Patent Publication Number: US-10788585-B2

Title: System and method for object detection using a probabilistic observation model

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application No. 62/558,896, filed on, Sep. 15, 2017, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The subject matter described herein relates in general to a system and method for detecting objects in a surrounding environment and, more particularly, to predicting the presence of occluded objects within the surrounding environment according to at least characteristics of an occluded region. 
     BACKGROUND 
     Robotic devices such as vehicles can be equipped with sensors that facilitate perceiving obstacles, pedestrians, and additional aspects of a surrounding environment. Perception and reasoning by the devices (e.g., autonomous/semi-autonomous vehicles) allow the devices to make decisions according to the perceived objects/obstacles. However, the sensors can provide an incomplete view of the surrounding environment. For example, a light detection and ranging (LIDAR) sensor uses light/lasers to scan the surrounding environment from a point of view of the LIDAR which results in detected objects occluding a view of other objects that may be positioned behind the detected objects. Thus, as the vehicle/robot moves through an environment and uses the LIDAR sensor to scan, the occluded objects can be undetected. Moreover, dynamic objects can become occluded as they move through the environment further complicating detection and tracking of such objects. Accordingly, perceiving aspects of a surrounding environment can encounter difficulties when objects are occluded from a point of view of provided sensors. 
     SUMMARY 
     In one embodiment, example systems and methods relate to a manner of predicting the presence of occluded objects using a probabilistic observation model. Accordingly, the presently disclosed systems and methods leverage, for example, the idea of unknown (occluded) space for determining or, assigning a probability to, the existence of an object (e.g., a vehicle) that is located in the occluded space. In one embodiment, an object detection system acquires sensor data about a surrounding environment and analyzes the sensor data in order to detect objects in the surrounding environment. Thus, the object detection system or another system to which the information is provided can, for example, localize a vehicle, perceive aspects of the environment for path planning, perform obstacle avoidance, and so on using the acquired sensor data. 
     Accordingly, as part of acquiring the sensor data and perceiving aspects of the surrounding environment, the object detection system determines a presence factor associated with each perceived object. That is, for example, the presence factor indicates a likelihood of an occluded object, such as a vehicle, existing within an occluded region associated with a perceived object. Consider that the perceived objects cause occurrences of occluded regions that result from “shadows” cast behind the perceived objects and which are obscured from perception by the sensors. Moreover, the various perceived objects cause various sizes/profiles of occlusions (i.e., occluded regions) resulting from observation of the perceived object. These various occluded regions can obscure different types of objects depending on size, shape, and so on. 
     Thus, the object detection system can assign different probabilities to perceived objects within the environment according to probabilistic observation models associated therewith. As such, observation models associated with different perceived objects can have an associated size, dimensions, profile, and so on. From this information, the object detection system can determine a size of an occlusion that results from observing the perceived object. In one embodiment, the object detection system determines a probability of an occluded object (e.g., a vehicle) being present in the occluded region based, at least in part, on a size of the occluded region cast by the perceived object. Accordingly, the object detection system generates the presence factor as the likelihood that a particular object or class of object is present within the occluded region. In this way, the object detection improves situational awareness about objects or probabilities of objects being present within the surrounding environment and can thus also improve path planning, collision avoidance, and other aspects relating to navigation through the environment. 
     In one embodiment, an object detection system for predicting a presence of occluded objects from a robotic device is disclosed. The object detection system includes one or more processors and a memory communicably coupled to the one or more processors. The memory storing a monitoring module including instructions that when executed by the one or more processors cause the one or more processors to, in response to acquiring sensor data about a surrounding environment, analyze the sensor data to identify a perceived object in the surrounding environment by determining at least a class of the perceived object. The memory further storing a detection module including instructions that when executed by the one or more processors cause the one or more processors to determine a presence factor associated with the perceived object according to an observation model, wherein the presence factor indicates a likelihood of an occluded object existing in an occluded region associated with the perceived object. The detection module includes instructions to control one or more systems of the robotic device according to the presence factor. 
     In one embodiment, a non-transitory computer-readable medium for predicting a presence of occluded objects from a robotic device is disclosed. The non-transitory computer-readable medium includes instructions that when executed by one or more processors cause the one or more processors to perform one or more functions. The instructions include instructions to, in response to acquiring sensor data about a surrounding environment, analyze the sensor data to identify a perceived object in the surrounding environment by determining at least a class of the perceived object. The instructions include instructions to determine a presence factor associated with the perceived object according to an observation model. The presence factor indicates a likelihood of an occluded object existing in an occluded region associated with the perceived object. The instructions include instructions to control one or more systems of the robotic device according to the presence factor. 
     In one embodiment, a method for predicting a presence of occluded objects from a robotic device is disclosed. The method includes predicting a presence of occluded objects from a robotic device. In one embodiment, a method includes, in response to acquiring sensor data about a surrounding environment, analyzing the sensor data to identify a perceived object in the surrounding environment by determining at least a class of the perceived object. The method includes determining a presence factor associated with the perceived object according to an observation model. The presence factor indicates a likelihood of an occluded object existing in an occluded region associated with the perceived object. The method includes controlling one or more systems of the robotic device according to the presence factor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various systems, methods, and other embodiments of the disclosure. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one embodiment of the boundaries. In some embodiments, one element may be designed as multiple elements or multiple elements may be designed as one element. In some embodiments, an element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale. 
         FIG. 1  illustrates one embodiment of a vehicle within which systems and methods disclosed herein may be implemented. 
         FIG. 2  illustrates one embodiment of an object detection system that is associated with predicting whether occluded objects are present. 
         FIGS. 3-4  illustrate LIDAR observation models that generally indicate forms of occluded regions for a particular object. 
         FIG. 5  illustrates one embodiment a method associated with detecting objects within occluded regions in a surrounding environment. 
         FIG. 6  illustrates an example LIDAR scan of a surrounding environment. 
     
