include recognized landmarks, road signature profiles, and any other road-related features useful in navigating a vehicle. Sparse maps consistent with the present disclosure may enable autonomous navigation of a vehicle based on relatively small amounts of data included in the sparse map. For example, rather than including detailed representations of a road, such as road edges, road curvature, images associated with road segments, or data detailing other physical features associated with a road segment, the disclosed embodiments of the sparse map may require relatively little storage space (and relatively little bandwidth when portions of the sparse map are transferred to a vehicle) but may still adequately provide for autonomous vehicle navigation. The small data footprint of the disclosed sparse maps, discussed in further detail below, may be achieved in some embodiments by storing representations of road-related elements that require small amounts of data but still enable autonomous navigation. 
     For example, rather than storing detailed representations of various aspects of a road, the disclosed sparse maps may store polynomial representations of one or more trajectories that a vehicle may follow along the road. Thus, rather than storing (or having to transfer) details regarding the physical nature of the road to enable navigation along the road, using the disclosed sparse maps, a vehicle may be navigated along a particular road segment without, in some cases, having to interpret physical aspects of the road, but rather, by aligning its path of travel with a trajectory (e.g., a polynomial spline) along the particular road segment. In this way, the vehicle may be navigated based mainly upon the stored trajectory (e.g., a polynomial spline) that may require much less storage space than an approach involving storage of roadway images, road parameters, road layout, etc. 
     In addition to the stored polynomial representations of trajectories along a road segment, the disclosed sparse maps may also include small data objects that may represent a road feature. In some embodiments, the small data objects may include digital signatures, which are derived from a digital image (or a digital signal) that was obtained by a sensor (e.g., a camera or other sensor, such as a suspension sensor) onboard a vehicle traveling along the road segment. The digital signature may have a reduced size relative to the signal that was acquired by the sensor. In some embodiments, the digital signature may be created to be compatible with a classifier function that is configured to detect and to identify the road feature from the signal that is acquired by the sensor, for example, during a subsequent drive. In some embodiments, a digital signature may be created such that the digital signature has a footprint that is as small as possible, while retaining the ability to correlate or match the road feature with the stored signature based on an image (or a digital signal generated by a sensor, if the stored signature is not based on an image and/or includes other data) of the road feature that is captured by a camera onboard a vehicle traveling along the same road segment at a subsequent time. 
     In some embodiments, a size of the data objects may be further associated with a uniqueness of the road feature. For example, for a road feature that is detectable by a camera onboard a vehicle, and where the camera system onboard the vehicle is coupled to a classifier that is capable of distinguishing the image data corresponding to that road feature as being associated with a particular type of road feature, for example, a road sign, and where such a road sign is locally unique in that area (e.g., there is no identical road sign or road sign of the same type nearby), it may be sufficient to store data indicating the type of the road feature and its location. 
     As will be discussed in further detail below, road features (e.g., landmarks along a road segment) may be stored as small data objects that may represent a road feature in relatively few bytes, while at the same time providing sufficient information for recognizing and using such a feature for navigation. In one example, a road sign may be identified as a recognized landmark on which navigation of a vehicle may be based. A representation of the road sign may be stored in the sparse map to include, e.g., a few bytes of data indicating a type of landmark (e.g., a stop sign) and a few bytes of data indicating a location of the landmark (e.g., coordinates). Navigating based on such data-light representations of the landmarks (e.g., using representations sufficient for locating, recognizing, and navigating based upon the landmarks) may provide a desired level of navigational functionality associated with sparse maps without significantly increasing the data overhead associated with the sparse maps. This lean representation of landmarks (and other road features) may take advantage of the sensors and processors included onboard such vehicles that are configured to detect, identify, and/or classify certain road features. 
     When, for example, a sign or even a particular type of a sign is locally unique (e.g., when there is no other sign or no other sign of the same type) in a given area, the sparse map may use data indicating a type of a landmark (a sign or a specific type of sign), and during navigation (e.g., autonomous navigation) when a camera onboard an autonomous vehicle captures an image of the area including a sign (or of a specific type of sign), the processor may process the image, detect the sign (if indeed present in the image), classify the image as a sign (or as a specific type of sign), and correlate the location of the image with the location of the sign as stored in the sparse map. 
     Generating a Sparse Map 
     In some embodiments, a sparse map may include at least one line representation of a road surface feature extending along a road segment and a plurality of landmarks associated with the road segment. In certain aspects, the sparse map may be generated via “crowdsourcing,” for example, through image analysis of a plurality of images acquired as one or more vehicles traverse the road segment. 
       FIG.  8    shows a sparse map  800  that one or more vehicles, e.g., vehicle  200  (which may be an autonomous vehicle), may access for providing autonomous vehicle navigation. Sparse map  800  may be stored in a memory, such as memory  140  or  150 . Such memory devices may include any types of non-transitory storage devices or computer-readable media. For example, in some embodiments, memory  140  or  150  may include hard drives, compact discs, flash memory, magnetic based memory devices, optical based memory devices, etc. In some embodiments, sparse map  800  may be stored in a database (e.g., map database  160 ) that may be stored in memory  140  or  150 , or other types of storage devices. 
     In some embodiments, sparse map  800  may be stored on a storage device or a non-transitory computer-readable medium provided onboard vehicle  200  (e.g., a storage device included in a navigation system onboard vehicle  200 ). A processor (e.g., processing unit  110 ) provided on vehicle  200  may access sparse map  800  stored in the storage device or computer-readable medium provided onboard vehicle  200  in order to generate navigational instructions for guiding the autonomous vehicle  200  as the vehicle traverses a road segment. 
     Sparse map  800  need not be stored locally with respect to a vehicle, however. In some embodiments, sparse map  800  may be stored on a storage device or computer-readable medium provided on a remote server that communicates with vehicle  200  or a device associated with vehicle  200 . A processor (e.g., processing unit  110 ) provided on vehicle  200  may receive data included in sparse map  800  from the remote server and may execute the data for guiding the autonomous driving of vehicle  200 . In such embodiments, the remote server may store all of sparse map  800  or only a portion thereof. Accordingly, the storage device or computer-readable medium provided onboard vehicle  200  and/or onboard one or more additional vehicles may store the remaining portion(s) of sparse map  800 . 
     Furthermore, in such embodiments, sparse map  800  may be made accessible to a plurality of vehicles traversing various road segments (e.g., tens, hundreds, thousands, or millions of vehicles, etc.). It should be noted also that sparse map  800  may include multiple sub-maps. For example, in some embodiments, sparse map  800  may include hundreds, thousands, millions, or more, of sub-maps that may be used in navigating a vehicle. Such sub-maps may be referred to as local maps, and a vehicle traveling along a roadway may access any number of local maps relevant to a location in which the vehicle is traveling. The local map sections of sparse map  800  may be stored with a Global Navigation Satellite System (GNSS) key as an index to the database of sparse map  800 . Thus, while computation of steering angles for navigating a host vehicle in the present system may be performed without reliance upon a GNSS position of the host vehicle, road features, or landmarks, such GNSS information may be used for retrieval of relevant local maps. 
     In general, sparse map  800  may be generated based on data collected from one or more vehicles as they travel along roadways. For example, using sensors aboard the one or more vehicles (e.g., cameras, speedometers, GPS, accelerometers, etc.), the trajectories that the one or more vehicles travel along a roadway may be recorded, and the polynomial representation of a preferred trajectory for vehicles making subsequent trips along the roadway may be determined based on the collected trajectories travelled by the one or more vehicles. Similarly, data collected by the one or more vehicles may aid in identifying potential landmarks along a particular roadway. Data collected from traversing vehicles may also be used to identify road profile information, such as road width profiles, road roughness profiles, traffic line spacing profiles, road conditions, etc. Using the collected information, sparse map  800  may be generated and distributed (e.g., for local storage or via on-the-fly data transmission) for use in navigating one or more autonomous vehicles. However, in some embodiments, map generation may not end upon initial generation of the map. As will be discussed in greater detail below, sparse map  800  may be continuously or periodically updated based on data collected from vehicles as those vehicles continue to traverse roadways included in sparse map  800 . 
     Data recorded in sparse map  800  may include position information based on Global Positioning System (GPS) data. For example, location information may be included in sparse map  800  for various map elements, including, for example, landmark locations, road profile locations, etc. Locations for map elements included in sparse map  800  may be obtained using GPS data collected from vehicles traversing a roadway. For example, a vehicle passing an identified landmark may determine a location of the identified landmark using GPS position information associated with the vehicle and a determination of a location of the identified landmark relative to the vehicle (e.g., based on image analysis of data collected from one or more cameras on board the vehicle). Such location determinations of an identified landmark (or any other feature included in sparse map  800 ) may be repeated as additional vehicles pass the location of the identified landmark. Some or all of the additional location determinations may be used to refine the location information stored in sparse map  800  relative to the identified landmark. For example, in some embodiments, multiple position measurements relative to a particular feature stored in sparse map  800  may be averaged together. Any other mathematical operations, however, may also be used to refine a stored location of a map element based on a plurality of determined locations for the map element. 
     The sparse map of the disclosed embodiments may enable autonomous navigation of a vehicle using relatively small amounts of stored data. In some embodiments, sparse map  800  may have a data density (e.g., including data representing the target trajectories, landmarks, and any other stored road features) of less than 2 MB per kilometer of roads, less than 1 MB per kilometer of roads, less than 500 kB per kilometer of roads, or less than 100 kB per kilometer of roads. In some embodiments, the data density of sparse map  800  may be less than 10 kB per kilometer of roads or even less than 2 kB per kilometer of roads (e.g., 1.6 kB per kilometer), or no more than 10 kB per kilometer of roads, or no more than 20 kB per kilometer of roads. In some embodiments, most, if not all, of the roadways of the United States may be navigated autonomously using a sparse map having a total of 4 GB or less of data. These data density values may represent an average over an entire sparse map  800 , over a local map within sparse map  800 , and/or over a particular road segment within sparse map  800 . 
     As noted, sparse map  800  may include representations of a plurality of target trajectories  810  for guiding autonomous driving or navigation along a road segment. Such target trajectories may be stored as three-dimensional splines. The target trajectories stored in sparse map  800  may be determined based on two or more reconstructed trajectories of prior traversals of vehicles along a particular road segment, for example. A road segment may be associated with a single target trajectory or multiple target trajectories. For example, on a two lane road, a first target trajectory may be stored to represent an intended path of travel along the road in a first direction, and a second target trajectory may be stored to represent an intended path of travel along the road in another direction (e.g., opposite to the first direction). Additional target trajectories may be stored with respect to a particular road segment. For example, on a multi-lane road one or more target trajectories may be stored representing intended paths of travel for vehicles in one or more lanes associated with the multi-lane road. In some embodiments, each lane of a multi-lane road may be associated with its own target trajectory. In other embodiments, there may be fewer target trajectories stored than lanes present on a multi-lane road. In such cases, a vehicle navigating the multi-lane road may use any of the stored target trajectories to guides its navigation by taking into account an amount of lane offset from a lane for which a target trajectory is stored (e.g., if a vehicle is traveling in the left most lane of a three lane highway, and a target trajectory is stored only for the middle lane of the highway, the vehicle may navigate using the target trajectory of the middle lane by accounting for the amount of lane offset between the middle lane and the left-most lane when generating navigational instructions). 
     In some embodiments, the target trajectory may represent an ideal path that a vehicle should take as the vehicle travels. The target trajectory may be located, for example, at an approximate center of a lane of travel. In other cases, the target trajectory may be located elsewhere relative to a road segment. For example, a target trajectory may approximately coincide with a center of a road, an edge of a road, or an edge of a lane, etc. In such cases, navigation based on the target trajectory may include a determined amount of offset to be maintained relative to the location of the target trajectory. Moreover, in some embodiments, the determined amount of offset to be maintained relative to the location of the target trajectory may differ based on a type of vehicle (e.g., a passenger vehicle including two axles may have a different offset from a truck including more than two axles along at least a portion of the target trajectory). 
     Sparse map  800  may also include data relating to a plurality of predetermined landmarks  820  associated with particular road segments, local maps, etc. As discussed in greater detail below, these landmarks may be used in navigation of the autonomous vehicle. For example, in some embodiments, the landmarks may be used to determine a current position of the vehicle relative to a stored target trajectory. With this position information, the autonomous vehicle may be able to adjust a heading direction to match a direction of the target trajectory at the determined location. 
     The plurality of landmarks  820  may be identified and stored in sparse map  800  at any suitable spacing. In some embodiments, landmarks may be stored at relatively high densities (e.g., every few meters or more). In some embodiments, however, significantly larger landmark spacing values may be employed. For example, in sparse map  800 , identified (or recognized) landmarks may be spaced apart by 10 meters, 20 meters, 50 meters, 100 meters, 1 kilometer, or 2 kilometers. In some cases, the identified landmarks may be located at distances of even more than 2 kilometers apart. 
     Between landmarks, and therefore between determinations of vehicle position relative to a target trajectory, the vehicle may navigate based on dead reckoning in which the vehicle uses sensors to determine its ego motion and estimate its position relative to the target trajectory. Because errors may accumulate during navigation by dead reckoning, over time the position determinations relative to the target trajectory may become increasingly less accurate. The vehicle may use landmarks occurring in sparse map  800  (and their known locations) to remove the dead reckoning-induced errors in position determination. In this way, the identified landmarks included in sparse map  800  may serve as navigational anchors from which an accurate position of the vehicle relative to a target trajectory may be determined. Because a certain amount of error may be acceptable in position location, an identified landmark need not always be available to an autonomous vehicle. Rather, suitable navigation may be possible even based on landmark spacings, as noted above, of 10 meters, 20 meters, 50 meters, 100 meters, 500 meters, 1 kilometer, 2 kilometers, or more. In some embodiments, a density of 1 identified landmark every 1 km of road may be sufficient to maintain a longitudinal position determination accuracy within 1 m. Thus, not every potential landmark appearing along a road segment need be stored in sparse map  800 . 
     Moreover, in some embodiments, lane markings may be used for localization of the vehicle during landmark spacings. By using lane markings during landmark spacings, the accumulation of during navigation by dead reckoning may be minimized. 
     In addition to target trajectories and identified landmarks, sparse map  800  may include information relating to various other road features. For example,  FIG.  9 A  illustrates a representation of curves along a particular road segment that may be stored in sparse map  800 . In some embodiments, a single lane of a road may be modeled by a three-dimensional polynomial description of left and right sides of the road. Such polynomials representing left and right sides of a single lane are shown in  FIG.  9 A . Regardless of how many lanes a road may have, the road may be represented using polynomials in a way similar to that illustrated in  FIG.  9 A . For example, left and right sides of a multi-lane road may be represented by polynomials similar to those shown in  FIG.  9 A , and intermediate lane markings included on a multi-lane road (e.g., dashed markings representing lane boundaries, solid yellow lines representing boundaries between lanes traveling in different directions, etc.) may also be represented using polynomials such as those shown in  FIG.  9 A . 
     As shown in  FIG.  9 A , a lane  900  may be represented using polynomials (e.g., a first order, second order, third order, or any suitable order polynomials). For illustration, lane  900  is shown as a two-dimensional lane and the polynomials are shown as two-dimensional polynomials. As depicted in  FIG.  9 A , lane  900  includes a left side  910  and a right side  920 . In some embodiments, more than one polynomial may be used to represent a location of each side of the road or lane boundary. For example, each of left side  910  and right side  920  may be represented by a plurality of polynomials of any suitable length. In some cases, the polynomials may have a length of about 100 m, although other lengths greater than or less than 100 m may also be used. Additionally, the polynomials can overlap with one another in order to facilitate seamless transitions in navigating based on subsequently encountered polynomials as a host vehicle travels along a roadway. For example, each of left side  910  and right side  920  may be represented by a plurality of third order polynomials separated into segments of about 100 meters in length (an example of the first predetermined range), and overlapping each other by about 50 meters. The polynomials representing the left side  910  and the right side  920  may or may not have the same order. For example, in some embodiments, some polynomials may be second order polynomials, some may be third order polynomials, and some may be fourth order polynomials. 
     In the example shown in  FIG.  9 A , left side  910  of lane  900  is represented by two groups of third order polynomials. The first group includes polynomial segments  911 ,  912 , and  913 . The second group includes polynomial segments  914 ,  915 , and  916 . The two groups, while substantially parallel to each other, follow the locations of their respective sides of the road. Polynomial segments  911 ,  912 ,  913 ,  914 ,  915 , and  916  have a length of about 100 meters and overlap adjacent segments in the series by about 50 meters. As noted previously, however, polynomials of different lengths and different overlap amounts may also be used. For example, the polynomials may have lengths of 500 m, 1 km, or more, and the overlap amount may vary from 0 to 50 m, 50 m to 100 m, or greater than 100 m. Additionally, while  FIG.  9 A  is shown as representing polynomials extending in 2D space (e.g., on the surface of the paper), it is to be understood that these polynomials may represent curves extending in three dimensions (e.g., including a height component) to represent elevation changes in a road segment in addition to X-Y curvature. In the example shown in  FIG.  9 A , right side  920  of lane  900  is further represented by a first group having polynomial segments  921 ,  922 , and  923  and a second group having polynomial segments  924 ,  925 , and  926 . 
     Returning to the target trajectories of sparse map  800 ,  FIG.  9 B  shows a three-dimensional polynomial representing a target trajectory for a vehicle traveling along a particular road segment. The target trajectory represents not only the X-Y path that a host vehicle should travel along a particular road segment, but also the elevation change that the host vehicle will experience when traveling along the road segment. Thus, each target trajectory in sparse map  800  may be represented by one or more three-dimensional polynomials, like the three-dimensional polynomial  950  shown in  FIG.  9 B . Sparse map  800  may include a plurality of trajectories (e.g., millions or billions or more to represent trajectories of vehicles along various road segments along roadways throughout the world). In some embodiments, each target trajectory may correspond to a spline connecting three-dimensional polynomial segments. 
     Regarding the data footprint of polynomial curves stored in sparse map  800 , in some embodiments, each third degree polynomial may be represented by four parameters, each requiring four bytes of data. Suitable representations may be obtained with third degree polynomials requiring about 192 bytes of data for every 100 m. This may translate to approximately 200 kB per hour in data usage/transfer requirements for a host vehicle traveling approximately 100 km/hr. 
     Sparse map  800  may describe the lanes network using a combination of geometry descriptors and meta-data. The geometry may be described by polynomials or splines as described above. The meta-data may describe the number of lanes, special characteristics (such as a car pool lane), and possibly other sparse labels. The total footprint of such indicators may be negligible. 
     Accordingly, a sparse map according to embodiments of the present disclosure may include at least one line representation of a road surface feature extending along the road segment, each line representation representing a path along the road segment substantially corresponding with the road surface feature. In some embodiments, as discussed above, the at least one line representation of the road surface feature may include a spline, a polynomial representation, or a curve. Furthermore, in some embodiments, the road surface feature may include at least one of a road edge or a lane marking. Moreover, as discussed below with respect to “crowdsourcing,” the road surface feature may be identified through image analysis of a plurality of images acquired as one or more vehicles traverse the road segment. 
     As previously noted, sparse map  800  may include a plurality of predetermined landmarks associated with a road segment. Rather than storing actual images of the landmarks and relying, for example, on image recognition analysis based on captured images and stored images, each landmark in sparse map  800  may be represented and recognized using less data than a stored, actual image would require. Data representing landmarks may still include sufficient information for describing or identifying the landmarks along a road. Storing data describing characteristics of landmarks, rather than the actual images of landmarks, may reduce the size of sparse map  800 . 
       FIG.  10    illustrates examples of types of landmarks that may be represented in sparse map  800 . The landmarks may include any visible and identifiable objects along a road segment. The landmarks may be selected such that they are fixed and do not change often with respect to their locations and/or content. The landmarks included in sparse map  800  may be useful in determining a location of vehicle  200  with respect to a target trajectory as the vehicle traverses a particular road segment. Examples of landmarks may include traffic signs, directional signs, general signs (e.g., rectangular signs), roadside fixtures (e.g., lampposts, reflectors, etc.), and any other suitable category. In some embodiments, lane marks on the road, may also be included as landmarks in sparse map  800 . 
     Examples of landmarks shown in  FIG.  10    include traffic signs, directional signs, roadside fixtures, and general signs. Traffic signs may include, for example, speed limit signs (e.g., speed limit sign  1000 ), yield signs (e.g., yield sign  1005 ), route number signs (e.g., route number sign  1010 ), traffic light signs (e.g., traffic light sign  1015 ), stop signs (e.g., stop sign  1020 ). Directional signs may include a sign that includes one or more arrows indicating one or more directions to different places. For example, directional signs may include a highway sign  1025  having arrows for directing vehicles to different roads or places, an exit sign  1030  having an arrow directing vehicles off a road, etc. Accordingly, at least one of the plurality of landmarks may include a road sign. 
     General signs may be unrelated to traffic. For example, general signs may include billboards used for advertisement, or a welcome board adjacent a border between two countries, states, counties, cities, or towns.  FIG.  10    shows a general sign  1040  (“Joe&#39;s Restaurant”). Although general sign  1040  may have a rectangular shape, as shown in  FIG.  10   , general sign  1040  may have other shapes, such as square, circle, triangle, etc. 
     Landmarks may also include roadside fixtures. Roadside fixtures may be objects that are not signs, and may not be related to traffic or directions. For example, roadside fixtures may include lampposts (e.g., lamppost  1035 ), power line posts, traffic light posts, etc. 
     Landmarks may also include beacons that may be specifically designed for usage in an autonomous vehicle navigation system. For example, such beacons may include stand-alone structures placed at predetermined intervals to aid in navigating a host vehicle. Such beacons may also include visual/graphical information added to existing road signs (e.g., icons, emblems, bar codes, etc.) that may be identified or recognized by a vehicle traveling along a road segment. Such beacons may also include electronic components. In such embodiments, electronic beacons (e.g., RFID tags, etc.) may be used to transmit non-visual information to a host vehicle. Such information may include, for example, landmark identification and/or landmark location information that a host vehicle may use in determining its position along a target trajectory. 
     In some embodiments, the landmarks included in sparse map  800  may be represented by a data object of a predetermined size. The data representing a landmark may include any suitable parameters for identifying a particular landmark. For example, in some embodiments, landmarks stored in sparse map  800 ) may include parameters such as a physical size of the landmark (e.g., to support estimation of distance to the landmark based on a known size/scale), a distance to a previous landmark, lateral offset, height, a type code (e.g., a landmark type—what type of directional sign, traffic sign, etc.), a GPS coordinate (e.g., to support global localization), and any other suitable parameters. Each parameter may be associated with a data size. For example, a landmark size may be stored using 8 bytes of data. A distance to a previous landmark, a lateral offset, and height may be specified using 12 bytes of data. A type code associated with a landmark such as a directional sign or a traffic sign may require about 2 bytes of data. For general signs, an image signature enabling identification of the general sign may be stored using 50 bytes of data storage. The landmark GPS position may be associated with 16 bytes of data storage. These data sizes for each parameter are examples only, and other data sizes may also be used. 
     Representing landmarks in sparse map  800  in this manner may offer a lean solution for efficiently representing landmarks in the database. In some embodiments, signs may be referred to as semantic signs and non-semantic signs. A semantic sign may include any class of signs for which there&#39;s a standardized meaning (e.g., speed limit signs, warning signs, directional signs, etc.). A non-semantic sign may include any sign that is not associated with a standardized meaning (e.g., general advertising signs, signs identifying business establishments, etc.). For example, each semantic sign may be represented with 38 bytes of data (e.g., 8 bytes for size: 12 bytes for distance to previous landmark, lateral offset, and height: 2 bytes for a type code; and 16 bytes for GPS coordinates). Sparse map  800  may use a tag system to represent landmark types. In some cases, each traffic sign or directional sign may be associated with its own tag, which may be stored in the database as part of the landmark identification. For example, the database may include on the order of 1000 different tags to represent various traffic signs and on the order of about 10000 different tags to represent directional signs. Of course, any suitable number of tags may be used, and additional tags may be created as needed. General purpose signs may be represented in some embodiments using less than about 100 bytes (e.g., about 86 bytes including 8 bytes for size; 12 bytes for distance to previous landmark, lateral offset, and height: 50 bytes for an image signature; and 16 bytes for GPS coordinates). 
     Thus, for semantic road signs not requiring an image signature, the data density impact to sparse map  800 , even at relatively high landmark densities of about 1 per 50 m, may be on the order of about 760 bytes per kilometer (e.g., 20 landmarks per km×38 bytes per landmark=760 bytes). Even for general purpose signs including an image signature component, the data density impact is about 1.72 kB per km (e.g., 20 landmarks per km×86 bytes per landmark=1.720 bytes). For semantic road signs, this equates to about 76 kB per hour of data usage for a vehicle traveling 100 km/hr. For general purpose signs, this equates to about 170 kB per hour for a vehicle traveling 100 km/hr. 
     In some embodiments, a generally rectangular object, such as a rectangular sign, may be represented in sparse map  800  by no more than 100 bytes of data. The representation of the generally rectangular object (e.g., general sign  1040 ) in sparse map  800  may include a condensed image signature (e.g., condensed image signature  1045 ) associated with the generally rectangular object. This condensed image signature may be used, for example, to aid in identification of a general purpose sign, for example, as a recognized landmark. Such a condensed image signature (e.g., image information derived from actual image data representing an object) may avoid a need for storage of an actual image of an object or a need for comparative image analysis performed on actual images in order to recognize landmarks. 
     Referring to  FIG.  10   , sparse map  800  may include or store a condensed image signature  1045  associated with a general sign  1040 , rather than an actual image of general sign  1040 . For example, after an image capture device (e.g., image capture device  122 ,  124 , or  126 ) captures an image of general sign  1040 , a processor (e.g., image processor  190  or any other processor that can process images either aboard or remotely located relative to a host vehicle) may perform an image analysis to extract/create condensed image signature  1045  that includes a unique signature or pattern associated with general sign  1040 . In one embodiment, condensed image signature  1045  may include a shape, color pattern, a brightness pattern, or any other feature that may be extracted from the image of general sign  1040  for describing general sign  1040 . 
     For example, in  FIG.  10   , the circles, triangles, and stars shown in condensed image signature  1045  may represent areas of different colors. The pattern represented by the circles, triangles, and stars may be stored in sparse map  800 , e.g., within the 50 bytes designated to include an image signature. Notably, the circles, triangles, and stars are not necessarily meant to indicate that such shapes are stored as part of the image signature. Rather, these shapes are meant to conceptually represent recognizable areas having discernible color differences, textual areas, graphical shapes, or other variations in characteristics that may be associated with a general purpose sign. Such condensed image signatures can be used to identify a landmark in the form of a general sign. For example, the condensed image signature can be used to perform a same-not-same analysis based on a comparison of a stored condensed image signature with image data captured, for example, using a camera onboard an autonomous vehicle. 
     Accordingly, the plurality of landmarks may be identified through image analysis of the plurality of images acquired as one or more vehicles traverse the road segment. As explained below with respect to “crowdsourcing,” in some embodiments, the image analysis to identify the plurality of landmarks may include accepting potential landmarks when a ratio of images in which the landmark does appear to images in which the landmark does not appear exceeds a threshold. Furthermore, in some embodiments, the image analysis to identify the plurality of landmarks may include rejecting potential landmarks when a ratio of images in which the landmark does not appear to images in which the landmark does appear exceeds a threshold. 
     Returning to the target trajectories a host vehicle may use to navigate a particular road segment,  FIG.  11 A  shows polynomial representations trajectories capturing during a process of building or maintaining sparse map  800 . A polynomial representation of a target trajectory included in sparse map  800  may be determined based on two or more reconstructed trajectories of prior traversals of vehicles along the same road segment. In some embodiments, the polynomial representation of the target trajectory included in sparse map  800  may be an aggregation of two or more reconstructed trajectories of prior traversals of vehicles along the same road segment. In some embodiments, the polynomial representation of the target trajectory included in sparse map  800  may be an average of the two or more reconstructed trajectories of prior traversals of vehicles along the same road segment. Other mathematical operations may also be used to construct a target trajectory along a road path based on reconstructed trajectories collected from vehicles traversing along a road segment. 
     As shown in  FIG.  11 A , a road segment  1100  may be travelled by a number of vehicles  200  at different times. Each vehicle  200  may collect data relating to a path that the vehicle took along the road segment. The path traveled by a particular vehicle may be determined based on camera data, accelerometer information, speed sensor information, and/or GPS information, among other potential sources. Such data may be used to reconstruct trajectories of vehicles traveling along the road segment, and based on these reconstructed trajectories, a target trajectory (or multiple target trajectories) may be determined for the particular road segment. Such target trajectories may represent a preferred path of a host vehicle (e.g., guided by an autonomous navigation system) as the vehicle travels along the road segment. 
     In the example shown in  FIG.  11 A , a first reconstructed trajectory  1101  may be determined based on data received from a first vehicle traversing road segment  1100  at a first time period (e.g., day 1), a second reconstructed trajectory  1102  may be obtained from a second vehicle traversing road segment  1100  at a second time period (e.g., day 2), and a third reconstructed trajectory  1103  may be obtained from a third vehicle traversing road segment  1100  at a third time period (e.g., day 3). Each trajectory  1101 ,  1102 , and  1103  may be represented by a polynomial, such as a three-dimensional polynomial. It should be noted that in some embodiments, any of the reconstructed trajectories may be assembled onboard the vehicles traversing road segment  1100 . 
     Additionally, or alternatively, such reconstructed trajectories may be determined on a server side based on information received from vehicles traversing road segment  1100 . For example, in some embodiments, vehicles  200  may transmit data to one or more servers relating to their motion along road segment  1100  (e.g., steering angle, heading, time, position, speed, sensed road geometry, and/or sensed landmarks, among things). The server may reconstruct trajectories for vehicles  200  based on the received data. The server may also generate a target trajectory for guiding navigation of autonomous vehicle that will travel along the same road segment  1100  at a later time based on the first, second, and third trajectories  1101 ,  1102 , and  1103 . While a target trajectory may be associated with a single prior traversal of a road segment, in some embodiments, each target trajectory included in sparse map  800  may be determined based on two or more reconstructed trajectories of vehicles traversing the same road segment. In  FIG.  11 A , the target trajectory is represented by  1110 . In some embodiments, the target trajectory  1110  may be generated based on an average of the first, second, and third trajectories  1101 ,  1102 , and  1103 . In some embodiments, the target trajectory  1110  included in sparse map  800  may be an aggregation (e.g., a weighted combination) of two or more reconstructed trajectories. 
       FIGS.  11 B and  11 C  further illustrate the concept of target trajectories associated with road segments present within a geographic region  1111 . As shown in  FIG.  11 B , a first road segment  1120  within geographic region  1111  may include a multilane road, which includes two lanes  1122  designated for vehicle travel in a first direction and two additional lanes  1124  designated for vehicle travel in a second direction opposite to the first direction. Lanes  1122  and lanes  1124  may be separated by a double yellow line  1123 . Geographic region  1111  may also include a branching road segment  1130  that intersects with road segment  1120 . Road segment  1130  may include a two-lane road, each lane being designated for a different direction of travel. Geographic region  1111  may also include other road features, such as a stop line  1132 , a stop sign  1134 , a speed limit sign  1136 , and a hazard sign  1138 . 
     As shown in  FIG.  11 C , sparse map  800  may include a local map  1140  including a road model for assisting with autonomous navigation of vehicles within geographic region  1111 . For example, local map  1140  may include target trajectories for one or more lanes associated with road segments  1120  and/or  1130  within geographic region  1111 . For example, local map  1140  may include target trajectories  1141  and/or  1142  that an autonomous vehicle may access or rely upon when traversing lanes  1122 . Similarly, local map  1140  may include target trajectories  1143  and/or  1144  that an autonomous vehicle may access or rely upon when traversing lanes  1124 . Further, local map  1140  may include target trajectories  1145  and/or  1146  that an autonomous vehicle may access or rely upon when traversing road segment  1130 . Target trajectory  1147  represents a preferred path an autonomous vehicle should follow when transitioning from lanes  1120  (and specifically, relative to target trajectory  1141  associated with a right-most lane of lanes  1120 ) to road segment  1130  (and specifically, relative to a target trajectory  1145  associated with a first side of road segment  1130 . Similarly, target trajectory  1148  represents a preferred path an autonomous vehicle should follow when transitioning from road segment  1130  (and specifically, relative to target trajectory  1146 ) to a portion of road segment  1124  (and specifically, as shown, relative to a target trajectory  1143  associated with a left lane of lanes  1124 . 
     Sparse map  800  may also include representations of other road-related features associated with geographic region  1111 . For example, sparse map  800  may also include representations of one or more landmarks identified in geographic region  1111 . Such landmarks may include a first landmark  1150  associated with stop line  1132 , a second landmark  1152  associated with stop sign  1134 , a third landmark associated with speed limit sign  1154 , and a fourth landmark  1156  associated with hazard sign  1138 . Such landmarks may be used, for example, to assist an autonomous vehicle in determining its current location relative to any of the shown target trajectories, such that the vehicle may adjust its heading to match a direction of the target trajectory at the determined location. 
     In some embodiments, sparse map  800  may also include road signature profiles. Such road signature profiles may be associated with any discernible/measurable variation in at least one parameter associated with a road. For example, in some cases, such profiles may be associated with variations in road surface information such as variations in surface roughness of a particular road segment, variations in road width over a particular road segment, variations in distances between dashed lines painted along a particular road segment, variations in road curvature along a particular road segment, etc.  FIG.  11 D  shows an example of a road signature profile  1160 . While profile  1160  may represent any of the parameters mentioned above, or others, in one example, profile  1160  may represent a measure of road surface roughness, as obtained, for example, by monitoring one or more sensors providing outputs indicative of an amount of suspension displacement as a vehicle travels a particular road segment. 
     Alternatively or concurrently, profile  1160  may represent variation in road width, as determined based on image data obtained via a camera onboard a vehicle traveling a particular road segment. Such profiles may be useful, for example, in determining a particular location of an autonomous vehicle relative to a particular target trajectory. That is, as it traverses a road segment, an autonomous vehicle may measure a profile associated with one or more parameters associated with the road segment. If the measured profile can be correlated/matched with a predetermined profile that plots the parameter variation with respect to position along the road segment, then the measured and predetermined profiles may be used (e.g., by overlaying corresponding sections of the measured and predetermined profiles) in order to determine a current position along the road segment and, therefore, a current position relative to a target trajectory for the road segment. 
     In some embodiments, sparse map  800  may include different trajectories based on different characteristics associated with a user of autonomous vehicles, environmental conditions, and/or other parameters relating to driving. For example, in some embodiments, different trajectories may be generated based on different user preferences and/or profiles. Sparse map  800  including such different trajectories may be provided to different autonomous vehicles of different users. For example, some users may prefer to avoid toll roads, while others may prefer to take the shortest or fastest routes, regardless of whether there is a toll road on the route. The disclosed systems may generate different sparse maps with different trajectories based on such different user preferences or profiles. As another example, some users may prefer to travel in a fast moving lane, while others may prefer to maintain a position in the central lane at all times. 
     Different trajectories may be generated and included in sparse map  800  based on different environmental conditions, such as day and night, snow, rain, fog, etc. Autonomous vehicles driving under different environmental conditions may be provided with sparse map  800  generated based on such different environmental conditions. In some embodiments, cameras provided on autonomous vehicles may detect the environmental conditions, and may provide such information back to a server that generates and provides sparse maps. For example, the server may generate or update an already generated sparse map  800  to include trajectories that may be more suitable or safer for autonomous driving under the detected environmental conditions. The update of sparse map  800  based on environmental conditions may be performed dynamically as the autonomous vehicles are traveling along roads. 
     Other different parameters relating to driving may also be used as a basis for generating and providing different sparse maps to different autonomous vehicles. For example, when an autonomous vehicle is traveling at a high speed, turns may be tighter. Trajectories associated with specific lanes, rather than roads, may be included in sparse map  800  such that the autonomous vehicle may maintain within a specific lane as the vehicle follows a specific trajectory. When an image captured by a camera onboard the autonomous vehicle indicates that the vehicle has drifted outside of the lane (e.g., crossed the lane mark), an action may be triggered within the vehicle to bring the vehicle back to the designated lane according to the specific trajectory. 
     Crowdsourcing a Sparse Man 
     In some embodiments, the disclosed systems and methods may generate a sparse map for autonomous vehicle navigation. For example, disclosed systems and methods may use crowdsourced data for generation of a sparse that one or more autonomous vehicles may use to navigate along a system of roads. As used herein, “crowdsourcing” means that data are received from various vehicles (e.g., autonomous vehicles) travelling on a road segment at different times, and such data are used to generate and/or update the road model. The model may, in turn, be transmitted to the vehicles or other vehicles later travelling along the road segment for assisting autonomous vehicle navigation. The road model may include a plurality of target trajectories representing preferred trajectories that autonomous vehicles should follow as they traverse a road segment. The target trajectories may be the same as a reconstructed actual trajectory collected from a vehicle traversing a road segment, which may be transmitted from the vehicle to a server. In some embodiments, the target trajectories may be different from actual trajectories that one or more vehicles previously took when traversing a road segment. The target trajectories may be generated based on actual trajectories (e.g., through averaging or any other suitable operation). 
     The vehicle trajectory data that a vehicle may upload to a server may correspond with the actual reconstructed trajectory for the vehicle or may correspond to a recommended trajectory, which may be based on or related to the actual reconstructed trajectory of the vehicle, but may differ from the actual reconstructed trajectory. For example, vehicles may modify their actual, reconstructed trajectories and submit (e.g., recommend) to the server the modified actual trajectories. The road model may use the recommended, modified trajectories as target trajectories for autonomous navigation of other vehicles. 
     In addition to trajectory information, other information for potential use in building a sparse data map  800  may include information relating to potential landmark candidates. For example, through crowd sourcing of information, the disclosed systems and methods may identify potential landmarks in an environment and refine landmark positions. The landmarks may be used by a navigation system of autonomous vehicles to determine and/or adjust the position of the vehicle along the target trajectories. 
     The reconstructed trajectories that a vehicle may generate as the vehicle travels along a road may be obtained by any suitable method. In some embodiments, the reconstructed trajectories may be developed by stitching together segments of motion for the vehicle, using, e.g., ego motion estimation (e.g., three dimensional translation and three dimensional rotation of the camera, and hence the body of the vehicle). The rotation and translation estimation may be determined based on analysis of images captured by one or more image capture devices along with information from other sensors or devices, such as inertial sensors and speed sensors. For example, the inertial sensors may include an accelerometer or other suitable sensors configured to measure changes in translation and/or rotation of the vehicle body. The vehicle may include a speed sensor that measures a speed of the vehicle. 
     In some embodiments, the ego motion of the camera (and hence the vehicle body) may be estimated based on an optical flow analysis of the captured images. An optical flow analysis of a sequence of images identifies movement of pixels from the sequence of images, and based on the identified movement, determines motions of the vehicle. The ego motion may be integrated over time and along the road segment to reconstruct a trajectory associated with the road segment that the vehicle has followed. 
     Data (e.g., reconstructed trajectories) collected by multiple vehicles in multiple drives along a road segment at different times may be used to construct the road model (e.g., including the target trajectories, etc.) included in sparse data map  800 . Data collected by multiple vehicles in multiple drives along a road segment at different times may also be averaged to increase an accuracy of the model. In some embodiments, data regarding the road geometry and/or landmarks may be received from multiple vehicles that travel through the common road segment at different times. Such data received from different vehicles may be combined to generate the road model and/or to update the road model. 
     The geometry of a reconstructed trajectory (and also a target trajectory) along a road segment may be represented by a curve in three dimensional space, which may be a spline connecting three dimensional polynomials. The reconstructed trajectory curve may be determined from analysis of a video stream or a plurality of images captured by a camera installed on the vehicle. In some embodiments, a location is identified in each frame or image that is a few meters ahead of the current position of the vehicle. This location is where the vehicle is expected to travel to in a predetermined time period. This operation may be repeated frame by frame, and at the same time, the vehicle may compute the camera&#39;s ego motion (rotation and translation). At each frame or image, a short range model for the desired path is generated by the vehicle in a reference frame that is attached to the camera. The short range models may be stitched together to obtain a three dimensional model of the road in some coordinate frame, which may be an arbitrary or predetermined coordinate frame. The three dimensional model of the road may then be fitted by a spline, which may include or connect one or more polynomials of suitable orders. 
     To conclude the short range road model at each frame, one or more detection modules may be used. For example, a bottom-up lane detection module may be used. The bottom-up lane detection module may be useful when lane marks are drawn on the road. This module may look for edges in the image and assembles them together to form the lane marks. A second module may be used together with the bottom-up lane detection module. The second module is an end-to-end deep neural network, which may be trained to predict the correct short range path from an input image. In both modules, the road model may be detected in the image coordinate frame and transformed to a three dimensional space that may be virtually attached to the camera. 
     Although the reconstructed trajectory modeling method may introduce an accumulation of errors due to the integration of ego motion over a long period of time, which may include a noise component, such errors may be inconsequential as the generated model may provide sufficient accuracy for navigation over a local scale. In addition, it is possible to cancel the integrated error by using external sources of information, such as satellite images or geodetic measurements. For example, the disclosed systems and methods may use a GNSS receiver to cancel accumulated errors. However, the GNSS positioning signals may not be always available and accurate. The disclosed systems and methods may enable a steering application that depends weakly on the availability and accuracy of GNSS positioning. In such systems, the usage of the GNSS signals may be limited. For example, in some embodiments, the disclosed systems may use the GNSS signals for database indexing purposes only. 
     In some embodiments, the range scale (e.g., local scale) that may be relevant for an autonomous vehicle navigation steering application may be on the order of 50 meters, 100 meters, 200 meters, 300 meters, etc. Such distances may be used, as the geometrical road model is mainly used for two purposes: planning the trajectory ahead and localizing the vehicle on the road model. In some embodiments, the planning task may use the model over a typical range of 40 meters ahead (or any other suitable distance ahead, such as 20 meters, 30 meters, 50 meters), when the control algorithm steers the vehicle according to a target point located 1.3 seconds ahead (or any other time such as 1.5 seconds, 1.7 seconds, 2 seconds, etc.). The localization task uses the road model over a typical range of 60 meters behind the car (or any other suitable distances, such as 50 meters, 100 meters, 150 meters, etc.), according to a method called “tail alignment” described in more detail in another section. The disclosed systems and methods may generate a geometrical model that has sufficient accuracy over particular range, such as 100 meters, such that a planned trajectory will not deviate by more than, for example, 30 cm from the lane center. 
     As explained above, a three dimensional road model may be constructed from detecting short range sections and stitching them together. The stitching may be enabled by computing a six degree ego motion model, using the videos and/or images captured by the camera, data from the inertial sensors that reflect the motions of the vehicle, and the host vehicle velocity signal. The accumulated error may be small enough over some local range scale, such as of the order of 100 meters. All this may be completed in a single drive over a particular road segment. 
     In some embodiments, multiple drives may be used to average the resulted model, and to increase its accuracy further. The same car may travel the same route multiple times, or multiple cars may send their collected model data to a central server. In any case, a matching procedure may be performed to identify overlapping models and to enable averaging in order to generate target trajectories. The constructed model (e.g., including the target trajectories) may be used for steering once a convergence criterion is met. Subsequent drives may be used for further model improvements and in order to accommodate infrastructure changes. 
     Sharing of driving experience (such as sensed data) between multiple cars becomes feasible if they are connected to a central server. Each vehicle client may store a partial copy of a universal road model, which may be relevant for its current position. A bidirectional update procedure between the vehicles and the server may be performed by the vehicles and the server. The small footprint concept discussed above enables the disclosed systems and methods to perform the bidirectional updates using a very small bandwidth. 
     Information relating to potential landmarks may also be determined and forwarded to a central server. For example, the disclosed systems and methods may determine one or more physical properties of a potential landmark based on one or more images that include the landmark. The physical properties may include a physical size (e.g., height, width) of the landmark, a distance from a vehicle to a landmark, a distance between the landmark to a previous landmark, the lateral position of the landmark (e.g., the position of the landmark relative to the lane of travel), the GPS coordinates of the landmark, a type of landmark, identification of text on the landmark, etc. For example, a vehicle may analyze one or more images captured by a camera to detect a potential landmark, such as a speed limit sign. 
     The vehicle may determine a distance from the vehicle to the landmark based on the analysis of the one or more images. In some embodiments, the distance may be determined based on analysis of images of the landmark using a suitable image analysis method, such as a scaling method and/or an optical flow method. In some embodiments, the disclosed systems and methods may be configured to determine a type or classification of a potential landmark. In case the vehicle determines that a certain potential landmark corresponds to a predetermined type or classification stored in a sparse map, it may be sufficient for the vehicle to communicate to the server an indication of the type or classification of the landmark, along with its location. The server may store such indications. At a later time, other vehicles may capture an image of the landmark, process the image (e.g., using a classifier), and compare the result from processing the image to the indication stored in the server with regard to the type of landmark. There may be various types of landmarks, and different types of landmarks may be associated with different types of data to be uploaded to and stored in the server, different processing onboard the vehicle may detects the landmark and communicate information about the landmark to the server, and the system onboard the vehicle may receive the landmark data from the server and use the landmark data for identifying a landmark in autonomous navigation. 
     In some embodiments, multiple autonomous vehicles travelling on a road segment may communicate with a server. The vehicles (or clients) may generate a curve describing its drive (e.g., through ego motion integration) in an arbitrary coordinate frame. The vehicles may detect landmarks and locate them in the same frame. The vehicles may upload the curve and the landmarks to the server. The server may collect data from vehicles over multiple drives, and generate a unified road model. For example, as discussed below with respect to  FIG.  19   , the server may generate a sparse map having the unified road model using the uploaded curves and landmarks. 
     The server may also distribute the model to clients (e.g., vehicles). For example, the server may distribute the sparse map to one or more vehicles. The server may continuously or periodically update the model when receiving new data from the vehicles. For example, the server may process the new data to evaluate whether the data includes information that should trigger an updated, or creation of new data on the server. The server may distribute the updated model or the updates to the vehicles for providing autonomous vehicle navigation. 
     The server may use one or more criteria for determining whether new data received from the vehicles should trigger an update to the model or trigger creation of new data. For example, when the new data indicates that a previously recognized landmark at a specific location no longer exists, or is replaced by another landmark, the server may determine that the new data should trigger an update to the model. As another example, when the new data indicates that a road segment has been closed, and when this has been corroborated by data received from other vehicles, the server may determine that the new data should trigger an update to the model. 
     The server may distribute the updated model (or the updated portion of the model) to one or more vehicles that are traveling on the road segment, with which the updates to the model are associated. The server may also distribute the updated model to vehicles that are about to travel on the road segment, or vehicles whose planned trip includes the road segment, with which the updates to the model are associated. For example, while an autonomous vehicle is traveling along another road segment before reaching the road segment with which an update is associated, the server may distribute the updates or updated model to the autonomous vehicle before the vehicle reaches the road segment. 
     In some embodiments, the remote server may collect trajectories and landmarks from multiple clients (e.g., vehicles that travel along a common road segment). The server may match curves using landmarks and create an average road model based on the trajectories collected from the multiple vehicles. The server may also compute a graph of roads and the most probable path at each node or conjunction of the road segment. For example, the remote server may align the trajectories to generate a crowdsourced sparse map from the collected trajectories. 
     The server may average landmark properties received from multiple vehicles that travelled along the common road segment, such as the distances between one landmark to another (e.g., a previous one along the road segment) as measured by multiple vehicles, to determine an arc-length parameter and support localization along the path and speed calibration for each client vehicle. The server may average the physical dimensions of a landmark measured by multiple vehicles travelled along the common road segment and recognized the same landmark. The averaged physical dimensions may be used to support distance estimation, such as the distance from the vehicle to the landmark. The server may average lateral positions of a landmark (e.g., position from the lane in which vehicles are travelling in to the landmark) measured by multiple vehicles travelled along the common road segment and recognized the same landmark. The averaged lateral portion may be used to support lane assignment. The server may average the GPS coordinates of the landmark measured by multiple vehicles travelled along the same road segment and recognized the same landmark. The averaged GPS coordinates of the landmark may be used to support global localization or positioning of the landmark in the road model. 
     In some embodiments, the server may identify model changes, such as constructions, detours, new signs, removal of signs, etc., based on data received from the vehicles. The server may continuously or periodically or instantaneously update the model upon receiving new data from the vehicles. The server may distribute updates to the model or the updated model to vehicles for providing autonomous navigation. For example, as discussed further below, the server may use crowdsourced data to filter out “ghost” landmarks detected by vehicles. 
     In some embodiments, the server may analyze driver interventions during the autonomous driving. The server may analyze data received from the vehicle at the time and location where intervention occurs, and/or data received prior to the time the intervention occurred. The server may identify certain portions of the data that caused or are closely related to the intervention, for example, data indicating a temporary lane closure setup, data indicating a pedestrian in the road. The server may update the model based on the identified data. For example, the server may modify one or more trajectories stored in the model. 
       FIG.  12    is a schematic illustration of a system that uses crowdsourcing to generate a sparse map (as well as distribute and navigate using a crowdsourced sparse map).  FIG.  12    shows a road segment  1200  that includes one or more lanes. A plurality of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may travel on road segment  1200  at the same time or at different times (although shown as appearing on road segment  1200  at the same time in  FIG.  12   ). At least one of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may be an autonomous vehicle. For simplicity of the present example, all of the vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  are presumed to be autonomous vehicles. 
     Each vehicle may be similar to vehicles disclosed in other embodiments (e.g., vehicle  200 ), and may include components or devices included in or associated with vehicles disclosed in other embodiments. Each vehicle may be equipped with an image capture device or camera (e.g., image capture device  122  or camera  122 ). Each vehicle may communicate with a remote server  1230  via one or more networks (e.g., over a cellular network and/or the Internet, etc.) through wireless communication paths  1235 , as indicated by the dashed lines. Each vehicle may transmit data to server  1230  and receive data from server  1230 . For example, server  1230  may collect data from multiple vehicles travelling on the road segment  1200  at different times, and may process the collected data to generate an autonomous vehicle road navigation model, or an update to the model. Server  1230  may transmit the autonomous vehicle road navigation model or the update to the model to the vehicles that transmitted data to server  1230 . Server  1230  may transmit the autonomous vehicle road navigation model or the update to the model to other vehicles that travel on road segment  1200  at later times. 
     As vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  travel on road segment  1200 , navigation information collected (e.g., detected, sensed, or measured) by vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may be transmitted to server  1230 . In some embodiments, the navigation information may be associated with the common road segment  1200 . The navigation information may include a trajectory associated with each of the vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  as each vehicle travels over road segment  1200 . In some embodiments, the trajectory may be reconstructed based on data sensed by various sensors and devices provided on vehicle  1205 . For example, the trajectory may be reconstructed based on at least one of accelerometer data, speed data, landmarks data, road geometry or profile data, vehicle positioning data, and ego motion data. In some embodiments, the trajectory may be reconstructed based on data from inertial sensors, such as accelerometer, and the velocity of vehicle  1205  sensed by a speed sensor. In addition, in some embodiments, the trajectory may be determined (e.g., by a processor onboard each of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 ) based on sensed ego motion of the camera, which may indicate three dimensional translation and/or three dimensional rotations (or rotational motions). The ego motion of the camera (and hence the vehicle body) may be determined from analysis of one or more images captured by the camera. 
     In some embodiments, the trajectory of vehicle  1205  may be determined by a processor provided aboard vehicle  1205  and transmitted to server  1230 . In other embodiments, server  1230  may receive data sensed by the various sensors and devices provided in vehicle  1205 , and determine the trajectory based on the data received from vehicle  1205 . 
     In some embodiments, the navigation information transmitted from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  to server  1230  may include data regarding the road surface, the road geometry, or the road profile. The geometry of road segment  1200  may include lane structure and/or landmarks. The lane structure may include the total number of lanes of road segment  1200 , the type of lanes (e.g., one-way lane, two-way lane, driving lane, passing lane, etc.), markings on lanes, width of lanes, etc. In some embodiments, the navigation information may include a lane assignment, e.g., which lane of a plurality of lanes a vehicle is traveling in. For example, the lane assignment may be associated with a numerical value “3” indicating that the vehicle is traveling on the third lane from the left or right. As another example, the lane assignment may be associated with a text value “center lane” indicating the vehicle is traveling on the center lane. 