    
    
     DETAILED DESCRIPTION 
     Systems, methods and other embodiments associated with detecting objects and determining the presence of objects in occluded areas are disclosed. As mentioned previously, robotic devices such as autonomous vehicles plan a path through an environment according to surrounding obstacles and the roadway. In general, an autonomous vehicle achieves this planning by using sensors to detect the obstacles and other aspects of the environment. However, various difficulties can complicate the noted detection and planning. For example, when the sensors do not perceive one or more objects because of occlusions in the environment an incomplete perception of the environment is then used to execute navigation and obstacle avoidance. That is, the autonomous vehicle, may not be aware of all possible obstacles/objects within an environment because of occlusions from detected objects. 
     Therefore, in one embodiment, an object detection system employs observation models associated with various types/classes of objects in order to determine a probability of whether the different types/classes of objects are present within occluded regions. As a preliminary note, while described herein as being implemented within an autonomous vehicle, the object detection system can be implemented in further machine vision applications, such as robotics, security, tracking, etc. In either case, the object detection system is generally implemented within a vehicle or other robotic device that also includes or is in communication with a sensor (e.g., LIDAR) that scans a surrounding environment. 
     Accordingly, as part of acquiring the sensor data and perceiving aspects of the surrounding environment, the object detection system determines a presence factor associated with each perceived object. For example, the presence factor indicates a likelihood of an occluded object, such as a vehicle, existing within an occluded region associated with a perceived object. Because the perceived objects cast “shadows,” which are areas obscured from perception by the sensors, the occluded objects can go undetected. Moreover, the various perceived objects cause various sizes/profiles of occlusions (i.e., occluded regions) resulting from observation of the perceived object. These various occluded regions can obscure different types of objects depending on size, shape, and so on. 
     Thus, the object detection system uses the sensor data about the perceived objects to, in one embodiment, classify the perceived objects according to at least a type and extrapolate therefrom information about the occluded region cast by the perceived object. For example, the object detection system can use the class of the perceived object as an input into the observation model. The object detection system uses the observation model in combination with the class to identify aspects of the occluded region such as shape, size, profile, etc. 
     Thereafter, the object detection system assigns different probabilities according to the occluded regions that specify a probability of an occluded object (e.g., a vehicle) being present in the occluded region. Accordingly, the object detection system generates the presence factor as the likelihood that a particular object or class of object (e.g., vehicle, pedestrian, bicycle, etc.) is present within the occluded region. In this way, the object detection improves path planning, collision avoidance, and other aspects relating to awareness of objects in the surrounding environment. 
     Prior to discussing particular embodiments of the presently disclosed systems and methods, an initial overview of the disclosed concepts will be provided. Consider a set of observations (e.g., LIDAR observations) Z={z i } n   i=1 , which are acquired by the object detection system where each z represents a ray, voxel, or other data element at angle θ i  with range r i .
 