     Server  1230  may store the navigation information on a non-transitory computer-readable medium, such as a hard drive, a compact disc, a tape, a memory, etc. Server  1230  may generate (e.g., through a processor included in server  1230 ) at least a portion of an autonomous vehicle road navigation model for the common road segment  1200  based on the navigation information received from the plurality of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  and may store the model as a portion of a sparse map. Server  1230  may determine a trajectory associated with each lane based on crowdsourced data (e.g., navigation information) received from multiple vehicles (e.g.,  1205 ,  1210 ,  1215 ,  1220 , and  1225 ) that travel on a lane of road segment at different times. Server  1230  may generate the autonomous vehicle road navigation model or a portion of the model (e.g., an updated portion) based on a plurality of trajectories determined based on the crowd sourced navigation data. Server  1230  may transmit the model or the updated portion of the model to one or more of autonomous vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  traveling on road segment  1200  or any other autonomous vehicles that travel on road segment at a later time for updating an existing autonomous vehicle road navigation model provided in a navigation system of the vehicles. The autonomous vehicle road navigation model may be used by the autonomous vehicles in autonomously navigating along the common road segment  1200 . 
     As explained above, the autonomous vehicle road navigation model may be included in a sparse map (e.g., sparse map  800  depicted in  FIG.  8   ). Sparse map  800  may include sparse recording of data related to road geometry and/or landmarks along a road, which may provide sufficient information for guiding autonomous navigation of an autonomous vehicle, yet does not require excessive data storage. In some embodiments, the autonomous vehicle road navigation model may be stored separately from sparse map  800 , and may use map data from sparse map  800  when the model is executed for navigation. In some embodiments, the autonomous vehicle road navigation model may use map data included in sparse map  800  for determining target trajectories along road segment  1200  for guiding autonomous navigation of autonomous vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  or other vehicles that later travel along road segment  1200 . For example, when the autonomous vehicle road navigation model is executed by a processor included in a navigation system of vehicle  1205 , the model may cause the processor to compare the trajectories determined based on the navigation information received from vehicle  1205  with predetermined trajectories included in sparse map  800  to validate and/or correct the current traveling course of vehicle  1205 . 
     In the autonomous vehicle road navigation model, the geometry of a road feature or target trajectory may be encoded by a curve in a three-dimensional space. In one embodiment, the curve may be a three dimensional spline including one or more connecting three dimensional polynomials. As one of skill in the art would understand, a spline may be a numerical function that is piece-wise defined by a series of polynomials for fitting data. A spline for fitting the three dimensional geometry data of the road may include a linear spline (first order), a quadratic spline (second order), a cubic spline (third order), or any other splines (other orders), or a combination thereof. The spline may include one or more three dimensional polynomials of different orders connecting (e.g., fitting) data points of the three dimensional geometry data of the road. In some embodiments, the autonomous vehicle road navigation model may include a three dimensional spline corresponding to a target trajectory along a common road segment (e.g., road segment  1200 ) or a lane of the road segment  1200 . 
     As explained above, the autonomous vehicle road navigation model included in the sparse map may include other information, such as identification of at least one landmark along road segment  1200 . The landmark may be visible within a field of view of a camera (e.g., camera  122 ) installed on each of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . In some embodiments, camera  122  may capture an image of a landmark. A processor (e.g., processor  180 ,  190 , or processing unit  110 ) provided on vehicle  1205  may process the image of the landmark to extract identification information for the landmark. The landmark identification information, rather than an actual image of the landmark, may be stored in sparse map  800 . The landmark identification information may require much less storage space than an actual image. Other sensors or systems (e.g., GPS system) may also provide certain identification information of the landmark (e.g., position of landmark). The landmark may include at least one of a traffic sign, an arrow marking, a lane marking, a dashed lane marking, a traffic light, a stop line, a directional sign (e.g., a highway exit sign with an arrow indicating a direction, a highway sign with arrows pointing to different directions or places), a landmark beacon, or a lamppost. A landmark beacon refers to a device (e.g., an RFID device) installed along a road segment that transmits or reflects a signal to a receiver installed on a vehicle, such that when the vehicle passes by the device, the beacon received by the vehicle and the location of the device (e.g., determined from GPS location of the device) may be used as a landmark to be included in the autonomous vehicle road navigation model and/or the sparse map  800 . 
     The identification of at least one landmark may include a position of the at least one landmark. The position of the landmark may be determined based on position measurements performed using sensor systems (e.g., Global Positioning Systems, inertial based positioning systems, landmark beacon, etc.) associated with the plurality of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . In some embodiments, the position of the landmark may be determined by averaging the position measurements detected, collected, or received by sensor systems on different vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  through multiple drives. For example, vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may transmit position measurements data to server  1230 , which may average the position measurements and use the averaged position measurement as the position of the landmark. The position of the landmark may be continuously refined by measurements received from vehicles in subsequent drives. 
     The identification of the landmark may include a size of the landmark. The processor provided on a vehicle (e.g.,  1205 ) may estimate the physical size of the landmark based on the analysis of the images. Server  1230  may receive multiple estimates of the physical size of the same landmark from different vehicles over different drives. Server  1230  may average the different estimates to arrive at a physical size for the landmark, and store that landmark size in the road model. The physical size estimate may be used to further determine or estimate a distance from the vehicle to the landmark. The distance to the landmark may be estimated based on the current speed of the vehicle and a scale of expansion based on the position of the landmark appearing in the images relative to the focus of expansion of the camera. For example, the distance to landmark may be estimated by Z=V*dt*R/D, where V is the speed of vehicle, R is the distance in the image from the landmark at time t1 to the focus of expansion, and D is the change in distance for the landmark in the image from t1 to t2, dt represents the (t2−t1). For example, the distance to landmark may be estimated by Z=V*dt*R/D, where V is the speed of vehicle, R is the distance in the image between the landmark and the focus of expansion, dt is a time interval, and D is the image displacement of the landmark along the epipolar line. Other equations equivalent to the above equation, such as Z=V*ω/Δω, may be used for estimating the distance to the landmark. Here, V is the vehicle speed, ω is an image length (like the object width), and Δω is the change of that image length in a unit of time. 
     When the physical size of the landmark is known, the distance to the landmark may also be determined based on the following equation: Z=f*W/ω, where f is the focal length, W is the size of the landmark (e.g., height or width), ω is the number of pixels when the landmark leaves the image. From the above equation, a change in distance Z may be calculated using ΔZ=f*W*Δω/ω 2 +f*ΔW/ω, where ΔW decays to zero by averaging, and where Δω is the number of pixels representing a bounding box accuracy in the image. A value estimating the physical size of the landmark may be calculated by averaging multiple observations at the server side. The resulting error in distance estimation may be very small. There are two sources of error that may occur when using the formula above, namely ΔW and Δω. Their contribution to the distance error is given by ΔZ=f*W*Δω/ω 2 +f*ΔW/ω. However, ΔW decays to zero by averaging; hence ΔZ is determined by Δω (e.g., the inaccuracy of the bounding box in the image). 
     For landmarks of unknown dimensions, the distance to the landmark may be estimated by tracking feature points on the landmark between successive frames. For example, certain features appearing on a speed limit sign may be tracked between two or more image frames. Based on these tracked features, a distance distribution per feature point may be generated. The distance estimate may be extracted from the distance distribution. For example, the most frequent distance appearing in the distance distribution may be used as the distance estimate. As another example, the average of the distance distribution may be used as the distance estimate. 
       FIG.  13    illustrates an example autonomous vehicle road navigation model represented by a plurality of three dimensional splines  1301 ,  1302 , and  1303 . The curves  1301 ,  1302 , and  1303  shown in  FIG.  13    are for illustration purpose only. Each spline may include one or more three dimensional polynomials connecting a plurality of data points  1310 . Each polynomial may be a first order polynomial, a second order polynomial, a third order polynomial, or a combination of any suitable polynomials having different orders. Each data point  1310  may be associated with the navigation information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . In some embodiments, each data point  1310  may be associated with data related to landmarks (e.g., size, location, and identification information of landmarks) and/or road signature profiles (e.g., road geometry, road roughness profile, road curvature profile, road width profile). In some embodiments, some data points  1310  may be associated with data related to landmarks, and others may be associated with data related to road signature profiles. 
       FIG.  14    illustrates raw location data  1410  (e.g., GPS data) received from five separate drives. One drive may be separate from another drive if it was traversed by separate vehicles at the same time, by the same vehicle at separate times, or by separate vehicles at separate times. To account for errors in the location data  1410  and for differing locations of vehicles within the same lane (e.g., one vehicle may drive closer to the left of a lane than another), server  1230  may generate a map skeleton  1420  using one or more statistical techniques to determine whether variations in the raw location data  1410  represent actual divergences or statistical errors. Each path within skeleton  1420  may be linked back to the raw data  1410  that formed the path. For example, the path between A and B within skeleton  1420  is linked to raw data  1410  from drives 2, 3, 4, and 5 but not from drive 1. Skeleton  1420  may not be detailed enough to be used to navigate a vehicle (e.g., because it combines drives from multiple lanes on the same road unlike the splines described above) but may provide useful topological information and may be used to define intersections. 
       FIG.  15    illustrates an example by which additional detail may be generated for a sparse map within a segment of a map skeleton (e.g., segment A to B within skeleton  1420 ). As depicted in  FIG.  15   , the data (e.g. ego-motion data, road markings data, and the like) may be shown as a function of position S (or S 1  or S 2 ) along the drive. Server  1230  may identify landmarks for the sparse map by identifying unique matches between landmarks  1501 ,  1503 , and  1505  of drive  1510  and landmarks  1507  and  1509  of drive  1520 . Such a matching algorithm may result in identification of landmarks  1511 ,  1513 , and  1515 . One skilled in the art would recognize, however, that other matching algorithms may be used. For example, probability optimization may be used in lieu of or in combination with unique matching. Server  1230  may longitudinally align the drives to align the matched landmarks. For example, server  1230  may select one drive (e.g., drive  1520 ) as a reference drive and then shift and/or elastically stretch the other drive(s) (e.g., drive  1510 ) for alignment. 
       FIG.  16    shows an example of aligned landmark data for use in a sparse map. In the example of  FIG.  16   , landmark  1610  comprises a road sign. The example of  FIG.  16    further depicts data from a plurality of drives  1601 ,  1603 ,  1605 ,  1607 ,  1609 ,  1611 , and  1613 . In the example of  FIG.  16   , the data from drive  1613  consists of a “ghost” landmark, and the server  1230  may identify it as such because none of drives  1601 ,  1603 ,  1605 ,  1607 ,  1609 , and  1611  include an identification of a landmark in the vicinity of the identified landmark in drive  1613 . Accordingly, server  1230  may accept potential landmarks when a ratio of images in which the landmark does appear to images in which the landmark does not appear exceeds a threshold and/or may reject potential landmarks when a ratio of images in which the landmark does not appear to images in which the landmark does appear exceeds a threshold. 
       FIG.  17    depicts a system  1700  for generating drive data, which may be used to crowdsource a sparse map. As depicted in  FIG.  17   , system  1700  may include a camera  1701  and a locating device  1703  (e.g., a GPS locator). Camera  1701  and locating device  1703  may be mounted on a vehicle (e.g., one of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 ). Camera  1701  may produce a plurality of data of multiple types, e.g., ego motion data, traffic sign data, road data, or the like. The camera data and location data may be segmented into drive segments  1705 . For example, drive segments  1705  may each have camera data and location data from less than 1 km of driving. 
     In some embodiments, system  1700  may remove redundancies in drive segments  1705 . For example, if a landmark appears in multiple images from camera  1701 , system  1700  may strip the redundant data such that the drive segments  1705  only contain one copy of the location of and any metadata relating to the landmark. By way of further example, if a lane marking appears in multiple images from camera  1701 , system  1700  may strip the redundant data such that the drive segments  1705  only contain one copy of the location of and any metadata relating to the lane marking. 
     System  1700  also includes a server (e.g., server  1230 ). Server  1230  may receive drive segments  1705  from the vehicle and recombine the drive segments  1705  into a single drive  1707 . Such an arrangement may allow for reduce bandwidth requirements when transferring data between the vehicle and the server while also allowing for the server to store data relating to an entire drive. 
       FIG.  18    depicts system  1700  of  FIG.  17    further configured for crowdsourcing a sparse map. As in  FIG.  17   , system  1700  includes vehicle  1810 , which captures drive data using, for example, a camera (which produces, e.g., ego motion data, traffic sign data, road data, or the like) and a locating device (e.g., a GPS locator). As in  FIG.  17   , vehicle  1810  segments the collected data into drive segments (depicted as “DS1 1,” “DS2 1,” “DSN 1” in  FIG.  18   ). Server  1230  then receives the drive segments and reconstructs a drive (depicted as “Drive 1” in  FIG.  18   ) from the received segments. 
     As further depicted in  FIG.  18   , system  1700  also receives data from additional vehicles. For example, vehicle  1820  also captures drive data using, for example, a camera (which produces. e.g., ego motion data, traffic sign data, road data, or the like) and a locating device (e.g., a GPS locator). Similar to vehicle  1810 , vehicle  1820  segments the collected data into drive segments (depicted as “DS1 2,” “DS2 2,” “DSN 2” in  FIG.  18   ). Server  1230  then receives the drive segments and reconstructs a drive (depicted as “Drive 2” in  FIG.  18   ) from the received segments. Any number of additional vehicles may be used. For example,  FIG.  18    also includes “CAR N” that captures drive data, segments it into drive segments (depicted as “DS1 N,” “DS2 N,” “DSN N” in  FIG.  18   ), and sends it to server  1230  for reconstruction into a drive (depicted as “Drive N” in  FIG.  18   ). 
     As depicted in  FIG.  18   , server  1230  may construct a sparse map (depicted as “MAP”) using the reconstructed drives (e.g., “Drive 1,” “Drive 2,” and “Drive N”) collected from a plurality of vehicles (e.g., “CAR 1” (also labeled vehicle  1810 ), “CAR 2” (also labeled vehicle  1820 ), and “CAR N”). 
       FIG.  19    is a flowchart showing an example process  1900  for generating a sparse map for autonomous vehicle navigation along a road segment. Process  1900  may be performed by one or more processing devices included in server  1230 . 
     Process  1900  may include receiving a plurality of images acquired as one or more vehicles traverse the road segment (step  1905 ). Server  1230  may receive images from cameras included within one or more of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . For example, camera  122  may capture one or more images of the environment surrounding vehicle  1205  as vehicle  1205  travels along road segment  1200 . In some embodiments, server  1230  may also receive stripped down image data that has had redundancies removed by a processor on vehicle  1205 , as discussed above with respect to  FIG.  17   . 
     Process  1900  may further include identifying, based on the plurality of images, at least one line representation of a road surface feature extending along the road segment (step  1910 ). Each line representation may represent a path along the road segment substantially corresponding with the road surface feature. For example, server  1230  may analyze the environmental images received from camera  122  to identify a road edge or a lane marking and determine a trajectory of travel along road segment  1200  associated with the road edge or lane marking. In some embodiments, the trajectory (or line representation) may include a spline, a polynomial representation, or a curve. Server  1230  may determine the trajectory of travel of vehicle  1205  based on camera ego motions (e.g., three dimensional translation and/or three dimensional rotational motions) received at step  1905 . 
     Process  1900  may also include identifying, based on the plurality of images, a plurality of landmarks associated with the road segment (step  1910 ). For example, server  1230  may analyze the environmental images received from camera  122  to identify one or more landmarks, such as road sign along road segment  1200 . Server  1230  may identify the landmarks using analysis of the plurality of images acquired as one or more vehicles traverse the road segment. To enable crowdsourcing, the analysis may include rules regarding accepting and rejecting possible landmarks associated with the road segment. For example, the analysis may include accepting potential landmarks when a ratio of images in which the landmark does appear to images in which the landmark does not appear exceeds a threshold and/or rejecting potential landmarks when a ratio of images in which the landmark does not appear to images in which the landmark does appear exceeds a threshold. 
     Process  1900  may include other operations or steps performed by server  1230 . For example, the navigation information may include a target trajectory for vehicles to travel along a road segment, and process  1900  may include clustering, by server  1230 , vehicle trajectories related to multiple vehicles travelling on the road segment and determining the target trajectory based on the clustered vehicle trajectories, as discussed in further detail below. Clustering vehicle trajectories may include clustering, by server  1230 , the multiple trajectories related to the vehicles travelling on the road segment into a plurality of clusters based on at least one of the absolute heading of vehicles or lane assignment of the vehicles. Generating the target trajectory may include averaging, by server  1230 , the clustered trajectories. By way of further example, process  1900  may include aligning data received in step  1905 . Other processes or steps performed by server  1230 , as described above, may also be included in process  1900 . 
     The disclosed systems and methods may include other features. For example, the disclosed systems may use local coordinates, rather than global coordinates. For autonomous driving, some systems may present data in world coordinates. For example, longitude and latitude coordinates on the earth surface may be used. In order to use the map for steering, the host vehicle may determine its position and orientation relative to the map. It seems natural to use a GPS device on board, in order to position the vehicle on the map and in order to find the rotation transformation between the body reference frame and the world reference frame (e.g., North, East and Down). Once the body reference frame is aligned with the map reference frame, then the desired route may be expressed in the body reference frame and the steering commands may be computed or generated. 
     The disclosed systems and methods may enable autonomous vehicle navigation (e.g., steering control) with low footprint models, which may be collected by the autonomous vehicles themselves without the aid of expensive surveying equipment. To support the autonomous navigation (e.g., steering applications), the road model may include a sparse map having the geometry of the road, its lane structure, and landmarks that may be used to determine the location or position of vehicles along a trajectory included in the model. As discussed above, generation of the sparse map may be performed by a remote server that communicates with vehicles travelling on the road and that receives data from the vehicles. The data may include sensed data, trajectories reconstructed based on the sensed data, and/or recommended trajectories that may represent modified reconstructed trajectories. As discussed below, the server may transmit the model back to the vehicles or other vehicles that later travel on the road to aid in autonomous navigation. 
       FIG.  20    illustrates a block diagram of server  1230 . Server  1230  may include a communication unit  2005 , which may include both hardware components (e.g., communication control circuits, switches, and antenna), and software components (e.g., communication protocols, computer codes). For example, communication unit  2005  may include at least one network interface. Server  1230  may communicate with vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  through communication unit  2005 . For example, server  1230  may receive, through communication unit  2005 , navigation information transmitted from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . Server  1230  may distribute, through communication unit  2005 , the autonomous vehicle road navigation model to one or more autonomous vehicles. 
     Server  1230  may include at least one non-transitory storage medium  2010 , such as a hard drive, a compact disc, a tape, etc. Storage device  1410  may be configured to store data, such as navigation information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  and/or the autonomous vehicle road navigation model that server  1230  generates based on the navigation information. Storage device  2010  may be configured to store any other information, such as a sparse map (e.g., sparse map  800  discussed above with respect to  FIG.  8   ). 
     In addition to or in place of storage device  2010 , server  1230  may include a memory  2015 . Memory  2015  may be similar to or different from memory  140  or  150 . Memory  2015  may be a non-transitory memory, such as a flash memory, a random access memory, etc. Memory  2015  may be configured to store data, such as computer codes or instructions executable by a processor (e.g., processor  2020 ), map data (e.g., data of sparse map  800 ), the autonomous vehicle road navigation model, and/or navigation information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . 
     Server  1230  may include at least one processing device  2020  configured to execute computer codes or instructions stored in memory  2015  to perform various functions. For example, processing device  2020  may analyze the navigation information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 , and generate the autonomous vehicle road navigation model based on the analysis. Processing device  2020  may control communication unit  1405  to distribute the autonomous vehicle road navigation model to one or more autonomous vehicles (e.g., one or more of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  or any vehicle that travels on road segment  1200  at a later time). Processing device  2020  may be similar to or different from processor  180 ,  190 , or processing unit  110 . 
       FIG.  21    illustrates a block diagram of memory  2015 , which may store computer code or instructions for performing one or more operations for generating a road navigation model for use in autonomous vehicle navigation. As shown in  FIG.  21   , memory  2015  may store one or more modules for performing the operations for processing vehicle navigation information. For example, memory  2015  may include a model generating module  2105  and a model distributing module  2110 . Processor  2020  may execute the instructions stored in any of modules  2105  and  2110  included in memory  2015 . 
     Model generating module  2105  may store instructions which, when executed by processor  2020 , may generate at least a portion of an autonomous vehicle road navigation model for a common road segment (e.g., road segment  1200 ) based on navigation information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . For example, in generating the autonomous vehicle road navigation model, processor  2020  may cluster vehicle trajectories along the common road segment  1200  into different clusters. Processor  2020  may determine a target trajectory along the common road segment  1200  based on the clustered vehicle trajectories for each of the different clusters. Such an operation may include finding a mean or average trajectory of the clustered vehicle trajectories (e.g., by averaging data representing the clustered vehicle trajectories) in each cluster. In some embodiments, the target trajectory may be associated with a single lane of the common road segment  1200 . 
     The road model and/or sparse map may store trajectories associated with a road segment. These trajectories may be referred to as target trajectories, which are provided to autonomous vehicles for autonomous navigation. The target trajectories may be received from multiple vehicles, or may be generated based on actual trajectories or recommended trajectories (actual trajectories with some modifications) received from multiple vehicles. The target trajectories included in the road model or sparse map may be continuously updated (e.g., averaged) with new trajectories received from other vehicles. 
     Vehicles travelling on a road segment may collect data by various sensors. The data may include landmarks, road signature profile, vehicle motion (e.g., accelerometer data, speed data), vehicle position (e.g., GPS data), and may either reconstruct the actual trajectories themselves, or transmit the data to a server, which will reconstruct the actual trajectories for the vehicles. In some embodiments, the vehicles may transmit data relating to a trajectory (e.g., a curve in an arbitrary reference frame), landmarks data, and lane assignment along traveling path to server  1230 . Various vehicles travelling along the same road segment at multiple drives may have different trajectories. Server  1230  may identify routes or trajectories associated with each lane from the trajectories received from vehicles through a clustering process. 
       FIG.  22    illustrates a process of clustering vehicle trajectories associated with vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  for determining a target trajectory for the common road segment (e.g., road segment  1200 ). The target trajectory or a plurality of target trajectories determined from the clustering process may be included in the autonomous vehicle road navigation model or sparse map  800 . In some embodiments, vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  traveling along road segment  1200  may transmit a plurality of trajectories  2200  to server  1230 . In some embodiments, server  1230  may generate trajectories based on landmark, road geometry, and vehicle motion information received from vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . To generate the autonomous vehicle road navigation model, server  1230  may cluster vehicle trajectories  1600  into a plurality of clusters  2205 ,  2210 ,  2215 ,  2220 ,  2225 , and  2230 , as shown in  FIG.  22   . 
     Clustering may be performed using various criteria. In some embodiments, all drives in a cluster may be similar with respect to the absolute heading along the road segment  1200 . The absolute heading may be obtained from GPS signals received by vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 . In some embodiments, the absolute heading may be obtained using dead reckoning. Dead reckoning, as one of skill in the art would understand, may be used to determine the current position and hence heading of vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  by using previously determined position, estimated speed, etc. Trajectories clustered by absolute heading may be useful for identifying routes along the roadways. 
     In some embodiments, all the drives in a cluster may be similar with respect to the lane assignment (e.g., in the same lane before and after a junction) along the drive on road segment  1200 . Trajectories clustered by lane assignment may be useful for identifying lanes along the roadways. In some embodiments, both criteria (e.g., absolute heading and lane assignment) may be used for clustering. 
     In each cluster  2205 ,  2210 ,  2215 ,  2220 ,  2225 , and  2230 , trajectories may be averaged to obtain a target trajectory associated with the specific cluster. For example, the trajectories from multiple drives associated with the same lane cluster may be averaged. The averaged trajectory may be a target trajectory associate with a specific lane. To average a cluster of trajectories, server  1230  may select a reference frame of an arbitrary trajectory C0. For all other trajectories (C1, . . . , Cn), server  1230  may find a rigid transformation that maps Ci to C0, where i=1, 2, . . . , n, where n is a positive integer number, corresponding to the total number of trajectories included in the cluster. Server  1230  may compute a mean curve or trajectory in the C0 reference frame. 
     In some embodiments, the landmarks may define an arc length matching between different drives, which may be used for alignment of trajectories with lanes. In some embodiments, lane marks before and after a junction may be used for alignment of trajectories with lanes. 
     To assemble lanes from the trajectories, server  1230  may select a reference frame of an arbitrary lane. Server  1230  may map partially overlapping lanes to the selected reference frame. Server  1230  may continue mapping until all lanes are in the same reference frame. Lanes that are next to each other may be aligned as if they were the same lane, and later they may be shifted laterally. 
     Landmarks recognized along the road segment may be mapped to the common reference frame, first at the lane level, then at the junction level. For example, the same landmarks may be recognized multiple times by multiple vehicles in multiple drives. The data regarding the same landmarks received in different drives may be slightly different. Such data may be averaged and mapped to the same reference frame, such as the C0 reference frame. Additionally or alternatively, the variance of the data of the same landmark received in multiple drives may be calculated. 
     In some embodiments, each lane of road segment  120  may be associated with a target trajectory and certain landmarks. The target trajectory or a plurality of such target trajectories may be included in the autonomous vehicle road navigation model, which may be used later by other autonomous vehicles travelling along the same road segment  1200 . Landmarks identified by vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  while the vehicles travel along road segment  1200  may be recorded in association with the target trajectory. The data of the target trajectories and landmarks may be continuously or periodically updated with new data received from other vehicles in subsequent drives. 
     For localization of an autonomous vehicle, the disclosed systems and methods may use an Extended Kalman Filter. The location of the vehicle may be determined based on three dimensional position data and/or three dimensional orientation data, prediction of future location ahead of vehicle&#39;s current location by integration of ego motion. The localization of vehicle may be corrected or adjusted by image observations of landmarks. For example, when vehicle detects a landmark within an image captured by the camera, the landmark may be compared to a known landmark stored within the road model or sparse map  800 . The known landmark may have a known location (e.g., GPS data) along a target trajectory stored in the road model and/or sparse map  800 . Based on the current speed and images of the landmark, the distance from the vehicle to the landmark may be estimated. The location of the vehicle along a target trajectory may be adjusted based on the distance to the landmark and the landmark&#39;s known location (stored in the road model or sparse map  800 ). The landmark&#39;s position/location data (e.g., mean values from multiple drives) stored in the road model and/or sparse map  800  may be presumed to be accurate. 
     In some embodiments, the disclosed system may form a closed loop subsystem, in which estimation of the vehicle six degrees of freedom location (e.g., three dimensional position data plus three dimensional orientation data) may be used for navigating (e.g., steering the wheel of) the autonomous vehicle to reach a desired point (e.g., 1.3 second ahead in the stored). In turn, data measured from the steering and actual navigation may be used to estimate the six degrees of freedom location. 
     In some embodiments, poles along a road, such as lampposts and power or cable line poles may be used as landmarks for localizing the vehicles. Other landmarks such as traffic signs, traffic lights, arrows on the road, stop lines, as well as static features or signatures of an object along the road segment may also be used as landmarks for localizing the vehicle. When poles are used for localization, the x observation of the poles (i.e., the viewing angle from the vehicle) may be used, rather than the y observation (i.e., the distance to the pole) since the bottoms of the poles may be occluded and sometimes they are not on the road plane. 
       FIG.  23    illustrates a navigation system for a vehicle, which may be used for autonomous navigation using a crowdsourced sparse map. For illustration, the vehicle is referenced as vehicle  1205 . The vehicle shown in  FIG.  23    may be any other vehicle disclosed herein, including, for example, vehicles  1210 ,  1215 ,  1220 , and  1225 , as well as vehicle  200  shown in other embodiments. As shown in  FIG.  12   , vehicle  1205  may communicate with server  1230 . Vehicle  1205  may include an image capture device  122  (e.g., camera  122 ). Vehicle  1205  may include a navigation system  2300  configured for providing navigation guidance for vehicle  1205  to travel on a road (e.g., road segment  1200 ). Vehicle  1205  may also include other sensors, such as a speed sensor  2320  and an accelerometer  2325 . Speed sensor  2320  may be configured to detect the speed of vehicle  1205 . Accelerometer  2325  may be configured to detect an acceleration or deceleration of vehicle  1205 . Vehicle  1205  shown in  FIG.  23    may be an autonomous vehicle, and the navigation system  2300  may be used for providing navigation guidance for autonomous driving. Alternatively, vehicle  1205  may also be a non-autonomous, human-controlled vehicle, and navigation system  2300  may still be used for providing navigation guidance. 
     Navigation system  2300  may include a communication unit  2305  configured to communicate with server  1230  through communication path  1235 . Navigation system  2300  may also include a GPS unit  2310  configured to receive and process GPS signals. Navigation system  2300  may further include at least one processor  2315  configured to process data, such as GPS signals, map data from sparse map  800  (which may be stored on a storage device provided onboard vehicle  1205  and/or received from server  1230 ), road geometry sensed by a road profile sensor  2330 , images captured by camera  122 , and/or autonomous vehicle road navigation model received from server  1230 . The road profile sensor  2330  may include different types of devices for measuring different types of road profile, such as road surface roughness, road width, road elevation, road curvature, etc. For example, the road profile sensor  2330  may include a device that measures the motion of a suspension of vehicle  2305  to derive the road roughness profile. In some embodiments, the road profile sensor  2330  may include radar sensors to measure the distance from vehicle  1205  to road sides (e.g., barrier on the road sides), thereby measuring the width of the road. In some embodiments, the road profile sensor  2330  may include a device configured for measuring the up and down elevation of the road. In some embodiment, the road profile sensor  2330  may include a device configured to measure the road curvature. For example, a camera (e.g., camera  122  or another camera) may be used to capture images of the road showing road curvatures. Vehicle  1205  may use such images to detect road curvatures. 
     The at least one processor  2315  may be programmed to receive, from camera  122 , at least one environmental image associated with vehicle  1205 . The at least one processor  2315  may analyze the at least one environmental image to determine navigation information related to the vehicle  1205 . The navigation information may include a trajectory related to the travel of vehicle  1205  along road segment  1200 . The at least one processor  2315  may determine the trajectory based on motions of camera  122  (and hence the vehicle), such as three dimensional translation and three dimensional rotational motions. In some embodiments, the at least one processor  2315  may determine the translation and rotational motions of camera  122  based on analysis of a plurality of images acquired by camera  122 . In some embodiments, the navigation information may include lane assignment information (e.g., in which lane vehicle  1205  is travelling along road segment  1200 ). The navigation information transmitted from vehicle  1205  to server  1230  may be used by server  1230  to generate and/or update an autonomous vehicle road navigation model, which may be transmitted back from server  1230  to vehicle  1205  for providing autonomous navigation guidance for vehicle  1205 . 
     The at least one processor  2315  may also be programmed to transmit the navigation information from vehicle  1205  to server  1230 . In some embodiments, the navigation information may be transmitted to server  1230  along with road information. The road location information may include at least one of the GPS signal received by the GPS unit  2310 , landmark information, road geometry, lane information, etc. The at least one processor  2315  may receive, from server  1230 , the autonomous vehicle road navigation model or a portion of the model. The autonomous vehicle road navigation model received from server  1230  may include at least one update based on the navigation information transmitted from vehicle  1205  to server  1230 . The portion of the model transmitted from server  1230  to vehicle  1205  may include an updated portion of the model. The at least one processor  2315  may cause at least one navigational maneuver (e.g., steering such as making a turn, braking, accelerating, passing another vehicle, etc.) by vehicle  1205  based on the received autonomous vehicle road navigation model or the updated portion of the model. 
     The at least one processor  2315  may be configured to communicate with various sensors and components included in vehicle  1205 , including communication unit  1705 , GPS unit  2315 , camera  122 , speed sensor  2320 , accelerometer  2325 , and road profile sensor  2330 . The at least one processor  2315  may collect information or data from various sensors and components, and transmit the information or data to server  1230  through communication unit  2305 . Alternatively or additionally, various sensors or components of vehicle  1205  may also communicate with server  1230  and transmit data or information collected by the sensors or components to server  1230 . 
     In some embodiments, vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may communicate with each other, and may share navigation information with each other, such that at least one of the vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may generate the autonomous vehicle road navigation model using crowdsourcing, e.g., based on information shared by other vehicles. In some embodiments, vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  may share navigation information with each other and each vehicle may update its own the autonomous vehicle road navigation model provided in the vehicle. In some embodiments, at least one of the vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225  (e.g., vehicle  1205 ) may function as a hub vehicle. The at least one processor  2315  of the hub vehicle (e.g., vehicle  1205 ) may perform some or all of the functions performed by server  1230 . For example, the at least one processor  2315  of the hub vehicle may communicate with other vehicles and receive navigation information from other vehicles. The at least one processor  2315  of the hub vehicle may generate the autonomous vehicle road navigation model or an update to the model based on the shared information received from other vehicles. The at least one processor  2315  of the hub vehicle may transmit the autonomous vehicle road navigation model or the update to the model to other vehicles for providing autonomous navigation guidance. 
     Mapping Lane Marks and Navigation Based on Mapped Lane Marks 
     As previously discussed, the autonomous vehicle road navigation model and/or sparse map  800  may include a plurality of mapped lane marks associated with a road segment. As discussed in greater detail below, these mapped lane marks may be used when the autonomous vehicle navigates. For example, in some embodiments, the mapped lane marks may be used to determine a lateral position and/or orientation relative to a planned trajectory. With this position information, the autonomous vehicle may be able to adjust a heading direction to match a direction of a target trajectory at the determined position. 
     Vehicle  200  may be configured to detect lane marks in a given road segment. The road segment may include any markings on a road for guiding vehicle traffic on a roadway. For example, the lane marks may be continuous or dashed lines demarking the edge of a lane of travel. The lane marks may also include double lines, such as a double continuous lines, double dashed lines or a combination of continuous and dashed lines indicating, for example, whether passing is permitted in an adjacent lane. The lane marks may also include freeway entrance and exit markings indicating, for example, a deceleration lane for an exit ramp or dotted lines indicating that a lane is turn-only or that the lane is ending. The markings may further indicate a work zone, a temporary lane shift, a path of travel through an intersection, a median, a special purpose lane (e.g., a bike lane, HOV lane, etc.), or other miscellaneous markings (e.g., crosswalk, a speed hump, a railway crossing, a stop line, etc.). 
     Vehicle  200  may use cameras, such as image capture devices  122  and  124  included in image acquisition unit  120 , to capture images of the surrounding lane marks. Vehicle  200  may analyze the images to detect point locations associated with the lane marks based on features identified within one or more of the captured images. These point locations may be uploaded to a server to represent the lane marks in sparse map  800 . Depending on the position and field of view of the camera, lane marks may be detected for both sides of the vehicle simultaneously from a single image. In other embodiments, different cameras may be used to capture images on multiple sides of the vehicle. Rather than uploading actual images of the lane marks, the marks may be stored in sparse map  800  as a spline or a series of points, thus reducing the size of sparse map  800  and/or the data that must be uploaded remotely by the vehicle. 
       FIGS.  24 A- 24 D  illustrate exemplary point locations that may be detected by vehicle  200  to represent particular lane marks. Similar to the landmarks described above, vehicle  200  may use various image recognition algorithms or software to identify point locations within a captured image. For example, vehicle  200  may recognize a series of edge points, corner points or various other point locations associated with a particular lane mark.  FIG.  24 A  shows a continuous lane mark  2410  that may be detected by vehicle  200 . Lane mark  2410  may represent the outside edge of a roadway, represented by a continuous white line. As shown in  FIG.  24 A , vehicle  200  may be configured to detect a plurality of edge location points  2411  along the lane mark. Location points  2411  may be collected to represent the lane mark at any intervals sufficient to create a mapped lane mark in the sparse map. For example, the lane mark may be represented by one point per meter of the detected edge, one point per every five meters of the detected edge, or at other suitable spacings. In some embodiments, the spacing may be determined by other factors, rather than at set intervals such as, for example, based on points where vehicle  200  has a highest confidence ranking of the location of the detected points. Although  FIG.  24 A  shows edge location points on an interior edge of lane mark  2410 , points may be collected on the outside edge of the line or along both edges. Further, while a single line is shown in  FIG.  24 A , similar edge points may be detected for a double continuous line. For example, points  2411  may be detected along an edge of one or both of the continuous lines. 
     Vehicle  200  may also represent lane marks differently depending on the type or shape of lane mark.  FIG.  24 B  shows an exemplary dashed lane mark  2420  that may be detected by vehicle  200 . Rather than identifying edge points, as in  FIG.  24 A , vehicle may detect a series of corner points  2421  representing corners of the lane dashes to define the full boundary of the dash. While  FIG.  24 B  shows each corner of a given dash marking being located, vehicle  200  may detect or upload a subset of the points shown in the figure. For example, vehicle  200  may detect the leading edge or leading corner of a given dash mark, or may detect the two corner points nearest the interior of the lane. Further, not every dash mark may be captured, for example, vehicle  200  may capture and/or record points representing a sample of dash marks (e.g., every other, every third, every fifth, etc.) or dash marks at a predefined spacing (e.g., every meter, every five meters, every 10 meters, etc.) Corner points may also be detected for similar lane marks, such as markings showing a lane is for an exit ramp, that a particular lane is ending, or other various lane marks that may have detectable corner points. Corner points may also be detected for lane marks consisting of double dashed lines or a combination of continuous and dashed lines. 
     In some embodiments, the points uploaded to the server to generate the mapped lane marks may represent other points besides the detected edge points or corner points.  FIG.  24 C  illustrates a series of points that may represent a centerline of a given lane mark. For example, continuous lane  2410  may be represented by centerline points  2441  along a centerline  2440  of the lane mark. In some embodiments, vehicle  200  may be configured to detect these center points using various image recognition techniques, such as convolutional neural networks (CNN), scale-invariant feature transform (SIFT), histogram of oriented gradients (HOG) features, or other techniques. Alternatively, vehicle  200  may detect other points, such as edge points  2411  shown in  FIG.  24 A , and may calculate centerline points  2441 , for example, by detecting points along each edge and determining a midpoint between the edge points. Similarly, dashed lane mark  2420  may be represented by centerline points  2451  along a centerline  2450  of the lane mark. The centerline points may be located at the edge of a dash, as shown in  FIG.  24 C , or at various other locations along the centerline. For example, each dash may be represented by a single point in the geometric center of the dash. The points may also be spaced at a predetermined interval along the centerline (e.g., every meter, 5 meters, 10 meters, etc.). The centerline points  2451  may be detected directly by vehicle  200 , or may be calculated based on other detected reference points, such as corner points  2421 , as shown in  FIG.  24 B . A centerline may also be used to represent other lane mark types, such as a double line, using similar techniques as above. 
     In some embodiments, vehicle  200  may identify points representing other features, such as a vertex between two intersecting lane marks.  FIG.  24 D  shows exemplary points representing an intersection between two lane marks  2460  and  2465 . Vehicle  200  may calculate a vertex point  2466  representing an intersection between the two lane marks. For example, one of lane marks  2460  or  2465  may represent a train crossing area or other crossing area in the road segment. While lane marks  2460  and  2465  are shown as crossing each other perpendicularly, various other configurations may be detected. For example, the lane marks  2460  and  2465  may cross at other angles, or one or both of the lane marks may terminate at the vertex point  2466 . Similar techniques may also be applied for intersections between dashed or other lane mark types. In addition to vertex point  2466 , various other points  2467  may also be detected, providing further information about the orientation of lane marks  2460  and  2465 . 
     Vehicle  200  may associate real-world coordinates with each detected point of the lane mark. For example, location identifiers may be generated, including coordinate for each point, to upload to a server for mapping the lane mark. The location identifiers may further include other identifying information about the points, including whether the point represents a corner point, an edge point, center point, etc. Vehicle  200  may therefore be configured to determine a real-world position of each point based on analysis of the images. For example, vehicle  200  may detect other features in the image, such as the various landmarks described above, to locate the real-world position of the lane marks. This may involve determining the location of the lane marks in the image relative to the detected landmark or determining the position of the vehicle based on the detected landmark and then determining a distance from the vehicle (or target trajectory of the vehicle) to the lane mark. When a landmark is not available, the location of the lane mark points may be determined relative to a position of the vehicle determined based on dead reckoning. The real-world coordinates included in the location identifiers may be represented as absolute coordinates (e.g., latitude/longitude coordinates), or may be relative to other features, such as based on a longitudinal position along a target trajectory and a lateral distance from the target trajectory. The location identifiers may then be uploaded to a server for generation of the mapped lane marks in the navigation model (such as sparse map  800 ). In some embodiments, the server may construct a spline representing the lane marks of a road segment. Alternatively, vehicle  200  may generate the spline and upload it to the server to be recorded in the navigational model. 
       FIG.  24 E  shows an exemplary navigation model or sparse map for a corresponding road segment that includes mapped lane marks. The sparse map may include a target trajectory  2475  for a vehicle to follow along a road segment. As described above, target trajectory  2475  may represent an ideal path for a vehicle to take as it travels the corresponding road segment, or may be located elsewhere on the road (e.g., a centerline of the road, etc.). Target trajectory  2475  may be calculated in the various methods described above, for example, based on an aggregation (e.g., a weighted combination) of two or more reconstructed trajectories of vehicles traversing the same road segment. 
     In some embodiments, the target trajectory may be generated equally for all vehicle types and for all road, vehicle, and/or environment conditions. In other embodiments, however, various other factors or variables may also be considered in generating the target trajectory. A different target trajectory may be generated for different types of vehicles (e.g., a private car, a light truck, and a full trailer). For example, a target trajectory with relatively tighter turning radii may be generated for a small private car than a larger semi-trailer truck. In some embodiments, road, vehicle and environmental conditions may be considered as well. For example, a different target trajectory may be generated for different road conditions (e.g., wet, snowy, icy, dry, etc.), vehicle conditions (e.g., tire condition or estimated tire condition, brake condition or estimated brake condition, amount of fuel remaining, etc.) or environmental factors (e.g., time of day, visibility, weather, etc.). The target trajectory may also depend on one or more aspects or features of a particular road segment (e.g., speed limit, frequency and size of turns, grade, etc.). In some embodiments, various user settings may also be used to determine the target trajectory, such as a set driving mode (e.g., desired driving aggressiveness, economy mode, etc.). 
     The sparse map may also include mapped lane marks  2470  and  2480  representing lane marks along the road segment. The mapped lane marks may be represented by a plurality of location identifiers  2471  and  2481 . As described above, the location identifiers may include locations in real world coordinates of points associated with a detected lane mark. Similar to the target trajectory in the model, the lane marks may also include elevation data and may be represented as a curve in three-dimensional space. For example, the curve may be a spline connecting three dimensional polynomials of suitable order the curve may be calculated based on the location identifiers. The mapped lane marks may also include other information or metadata about the lane mark, such as an identifier of the type of lane mark (e.g., between two lanes with the same direction of travel, between two lanes of opposite direction of travel, edge of a roadway, etc.) and/or other characteristics of the lane mark (e.g., continuous, dashed, single line, double line, yellow, white, etc.). In some embodiments, the mapped lane marks may be continuously updated within the model, for example, using crowdsourcing techniques. The same vehicle may upload location identifiers during multiple occasions of travelling the same road segment or data may be selected from a plurality of vehicles (such as  1205 ,  1210 ,  1215 ,  1220 , and  1225 ) travelling the road segment at different times. Sparse map  800  may then be updated or refined based on subsequent location identifiers received from the vehicles and stored in the system. As the mapped lane marks are updated and refined, the updated road navigation model and/or sparse map may be distributed to a plurality of autonomous vehicles. 
     Generating the mapped lane marks in the sparse map may also include detecting and/or mitigating errors based on anomalies in the images or in the actual lane marks themselves.  FIG.  24 F  shows an exemplary anomaly  2495  associated with detecting a lane mark  2490 . Anomaly  2495  may appear in the image captured by vehicle  200 , for example, from an object obstructing the camera&#39;s view of the lane mark, debris on the lens, etc. In some instances, the anomaly may be due to the lane mark itself, which may be damaged or worn away, or partially covered, for example, by dirt, debris, water, snow or other materials on the road. Anomaly  2495  may result in an erroneous point  2491  being detected by vehicle  200 . Sparse map  800  may provide the correct the mapped lane mark and exclude the error. In some embodiments, vehicle  200  may detect erroneous point  2491  for example, by detecting anomaly  2495  in the image, or by identifying the error based on detected lane mark points before and after the anomaly. Based on detecting the anomaly, the vehicle may omit point  2491  or may adjust it to be in line with other detected points. In other embodiments, the error may be corrected after the point has been uploaded, for example, by determining the point is outside of an expected threshold based on other points uploaded during the same trip, or based on an aggregation of data from previous trips along the same road segment. 
     The mapped lane marks in the navigation model and/or sparse map may also be used for navigation by an autonomous vehicle traversing the corresponding roadway. For example, a vehicle navigating along a target trajectory may periodically use the mapped lane marks in the sparse map to align itself with the target trajectory. As mentioned above, between landmarks the vehicle may navigate based on dead reckoning in which the vehicle uses sensors to determine its ego motion and estimate its position relative to the target trajectory. Errors may accumulate over time and vehicle&#39;s position determinations relative to the target trajectory may become increasingly less accurate. Accordingly, the vehicle may use lane marks occurring in sparse map  800  (and their known locations) to reduce the dead reckoning-induced errors in position determination. In this way, the identified lane marks included in sparse map  800 ) may serve as navigational anchors from which an accurate position of the vehicle relative to a target trajectory may be determined. 
       FIG.  25 A  shows an exemplary image  2500  of a vehicle&#39;s surrounding environment that may be used for navigation based on the mapped lane marks. Image  2500  may be captured, for example, by vehicle  200  through image capture devices  122  and  124  included in image acquisition unit  120 . Image  2500  may include an image of at least one lane mark  2510 , as shown in  FIG.  25 A . Image  2500  may also include one or more landmarks  2521 , such as road sign, used for navigation as described above. Some elements shown in  FIG.  25 A , such as elements  2511 ,  2530 , and  2520  which do not appear in the captured image  2500  but are detected and/or determined by vehicle  200  are also shown for reference. 
     Using the various techniques described above with respect to  FIGS.  24 A-D  and  24 F, a vehicle may analyze image  2500  to identify lane mark  2510 . Various points  2511  may be detected corresponding to features of the lane mark in the image. Points  2511 , for example, may correspond to an edge of the lane mark, a corner of the lane mark, a midpoint of the lane mark, a vertex between two intersecting lane marks, or various other features or locations. Points  2511  may be detected to correspond to a location of points stored in a navigation model received from a server. For example, if a sparse map is received containing points that represent a centerline of a mapped lane mark, points  2511  may also be detected based on a centerline of lane mark  2510 . 
     The vehicle may also be configured to determine a longitudinal position represented by element  2520  and located along a target trajectory. Longitudinal position  2520  may be determined from image  2500 , for example, by detecting landmark  2521  within image  2500  and comparing a measured location to a known landmark location stored in the road model or sparse map  800 . The location of the vehicle along a target trajectory may then be determined based on the distance to the landmark and the landmark&#39;s known location. The longitudinal position  2520  may also be determined from images other than those used to determine the position of a lane mark. For example, longitudinal position  2520  may be determined by detecting landmarks in images from other cameras within image acquisition unit  120  taken simultaneously or near simultaneously to image  2500 . In some instances, the vehicle may not be near any landmarks or other reference points for determining longitudinal position  2520 . In such instances, the vehicle may be navigating based on dead reckoning and thus may use sensors to determine its ego motion and estimate a longitudinal position  2520  relative to the target trajectory. The vehicle may also be configured to determine a distance  2530  representing the actual distance between the vehicle and lane mark  2510  observed in the captured image(s). The camera angle, the speed of the vehicle, the width of the vehicle, or various other factors may be accounted for in determining distance  2530 . 
       FIG.  25 B  illustrates a lateral localization correction of the vehicle based on the mapped lane marks in a road navigation model. As described above, vehicle  200  may determine a distance  2530  between vehicle  200  and a lane mark  2510  using one or more images captured by vehicle  200 . Vehicle  200  may also have access to a road navigation model, such as sparse map  800 , which may include a mapped lane mark  2550  and a target trajectory  2555 . Mapped lane mark  2550  may be modeled using the techniques described above, for example using crowdsourced location identifiers captured by a plurality of vehicles. Target trajectory  2555  may also be generated using the various techniques described previously. Vehicle  200  may also be configured to determine or estimate a longitudinal position  2520  along target trajectory  2555  as described above with respect to  FIG.  25 A . Vehicle  200  may then determine an expected distance  2540  based on a lateral distance between target trajectory  2555  and mapped lane mark  2550  corresponding to longitudinal position  2520 . The lateral localization of vehicle  200  may be corrected or adjusted by comparing the actual distance  2530 , measured using the captured image(s), with the expected distance  2540  from the model. 
       FIG.  26 A  is a flowchart showing an exemplary process  2600 A for mapping a lane mark for use in autonomous vehicle navigation, consistent with disclosed embodiments. At step  2610 , process  2600 A may include receiving two or more location identifiers associated with a detected lane mark. For example, step  2610  may be performed by server  1230  or one or more processors associated with the server. The location identifiers may include locations in real-world coordinates of points associated with the detected lane mark, as described above with respect to  FIG.  24 E . In some embodiments, the location identifiers may also contain other data, such as additional information about the road segment or the lane mark. Additional data may also be received during step  2610 , such as accelerometer data, speed data, landmarks data, road geometry or profile data, vehicle positioning data, ego motion data, or various other forms of data described above. The location identifiers may be generated by a vehicle, such as vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 , based on images captured by the vehicle. For example, the identifiers may be determined based on acquisition, from a camera associated with a host vehicle, of at least one image representative of an environment of the host vehicle, analysis of the at least one image to detect the lane mark in the environment of the host vehicle, and analysis of the at least one image to determine a position of the detected lane mark relative to a location associated with the host vehicle. As described above, the lane mark may include a variety of different marking types, and the location identifiers may correspond to a variety of points relative to the lane mark. For example, where the detected lane mark is part of a dashed line marking a lane boundary, the points may correspond to detected corners of the lane mark. Where the detected lane mark is part of a continuous line marking a lane boundary, the points may correspond to a detected edge of the lane mark, with various spacings as described above. In some embodiments, the points may correspond to the centerline of the detected lane mark, as shown in  FIG.  24 C , or may correspond to a vertex between two intersecting lane marks and at least one two other points associated with the intersecting lane marks, as shown in  FIG.  24 D . 
     At step  2612 , process  2600 A may include associating the detected lane mark with a corresponding road segment. For example, server  1230  may analyze the real-world coordinates, or other information received during step  2610 , and compare the coordinates or other information to location information stored in an autonomous vehicle road navigation model. Server  1230  may determine a road segment in the model that corresponds to the real-world road segment where the lane mark was detected. 
     At step  2614 , process  2600 A may include updating an autonomous vehicle road navigation model relative to the corresponding road segment based on the two or more location identifiers associated with the detected lane mark. For example, the autonomous road navigation model may be sparse map  800 , and server  1230  may update the sparse map to include or adjust a mapped lane mark in the model. Server  1230  may update the model based on the various methods or processes described above with respect to  FIG.  24 E . In some embodiments, updating the autonomous vehicle road navigation model may include storing one or more indicators of position in real world coordinates of the detected lane mark. The autonomous vehicle road navigation model may also include a at least one target trajectory for a vehicle to follow along the corresponding road segment, as shown in  FIG.  24 E . 
     At step  2616 , process  2600 A may include distributing the updated autonomous vehicle road navigation model to a plurality of autonomous vehicles. For example, server  1230  may distribute the updated autonomous vehicle road navigation model to vehicles  1205 ,  1210 ,  1215 ,  1220 , and  1225 , which may use the model for navigation. The autonomous vehicle road navigation model may be distributed via one or more networks (e.g., over a cellular network and/or the Internet, etc.), through wireless communication paths  1235 , as shown in  FIG.  12   . 