 p ( obj   c   |Z ),  (1)
 
     obj c  represents a perceived object of class c that exists at some position (x, y) within the surrounding environment and at some angle θ object  in relation to a point of observation (e.g., from a vehicle). For purposes of explanation, stars and boxes of variable size will be discussed as the perceived and/or occluded objects. Additionally, a model p(obj no obj . Z), of the probability that no object exists at (x, y) is used. Accordingly, using Bayes&#39; rule and assuming conditionally independent observations given the object: 
     
       
         
           
             
               
                 
                   
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     Taking the log probability provides: 
                       log   ⁢           ⁢     p   ⁡     (       obj   c     |   Z     )         =       log   ⁢           ⁢   η     +       ∑     i   =   1       ⁢           ⁢     log   ⁢           ⁢     p   ⁡     (       z   i     |     obj   c       )           +     log   ⁢           ⁢     p   ⁡     (     obj   c     )             ,     
     ⁢       where   ⁢           ⁢   η     =     1     p   ⁡     (   z   )                   (   4   )               
is a normalization constant.
 
     Additionally, consider p(z i |obj c ) and assume that θ i  is known, and thus the noted system models p(r i |obj c , θ i ) by, for example, implementing a lookup table of histograms from simulated data or collected data labeled with ground truth objects within the object detection system. 
     In general, a number of simulated environments with objects placed in random positions and orientations can be used to generate the histograms. Thereafter, the object detection system can generate simulated LIDAR data. The system takes each z i  generated. Additionally, the system can project rays into a frame of the object. The system computes the relative angle between the ray and the object, φ=θ i  θ object . The system also computes a closest distance between the ray and the center of the object location, d ray . Finally, the system computes d obs , the position of the range r i  along the ray, relative to the closest point along the ray to the object center. This is given by:
 
ϕ=θ i −θ object ,  (5)
 
 d   ray   =x  sin θ i   −y  cos θ i ,  (6)
 
 d   obs   =r   i   −x  cos θ i   −y  sin θ i .  (7)
 
     Thus, (ω, d ray ) parameterizes the ray for the z i  that is being considered, and d obs  represents the observation, relative to the location of the object. (Note that these can be positive or negative). Thus:
 
 p ( r   i   |obj   c ,θ i )= p   obj     c   ( d   obs   |ϕ,d   ray ).  (8)
 
     Maintaining a two-dimensional array (e.g., lookup table) of histograms, parameterized by (φ, d ray ) and building the observation model, for each z i , the object detection system determines the histograms and updates with d obs . Visualizing the result of these histograms by querying the log probability of a potential LIDAR observation given an object of a certain class with a certain state. Thus equation (4) becomes: 
     
       
         
           
             
               
                 
                   
                     
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     Assume that at any given location (x, y), there can only be one object across all classes (including the no object class) and orientations: 
     
       
         
           
             
               
                 
                   
                     
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     Thus, computing log η and then p(objc|Z) for all classes and orientations. Recall that equation (3) assumed conditionally independent observations given the object (namely, its position and class): 
     
       
         
           
             
               
                 
                   
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     Consider intra-class variation of objects. A star object might not always have the same size. In this case, one observation might capture some of this variation, and thus be informative for the next observation. For example, if a LIDAR observation is closer, that might indicate that the object is on the large size, and thus the next observation is likely to be close as well. In one approach, an approximation (e.g., Chow-Liu tree) is implemented. Alternatively, the system captures the full distribution p(Z objc). Creating a “2-gram” model: 
     
       
         
           
             
               
                 
                   
                     