     In some embodiments, the lane marks may be mapped using data received from a plurality of vehicles, such as through a crowdsourcing technique, as described above with respect to  FIG.  24 E . For example, process  2600 A may include receiving a first communication from a first host vehicle, including location identifiers associated with a detected lane mark, and receiving a second communication from a second host vehicle, including additional location identifiers associated with the detected lane mark. For example, the second communication may be received from a subsequent vehicle travelling on the same road segment, or from the same vehicle on a subsequent trip along the same road segment. Process  2600 A may further include refining a determination of at least one position associated with the detected lane mark based on the location identifiers received in the first communication and based on the additional location identifiers received in the second communication. This may include using an average of the multiple location identifiers and/or filtering out “ghost” identifiers that may not reflect the real-world position of the lane mark. 
       FIG.  26 B  is a flowchart showing an exemplary process  2600 B for autonomously navigating a host vehicle along a road segment using mapped lane marks. Process  2600 B may be performed, for example, by processing unit  110  of autonomous vehicle  200 . At step  2620 , process  2600 B may include receiving from a server-based system an autonomous vehicle road navigation model. In some embodiments, the autonomous vehicle road navigation model may include a target trajectory for the host vehicle along the road segment and location identifiers associated with one or more lane marks associated with the road segment. For example, vehicle  200  may receive sparse map  800  or another road navigation model developed using process  2600 A. In some embodiments, the target trajectory may be represented as a three-dimensional spline, for example, as shown in  FIG.  9 B . As described above with respect to  FIGS.  24 A-F , the location identifiers may include locations in real world coordinates of points associated with the lane mark (e.g., corner points of a dashed lane mark, edge points of a continuous lane mark, a vertex between two intersecting lane marks and other points associated with the intersecting lane marks, a centerline associated with the lane mark, etc.). 
     At step  2621 , process  2600 B may include receiving at least one image representative of an environment of the vehicle. The image may be received from an image capture device of the vehicle, such as through image capture devices  122  and  124  included in image acquisition unit  120 . The image may include an image of one or more lane marks, similar to image  2500  described above. 
     At step  2622 , process  2600 B may include determining a longitudinal position of the host vehicle along the target trajectory. As described above with respect to  FIG.  25 A , this may be based on other information in the captured image (e.g., landmarks, etc.) or by dead reckoning of the vehicle between detected landmarks. 
     At step  2623 , process  2600 B may include determining an expected lateral distance to the lane mark based on the determined longitudinal position of the host vehicle along the target trajectory and based on the two or more location identifiers associated with the at least one lane mark. For example, vehicle  200  may use sparse map  800  to determine an expected lateral distance to the lane mark. As shown in  FIG.  25 B , longitudinal position  2520  along a target trajectory  2555  may be determined in step  2622 . Using spare map  800 , vehicle  200  may determine an expected distance  2540  to mapped lane mark  2550  corresponding to longitudinal position  2520 . 
     At step  2624 , process  2600 B may include analyzing the at least one image to identify the at least one lane mark. Vehicle  200 , for example, may use various image recognition techniques or algorithms to identify the lane mark within the image, as described above. For example, lane mark  2510  may be detected through image analysis of image  2500 , as shown in  FIG.  25 A . 
     At step  2625 , process  2600 B may include determining an actual lateral distance to the at least one lane mark based on analysis of the at least one image. For example, the vehicle may determine a distance  2530 , as shown in  FIG.  25 A , representing the actual distance between the vehicle and lane mark  2510 . The camera angle, the speed of the vehicle, the width of the vehicle, the position of the camera relative to the vehicle, or various other factors may be accounted for in determining distance  2530 . 
     At step  2626 , process  2600 B may include determining an autonomous steering action for the host vehicle based on a difference between the expected lateral distance to the at least one lane mark and the determined actual lateral distance to the at least one lane mark. For example, as described above with respect to  FIG.  25 B , vehicle  200  may compare actual distance  2530  with an expected distance  2540 . The difference between the actual and expected distance may indicate an error (and its magnitude) between the vehicle&#39;s actual position and the target trajectory to be followed by the vehicle. Accordingly, the vehicle may determine an autonomous steering action or other autonomous action based on the difference. For example, if actual distance  2530  is less than expected distance  2540 , as shown in  FIG.  25 B , the vehicle may determine an autonomous steering action to direct the vehicle left, away from lane mark  2510 . Thus, the vehicle&#39;s position relative to the target trajectory may be corrected. Process  2600 B may be used, for example, to improve navigation of the vehicle between landmarks. 
     Map Management Using an Electronic Horizon 
     Although processing power and storage capacity has increased and become less costly, it may still be desirable to use them more efficiently. The systems and methods disclosed herein may allow a vehicle to dynamically receive and load map data that is pertinent to its travel route, rather than loading a large set of map data that the vehicle may not use during a trip. In doing so, the systems and methods may reduce hardware requirements of a vehicle by receiving and processing the map data that the vehicle is likely to need. Additionally, the systems and methods may also allow reduction in transmission costs of data exchanged between a vehicle and, for example, a central server that deploys the map data. Furthermore, the disclosed systems and methods may allow the vehicle to receive the most recent map data that the vehicle may need more frequently. For example, the systems and methods may determine a potential travel area (or a potential travel envelope) for the vehicle based on navigational information, such as the vehicle&#39;s location, speed, driving direction, etc. The systems and methods may also be configured to determine one or more road segments associated with the potential travel area from the vehicle and transmit the map data relating to the road segments to the vehicle. The vehicle (and/or the driver) may navigate according to the received map data. 
       FIG.  27    illustrates an exemplary system  2700  for providing one or more map segments to one or more vehicles, consistent with the disclosed embodiments. As illustrated in  FIG.  27   , system  2700  may include a server  2701 , one or more vehicles  2702 , and one or more vehicle devices  2703  associated with a vehicle, a database  2704 , and a network  2705 . Server  2701  may be configured to providing one or more map segments to one or more vehicles based on navigational information received from one or more vehicles (and/or one or more vehicle devices associated with a vehicle). For example, vehicle  2702  and/or vehicle device  2703  may be configured to collect navigational information and transmit the navigational information to server  2701 . Server  2701  may send to vehicle  2702  and/or vehicle device  2703  one or more map segments including map information for a geographical region based on the received navigational information. Database  2704  may be configured to store information for the components of system  2700  (e.g., server  2701 , vehicle  2702 , and/or vehicle device  2703 ). Network  2705  may be configured to facilitate communications among the components of system  2700 . 
     Server  2701  may be configured to receive navigational information from vehicle  2702  (and/or vehicle device  2703 ). In some embodiments, navigational information may include the location of vehicle  2702 , the speed of vehicle  2702 , and the direction of travel of vehicle  2702 . Server  2701  may also be configured to analyze the received navigational information and determine a potential travel envelope for vehicle  2702 . A potential travel envelope of a vehicle may be an area surrounding the vehicle. For example, a potential travel envelope of a vehicle may include an area covering a first predetermined distance from the vehicle in the driving direction of the vehicle, a second predetermined distance from the vehicle in a direction opposite to the driving direction of the vehicle, a third predetermined distance from the vehicle to the left of the vehicle, and a fourth predetermined distance from the vehicle to the right of the vehicle. In some embodiments, the first predetermined distance from the vehicle in the driving direction of the vehicle may include a predetermined distance ahead of the vehicle that may constitute an electronic horizon of the vehicle. In some embodiments, a potential travel envelope of a vehicle may include one or more distances (one, two, three . . . , n) from the vehicle in one or more (or all) possible driving directions for the vehicle relative to its current position. For example, in a road where a vehicle may be capable of making a U-turn, a potential travel envelope of the vehicle may include a predetermined distance from the vehicle in the opposite direction in addition to a predetermined distance in at least the forward direction, since the vehicle may perform a U-turn and may navigate in a direction that is (generally) opposite to its current motion direction. As another example, if traveling at the opposite direction is not possible (e.g., there is a physical barrier) at the current location, and no U-turn is possible for some distance ahead of the current location, a potent travel envelop may not include a distance in the opposite direction. Similar to an actual horizon in the real world, the electronic horizon may be correlated to a potential travel distance of the vehicle within a certain time window based on a current speed of the host vehicle and a current direction of travel. Server  2701  may further be configured to send to the vehicle one or more map segments including map information for a geographical region at least partially overlapping with the potential travel envelope of vehicle  2702 . 
     In some embodiments, server  2701  may be a cloud server that performs the functions disclosed herein. The term “cloud server” refers to a computer platform that provides services via a network, such as the Internet. In this example configuration, server  2701  may use virtual machines that may not correspond to individual hardware. For example, computational and/or storage capabilities may be implemented by allocating appropriate portions of desirable computation/storage power from a scalable repository, such as a data center or a distributed computing environment. In one example, server  2701  may implement the methods described herein using customized hard-wired logic, one or more Application Specific Integrated Circuits (ASICs) or Field Programmable Gate Arrays (FPGAs), firmware, and/or program logic which, in combination with the computer system, cause server  2701  to be a special-purpose machine. 
     Vehicle  2702  and/or vehicle device  2703  may be configured to collect navigational information and transmit the navigational information to server  2701 . For example, vehicle  2702  and/or vehicle device  2703  may be configured to receive data from one or more sensors and determine navigational information, such as the vehicle&#39;s location, speed, and/or driving direction, based on the received data. In some embodiments, navigational information may include sensor data received from one or more sensors associated with vehicle  3302  (e.g., from a GPS device, a speed sensor, an accelerometer, a suspension sensor, a camera, a LIDAR device, a Visual Detection and Ranging (VIDAR) device, or the like, or a combination thereof). Vehicle  2702  and/or vehicle device  2703  may also be configured to transmit the navigational information to server  2701  via, for example, network  2705 . Alternatively or additionally, vehicle  2702  and/or vehicle device  2703  may be configured to transmit sensor data to server  2701 . Vehicle  2702  and/or vehicle device  2703  may also be configured to receive map information from server  2701  via, for example, network  2705 . Map information may include data relating to the position in a reference coordinate system of various items, including, for example, roads, water features, geographic features, businesses, points of interest, restaurants, gas stations, a sparse data model including polynomial representations of certain road features (e.g., lane markings), target trajectories for the host vehicle, or the like, or a combination thereof. In some embodiments, vehicle  2702  and/or vehicle device  2703  may be configured to plan a routing path and/or navigate vehicle  2702  according to the map information. For example, vehicle  2702  and/or vehicle device  2703  may be configured to determine a route to a destination based on the map information. Alternatively or additionally, vehicle  2702  and/or vehicle device  2703  may be configured to perform at least one navigational action (e.g., making a turn, stopping at a location, etc.) based on the received map information. In some embodiments, vehicle  2702  may include a device having a similar configuration and/or performing similar functions as system  100  described above. Alternatively or additionally, vehicle device  2703  may have a similar configuration and/or performing similar functions as system  100  described above. 
     Database  2704  may include a map database configured to store map data for the components of system  2700  (e.g., server  2701 , vehicle  2702 , and/or vehicle device  2703 ). In some embodiments, server  2701 , vehicle  2702 , and/or vehicle device  2703  may be configured to access database  2704 , and obtain data stored from and/or upload data to database  2704  via network  2705 . For example, server  2701  may transmit data relating to map information to database  2704  for storage. Vehicle  2702  and/or vehicle device  2703  may download map information and/or data from database  2704 . In some embodiments, database  2704  may include data relating to the position, in a reference coordinate system, of various items, including roads, water features, geographic features, businesses, points of interest, restaurants, gas stations, or the like, or a combination thereof. In some embodiments, database  2704  may include a database similar to map database  160  described elsewhere in this disclosure. 
     Network  2705  may be any type of network (including infrastructure) that provides communications, exchanges information, and/or facilitates the exchange of information between the components of system  2700 . For example, network  2705  may include or be part of the Internet, a Local Area Network, wireless network (e.g., a Wi-Fi/302.11 network), or other suitable connections. In other embodiments, one or more components of system  2700  may communicate directly through dedicated communication links, such as, for example, a telephone network, an extranet, an intranet, the Internet, satellite communications, off-line communications, wireless communications, transponder communications, a local area network (LAN), a wide area network (WAN), a virtual private network (VPN), and so forth. 
     As described elsewhere in this disclosure, vehicle  2702  may transmit navigational information to server  2701  via network  2705 . Server  2701  may analyze the navigational information received from vehicle  2702  and determine a potential travel envelope for vehicle  2702  based on the analysis of the navigational information. A potential travel envelop may encompass the location of vehicle  2702 . In some embodiments, a potential travel envelope may include a boundary. The boundary of the potential travel envelope may have a shape, including, for example, a triangular shape, a quadrilateral shape, a parallelogram shape, a rectangular shape, a square (or substantially square) shape, a trapezoid shape, a diamond shape, a hexagon shape, an octagon shape, a circular (or substantially circular) shape, an oval shape, an egg shape, an irregular shape, or the like, or a combination thereof.  FIGS.  28 A- 28 D  illustrate exemplary potential travel envelopes for a vehicle in an area  2800 , consistent with disclosed embodiments. As illustrated in  FIG.  28 A , server  2701  may determine a potential travel envelope having a boundary  2811 , which may include a trapezoid shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28 B , server  2701  may determine a potential travel envelope having a boundary  2812 , which may include an oval shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28   , server  2701  may determine a potential travel envelope having a boundary  2813 , which may include a triangle shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28   , server  2701  may determine a potential travel envelope having a boundary  2814 , which may include a rectangular shape, for vehicle  2702 . Alternatively or additionally, the shape of the potential travel envelope may have a boundary that is determined by one or more potential paths that the vehicle may travel on starting from a location (e.g., a current location) of the vehicle. One skilled in the art would understand that the shape of a potential travel envelope is not limited to the exemplary shapes described in this disclosure. Other shapes are also possible. For example, a potential travel envelope may include an irregular shape (e.g., determined based on one or more boundaries of jurisdictions, such as countries, states, counties, cities, and/or roads) and/or a portion of any of the shapes described herein. 
     As described elsewhere in this disclosure, server  2701  may also be configured to transmit to vehicle  2702  one or more map segments including map information for a geographical region at least partially overlapping with the potential travel envelope of the vehicle. In some embodiments, the one or more map segments sent to vehicle  2702  may include one or more tiles representing a region of a predetermined dimension. The size and/or shape of a tile may vary. In some embodiments, the dimension of a tile in a region may be in a range of 0.25 to 100 square kilometers, which may be restricted into a subrange of 0.25 square kilometers to 1 square kilometer, 1 square kilometers to 10 square kilometers, and 10 to 25 square kilometers, 25 to 50 square kilometers, and 50 to 100 square kilometers. In some embodiments, the predetermined dimension of the tile(s) may be less than or equal to ten square kilometers. Alternatively, the predetermined dimension of the tile(s) may be less than or equal to one square kilometer. Alternatively, the predetermined dimension of the tile(s) may be less than or equal to ten square kilometers. Alternatively or additionally, the size of a tile may vary based on the type of the region in which a tile is. For example, the size of a tile in a rural area or an area with fewer roads than may be larger than the size of a tile in an urban area or area with more roads. In some embodiments, the size of the tile may be determined based on the density of the information around a current location of the vehicle (or the location where the data is obtained), possible paths for the vehicle, the number of possible routes in the area, the type of routes (e.g., main, urban, rural, dirt, etc.) in the area and general navigational patterns, and/or trends in the relevant area. For example, if a large percentage of vehicles typically remain on a main road in a particular area or region, map information for a small distance along side roads may be retrieved. If a vehicle does in fact navigate onto a side road that is typically less traveled, then more map information for the side road (e.g., for a greater distance along the side road) may be obtained and/or transmitted to the vehicle. In some embodiments, a tile may have a rectangle shape, a square shape, a hexagon shape, or the like, or a combination thereof. One skilled in the art would understand that the shape of a tile is not limited to the shapes described in this disclosure. For example, a tile may include an irregular shape (e.g., determined according to at least a boundary of a jurisdiction (states, counties, cities, or towns) or other regions (e.g., streets, highways)). Alternatively or additionally, a tile may include a portion of any shape disclosed herein. 
       FIGS.  28 E- 28 H  illustrates exemplary map tiles for potential travel envelopes for a vehicle, consistent with disclosed embodiments. As illustrated in  FIGS.  28 E- 28 H , server  2701  may divide area  2800  (or a smaller or a larger area) into multiple tiles  2811 . Server  2701  may also be configured to determine one or more tiles that at least partially overlap with the potential travel envelope of vehicle  2702 . For example, as illustrated in  FIG.  28 E , server  2701  may determine an area  2831  having tiles that intersect with or are within boundary  2821  of a potential travel envelope for vehicle  2702 . As another example, as illustrated in  FIG.  28 F , server  2701  may determine an area  2832  having tiles that intersect with or are within boundary  2822  of a potential travel envelope for vehicle  2702 . As another example, as illustrated in  FIG.  28 G , server  2701  may determine an area  2833  having tiles that intersect with or are within boundary  2823  of a potential travel envelope for vehicle  2702 . As another example, as illustrated in  FIG.  28 H , server  2701  may determine an area  2834  having tiles that intersect with or are within boundary  2824  of a potential travel envelope for vehicle  2702 . In some embodiments, server  2701  may transmit the map information and/or data relating to one or more road segments in the determined area to vehicle  2702 . 
       FIGS.  29 A and  29 B  illustrate exemplary map tiles, consistent with disclosed embodiments. As illustrated in  FIG.  29 A , an area (or a map) may be divided into a plurality of tiles at different levels. For example, in some embodiments, an area may be divided in a plurality of tiles at level 1, each of which may be divided into a plurality of tiles at level 2. Each of the tiles at level 2 may be divided into a plurality of tiles at level 3, and so on.  FIG.  29 B  illustrates a plurality of tiles in a region. Alternatively or additionally, a region or a country may be divided into a plurality of tiles based on jurisdictions (e.g., states, counties, cities, towns) and/or other regions (e.g., streets, highways). In some embodiments, the dimension of a tile may, vary. For example, as illustrated in  FIGS.  29 A and  29 B , an area (or a map) may be divided into different levels, and a tile at a particular level may have a particular dimension. 
     In some embodiments, a tile may be presented in a data blob, which may include a metadata block (e.g., 64 bytes), a signature block (e.g., 256 bytes), and an encoded map data block (e.g., various sizes in the MapBox format). 
     In some embodiments, server  2701  may retrieve data relating to one or more tiles in a region and transmit the data to vehicle  2702  via, for example, network  2705 . 
     Alternatively or additionally, vehicle  2702  may retrieve the data relating to one or more tiles from a storage device. For example, vehicle  2702  may receive one or more road segments from server  2701  as described elsewhere in this disclosure. Vehicle  2702  may also store the received one or more road segments into a local storage and load one or more tiles included in the one or more road segments into a memory for processing. Alternatively, rather receiving one or more road segments from server  2701 , vehicle  2702  may include a local storage configured to store one or more road segments and retrieve the data relating to the one or more road segments from the local storage. 
     In some embodiments, vehicle  2702  may retrieve the data (e.g., map information) relating to one or more tiles based on the location of the vehicle. For example, vehicle  2702  may determine its current location (as described elsewhere in this disclosure) and determine a first tile in which the current location resides. Vehicle  2702  may also retrieve the first tile and one or more (or all) tiles adjacent to the first tile. Alternatively or additionally, vehicle  2702  may retrieve one or more (or all) tiles within a predetermined distance from the first tile. Alternatively or additionally, vehicle  2702  may retrieve one or more (or all) tiles within a predetermined degree of separation from the first tile (e.g., one or more (or all) tiles that are within the second degree of separation; that is, one or more (or all) tiles that are adjacent to the first tile or adjacent to a title that is adjacent to the first tile). When vehicle  2702  moves to a second tile, vehicle  2702  may retrieve the second tile. Vehicle  2702  may also retrieve the first tile and one or more (or all) tiles adjacent to the second tile. Alternatively or additionally, vehicle  2702  may retrieve one or more (or all) tiles within a predetermined distance from the second tile. Alternatively or additionally, vehicle  2702  may retrieve one or more (or all) tiles within a predetermined degree of separation from the second tile (e.g., one or more (or all) tiles that are within the second degree of separation; that is, one or more (or all) tiles that are adjacent to the second tile or adjacent to a title that is adjacent to the second tile). In some embodiments, vehicle  2702  may also delete (or overwrite) the first tile and/or the previously retrieved tiles that are not adjacent to the second tile. Alternatively or additionally, vehicle  2702  may delete (or overwrite) one or more previously retrieved tiles that are not within a predetermined distance from the second tile. Alternatively or additionally, vehicle  2702  may delete (or overwrite) one or more (or all) previously retrieved tiles that are not within a predetermined degree of separation from the second tile. 
       FIG.  30    illustrates an exemplary process for retrieving one or more tiles. As illustrated in  FIG.  30   , vehicle  2702  (and/or server  2701 ) may be configured to determine that the location of vehicle  2702  is in tile 5 at time point 1. Vehicle  2702  may also be configured to retrieve (or load) adjacent tiles 1-4 and 6-9. At time point 2, vehicle  2702  (and/or server  2701 ) may be configured to determine that the location of vehicle  2702  moves to tile 3 from tile 5. Vehicle  2702  may be configured to retrieve (or load) new tiles 10-14, which are adjacent to tile 3. Vehicle  2702  may also be configured to keep tiles 2, 3, 5, and 6, and delete tiles 1, 4, and 7-9. As such, vehicle  2702  may retrieve (or load) a subset of the tiles (e.g., 9 tiles) at a time to reduce the memory usage and/or computation load. In some embodiments, vehicle  2702  may be configured to decode a tile before loading the data into the memory. 
     Alternatively or additionally, vehicle  2702  may determine a subpart of a tile that its location falls within the tile and load the tiles adjacent to the subpart. By way of example, as illustrated in  FIG.  31 A , vehicle  2702  may determine that the location of vehicle  2702  is in a sub-tile (a sub-tile having a pattern of dots in tile 5) and load map data of the tiles that are adjacent to the sub-tile (i.e., tiles 4, 7, and 9) into the memory for processing. As another example, as illustrated in  FIG.  31 B , vehicle  2702  may determine that the location of vehicle  2702  is in the left-top sub-tile of tile 5. Vehicle  2702  may also load the tiles adjacent to the left-top sub-tile of tile 5 (i.e., tiles 1, 2, and 4). As such, vehicle  2702  may retrieve (or load) a subset of the tiles (e.g., 4 tiles) at a time to reduce the memory usage and/or computation load. As another example, as illustrated in  FIG.  31 C , vehicle  2702  may determine that the location of vehicle  2702  is in the right-top sub-tile and load map data of the tiles that are adjacent to the sub-tile (i.e., tiles 2, 3, and 6) into the memory for processing. As another example, as illustrated in  FIG.  31 D , vehicle  2702  may, determine that the location of vehicle  2702  is in the right-bottom sub-tile and load map data of the tiles that are adjacent to the sub-tile (i.e., tiles 6, 8, and 9) into the memory for processing. In some embodiments, vehicle  2702  may be configured to decode a tile before loading the data into the memory. 
       FIG.  32    is a flowchart showing an exemplary process for providing one or more map segments to one or more vehicles, consistent with the disclosed embodiments. One or more steps of process  3200  may be performed by a vehicle (e.g., vehicle  2702 ), a device associated with the host vehicle (e.g., vehicle device  2703 ), and/or a server (e.g., server  2701 ). While the descriptions of process  3200  provided below use server  2701  as an example, one skilled in the art would appreciate that one or more steps of process  3200  may be performed by a vehicle (e.g., vehicle  2702 ) and a vehicle device (e.g., vehicle device  2703 ). For example, vehicle  2702  may determine a potential travel envelope based on navigational information. In additional to or alternative to receiving map data from server  2701 , vehicle  2702  may retrieve portion of map data relating to the potential travel envelope from a local storage and load the retrieved data into a memory for processing. 
     At step  3201 , navigational information may be received from a vehicle. For example, server  2701  may receive navigational information from vehicle  2702  via, for example, network  2705 . In some embodiments, the navigational information received from a vehicle may include an indicator of a location of the vehicle, an indicator of a speed of the vehicle, and an indicator of a direction of travel of the vehicle. For example, vehicle  2702  may be configured to receive data from one or more sensors, including, for example, a GPS device, a speed sensor, an accelerometer, a suspension sensor, or the like, or a combination thereof. Vehicle  2702  may also be configured to determine navigational information, such as the vehicle&#39;s location, speed, and/or driving direction, based on the received data. Vehicle  2702  may also be configured to transmit the navigational information to server  2701  via, for example, network  2705 . Alternatively or additionally, vehicle  2702  may be configured to transmit the sensor data to server  2701 . Server  2701  may be configured to determine navigational information, which may include the location of vehicle  2702 , speed of vehicle  2702 , and/or direction of travel of vehicle  2702 , based on the received sensor data. 
     In some embodiments, vehicle  2702  may transmit the navigational information (and/or sensor data) to server  2701  continuously. Alternatively, vehicle  2702  may transmit the navigational information (and/or sensor data) to server  2701  intermittently. For example, vehicle  2702  may transmit the navigational information (and/or sensor data) to server  2701  a number of times over a period of time. By way of example, vehicle  2702  may transmit the navigational information (and/or sensor data) to server  2701  once per minute. Alternatively, the vehicle may transmit the navigational information when it has access to a more reliable and/or faster network (e.g., having a stronger wireless signal, via a WIFI connection, etc.). 
     At step  3202 , the received navigational information may be analyzed and a potential travel envelope for the vehicle may be determined. For example, server  2701  may analyze vehicle  2702 &#39;s location, speed, and/or driving direction, and determine a potential travel envelope, which may include a determined area relative to vehicle  2702 . By way of example, as illustrated in  FIG.  28 A , server  2701  may determine an area that encompasses the location of vehicle  2702  and determine a potential travel envelope having a boundary  2811 , based on the determined area. 
     In some embodiments, server  2701  may be configured to determine a potential travel envelope extending from the location of vehicle  2702  and surrounding the location of vehicle  2702 . For example, as illustrated in  FIG.  28 A , server  2701  may determine a line  2802  passing the location of vehicle  2702  (or the centroid of vehicle  2702 ). Server  2701  may also be configured to determine a side of the boundary of the potential travel envelope in the direction of travel of vehicle  2702  and determine another side of the boundary of the potential travel envelope in a direction opposite to the direction of travel. By way of example, server  2701  may determine the upper boundary of the potential travel envelope in the direction of travel of vehicle  2702  and determine the lower boundary of the potential travel envelope in the direction opposite to the direction of travel of vehicle  2702 . In some embodiments, the potential travel envelope may extend further along the direction of travel of the vehicle than in a direction opposite to the direction of travel of the vehicle. For example, as illustrated in  FIG.  28 A , the upper boundary of the potential travel envelope may have a distance  2803  from line  2802  (or a first distance from the location of vehicle  2702 ), and the lower boundary of the potential travel envelope have a distance  2804  from line  2802  (or a second distance from the location of vehicle  2702 ). Distance  2803  may be greater than distance  2804  (and/or the first distance may be greater than the second distance). In some embodiments, the location of a centroid of the boundary may be offset from the location of vehicle  2702  along the direction of travel of vehicle  2702 . 
     Alternatively or additionally, in determining the potential travel envelope for vehicle  2702 , server  2701  may take a potential travel distance over a period of time (or a time window) into account. For example, server  2701  may determine a potential travel distance over a predetermined amount of time and determine the potential travel envelope including the potential travel distance. In some embodiments, the potential travel distance over the predetermined amount of time may be determined based on the location of vehicle  2702  and/or the speed of vehicle  2702 . In some embodiments, server  2701  may determine the potential travel envelope further based on a selected or predetermined time window. The time window may be selected or determined based on the indicator of the speed of the vehicle. The predetermined amount of time (or a time window) may be in the range of 0.1 seconds to 24 hours. In some embodiments, the predetermined amount of time (or a time window) may be restricted into subranges of 0.1 seconds to 1 second, 1 second to 5 seconds, 5 to 10 seconds, 10 to 60 seconds, 1 minute to 5 minutes, 5 to 10 minutes, 10 to 60 minutes, 1 hour to 5 hours, 5 to 10 hours, and 10 to 24 hours. In some embodiments, the predetermined amount of time (or a time window) may be determined based on the transmission frequency of the navigational information from vehicle  2702  to server  2701 . For example, server  2701  may determine the predetermined amount of time (or a time window) based on the interval between two transmissions of the navigational information from vehicle  2702 . Server  2701  may determine a longer time period for determining the potential travel distance for a longer transmission interval. 
     In some embodiments, a potential travel envelope may include a boundary. The boundary of the potential travel envelope may have a shape, including, for example, a triangular shape, a quadrilateral shape, a parallelogram shape, a rectangular shape, a square (or substantially square) shape, a trapezoid shape, a diamond shape, a hexagon shape, an octagon shape, a circular (or substantially circular) shape, an oval shape, an egg shape, an irregular shape, or the like, or a combination thereof.  FIGS.  28 A- 28 D  illustrate exemplary potential travel envelopes for a vehicle in an area  2800 , consistent with disclosed embodiments. As illustrated in  FIG.  28 A , server  2701  may determine a potential travel envelope having a boundary  2811 , which may include a trapezoid shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28 B , server  2701  may determine a potential travel envelope having a boundary  2812 , which may include an oval shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28   , server  2701  may determine a potential travel envelope having a boundary  2813 , which may include a triangle shape, for vehicle  2702 . As another example, as illustrated in  FIG.  28   , server  2701  may determine a potential travel envelope having a boundary  2814 , which may include a rectangular shape, for vehicle  2702 . 
     In some embodiments, vehicle  2702  (and/or vehicle device  2703 ) may determine a potential travel envelope based on the navigational information. 
     At step  3203 , one or more map segments may be sent to vehicle  2702 . In some embodiments, the map segment(s) may include map information for a geographical region at least partially overlapping with the potential travel envelope of vehicle  2702 . For example, server  2701  may send the one or more map segments including map data of a geographical region at least partially overlapping with the potential travel envelope of vehicle  2702  via network  2705 . 
     In some embodiments, the one or more map segments include one or more tiles representing a region of a predetermined dimension. For example, as illustrated in  FIG.  28 E , server  2701  may determine one or more tiles  2831  that at least partially overlaps with the potential travel envelope of vehicle  2702  (i.e., the potential travel envelope having boundary  2821 ) and transmit map data relating to tiles  2831  to vehicle  2702  via network  2705 . 
     In some embodiments, the dimension of a tile sent to vehicle  2702  may vary. For example, as illustrated in  FIGS.  29 A and  29 B , an area (or a map) may be divided into different levels, and a tile at a particular level may have a particular dimension. In some embodiments, the predetermined dimension of the tile(s) sent to vehicle  2702  may be in a range of 0.25 to 100 square kilometers, which may be restricted in a subrange of 0.25 square kilometers to 1 square kilometer, 1 square kilometers to 10 square kilometers, and 10 to 25 square kilometers, 25 to square kilometers, and 50 to 100 square kilometers. In some embodiments, the predetermined dimension of the tile(s) may be less than or equal to ten square kilometers. Alternatively, the predetermined dimension of the tile(s) may be less than or equal to one square kilometer. Alternatively, the predetermined dimension of the tile(s) may be less than or equal to ten square kilometers. In some embodiments, a tile may have a rectangle shape, a square shape, a hexagon shape, or the like, or a combination thereof. 
     In some embodiments, the map information sent to vehicle  2702  may include a polynomial representation of a target trajectory along the one or more road segments, as described elsewhere in this disclosure. For example, the map information may include a polynomial representation of a portion of a road segment consistent with the disclosed embodiments illustrated in  FIG.  9 A .  FIG.  9 B , and  FIG.  11 A . For example, the map information may include a polynomial representation of a target trajectory that is determined based on two or more reconstructed trajectories of prior traversals of vehicles along the one or more road segments. 
     In some embodiments, after receiving the one or more road segments, vehicle  2702  may navigate according to the one or more road segments, as described elsewhere in this disclosure. For example, vehicle  2702  may be configured to perform one or more navigational actions (e.g., making a turn, stopping at a location, etc.) based on the received one or more road segments. Alternatively or additionally, vehicle  2702  may be configured to perform one or more navigational actions based on the polynomial representation of a target trajectory along the one or more road segments. 
     In some embodiments, vehicle  2702  may receive the one or more road segments and store the one or more road segments into a storage device. Vehicle  2702  may also load one or more tiles included in the one or more road segments into a memory for processing. For example, as illustrated in  FIG.  30   , vehicle  2702  (and/or server  2701 ) may be configured to determine that the location of vehicle  2702  is in tile 5 at time point 1. Vehicle  2702  may also be configured to retrieve (or load) adjacent tiles 1-4 and 6-9. At time point 2, vehicle  2702  (and/or server  2701 ) may be configured to determine that the location of vehicle  2702  moves to tile 3 from tile 5. Vehicle  2702  may be configured to retrieve (or load) new tiles 10-14, which are adjacent to tile 3. Vehicle  2702  may also be configured to keep tiles 2, 3, 5, and 6, and delete tiles 1, 4, and 7-9. 
     Alternatively or additionally, vehicle  2702  may determine a subpart of a tile that its location falls within a tile and load the tiles adjacent to the subpart. By way of example, as illustrated in  FIG.  31 A , vehicle  2702  may determine that the location of vehicle  2702  is in a sub-tile (a sub-tile having a pattern of dots in tile 5) and load map data of the tiles that are adjacent to the sub-tile (i.e., tiles 4, 7, and 9) into the memory for processing. As another example, as illustrated in  FIG.  31 B , vehicle  2702  may determine that the location of vehicle  2702  is in the left-top sub-tile of tile 5. Vehicle  2702  may also load the tiles adjacent to the left-top sub-tile of tile 5 (i.e., tiles 1, 2, and 4). In some embodiments, vehicle  2702  may be configured to decode the tiles before loading the data into the memory. 
     In some embodiments, rather than receiving the one or more road segments from server  2701  through network  2705 , vehicle  2702  may retrieve the one or more road segments from a local storage. For example, vehicle  2702  may determine the potential travel envelope based on the analysis of the navigational information and determine one or more road segments including map information for a geographical region at least partially overlapping with the potential travel envelope of vehicle  2702 . Vehicle  2702  may also retrieve the data of the one or more road segments from a local storage. In some embodiments, vehicle  2702  may load the data of the one or more road segments into its memory for processing. 
     Bandwidth Management for Map Generation and Refinement 
     As described elsewhere in this disclosure, harnessing and interpreting vast volumes of data (e.g., captured image data, map data. GPS data, sensor data, etc.) collected by vehicles poses a multitude of design challenges. For example, the data collected by a vehicle may need to be uploaded to a server. The sheer quantity of data to be uploaded may easily cripple or hinder the transmission bandwidth of the vehicle. Additionally, analyzing new data by a server to update the relevant portion of a map based on the new data may also be challenging. Moreover, different density levels may be used for mapping different types of features. For example, a density level of 330 kB per km may be needed for mapping non-semantic features, compared with about a density level of 20 kB per km for semantic features. Given the computation resources required for collecting non-semantic feature information and certain hard limit bandwidth caps (e.g., 100 MB per year) that may be imposed to each of the vehicles, there may be insufficient resources available to the vehicles to collect non-semantic feature information all the time. 
     The systems and methods may enable controlling not only whether drive data is collected, but also when and how drive data is collected. For example, the disclosed systems and methods may enable a server to determine whether a host vehicle is entering a zone including a region of interest. Upon confirmation that the vehicle has entered the zone, the server can cause the vehicle to begin collecting higher density non-semantic features information. If the vehicle is determined to have driven through the point of interest, then the server can cause the vehicle to upload the collected non-semantic features information. If the vehicle is determined not to have driven through the region of interest, the server may cause the host vehicle to discard the collected non-semantic features information. The disclosed systems and methods may also enable the server to update a map based on the non-semantic features information collected by the vehicle. 
       FIG.  33    illustrates an exemplary system for automatically generating a navigational map relative to one or more road segments, consistent with the disclosed embodiments. As illustrated in  FIG.  33   , system  3300  may include a server  3301 , one or more vehicles  3302 , and one or more vehicle devices  3303  associated with a vehicle, a database  3304 , and a network  3305 . For example, vehicle  3302  and/or vehicle device  3303  may be configured to collect, at a first density level, first navigational information associated with the environment traversed by vehicle  3302  when vehicle  3302  travels outside of a predetermined distance from a geographical region of interest. Vehicle  3302  and/or vehicle device  3303  may also be configured to collect, at a second density level that may be greater than the first density level, second navigational information associated with the environment traversed by vehicle  3302  when vehicle  3302  travels at or within the predetermined distance from the geographical region of interest. 
     Server  3301  may be configured to receive the first and/or second navigational information associated with the environment traversed by vehicle  3302 . Database  3304  may be configured to store information for the components of system  3300  (e.g., server  3301 , vehicle  3302 , and/or vehicle device  3303 ). Network  3305  may be configured to facilitate communications among the components of system  3300 . 
     Server  3301  may be configured to cause collection of first navigational information associated with an environment traversed by vehicle  3302 . The first navigational information may be collected at a first density level. Server  3301  may also be configured to determine the location of vehicle  3302  based on output associated with a GPS sensor associated with vehicle  3302 . Server  3301  may further be configured to determine whether vehicle  3302  is at or within a predetermined distance from the geographical region of interest (or a boundary thereof). Server  3301  may also be configured to cause collection of second navigational information associated with the environment traversed by vehicle  3302 , based on the determination that the location of vehicle  3302  is at or within the predetermined distance from the geographical region of interest. The second navigational information may be collected at a second density level that may greater than the first density level. Server  3301  may further be configured to cause vehicle  3302  to upload at least one of the collected first navigational information or the collected second navigational information (or a portion thereof) from vehicle  3302 . Server  3301  may also be configured to update a navigational map based on the uploaded at least one of the collected first navigational information or the collected second navigational information. In some embodiments, server  3301  may be a cloud server that performs the functions disclosed herein. The term “cloud server” refers to a computer platform that provides services via a network, such as the Internet. In this example configuration, server  3301  may use virtual machines that may not correspond to individual hardware. For example, computational and/or storage capabilities may be implemented by allocating appropriate portions of desirable computation/storage power from a scalable repository, such as a data center or a distributed computing environment. In one example, server  3301  may implement the methods described herein using customized hard-wired logic, one or more Application Specific Integrated Circuits (ASICs) or Field Programmable Gate Arrays (FPGAs), firmware, and/or program logic which, in combination with the computer system, cause server  3301  to be a special-purpose machine. 
     Vehicle  3302  and/or vehicle device  3303  may be configured to collect first navigational information when it travels beyond the predetermined distance from the geographical region of interest (or a boundary thereof). Vehicle  3302  and/or vehicle device  3303  may also be configured to collect second navigational information when it travels at or within the predetermined distance from the geographical region of interest (or a boundary thereof). Vehicle  3302  and/or vehicle device  3303  may further be configured to upload at least one the collected first navigational information and the collected second navigational information (or a portion thereof). In some embodiments, vehicle  3302  may receive map information (e.g., an updated map) from server  3301 . Map information may include data relating to the position in a reference coordinate system of various items, including, for example, roads, water features, geographic features, businesses, points of interest, restaurants, gas stations, a sparse data model including polynomial representations of certain road features (e.g., lane markings), target trajectories for the host vehicle, or the like, or a combination thereof. In some embodiments, vehicle  3302  and/or vehicle device  3303  may also be configured to plan a routing path and/or navigate vehicle  3302  according to the map information. For example, vehicle  3302  and/or vehicle device  3303  may be configured to determine a route to a destination based on the map information. Alternatively or additionally, vehicle  3302  and/or vehicle device  3303  may be configured to perform at least one navigational action (e.g., making a turn, stopping at a location, etc.) based on the received map information. In some embodiments, vehicle  3302  may include a device having a similar configuration and/or performing similar functions as system  100  described above. Alternatively or additionally, vehicle device  3303  may have a similar configuration and/or performing similar functions as system  100  described above. 
     Database  3304  may include a map database configured to store map information for the components of system  3300  (e.g., server  3301 , vehicle  3302 , and/or vehicle device  3303 ). In some embodiments, server  3301 , vehicle  3302 , and/or vehicle device  3303  may be configured to access database  3304 , and obtain data stored from and/or upload data to database  3304  via network  3305 . For example, server  3301  may transmit data relating to map information to database  3304  for storage. Vehicle  3302  and/or vehicle device  3303  may download map information and/or data from database  3304 . In some embodiments, database  3304  may include data relating to the position, in a reference coordinate system, of various items, including roads, water features, geographic features, businesses, points of interest, restaurants, gas stations, or the like, or a combination thereof. In some embodiments, database  3304  may include a database similar to map database  160  described elsewhere in this disclosure. 
     Network  3305  may be any type of network (including infrastructure) that provides communications, exchanges information, and/or facilitates the exchange of information between the components of system  3300 . For example, network  3305  may include or be part of the Internet, a Local Area Network, wireless network (e.g., a Wi-Fi/302.11 network), or other suitable connections. In other embodiments, one or more components of system  3300  may communicate directly through dedicated communication links, such as, for example, a telephone network, an extranet, an intranet, the Internet, satellite communications, off-line communications, wireless communications, transponder communications, a local area network (LAN), a wide area network (WAN), a virtual private network (VPN), and so forth. 
       FIGS.  34 A,  34 B, and  34 C  illustrate an exemplary process for collecting navigational information, consistent with disclosed embodiments. As illustrated in  FIG.  34 A , vehicle  3302  may travel in a region  3400 . Server  3301  may be configured to determine the location of vehicle  3302  based on, for example, GPS data received from a GPS device associated with vehicle  3302 . Server  3301  may also be configured to determine that vehicle  3302  is beyond a predetermined distance d from geographical region of interest  3401 . Server  3301  may further be configured to cause vehicle  3302  to collect, at a first density level, first navigational information associated with the environment traversed by vehicle  3302 . Vehicle  3302  may move in region  3400  as illustrated in  FIG.  34 B . Server  3301  may be configured to determine that vehicle  3302  is within the predetermined distance d from geographical region of interest  3401  based on the location of vehicle  3302 . Server  3301  may also be configured to cause vehicle  3302  to collect, at a second density level that may be greater than the first density level, second navigational information associated with the environment traversed by vehicle  3302 . Vehicle  3302  may move in region  3400  as illustrated in  FIG.  34 C . 
     A greater density level may indicate a greater amount of collected data per a unit length of a road segment. For example, the second navigational information collected at the second density level may include a denser set of similar objects (e.g., more landmarks) than the first navigational information collected at the first density level. Alternatively or additionally, the second navigational information collected at the second density level may include more categories of data collected than the first navigational information collected at the first density level. For example, the second navigational information collected at the second density level may include more non-sematic features (e.g., descriptors), which may need more data compared to that for sematic features, than the first navigational information has. In some embodiments, the second navigational information may include one or more non-sematic features, while the first navigational information may not include any non-sematic features. Examples of semantic features and non-semantic features were discussed earlier in this disclosure. Alternatively or additionally, the second navigational information collected at the second density level may include sensor data from more and/or different sensors than the first navigational information collected at the first density level. For example, the first navigational information may include GPS data received from a GPS sensor. The second navigational information may include GPS data and LIDAR data received from a LIDAR system. As another example, the first navigational information may include GPS data and LIDAR data, and the second navigational information may include GPS data and image (and/or VIDAR) data received from a VIDAR system. As still another example, the first navigational information may include one or more images captured by a camera installed on the vehicle, and the second navigational information may include one or more images captured by the camera and LIDAR data received from a LIDAR system. As still another example, the first navigational information may include the data received from an accelerometer sensor and data received from a LIDAR system, and the data received from the accelerometer sensor and image (and/or VIDAR) data received from a VIDAR system. 
     In some embodiments, a landmark may include a combination of objects (or landmarks) as long as the combination of objects is distinguishable (it can be distinguished from other nearby sets of objects). For example, landmarks of the same type, including a set of landmarks that may constitute a combination landmark (a landmark that may be constituted by a combination of semantic objects) may distanced apart from one another by a certain distance (e.g., the distance that corresponds (or is equal) to the minimal resolution of the GPS device associated with a vehicle. 
     Server  3301  may be configured to determine that vehicle  3302  is within geographical region of interest  3401 . Vehicle  3302  may be configured to continue to collect second navigational information at the second density level when it travels within geographical region of interest  3401 . Server  3301  may also be configured to cause vehicle  3302  to upload at least one of the first navigational information and the second navigational information to server  3301 . 
       FIG.  35    is a flowchart showing an exemplary process for automatically generating a navigational map relative to one or more road segments, consistent with the disclosed embodiments. One or more steps of process  3500  may be performed by a vehicle (e.g., vehicle  3302 ), a device associated with the host vehicle (e.g., vehicle device  3303 ), and/or a server (e.g., server  3301 ). While the descriptions of process  3500  provided below use server  3301  as an example, one skilled in the art would appreciate that one or more steps of process  3500  may be performed by a vehicle (e.g., vehicle  3302 ) and a vehicle device (e.g., vehicle device  2703 ). In addition, in various steps described herein, a vehicle may upload certain information and/or data to a server, and one skilled in the art would understand that, alternatively or additionally, the vehicle may upload the information and/or data to a database (e.g., database  3304 ) via a network. Moreover, one skilled in the art would understand that although the descriptions of process  3500  provided below use vehicle  3302  as an example, process  3500  is not limited to one vehicle. For example, server  3301  may be configured to determine the locations of a plurality of vehicles and cause the plurality of vehicles to collect first and/or second navigational information. Server  3301  may also be configured to cause the plurality of vehicles to upload the collected first and/or second navigational information, and update a navigational map based on the received first and/or second navigational information. 
     At step  3501 , first navigational information associated with an environment traversed by a host vehicle may be collected. For example, server  3301  may be configured to cause collection of first navigational information, by vehicle  3302  at a first density level, associated with an environment traversed by vehicle  3302 . By way of example, as illustrated in  FIG.  34 A , vehicle  3302  may travel in a region  3400 . Server  3301  may be configured to cause vehicle  3302  to collect navigational information associated with vehicle  3302 &#39;s environment by transmitting a request to vehicle  3302  to collect navigational information at the first level. 
     In some embodiments, vehicle  3302  may collect navigational information determined based on signals received from one or more sensors, such as a GPS device, a speed sensor, an accelerometer, a suspension sensor, a camera, and a LIDAR device, or the like, or a combination thereof. Exemplary navigational information may include information and/or data relating to the locations of the vehicle, speeds of the vehicle, driving directions of the vehicle, landmarks associated with one or more road segments, roads, one or more road features, one or more infrastructure objects, water features, geographic features, points of interest (e.g., office buildings, restaurants, gas stations, etc.), one or more images associated with one or more road segments, LIDAR data associated with one or more road segments, a sparse data model including polynomial representations of certain road features (e.g., lane markings), target trajectories for the host vehicle, or the like, or a combination thereof. For example, the first navigational information may include location information associated with one or more landmarks associated with the one or more road segments. Alternatively or additionally, the first navigational information may include location information associated with one or more road features associated with the one or more road segments. 
     In some embodiments, the first navigational information may be associated with a first density level. A density level may indicate certain categories of navigational information to collect (e.g., one or more types of navigational information collected), a collection rate of navigational information (e.g., how many data points per unit time, such as per second, per minute, per hour, etc.), an accuracy level of navigational information (e.g., a higher or lower data resolution), or the like, or a combination thereof. In some embodiments, a density level may be associated with a data density (e.g., less than 10 MB per kilometer of roads, less than 5 MB per kilometer of roads, 2 MB per kilometer of roads, less than 1 MB per kilometer of roads, less than 500 kB per kilometer of roads, less than 100 kB per kilometer of roads, less than 10 kB per kilometer of roads, or less than 2 kB per kilometer of roads). 
     In some embodiments, vehicle  3302  may collect first navigational information without input or a request from server  3301 . For example, vehicle  3302  may operate in a “default” collection mode in which navigational information is collected at a predetermined density level (e.g., the first density level). Alternatively, vehicle  3302  may collect navigational information at a predetermined density level based on a setting associated with a condition of vehicle  3302  (e.g., a speed, heading direction, etc.). As yet another alternative, vehicle  3302  may collect navigational information based on a density level transmitted from server  3301  to vehicle  3302 . 
     At step  3502 , a location of the host vehicle may be determined based on output associated with one or more sensors of the host vehicle. For example, vehicle  3302  may be configured to receive output associated with a GPS sensor and transmit the output to server  3301 . Server  3301  may be configured to determine the location of vehicle  3302  based on received output associated with the GPS sensor. Alternatively or additionally, vehicle  3302  may be configured to determine its location based on the received output associated with the GPS sensor and transmit the location of vehicle  3302  to server  3301 . Exemplary sensors may include a speed sensor, an accelerometer, a camera, a LIDAR device, or the like, or a combination thereof. Alternatively or additionally, vehicle  3302  may use map information to determine a location. 
     In some embodiments, the location of the vehicle  3302  may be determined at predetermined time intervals. For example, the location of vehicle  3302  may be determined once every second or every minute. Alternatively or additionally, the location of vehicle  3302  may be determined based on the speed of the vehicle  3302 . For example, the location of vehicle  3302  may be determined more frequently if it is determined (by vehicle  3302  and/or server  3301 ) that vehicle  3302  travels at a higher speed. Alternatively or additionally, the location of vehicle  3302  may be determined based on the region in which vehicle  3302  is. For example, the location of vehicle  3302  may be determined more frequently if it is determined (by vehicle  3302  and/or server  3301 ) that vehicle  3302  is in an urban area (or less frequently if vehicle  3302  is in a rural area). 
     At step  3503 , whether the location of the host vehicle is at or within a predetermined distance from a geographical region of interest may be determined. For example, as illustrated in  FIGS.  34 A and  34 B , server  3301  may be configured to determine a geographical region of interest  3401  and a predetermined distance d from geographical region of interest  3401  (or a boundary thereof). Server  3301  may also be configured to determine whether vehicle  3302  is at or within the predetermined distance d from geographical region of interest  3401  (or a boundary thereof). As illustrated in  FIG.  34 A , server  3301  may be configured to determine that vehicle  3302  is not at or within the predetermined distance d from geographical region of interest  3401  (or a boundary thereof). Alternatively, as illustrated in  FIG.  34 B , server  3301  may be configured to determine that vehicle  3302  is at or within the predetermined distance d from geographical region of interest  3401  (or a boundary thereof). Alternatively or additionally, vehicle  3302  may be configured to determine whether vehicle  3302  is at or within the predetermined distance d from geographical region of interest  3401  (or a boundary thereof). For example, server  3301  may transmit a geographical region of interest  3401  and a predetermined distance d from geographical region of interest  3401  (or a boundary thereof) to vehicle  3302 . Vehicle  3302  may be configured to determine whether vehicle  3302  is at or within the predetermined distance d from geographical region of interest  3401  (or a boundary thereof) based on the location of the vehicle  3302  determined as described elsewhere in this disclosure. Vehicle  3302  may be configured to transmit the result of the determination of being at or within (or outside of) the predetermined distance d from geographical region of interest  3401  (or a boundary thereof) to server  3301 . 
     In some embodiments, server  3301  may be configured to determine a geographical region of interest based on existing information of the geographical region of interest. For example, server  3301  may be configured to determine that the existing map data of a region may be inadequate (e.g., does not include certain details regarding a road feature associated with a road segment in the region). By way of example, server  3301  may be configured to determine a particular road segment (e.g., 1 km in length) that may need accurate alignment. Server  3301  may also be configured to determine a geographical region of interest (e.g., a square or circle that covers the road segment). As another example, server  3301  may determine to update map information of a region and may designate the region as a geographical region of interest. 