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     where each observation depends, for example, on a directly preceding observation (note that with this terminology, reference to the previous model is made as the “1-gram” model). In one embodiment, the object detection system builds a map that represents the probability that an object of a particular class exists at any particular position (x, y) and orientation θ: p(object of class c at (x, y) and orientation θ|Z). This is the local map. To build this map for every class c, position (x, y) and θ, the object detection system computes the map using, for example, the 2-grams. 
     To build the observation model, the object detection system, in one embodiment, populates histograms according to generated LIDAR scans of multiple environments over time. Subsequently, the object detection system generates a LIDAR scan from a previously unseen environment with multiple objects. The object detection system can then analyze the LIDAR sensor data of the surrounding environment using the previously generated observation model. In this way, the object detection system learns aspects relating to various configurations of occluded regions and predicts the presence of occluded objects in a surrounding environment by generating the noted presence factors from the generated observation model. Further aspects of the particular implementations of the object detection system will now be discussed. 
     Referring to  FIG. 1 , an example of the vehicle  100  is illustrated. As used herein, a “vehicle” is any form of motorized transport. In one or more implementations, the vehicle  100  is an automobile. While arrangements will be described herein with respect to automobiles, it will be understood that embodiments are not limited to automobiles. In some implementations, the vehicle  100  may be any robotic device or form of motorized transport that, for example, can operate/navigate at least semi-autonomously and/or can indicate contextual information to an operator/driver, and thus benefits from the functionality discussed herein. 
     The vehicle  100  also includes various elements. It will be understood that in various embodiments it may not be necessary for the vehicle  100  to have all of the elements shown in  FIG. 1 . The vehicle  100  can have any combination of the various elements shown in  FIG. 1 . Further, the vehicle  100  can have additional elements to those shown in  FIG. 1 . In some arrangements, the vehicle  100  may be implemented without one or more of the elements shown in  FIG. 1 . While the various elements are shown as being located within the vehicle  100  in  FIG. 1 , it will be understood that one or more of these elements can be located external to the vehicle  100 . Further, the elements shown may be physically separated by large distances. 
     Some of the possible elements of the vehicle  100  are shown in  FIG. 1  and will be described along with subsequent figures. However, a description of many of the elements in  FIG. 1  will be provided after the discussion of  FIGS. 2-6  for purposes of brevity of this description. Additionally, it will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, the discussion outlines numerous specific details to provide a thorough understanding of the embodiments described herein. Those of skill in the art, however, will understand that the embodiments described herein may be practiced using various combinations of these elements. 
     In either case, the vehicle  100  includes an object detection system  170  that is implemented to perform methods and other functions as disclosed herein relating to predicting the presence of occluded objects in relation to perceived objects. The noted functions and methods will become more apparent with a further discussion of the figures. 
     With reference to  FIG. 2 , one embodiment of the object detection system  170  of  FIG. 1  is further illustrated. The object detection system  170  is shown as including a processor  110  from the vehicle  100  of  FIG. 1 . Accordingly, the processor  110  may be a part of the object detection system  170 , the object detection system  170  may include a separate processor from the processor  110  of the vehicle  100 , or the object detection system  170  may access the processor  110  through a data bus or another communication path. In one embodiment, the object detection system  170  includes a memory  210  that stores a monitoring module  220  and a detection module  230 . The memory  210  is a random-access memory (RAM), read-only memory (ROM), a hard-disk drive, a flash memory, or other suitable memory for storing the modules  220  and  230 . The modules  220  and  230  are, for example, computer-readable instructions that when executed by the processor  110  cause the processor  110  to perform the various functions disclosed herein. 
     Accordingly, the monitoring module  220  generally includes instructions that function to control the processor  110  to receive data inputs from one or more sensors of the vehicle  100 . The inputs are sensor data collected from one or more sensors of the sensor system  120 . In general, the sensor data is, in one embodiment, observations of one or more objects in a surrounding environment proximate to the vehicle  100  and/or other aspects about the surroundings. Consequently, the monitoring module  220 , in one embodiment, analyzes the sensor data to detect surrounding vehicles/objects and, for example, generate tracks or other information about the objects/vehicles. The tracks are, for example, trajectories that include present velocities, positions, and headings for the object as determined from the respective sensor inputs. 
     In either case, the monitoring module  220  analyzes the sensor data to identify perceived objects (i.e., objects embodied within the sensor data). In one embodiment, the monitoring module  220  identifies a class of a perceived object. That is, the monitoring module  220  generally determines whether the perceived object is a car, pedestrian, motorcycle, barrel, sign post, and so on. Accordingly, in various implementations, the monitoring module  220  outputs the noted determination of a class for the perceived object along with, for example, a location relative to the vehicle  100 . In further embodiments, the monitoring module  220  can generate a 3D representation of the perceived object, however, as discussed herein, the monitoring module  220  generally indicates a class. 
     Moreover, in one embodiment, the object detection system  170  includes the database  240 . The database  240  is, in one embodiment, an electronic data structure stored in the memory  210  or another data store and that is configured with routines that can be executed by the processor  110  for analyzing stored data, providing stored data, organizing stored data, and so on. Thus, in one embodiment, the database  240  stores data (e.g., sensor data) used by the modules  220  and  230  in executing various functions. In one embodiment, the database  240  includes the observation model  250  along with, for example, sensor data and or other information that is used by the modules  220  and  230 . For example, the database  240  can include location coordinates (e.g., longitude and latitude), relative map coordinates, time/date stamps from when the separate sensor data was generated, and so on. 
     Moreover, the observation model  250  may include various data structures storing learned information about objects (e.g., vehicles, pedestrians, etc.) that is used to formulate estimations of whether objects exist within occluded regions. Moreover, the observation model  250  includes, in one embodiment, information regarding poses, sizes, relative shapes of occluded regions cast by objects, histograms of parameters associated with different classes/types of objects, and so on. In one embodiment, the observation model  250  is implemented as a lookup table that is referenced according to, for example, at least a type/class of a perceived object in order to determine aspects relating to an occluded region cast by the perceived object. Additionally, in further embodiments, the database  240  and/or the memory  210  store the observation model  250  in various portions. 
     In one embodiment, the detection module  230  generally includes instructions that function to control the processor  110  to predict a presence of occluded objects in occluded regions. Moreover, while the observation model  250  is discussed as being stored in the database  240 , in one or more embodiments, the observation model  250  is at least partially integrated with the detection module  230 . That is, for example, a portion (e.g., index) of the observation model  250  can be implemented within the detection module  230  and executed on the processor  110  while the noted data structures may be stored in the database  240  and/or in the memory  210 . In either case, the detection module  230  implements the observation model  250  to predict the existence of objects within occluded regions. 
     In one embodiment, the detection module  230  is configured in a manner so as to predict the presence of occluded objects according to at least perceived objects and relative occluded regions cast by the perceived objects. Thus, the detection module  230 , in one embodiment, generates a presence factor for separate occluded regions that indicates a likelihood of the presence of the occluded object(s) of a particular class (e.g., vehicle). Additionally, the object detection system  170  provides the presence factor to additional aspects of the vehicle  100  such as the autonomous driving module  160 . In further aspects, the object detection system  170  controls aspects of the vehicle  100  directly such as controlling the vehicle  100  to execute an emergency maneuver (e.g., pullover) and/or to render visual display alerts or audible alerts to occupants of the vehicle  100 . In this way, the object detection system improves the operation of the vehicle  100  by improving detection of potentially occluded objects and thus also improves planning and execution of maneuvers, improving the operation of one or more computers through more efficient planning, improving safety through better awareness of the presence of possible objects, and so on. 
     By way of example, consider  FIG. 3  which generally illustrates an example of an observation model  300  for a star-shaped object  310  as perceived by a LIDAR sensor such as the LIDAR sensor  124 . It should be appreciated that the model  300  is generally illustrative of how a LIDAR sensor perceives an object in two-dimensions and, in further aspects, histograms/models of the observation model  250  may include further dimensions. Thus, the model  300  is shown from a top-down perspective. Accordingly, the star-shaped object  310  generally has a top-down profile that is in the form of a star. For purposes of this discussion, remaining portions of the star-shaped object in a dimension into/out of the paper should be considered to be consistent with the general profile as illustrated. In either case, the model  300  of the perceived star-shaped object  310  illustrates how the object  310  casts an occluded region  320 . Moreover, it should be appreciated that depending on a particular distance of the LIDAR sensor  124 , size of the object  310 , and angle in relation to the object  310 , the precise dimensions of the occluded region  320  may be adjusted. However, whichever orientation that is determined, the occluded region  320  generally remains as an area for which the LIDAR sensor does not perceive information and is thus generally unaware of what may exist in the region  320 . 