     A geographical region of interest may be a geographic region in a map or a coordinate system. A geographical region of interest may include one or more of road segments, streets, intersections, highways, highway junctions, landmarks, infrastructure objects, geographic features, points of interest (such as businesses, restaurants, gas stations, etc.), or the like, or a combination thereof. Geographical regions of interest may vary in shape and/or size. A geographical region of interest may include a triangular shape, a quadrilateral shape, a parallelogram shape, a rectangular shape, a square (or substantially square) shape, a trapezoid shape, a diamond shape, a hexagon shape, an octagon shape, a circular (or substantially circular) shape, an oval shape, an egg shape, or the like, or a combination thereof. One skilled in the art would understand that the shape of a geographical region of interest is not limited to the exemplary shapes described in this disclosure. Other shapes are also possible. For example, a geographical region of interest may include an irregular shape (e.g., determined based on one or more boundaries of jurisdictions, such as countries, states, counties, cities, and/or roads) and/or a portion of any of the shapes described herein. The size of a geographical region of interest may be in a range of 1 square meter to 100 square kilometers. In some embodiments, the size of a geographical region of interest may be restricted into a subrange of 1 square meter to 0.1 square kilometers, 0.1 to 0.25 square kilometers, 0.25 square kilometers to 1 square kilometer, 1 square kilometers to 10 square kilometers, and 10 to 25 square kilometers, 25 to square kilometers, and 50 to 100 square kilometers. 
     In some embodiments, the predetermined distance may include a direct distance, a route distance (e.g., a distance for the host vehicle to travel to the geographical region of interest), or the like, or a combination thereof. The predetermined distance may be in a range of 1 meter to 100 kilometers. In some embodiments, the predetermined distance may be restricted into subranges of 1 to 5 meters, 5 to 10 meters, 10 to 50 meters, 50 to 100 meters, 100 to 500 meters, 500 to 1000 meters, 1 to 5 kilometers, 5 to 10 kilometers, 10 to 50 kilometers, and 50 to 100 kilometers. Alternatively or additionally, the predetermined distance may include a distance indicator based on the separation of the vehicle from the geographical region of interest (or a boundary thereof) in terms of the number of street blocks, the number of exits on a highway, or the like, or a combination thereof. For example, a predetermined distance may include a distance indicator indicating three street blocks. 
     In some embodiments, server  3301  may be configured to determine an approximation of a geographical region based on the geographical region of interest. For example, server  3301  may extend the geographical region of interest by adding the predetermined distance to the boundaries of the geographical region of interest to obtain a rough geographical region. Server  3301  (and/or vehicle  3302 ) may also be configured to determine whether vehicle  3302  is at or within the rough geographical region based on the location of vehicle  3302 . 
     In some embodiments, server  3301  may transmit information relating to the geographical region of interest and/or predetermined distance to vehicle  3302 . For example, server  3301  may transmit the boundaries of the geographical region of interest and/or the predetermined distance to vehicle  3302 . 
     At step  3504 , in response to the determination that the location of the host vehicle is at or within the predetermined distance from the geographical region of interest, second navigational information associated with the environment traversed by the host vehicle may be collected. For example, server  3301  may be configured to cause collection of second navigational information associated with the environment traversed by vehicle  3302 , based on the determination that the location of vehicle  3302  is at or within the predetermined distance from the geographical region of interest. 
     For example, as illustrated in  FIG.  34 B , server  3301  may be configured to determine that vehicle  3302  is within geographical region of interest  3401 . Server  3301  may also be configured to transmit an instruction to vehicle  3302  to collect second navigational information, and vehicle  3302  may collect second navigational information in response to the received instruction. 
     In some embodiments, the second navigational information may include more categories of information than the first navigational information. For example, the first navigational information may include landmarks and road features associated with one or more road segments (i.e., two categories of information). The second navigational information may include not only landmarks and road features associated with one or more road segments, but also one or more infrastructure objects, water features, geographic features, and/or points of interest associated with one or more road segments. 
     In some embodiments, the second navigational information may be associated with a second density level that is higher than the first density level. For example, the second density level may be at least two times greater than the first density level. By way of example, the first navigational information may include cloud point data measured at a first density level (e.g., 300 points every 15 meters) by a LIDAR device associated with vehicle  3302 . The second navigational information may include cloud point data measured by the LIDAR device at a second density level (e.g., 800 points every 15 meters), which is more than two times greater than the first density level. As another example, the second density level may be at least five times greater than the first density level. As another example, the second density level may be at least ten times greater than the first density level. 
     Alternatively or additionally, the second navigational information may be collected at a collection rate higher than a collection rate at which the first navigational information is collected. By way of example, the first navigational information may include images of the environment of vehicle  3302  captured by a camera onboard vehicle  3302  at a first image collection rate. The second navigational information may include images of the environment of vehicle  3302  captured by the camera onboard vehicle  3302  at a second image collection rate that is higher than the first image collection rate. An image collection rate may include a collection rate based on time and/or distance that vehicle  3302  travels. For example, a first image collection rate may be 10 frames per second (FPS), and a second image collection rate may be 30 or 60 FPS. As another example, a first image collection rate may be 1 frame per meter that vehicle  3302  travels, and a second image collection rate may be 5 or 10 frames per meter that vehicle  3302  travels. Alternatively or additionally, the second navigational information is associated with an image resolution from a camera onboard vehicle  3302  that is higher than an image resolution associated with the first navigational information. For example, the first navigational information may include one or more images captured by a camera onboard vehicle  3302  at a first resolution of 1392×1024, and the second navigational information may include one or more images captured by the camera onboard vehicle  3302  at a second resolution of 1600×1200 (or higher). 
     As described elsewhere in this disclosure, exemplary second navigational information may include information and/or data relating to the locations of the vehicle, speeds of the vehicle, driving directions of the vehicle, landmarks associated with one or more road segments, roads, one or more road features, one or more infrastructure objects, water features, geographic features, points of interest (e.g., office buildings, restaurants, gas stations, etc.), one or more images associated with one or more road segments, LIDAR data associated with one or more road segments, a sparse data model including polynomial representations of certain road features (e.g., lane markings), target trajectories for the host vehicle, or the like, or a combination thereof. For example, the second navigational information may include location information associated with one or more landmarks associated with the one or more road segments. Alternatively or additionally, the second navigational information may include location information associated with one or more road features associated with the one or more road segments. 
     In some embodiments, the first navigational information and/or second navigational information may also include video detection and ranging (VIDAR) data. For example, vehicle  3302  may include a set of cameras configured to generate a dense point cloud of the environment of the vehicle at a particular point in time using the VIDAR technology. By way of example, vehicle  3302  (and/or server  3301 ) may generate the cloud by learning monocular features and correlation features to infer the depth at each pixel in a subset of the cameras. In some embodiments, the first navigational information and/or second navigational information may both LIDAR and VIDAR data. In some embodiments, the LIDAR and VIDAR data may be collected around the same time. 
     In some embodiments, the first navigational information may include LIDAR data, and the second navigational information may include VIDAR data, which may have a greater density level than that of LIDAR data. 
     In some embodiments, vehicle  3302  may be configured to continue to collect the second navigational information if it is determined that vehicle  3302  is at or within the predetermined distance from the geographical region of interest (or a boundary thereof). For example, server  3301  (and/or vehicle  3302 ) may be configured to determine the locations of vehicle  3302  and determine whether vehicle  3302  is at or within the predetermined distance from the geographical region of interest (or a boundary thereof) as described elsewhere in this disclosure. Server  3301  may transmit an instruction to vehicle  3302  to continue to collect the second navigational information unless a subsequent instruction to switch to collecting the first navigational information is received by vehicle  3302 . In some embodiments, server  3301  (and/or vehicle  3302 ) may be configured to determine whether vehicle  3302  travels beyond the predetermined distance from geographical region of interest  3401  after it has been determined that vehicle  3302  is at or within the predetermined distance from geographical region of interest  3401 . Server  3301  (and/or vehicle  3302 ) may also be configured to cause vehicle  3302  to switch back to collecting the first navigational information. 
     At step  3505 , at least one of the collected first navigational information or the collected second navigational information from the host vehicle may be uploaded. For example, server  3301  may be configured to cause vehicle  3302  to upload at least one of the collected first navigational information or the collected second navigational information (or a portion thereof) from vehicle  3302 . Vehicle  3302  may upload at least one of the collected first navigational information or the collected second navigational information via a transceiver associated with vehicle  3302 . In some embodiments, vehicle  3302  may transmit the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) to server  3301  continuously. Alternatively, vehicle  3302  may transmit the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) to server  3301  intermittently. For example, vehicle  3302  may transmit the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) to server  3301  a number of times over a period of time. By way of example, vehicle  3302  may transmit the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) to server  3301  once per minute. Alternatively, the vehicle may transmit the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) when vehicle  3302  has access to a more reliable and/or faster network (e.g., having a stronger wireless signal, via a WIFI connection, etc.). In some embodiments, vehicle  3302  may the first navigational information and/or second navigational information (or a portion of the first navigational information and/or a portion of the second navigational information) upon a request received from server  3301 . For example, server  3301  may transmit a request to vehicle  3302  requesting transmission of a subset of the first navigational information or the second navigational information collected by vehicle  3302 . Vehicle  3302  may transmit the requested navigational information (e.g., the subset of the first navigational information or the second navigational information) based on the received request. In some embodiments, the request may include at least one time stamp. 
     In some embodiments, vehicle  3302  may be configured to upload both first and second navigational information to server  3301 , and server  3301  may be configured to receive and store both the first navigational information and the second navigational information. 
     In some embodiments, server  3301  may, be configured to cause vehicle  3302  to upload the collected second navigational information (or a portion thereof) based on a determination of whether vehicle  3302  traveled within the geographical region of interest. For example, as illustrated in  FIG.  35 C , server  3301  may be configured to determine that vehicle  3302  traveled within geographical region of interest  3401 . Server  3301  may be configured to cause vehicle  3302  to upload the collected second navigational information (or a portion thereof) to server  3301 . Alternatively or additionally, server  3301  may be configured to cause vehicle  3302  to upload a portion of the collected second navigational information that is associated with geographical region of interest  3401  to server  3301 . In some embodiments, server  3301  may also be configured to cause vehicle  3302  to discard a portion of the collected second navigational information that is not associated with geographical region of interest  3401 . 
     In some embodiments, server  3301  may, be configured to determine that vehicle  3302  did not travel within the geographical region of interest. Server  3301  may further be configured to cause vehicle  3302  not to upload all of or at least a portion of the second navigational information if vehicle  3302  did not travel within the geographical region of interest. Alternatively or additionally, server  3301  may be configured to cause vehicle  3302  to discard (and/or overwrite) all of or at least a portion of the second navigational information (or mark all or at least a portion of the second navigational information as being eligible for being overwritten) based on the determination that vehicle  3302  did not travel within the geographical region of interest. In some embodiments, server  3301  may be configured to determine whether vehicle  3302  traveled within geographical region of interest  3401  after determining that vehicle  3302  vehicle approached to within the predetermined distance to geographical region of interest  3401  and then moved away to at least the predetermined distance away from geographical region of interest  3401 . 
     In some embodiments, vehicle  3302  may upload the first navigational information and/or the second navigational information without input or an instruction from server  3301 . For example, vehicle  2702  may transmit the first and/or second navigational information (and/or sensor data) to server  2701  when such information is collected. Alternatively, vehicle  2702  may transmit the first and/or navigational information (and/or sensor data) to server  2701  upon a trigger event. For example, vehicle  3302  may determine that a predetermined period of time or a predetermined distance has passed since the last semantic object is detected. Vehicle  3302  may also upload the first and/or second navigational information (and/or sensor data) collected to server  2701 . 
     At step  3506 , a navigational map be updated. For example, server  3301  may be configured to update the navigational map based on the uploaded at least one of the collected first navigational information or the collected second navigational information. For example, server  3301  may be configured to update the navigational map associated with the geographical region of interest (and/or other region(s) based on the received first and/or second navigational information collected by vehicle  3302 . Server  3301  may also be configured to store the updated navigational map into a storage and/or a database (e.g., database  3304 ). In some embodiments, server  3301  may transmit the updated navigational map to one or more vehicles. For example, server  3301  may transmit the updated navigational map to vehicle  3302  via, for example, network  3305 . Alternatively or additionally, server  3301  may store the updated navigational map into database  3304 , and one or more vehicles (e.g., vehicle  3302 ) may obtain the updated navigational map from database  3304 . 
     In some embodiments, server  3301  may update a navigational map based on (first and/or second) navigational information received from two or more vehicles. For example, server  3301  may aggregate first and/or second navigational information received from two or more vehicles that are associated with the same road segment. In some embodiments, the navigational information collected when the vehicle drives in a direction along a road segment may be different from the navigational information collected when the vehicle drives in the opposite direction even along the same road segment. Server  3301  may aggregate first and/or second navigational information received from two or more vehicles that are associated with the same road segment in the same driving direction (and/or a direction opposite to the same driving direction). For example, server  3301  may align the navigational information received from two or more vehicles that drove in the same direction along a road segment based on the feature points determined based on the navigational information. Server  3301  may also update a navigational map based on the aggregated (first and/or second) navigational information. 
     In some embodiments, server  3301  may be configured to determine that the update of the navigational map associated with the geographical region of interest is completed (or at least in a period of time). Server  3301  may be configured to transmit an instruction to one or more vehicles not to collect second navigational information associated with the geographical region of interest. 
     In some embodiments, server  3301  may use more resources to process or use the second navigational information as compared to when server  3301  processes or uses the first navigational information. 
     Harvesting Images for Vehicle Navigation 
     As described throughout the present disclosure, vehicles may capture and analyze images, which may be uploaded to a server for various purposes, such as enhancing maps. For example, the server may analyze these images to identify various features in the environment of the vehicle and store representations of the features in a navigational map. In some embodiments, this may include requesting specific images or types of images from vehicles. For example, the server may recognize a need for additional information about a particular geographic region and may request image data to supplement a navigational map (or portion of a navigational map) associated with this region. In some embodiments, the requests may include data associated with specific events (e.g., a road hazard, a road obstacle, road conditions, etc.), data associated with a particular object (e.g., a road sign, a lane mark, etc.), or any other requests for specific data that may be needed. 
     In some embodiments, requesting data in this manner may present security or privacy concerns for users of the system. For example, users of the vehicles may not wish to have their locations tracked, which may make it difficult for the server to know which vehicles to request image data from for a particular geographic region. Further, images (or metadata associated with images) may include data that may identify particular vehicles, which may present similar privacy concerns. For example, intrinsic calibration parameters of the camera may be considered private data, since they can be used to identify the host vehicle. Additionally, images may contain faces of pedestrians, license plates, or other sensitive information that may present similar privacy concerns. Further, frequently broadcasting and/or transmitting requests and receiving image data may place a significant demand on the system in terms of data transmission bandwidth, data storage, and/or data processing. Accordingly, in view of these and other issues, solutions are needed for improved methods for acquiring image for vehicle navigation. 
     Some embodiments of the present disclosure may include “harvesting” image data and localizing that data (e.g., within a navigational map) for later use. In some embodiments, the system may use one or more object models for recognizing objects. For example, objects identified using a first set of models may be used for localizing the images relative to a navigational map. However, the images may also include other valuable information that may not be exploitable using the first set of object models. For example, the images may include representations of objects that are not yet recognizable by the system or that are not relevant to the immediate tasks being performed. Accordingly, the harvested images may be stored for subsequent analysis and, at some point in time thereafter (e.g., a month after the images were received), a second set of object models may be used to identify objects (and their locations) in the previously captured images. The disclosed embodiments thus allow for application of detection and localization methods that were not available at the harvesting time. Enriching maps using previously harvested images, as disclosed herein, may reduce the need for subsequent requests for data, thereby reducing privacy and data transmission concerns described above. 
     Further, to preserve the anonymity of the vehicles that capture the harvested images, the proposed system may transform the images into a canonical form and avoid sending any private camera parameters. In addition, the disclosed system may identify pedestrians, vehicles, or other road users and may blur these features within the images. For example, instead of applying facial recognition and blurring faces, the disclosed system may blur an entire representation of a pedestrian, or other area of the image associated with the pedestrian. 
     In some embodiments, this anonymization may lead to further issues with on-demand image harvesting if the server cannot interact with specific vehicles. For example, a server may not be able to send data requests to particular vehicles if their identity and/or location is hidden from the server. The disclosed systems and methods may further address these issues by allowing for harvesting data on demand while maintaining anonymity of individual vehicles. According to the disclosed embodiments, the server may broadcast an image harvesting request for a geographical region. According to some embodiments, harvesting agents (e.g. host vehicles equipped with the various navigation systems described herein) can be configured to send their location to a server from time to time. For example, harvesting agents can send a summary communication, which may include the location of the vehicle and possibly additional auxiliary information such as signal quality or other auxiliary information. The server may communicate the image harvesting request for a particular geographical region according to the locations reported by the harvesting agents (e.g., via the summary communication). By way of example, the server may select vehicles that are located within a certain area (e.g., within a certain radius, within a predetermined threshold, etc.) from the point or area of interest. In another example, harvesting agents that are located within a certain driving distance from the point or area of interest can be selected. Other filtering and selection schemes can also be used. The image harvesting request may cause the vehicles to which the request was addressed (and which received the request) to collect an image or images, which may be at least temporarily stored in the host vehicle (e.g. in a cache memory unit). In some embodiments, the vehicles may notify the server about potential image availability per a specific region, and the server may decide whether to fetch their data. Alternatively or additionally, the vehicles may automatically send harvested images in response to the request. Accordingly, since the server may selectively request data from a subset of the harvesting agents connected to the server and limit the requests to a particular area, the disclosed techniques enable the collection of images from anonymous data collectors, on an as-needed basis and in an efficient manner. 
       FIG.  36    is an illustration of an example system  3600  for harvesting images for vehicle navigation, consistent with the disclosed embodiments. As shown, system  3600  may include a host vehicle  3610 , which may be an autonomous or semi-autonomous vehicle. According to the disclosed embodiments, host vehicle  3610  may be configured to capture one or more images from the environment of host vehicle  3610 . For example, host vehicle  3610  may capture image  3620  using camera  3612 . Host vehicle  3610  may use captured images, such as image  3620  for navigating an environment of host vehicle  3610 . Host vehicle  3610  (e.g., using processing device  3614 ) may transmit image  3620  and/or other navigation information to server  3630 , as illustrated in  FIG.  36   . Server  3630  may be associated with a map database  3632 , which may include at least one road navigational map, as described above. For example, map database  3632  may include a sparse map including representations of one or more road segments based on information collected by a plurality of vehicles, as described throughout the present disclosure. 
     In some embodiments, host vehicle  3610  may correspond to vehicle  200  (or vehicles  1205 ,  1210 ,  1215 ,  1220 , or  1225 ) discussed above. Accordingly, any of the features or embodiments described herein in reference to vehicle  200  may equally apply to host vehicle  3610 . Host vehicle  3610  may be equipped with at least one camera  3612 , which may correspond to one or more of image capture devices  122 ,  124 , and  126  described above. Further, host vehicle  3610  may include at least one processing device  3614 , which may correspond to processing unit  110 . Processing unit  110  and camera  3612  may be included on a navigation system of host vehicle  3610 , at least part of which may be located within host vehicle  3610 . Similarly, server  3630  may correspond to server  1230  described above. Accordingly, any of the features or embodiments described herein in reference to server  1230  may equally apply to host server  3630 , and vice versa. For example, server  3630  may be configured to receive captured images and other navigational information from a plurality of vehicles. 
     In some embodiments, system  3600  may be used to enrich maps using previously harvested images. For example, image  3620  may be captured during a first time period and may be uploaded to server  3630 . Server  3630  may be configured to localize image  3620  relative to a navigational map (which may be stored in map database  3632 ), as described throughout the present disclosure. For example, this may include detecting landmarks identified in image  3620  and comparing the detected landmarks to representations of landmarks stored in the navigational map. In some embodiments, image  3620  may be localized based on other information, as described above. For example, localizing the at least one image relative to the map may include using at least an indicator of a vehicle location at a time the at least one image was captured. For example, the indicator may be a location of host vehicle  3610  at the time image  3620  was captured, which may be based on GPS data, an ego motion calculation, or the like. In some embodiments, server  3630  may store data associated with image  3620  in the map database. For example, this may include location information, date or time information, information about camera  3612  and/or host vehicle  3610 , or various other information that may be associated with image  3620 , including any other type of information described throughout the present disclosure. 
     In some embodiments, server  3630  may be configured to identify one or more objects within captured images, as described herein. In some embodiments, this may include using one or more object models, such as object models  3634  and  3636 . Each object model may be trained or otherwise configured to detect a particular object or class of objects. For example, in the example shown in  FIG.  36   , an object model  3634  may be used by server  3630  to recognize representations of traffic lights, such as traffic light  3622  represented in image  3620 . Object model  3636  may be configured to detect another object or class of objects, such as a representation of vehicle  3624  in image  3620 . In some embodiments, the object models may be included in one or more groups of object models. For example, object model  3624  may be included in a group of first object models, which may be used to identify a plurality of first objects. Object model  3636  may be included in a group of second object models, which may be used to identify a plurality of second objects. Alternatively or additionally, object model  3636  may be included in the same group as object model  3634  (e.g., the group of first model objects). 
     In some embodiments, object model  3634  may be applied at a different time than object model  3634 . For example, object model  3634  (e.g., a first model) may be applied at a second time period, which may be after the first time period during which image  3620  was captured. Then, during a third time period after the second time period object model  3636  (e.g., a second object model) may be used to identify a second object in image  3620 . Referring to the example show in  FIG.  36   , this may include using object model  3636  to detect vehicle  3626  in image  3620 . The third time period may be a short period after the second time period (e.g., a few seconds, a few minutes, etc.) or may be a longer time period. For example, the third time period may be at least a week, a month, a year, or any other suitable time period after the second time period. To enable this subsequent object recognition, server  3630  may be configured to store image  3620  in map database  3632 . 
     The stored images may be accessed and processed at a later time to identify additional one or more objects in the images. In some embodiments, the second object model may not have been available to the system during the second time period. For example, object model  3636  may have been developed and/or implemented after object model  3634  (e.g., after the second time period). In some embodiments, object model  3636  may detect different objects or classes of objects than object model  3634 . For example, the second object may include at least one object unidentifiable using the first object model. This may be applicable when a new type or class of objects is identified as important for a navigational map, as part of a separate task or query that involves new or different objects, in a multi-stage map enrichment process, or any other situation in which new or different objects may be of interest at a later time period. As another example, the second object model may be an improved model able to more accurately detect the same class of objects as the first object model. For example, the second object model may be an improved implementation of object model  3634  and may be able to detect objects that may have been missed using object model  3634 . In some embodiments, server  3630  may continue to monitor and/or update information regarding the first object. For example, server  3630  may be programmed to identify at least one change to the first object after the second period of time and before the third period of time, and provide an output indicative of the identified change. In some embodiments, server  3630  may use images stored in map database  3632  for training additional object models. For example, server  3630  may be configured to identify images stored in map database  3632  for use as training images and may compiles images from database  3632  to serve as a training data set. Accordingly, object model  3636  may have been trained, at least in part, using image  3720 . 
     Accordingly, by storing image  3620  for later analysis, server  3630  may not need to rely on other images captured by host vehicles closer to the third time period. This may greatly reduce the amount of information that is collected by server  3630 , which may reduce the demand for bandwidth within the system. In some embodiments, server  3630  may determine a need for additional information, but may forego causing an image request to be transmitted to an additional host vehicle based on the at least one image being stored in the map database. For example, server  3630  may determine a need for capturing image data associated with object  3624 , but may forego causing the image request to be transmitted based on a determination that image  3620  includes a representation of object  3634 . This may also reduce the risk of privacy concerns by not requiring as frequent requests for data from vehicles. 
     In some embodiments, various additional information may be included in or appended to image  3620 . For example, image  3620  may include metadata with auxiliary information based on or associated with image  3620 . This auxiliary information may include any information about the host vehicle  3610 , an environment of host vehicle  3610 , how or when image  3620  was captured, or the like. For example, the auxiliary information may include a time image  3620  was captured, a location of host vehicle  3610  when image  3620  was captured, a location of an object represented in image  3620 , a type of vehicle of host vehicle  3610 , properties of camera  3614 , or the like. In some embodiments, this metadata may be stored in association with image  3620  in map database  3632 . As described above, object model  3636  may have been trained, at least in part, using image  3620 . In some embodiments, server  3630  may be configured to process or analyze the metadata associated with image  3620  to select image  3620  for inclusion in a training data set for training object model  3636 . 
     As indicated above, it may further be advantageous to remove one or more personal details from harvested images.  FIG.  37    is an illustration of an example process for anonymizing harvested images, consistent with the disclosed embodiments. As described above, host vehicle  3610  may be an autonomous or semi-autonomous vehicle and may be configured to capture one or more images from the environment of host vehicle  3610 . For example, host vehicle  3610  may capture image  3720  using camera  3612 . Host vehicle  3610  may transmit image  3720  and/or other navigation information to server  3630 , which may be used for updating or enhancing a navigational map, as described herein. In some embodiments, host vehicle  3610  may anonymize images prior to transmitting them to server  3630 . Accordingly, server  3630  may receive a canonicalized form of image  3720  with various personal or sensitive data having been removed. 
     Consistent with the present disclosure, processing device  3416  (which may correspond to processing unit  110 ) may receive at least one image acquired by an image capture device of a host vehicle from an environment of the host vehicle. For example, this may include receiving image  3720  captured by camera  3612 , as described above. Processing device  3416  may further be programmed to anonymize the at least one image. In some embodiments, this may include removing one or more intrinsic calibration parameters of the image capture device that are associated with the image. For example, intrinsic calibration parameters of camera  3612  may be removed from image  3720 . As used herein, intrinsic calibration parameters may refer to any parameters associated with an image that are internal, non-transient and/or fixed to a particular camera or setup. One skilled in the art will appreciate that typical camera setups for ADAS or autonomous vehicle (AV) applications are designed such that intrinsic calibration parameters of a camera stay fixed, unless some dramatic event (such as an accident) or a serious malfunction in the camera (corruption of the calibration data) occurs. In terms of image processing, intrinsic calibration parameters may allow a mapping between pixel coordinates of an image with the corresponding coordinates in the camera reference frame. For example, intrinsic calibration parameters may include a principal point (e.g., the center of an image), focal length, image sensor format (e.g., shape and size of the image sensor), lens distortion, or other calibration factors. 