     Moreover, an additional example of an observation model is provided in  FIG. 4 , which illustrates a model  400  for a rectangular shaped object  410 . The rectangular shaped object  410 , as in the case of the star-shaped object  310 , is illustrated from a top-down view. In either case, when the object  410  is scanned by the LIDAR  124  from the angle illustrated in  FIG. 4 , an occluded region  420  results therefrom. It should be understood that the occluded region  420  is of a larger more significant size because of, for example, the shape of the object  410  itself but also because of the size of the object  410  in comparison to the object  310 . Accordingly, in various implementations, the detection module  230  accounts for a size in addition to the class of the noted perceived object. 
     Thus, the object detection system  170  assigns a probability of the existence of an object of a particular class within the occluded region  320 . For purposes of this example, consider that the detection module  230  generates a presence factor for a rectangle being behind the star within the occluded region  320 . Since the rectangle may be large in comparison to the occluded region  320 , the probability of the existence of the rectangle within the occluded region is determined to be, for example, low. In essence, the rectangle does not fit wholly within the occluded region  320  and would thus be perceived, at least in part, by the vehicle  100 . Thus, the detection module  230 , in one embodiment, generates the presence factor, as a function of the observation model  250 , to indicate that the rectangle is unlikely to exist behind the star  310  and be completely occluded within the occluded region  320 . 
     However, the detection module  230 , in one embodiment, determines that the probability of a different class of object, such as a smaller circle, being present in the occluded region  320  is high in comparison to the rectangle, since the observation model  250  indicates that the circle is small enough to fit into the occluded region  320 . Additionally, in one embodiment, the detection module  230  can leverage previous observations (e.g., at different times) for computing the probability. In this way, the object detection system  170  can provide more robust probability calculations and/or associate the calculations with previously detected dynamic objects moving through the environment. 
     As an applied example, consider that the star is instead a sport utility vehicle (SUV) or other vehicle while the rectangle is a semi-truck. Moreover, consider that the circle is actually a pedestrian. The object detection system may observe the SUV and assign a probability of a semi-truck and a pedestrian existing in the occluded area behind the SUV. Moreover, the object detection system may indicate that the probability of a semi-truck being located behind the SUV is small, but a pedestrian may be located in the occluded area. In this way, the object detection improves situational awareness about objects or probabilities of objects being present within the surrounding environment and can thus also improve functional aspects of the vehicle  100  such as path planning, collision avoidance, and other aspects relating to navigation through the environment. 
     Additional aspects of predicting whether objects exist within occluded regions of perceived objects will be discussed in relation to  FIG. 5 .  FIG. 5  illustrates a flowchart of a method  500  that is associated with detecting occluded objects in relation to perceived objects. Method  500  will be discussed from the perspective of the object detection system  170  of  FIGS. 1, and 2 . While method  500  is discussed in combination with the object detection system  170 , it should be appreciated that the method  500  is not limited to being implemented within object detection system  170 , but is instead one example of a system that may implement the method  500 . 
     As a preliminary matter, it should be appreciated that the object detection system  170  is, in one embodiment, initially trained or otherwise configured with the observation model  250 . The observation model  250  characterizes occluded regions that are cast by perceived objects and likelihoods of different classes of objects (e.g., vehicles, pedestrians, etc.) existing within the occluded regions while otherwise being undetected. In various implementations, the observation model  250  is implemented in different forms but is generally discussed within this disclosure as being a lookup table of histograms. However, in further aspects, the observation model  250  is a neural network or other machine learning algorithm that outputs the presence factor when, for example, provided with electronic inputs describing the occluded region. 
     At  510 , the monitoring module  220  acquires sensor data from at least one sensor of the vehicle  100 . In one embodiment, the monitoring module  220  collects the sensor data in real-time from a stream of sensor data provided by the vehicle sensor system  120 . Accordingly, in one embodiment, the monitoring module  220  collects the sensor data from multiples ones of the sensors. In further embodiments, the monitoring module  220  acquires the sensor data from a select one of the sensors  120  such as the LIDAR sensor  124 . In either case, the sensor data itself generally includes information about a surrounding environment of the vehicle  100  in which various aspects of the surrounding environment are captured/perceived. 
     At  520 , the monitoring module  220  analyzes the sensor data to identify perceived objects embodied by the sensor data. In one embodiment, the monitoring module  220  applies image recognition techniques, LIDAR processing techniques (e.g., machine learning for point cloud recognition), and/or another approach to identify objects in the sensor data and discriminate between the objects. Thus, the monitoring module  220 , for example, identifies aspects of the sensor data that correlate with separate objects and at least a class for the separate perceived objects. The class indicates, in one embodiment, a type of the perceived object that generally correlates with a profile in shape. That is, the class may indicate that the perceived object is a vehicle, pedestrian, etc. In further aspects, the class may also indicate general dimensions of the perceived object. Moreover, in further implementations, the class can indicate a 3D model of the perceived object that is derived from the sensor data. In either case, the monitoring module  220  analyzes the sensor data to extract perceived objects from the sensor data for further processing subsequently. 
     At  530 , the detection module  230  determines characteristics of an occluded region that is cast by a perceived object. As previously indicated, the occluded region is generally an area that is blocked from being perceived by sensors of the vehicle  100 . Thus, systems of the vehicle  100  are generally not aware of whether an object such as a pedestrian or another vehicle exists within the occluded region. Accordingly, the detection module  230 , in one embodiment, provides inputs to the observation model  250  in the form of a class of the perceived object, and a relative location/pose in relation to the perceived object to determine the characteristics of the occluded region (e.g., shape, size, etc.). While the detection module  230  is disclosed as determining the characteristics of the occluded region prior to generating the presence factor, in one embodiment, the functions disclosed at blocks  530  and  540  may be combined into a single step. 
     At  540 , the detection module  230  uses the observation model  250  to determine the presence factor. In general, the presence factor characterizes whether the occluded region cast by the perceived object is sufficient to obscure the occluded object. Thus, the presence factor indicates a likelihood of an occluded object existing in the occluded region associated with the perceived object. The detection module  230  generates the presence factor by, for example, using the observation model  250  as a lookup table. That is, the observation model  250 , in one embodiment, is indexed according to various factors and produces the presence factor as an output. For example, the detection module  230  uses a pose, a class of the perceived object, and/or other aspects of the surrounding environment as an input to the observation model  250 . In one embodiment, the observation model  250  includes different heuristics/models at different indexed locations that generate the presence factor. That is, the observation model  250  can be a collection of functions as previously defined that are indexed according to aspects of the perceived object and can be used to produce the presence factor according to the acquired sensor data and characteristics fo the perceived object. 
     In further aspects, the observation model  250  itself includes, in one embodiment, histograms associated with the various inputs that indicate the presence factors for various occluded objects or at least provide information that is further analyzed by the detection module  230  to produce the presence factor. As an additional matter, the detection module  230 , in one embodiment, selects the occluded object or a set of possible occluded objects for which the presence factor is generated. That is, because different objects that may be occluded within the occluded region have varying shapes and sizes, the detection module  230  can select which occluded objects are used as a basis for the determining the presence factor. 
     For example, in one embodiment, the detection module  230  selects the occluded objects for analysis according to previously identified objects in the environment, objects that are likely within the surrounding environment as determined according to characteristics of the surrounding environment (E.g., school zone, highway, urban area, etc.), characteristics of the occluded region (e.g., shape and size), and so on. Thus, the occluded object can include a set of possible objects for which the presence factor is determined. In either case, the detection module  230  uses knowledge of the occluded region and generates the presence factor as a likelihood of whether one or more occluded objects exist within the occluded region. 
     At  550 , the detection module  230  provides the presence factor as an output. In one embodiment, the detection module  230  generates an electronic output on one or more communication subsystems of the vehicle  100  to provide the presence factor to various systems  140 . In general, the detection module  230  provides the presence factor as a percentage that indicates the likelihood of the presence of an object in general. In further aspects, the percentage may be specified separately for different classes of objects. In still further aspects, the detection