     To anonymize these parameters, processing device  3416  may distort image  3720  such that modified calibration parameters are associated with image  3720 . Accordingly, processing device  3416  may use the intrinsic parameters of camera  3412  to rectify image  3720  during runtime and may distort image  3720  according to a modified set of calibration parameters. In some embodiments, host vehicle  3610  may be equipped with a modified calibration model, which may be configured to provide the modified calibration parameters. For example, to obscure the focal length or other parameters of camera  3612 , images may be cropped to simulate a different focal length. As another example, to obscure a lens distortion or other parameters of camera  3612 , images may be warped to simulate a different lens distortion. The modified set may be a randomized set of values or may be a set of standard values used for an entire fleet of vehicles or a portion of a fleet of vehicles. Alternatively or additionally, the modified set can be obtained by applying the modified calibration model to an image or to a group of images. Accordingly, the modified set of calibration parameters may be generated to simulate an existing image or group of images. In some embodiments, the modified calibration model can be configured to provide different modified sets for different images. In some embodiments, anonymizing the image may include removing other information, which may be stored as metadata of image  3720  (or embedded within image  3720 ). For example, this may include removing device hardware information (e.g., information identifying a device manufacturer, device model, device aperture, aspect ratio, lens model, RAM available, ROM available, processor model, processor ID), geotag data, timestamp data, software or image processing data (e.g., OS version, brightness values, contrast values, saturation values, resolution, color model, compression parameters, depth, orientation, digital zoom, author, title, description, shutter speed, exposure time, etc.), a vehicle identifier, or any other properties or data that may be associated with a particular vehicle or camera. 
     In some embodiments, anonymizing the at least one image may further include blurring an area associated with an object represented in the at least one image. For example, this may include blurring portion  3722  of image  3720 , as shown in  FIG.  37   . In some embodiments, the area may include a portion of an entire representation of the object in the at least one image. For example, as shown in  FIG.  37   , the object may be a person  3724 , and the area may include a face of the person. As another example, the object may be a vehicle and the area may include a plate identifier of the vehicle. Alternatively or additionally, the area may include the entire representation of the object in the at least one image. Processor  3416  may then transmit the anonymized at least one image to a server for updating a map database. In some embodiments, the anonymized image may be transmitted based on some form of trigger event, as described herein. For example, transmitting the anonymized at least one image may be based on at least one of a location of the host vehicle, a request received by a navigation system of the host vehicle, or various other events. 
     The disclosed systems may further allow for harvesting data on demand while maintaining anonymity of individual vehicles.  FIG.  38    illustrates an example process  3800  for anonymous on demand data harvesting, consistent with the disclosed embodiments. As described above, server  3630  may be configured to receive captured images and other navigational information from a plurality of host vehicles. In this example, server  3630  may be configured to collect data from host vehicles  3810 A,  3810 B,  3810 C,  3810 D,  3810 E, and  3810 F. Similar to host vehicle  3610 , host vehicles  3810 A-F may, be configured to capture images and other navigational information as they traverse one or more road segments. For example, host vehicle  3810 A may capture an image  3820  to be transmitted to server  3630 . In some embodiments, image  3820  may be an anonymized (or canonicalized) image, as described above with respect to image  3720 . Host vehicles  3810 A-F may correspond to one or more of host vehicles  200 ,  1205 ,  1210 ,  1215 ,  1220 ,  1225 , or  3610 , as described above. Accordingly, any of the features or embodiments described herein in reference to other host vehicles may equally apply to one or more of host vehicles  3810 A-F, and vice versa. For example, each of host vehicles  3810 A-F may include a camera (e.g., camera  3612 ) and processing device (e.g., processing device  3416 ), consistent with the disclosed embodiments. 
     As described above, server  3630  may be configured to acquire images and other navigational information from host vehicles  3810 A-F on demand. In some embodiments, this may be based on geographical locations. For example, server  3630  may identify, a need to fill in information in a map database if data is missing, outdated, or otherwise needing supplemental information. As shown by way of example in  FIG.  38   , server  3630  may identify a geographical region  3804  to be updated in a map database. For example, map database  3632  may include data in a navigational map  3802  that may need to be updated. Server  3630  may broadcast a request for image data collected from the geographical region to a plurality of vehicles. In some embodiments, the request may be transmitted to all vehicles associated with server  3630  (e.g., all host vehicles in a fleet of host vehicles). However, this may place a significant demand bandwidth within system  3600  and/or processing requirements for server  3600  and/or host vehicles  3810 A-F. 
     Accordingly, server  3630  may transmit a request that is addressed to a subset of vehicles within a fleet that may be associated with geographical region  3630 . The subset of vehicles may be selected in various ways. In some embodiments, the subset may be selected based on reported locations of the vehicles. For example, each vehicle may periodically report their location to server  3630 , which may allow  3630  to identify vehicles near a geographical region (e.g., within a predetermined distance threshold, etc.). In some embodiments, the period at which vehicles report their location may be selected to minimize privacy concerns for users of the vehicles. For example, vehicles may report their location every 20 minutes, 1 hour, 2 hours, 1 day, 1 week, or any other suitable time period that may reduce concerns of a vehicle&#39;s location being tracked continuously. As another example, vehicles may send their location only based on a request from server  3630 . For example, server  3630  may send a location request to vehicles in a fleet and, in response, the vehicles may transmit their location. In some embodiments, vehicles may anonymize their location such that a precise location is not transmitted. For example, vehicles may identify a region or area they are located in, an approximate location (e.g., based on applying a random variation to their current location within a predetermined range), a previous location (e.g., a location from 5 minutes ago, etc.), or various other means for at least partially anonymizing their locations. In some embodiments, server  3630  may select vehicles based on a location previously associated with a vehicle, rather than a current reported location. For example, each vehicle may be associated with a particular region (e.g., a state, a city, a county, etc.) where the host vehicle typically navigates and host vehicles typically near geographical region  3630  may be selected to receive the request. While geographical region  3804  is illustrated as a circular envelope, various other regions may be identified. For example, this may include various other shapes, a particular road segment, a particular point, or any other geographical regions that may be used. 
     Server  3630  may select at least one vehicle of the subset of the plurality of vehicles for collecting the image data from the geographical region. The at least one vehicle may be selected in various ways. In some embodiments, the at least one vehicle may be the same as the subset of vehicles. For example, server  3630  may identify vehicles within a geographic location of interest (or within a vicinity of a geographic location of interest) and may select all of the vehicles determined to be within or within a close proximity (e.g., a predetermined distance) of the geographic location of interest. Alternatively or additionally, the selected at least one vehicle may be a further subset of the subset of vehicles. The selection of vehicles by the server may be based on various factors or a combination thereof. In some embodiments, the selected at least one vehicle may be selected based on a bandwidth limitation. For example, server  3630  may select a number of host vehicles such that receiving the images will not exceed the bandwidth limitation. As another example, the selected at least one vehicle may be selected based on a proximity of the selected at least one vehicle to the geographical region. For example, server  3630  may select host vehicles  3810 A-C based on their proximities to geographical region  3804 . As another example, the selected at least one vehicle may be selected based on a driving path of the selected at least one vehicle. For example, server  3630  may determine that host vehicle  3810 F may be (e.g., based on a probability analysis) traveling along a driving path that includes or may include geographical region  3804 . This may also include determining whether a potential or probable driving path of the selected at least one vehicle includes or may include a particular portion of geographical region  3804  or point within geographical region  3804 . 
     In some embodiments, server  3630  may poll the subset of vehicles for their availability to capture image data associated with a region (or a particular feature or event within a region). For example, server  3630  may be configured to broadcast to the subset of the plurality of vehicles an initial request for image data collected from the geographical region. Server  3630  may then receive, from the at least one vehicle, a confirmation of availability to provide image data collected from the geographical region. Accordingly, the at least one vehicle may be selected based on the confirmation. Referring to  FIG.  28   , based on the initial request, each of host vehicles  3810 A-F may determine whether they are available to provide image data collected from geographical region  3804  and may report their availability to server  3630 . 
     The availability may be determined in various ways. In some embodiments, this may be based on a current location of the host vehicle. For example, host vehicles  3810 A,  3810 B,  3810 C, and  3810 D may indicate they are available because they are within geographical region  3804  or near geographical region  3804  (e.g., within a threshold distance, etc.). In some embodiments, the threshold distance may be a road travel distance, rather than a direct distance. In other words, host vehicles may determine their ability based on a distance they would have to travel along roadway s to reach a geographic region. As another example, the availability may be determined based on a previous location of the host vehicle. For example, although host vehicle  3810 D is leaving geographical region  3804 , it may have acquired data from within geographical region  3804  and may have stored images and other data at least temporarily. As another example, the availability may be determined based on a planned route of the host vehicle. For example, host vehicle  3810 F may not be within geographical region  3804  but may be approaching geographical region  3804  and may be navigating along a path that includes geographical region  3804 . Various other means for determining availability may also be used. In some embodiments, based on determining it is available, the host vehicle may begin collecting images and other data within geographical region  3804 . Alternatively or additionally, this may include refraining from deleting or overwriting data collected from within geographical region  3804 . For example, the host vehicles may continuously collect data and store it in memory location (e.g., memory  140  or  150 ) at least temporarily. In some embodiments, the indication of availability may include other information, such as location information, planned navigation routes, or other information that may be used by server  3630  to select host vehicles. 
     In this example, server  3630  may select host vehicles  3810 A-C and  3810 F. In some embodiments, server  3630  may further instruct at least one unselected vehicle of the subset of the plurality of vehicles to discard image data collected from the geographical region without uploading the image data. For example, although host vehicle  3810 D may, have indicated it was available to provide image data collected from geographical region  3804 , server  3630  may instruct host vehicle  3810 D to discard data collected from geographical region  3804 . 
     Server  3630  may then transmit a request for image data collected from the geographical region to the selected at least one vehicle. In response, server  3630  may receive image data from the selected at least one vehicle and may store the received image data in the map database. As noted above, in some embodiments, the image data includes images that were anonymized by the selected at least one vehicle prior to transmission. Accordingly, despite the image data being anonymized, server  3630  may be enabled to request image data from vehicles on demand using the disclosed embodiments described herein. 
     In some embodiments, rather than a general data request for images from within geographical region  3804 , server  3630  may request a particular type of data. Accordingly, image data may be used to validate existing features or other data within a map database. For example, server  3630  may be configured to compare an image position of the representation of an object determined based on analysis of an image with an expected position of the at least one object within a navigational map. Accordingly, server  3630  may validate the navigational map based on the comparison.  FIG.  39    is a diagrammatic illustration of an example validation performed through image harvesting, consistent with the disclosed embodiments. In this example, server  3630  may determine that additional information is needed for a particular feature  3920  within geographical region  3804 . In some embodiments, a need may be identified based on a time elapsed since data was last collected associated with a feature. For example, server  3630  may request additional images to determine if a road feature has changed, moved, or otherwise been updated. As another example, a need may be identified based on a quantity or quality of data associated with a feature. For example, if data associated with a particular feature has been collected below a threshold number of times, this may indicate a need for additional data. As another example, if image data associated with a feature is of poor quality (e.g., blurry, at a bad or alternate angle, etc.), this may trigger a need for additional image data. In some embodiments, a need may be identified based on a perceived difficulty of vehicles to identify a feature. For example, if vehicles are not identify ing a particular feature when navigating near the feature (e.g., by comparing a number of vehicles that miss the feature to a threshold, comparing a percentage of vehicles that miss the feature to a threshold, etc.), a need may be identified to further define the feature through image data. As another example, server  3630  may determine a need for obtaining image data for training a machine learning model (e.g., object model  3634  or  3636  described above). For example, in some embodiments, boosting may be is needed to support a machine learning process for a new trained model and the map data indicate that there is a candidate feature (or environment) that may be useful for training the model in a specific location. Accordingly, server  3630  may request that host vehicles within the vicinity of the candidate feature collect images of the candidate feature to include in a set of training data for training the model. As used herein, a feature may refer to any object or element within an environment of a vehicle for which image data may be captured. For example, this may include road signs, lane markings, buildings, lamp posts, highway exit ramps, traffic lights, hazardous objects, and the like. 
     In some embodiments, server  3630  may request data associated with a particular road event. For example, as shown in  FIG.  39   , server  3630  may request information about a road event  3930 . As used herein, a road event may refer to any event that may occur along a roadway. In some embodiments, a road event may be associated with a hazardous object along a roadway. For example, this may include a stalled vehicle, parts of a truck tire or other debris, potholes, obstacles such as fallen trees or signs, loose cargo, animals, and the like. In some embodiments, a road event may include a surface condition of a roadway. For example, a road event may include an icy surface, a wet surface, a damaged or eroded surface, or the like. Road events may include various other events, such as a lane closure, a public event (e.g., a parade, festival, etc.), an emergency or service vehicle, a construction vehicle or construction zone, a modification to a traffic pattern (e.g., repainting of lane marks, etc.), or various other events that may affect navigation of vehicles. In some embodiments, server  3630  may receive an indication of the road event. For example, the road event may be reported by one or more host vehicles or may be received from a third-party server, such as local municipal database, an event tracking service (e.g., Waze™ or similar services), or various other sources. In some embodiments, a road event may be determined based on data collected from host vehicles. For example, if vehicles are traveling slow within a certain area, this may indicate a road event is present. As another example, one host vehicle may capture an image including a representation of a previously unidentified road event and server  3630  may request additional information about the event. 
     Server  3630  may select one or more vehicles to collect data about a road event, as described above. For example, server  3630  may select host vehicle  3910 A and  3910 B to collect image data associated with feature  3920  and road event  3930 , respectively. In this example, feature  3920  may be a road sign for which server  3620  needs additional information. Accordingly, host vehicle  3910 A may capture an image  3922  of feature  3920 . Similarly, road event  3930  may be a stalled vehicle and host vehicle  3910 B may capture an image  3932  of stalled vehicle  3934 . In some embodiments, an entire image (or multiple images) may be transmitted, as shown for image  3932 . Alternatively or additionally, the image may be cropped to include a feature or road event of interest. This may include cropping out all (or substantially all) of the image not associated with the feature or road event. For example, image  3922  may be a cropped image showing the face of a road sign. In some embodiments, the collected images may include various metadata as described above. According to some embodiments, this metadata may identify a location associated with the collection of the image data within the geographical region. For example, the metadata for images  3922  and  3932  may include locations for feature  3920  and road event  3930 , respectively. In some embodiments, the metadata may exclude information identifying the at least one vehicle. Further the images may be anonymized to remove faces or license plates, to obscure intrinsic calibration data (e.g., focal length, lens distortion, etc.), or various other forms of anonymization described above. In some embodiments, the metadata may further identify a reason for capturing an image. For example, this may include a reference to a request (e.g., a request ID) that triggered the image capture, a classification of a feature or road event (e.g., information indicating the image includes a road sign, a stalled vehicle, etc.). 
       FIG.  40    is a flowchart showing an example process  4000  for enriching a navigational map using previously captured images, consistent with the disclosed embodiments. Process  4000  may be performed by at least one processing device of a server, such as a processing of server  3630 , as described above. It is to be understood that throughout the present disclosure, the term “processor” is used as a shorthand for “at least one processor.” In other words, a processor may include one or more structures that perform logic operations whether such structures are collocated, connected, or dispersed. In some embodiments, a non-transitory computer readable medium may contain instructions that when executed by a processor cause the processor to perform process  4000 . Further, process  4000  is not necessarily limited to the steps shown in  FIG.  40   , and any steps or processes of the various embodiments described throughout the present disclosure may also be included in process  4000 , including those described above with respect to  FIGS.  36 ,  37 ,  38 , and  39   . 
     In step  4010 , process  4000  includes receiving at least one image captured by a camera of a vehicle from an environment of the vehicle during a first time period. For example, as described above with respect to  FIG.  36   , this may include receiving image  3620 , which may have been captured during a first time period. In some embodiments, the at least one image comprises at least one anonymized image, the at least one anonymized image. As described above, the at least one image may have been anonymized by the host vehicle prior to being received in step  4010 . For example, the anonymization by the host vehicle may include removing one or more intrinsic calibration parameters of the camera from data associated with the at least one image or blurring at least a portion of a representation of an object (which may be the first or second object described below, or a third object) in the at least one image. In some embodiments, the object may include at least one of a face or a license plate number. 
     In some embodiments, the at least one image may have been harvested through anonymous data puling techniques, as described above with respect to  FIGS.  38  and/or  39   . For example, receiving the at least one image may include: identifying a geographical region to be updated in the map database; receiving from a plurality of vehicles indications of locations of the plurality of vehicles; determining, based on the indications of locations of the plurality of vehicles, a subset of the plurality of vehicles: selecting the vehicle from the subset of the plurality of vehicles; and transmitting to the vehicle a request for image data collected from the geographical region. As described above, the vehicle may be selected based on at least one of a bandwidth limitation, a signal quality or strength, a driving path of the vehicle, or a proximity of the vehicle to the geographical region. In some embodiments, step  4010  may further include instruct at least one unselected vehicle of the subset of the plurality of vehicles to discard image data collected from the geographical region without uploading the image data. 
     In step  4020 , process  4000  includes using a first object model to identify a representation of a first object in the at least one image. For example, this may include using object model  3634  to identify object  3622  represented in image  3630 . As described above, the first object model may be included in a plurality of first object models used to identify a plurality of first objects. In some embodiments, step  4020  may be performed during a second time period after the frst time period. 
     Step  4020  may further include localizing the at least one image relative to a map database based on the representation of the first object. For example, this may include determining a location associated with image  3630  within map database  3632 . This may include a location where the at least one image was captured, a location of an object represented in the at least one image, or the like. For example, localizing the at least one image relative to the map may include using analyzing the at least one image to determine a location of the first object relative to the host vehicle and comparing the location of the first object relative to the host vehicle to a position of a representation of the first object in the map database. Alternatively or additionally, localizing the at least one image relative to the map may include using at least an indicator of a vehicle location at a time the at least one image was captured. For example, the indicator of the vehicle location may include GPS coordinates of the vehicle, a location of the vehicle determined based on image analysis, a location of the vehicle determined based dead reckoning, or the like. 
     In step  4030 , process  4000  includes storing the at least one image in the map database based on the localization. For example, this may include storing image  3630  in a manner associating image  3630  with a location within map database  3632 , as described above. In some embodiments, step  4030  may further include storing data associated with the at least one image in the map database. For example, this may include storing an attribute of at least one of the at least one image, the camera, or the host vehicle, or information about the environment where the image was captured. In some embodiments, step  4030  may be performed during the second time period. 
     In step  4040 , process  4000  includes using a second object model to identify a representation of a second object in the at least one image. For example, this may include using object model  3636  to identify object  3652  represented in image  3620 . Step  4040  may be performed during a third time period, which may be after the second time period. For example, the third time period may be at least a week after the second time period, as described above. In some embodiments, the second object model may not have been available to the system during the second time period. For example, the second object model may have been made available to the at least one processor after the second time period. In some embodiments, the first and second object models may identify different classes of objects. For example, the first object model may be configured to identify a first class of objects and the second object model may be configured to identify a second class of objects, where the first object belongs to the first class of objects and the second object belongs to the second class of objects. Alternatively or additionally, the first and second object models may both be used to identify the same class of objects. For example, the first object model and the second object model may both configured to identify a specific class of objects and the first object and the second object may both belong to the specific class of objects. Accordingly, the second object model may be an improved model able to better identify objects in the specific class of objects. In some embodiments, the system may identify changes in objects over time using different object models. For example, process  4000  may include identifying at least one change to the first object after the second period of time and before the third period of time. Process  4000  may further include providing an output indicative of the identified change. 
     In some embodiments, the second object model may be trained using a training data set, where the training data set includes the at least one image. For example, process  4000  may further include selecting the at least one image to be included in a training data set and training the second object model using the training data set. The at least one image may be selected for training the second object model in various ways. In some embodiments, the at least one image may be selected based on metadata associated with the at least one image. For example, server  3630  may identify a location of the second object within a map database and may determine the second object is a candidate for training the second object model. Accordingly, process  4000  may include determining that the at least one image contains (or likely contains) a representation of the second object based on a location associated with the at least one image (e.g., the location from which the at least one image was captured, the location of the first object represented in the at least one image, or the like). 
     In some embodiments, identifying the representation of a second object in the at least one image may allow server  3630  to forego requesting additional data from vehicles. For example, process  4000  may include foregoing causing an image request to be transmitted to an additional host vehicle based on the at least one image being stored in the map database. 
       FIG.  41    is a flowchart showing an example process  4100  for selectively collecting images to enrich a navigational map, consistent with the disclosed embodiments. Process  4100  may be performed by at least one processing device of a server, such as a processing of server  3630 , as described above. In some embodiments, a non-transitory computer readable medium may contain instructions that when executed by a processor cause the processor to perform process  4100 . Further, process  4100  is not necessarily limited to the steps shown in  FIG.  41   , and any steps or processes of the various embodiments described throughout the present disclosure may also be included in process  4100 , including those described above with respect to  FIGS.  36 ,  37 ,  38 , and  39   . 
     In step  4110 , process  4100  includes identifying a geographical region associated with a map database. For example, this may include identifying geographical region  3804  as described above. 
     In step  4120 , process  4100  includes receiving from a plurality of vehicles indications of locations of the plurality of vehicles. For example, this may include receiving indications of locations of host vehicles  3810 A,  3810 B,  3810 C,  3810 D,  3810 E, and  3810 F, as described above. In some embodiments, the indications of locations of the plurality of vehicles may be received periodically. For example, this may include receiving indications of locations at an interval that does not define a path traveled by the plurality of vehicles, as described above. For example, vehicles may report their location every 20 minutes, 1 hour, 2 hours, 1 day, 1 week, or any other suitable time period that may reduce concerns of a vehicle&#39;s location being tracked continuously. 
     In step  4130 , process  4100  includes determining, based on the indications of locations of the plurality of vehicles, a subset of the plurality of vehicles. For example, this may include selecting a subset of vehicles  3810 A,  3810 B,  3810 C, and  3810 D. The subset of the plurality of vehicles may be determined in various ways. For example, this may include vehicles within the geographic region, vehicles within a predetermined distance of the geographic region, vehicles traveling towards the geographical region, or the like. 
     In step  4140 , process  4100  includes selecting at least one vehicle of the subset of the plurality of vehicles. For example, this may include selecting vehicles  3810 A,  3810 B, and  3810 C (or various other vehicles). The at least one vehicle may be selected in various ways. For example, the at least one vehicle may be selected based on at least one of a bandwidth limitation, a driving path of the selected at least one vehicle, or a proximity of the selected at least one vehicle to the geographical region, as described above. As another example, the at least one vehicle may be selected based on an indication the vehicle is available to collect and provide image data. For example, step  4140  may include broadcasting to the subset of the plurality of vehicles an initial request for image data collected from the geographical region; and receiving, from the at least one vehicle, a confirmation of availability to provide image data collected from the geographical region. The at least one vehicle may then be selected based on the confirmation. 
     In step  4150 , process  4100  includes transmitting to the selected at least one vehicle a request for image data collected from the geographical region. In some embodiments, this may be a general request for image data from within the geographical region. Alternatively or additionally, this may include a request for specific image data. For example, process  4100  may include receiving an indication of a road event and the request for image data may include a request for an image of the road event. As described above, the road event may include at least one of a stalled vehicle, an obstacle in the road, or a road surface condition. As another example, the request may be a request for image data associated with a particular feature, such as a road sign or other object. 
     In step  4160 , process  4100  includes receiving image data from the at least one vehicle. As described above, the image data may include metadata identifying a location associated with the collection of the image data within the geographical region. For example, this may include a location where the image was captured from, a location of an object represented in the image, or the like. In some embodiments, the metadata may not include information identifying the at least one vehicle. For example, the at least one vehicle may remove or exclude an identifier of the vehicle from being included in the image metadata. In some embodiments, this may further include canonicalizing the image or otherwise anonymizing the image or metadata as described above. In some embodiments, the metadata may identify a reason for capturing the image. For example, the metadata may include an indication that the image data was captured in response to the request (e.g., including a request ID or other identifier of the request), an indication that the image data includes a certain feature or event, or the like. According to some embodiments, the received image data may include at least one cropped image including a representation of an object. For example, the image may be cropped to include a specific feature or event, as described above with respect to image  3922 . 
     In step  4170 , process  4100  includes storing the received image data in the map database. For example, this may include storing one or more of images  3820 ,  3922 , and  3932  in map database  3632 . In some embodiments, process  4100  may further include instructing at least one unselected vehicle of the subset of the plurality of vehicles to discard image data collected from the geographical region without uploading the image data. For example, if host vehicle  3810 D was not selected but is included in the subset of the plurality of vehicles, server  3630  may instruct host vehicle  3810 D to discard image data collected in geographical region  3804 . 
     The foregoing description has been presented for purposes of illustration. It is not exhaustive and is not limited to the precise forms or embodiments disclosed. Modifications and adaptations will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments. Additionally, although aspects of the disclosed embodiments are described as being stored in memory, one skilled in the art will appreciate that these aspects can also be stored on other types of computer readable media, such as secondary storage devices, for example, hard disks or CD ROM, or other forms of RAM or ROM, USB media, DVD, Blu-ray, 4K Ultra HD Blu-ray, or other optical drive media. 
     Computer programs based on the written description and disclosed methods are within the skill of an experienced developer. The various programs or program modules can be created using any of the techniques known to one skilled in the art or can be designed in connection with existing software. For example, program sections or program modules can be designed in or by means of .Net Framework, .Net Compact Framework (and related languages, such as Visual Basic, C, etc.), Java. C++, Objective-C, HTML, HTML/AJAX combinations, XML, or HTML with included Java applets. 
     Moreover, while illustrative embodiments have been described herein, the scope of any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those skilled in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application. The examples are to be construed as non-exclusive. Furthermore, the steps of the disclosed methods may be modified in any manner, including by reordering steps and/or inserting or deleting steps. It is intended, therefore, that the specification and examples be considered as illustrative only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents.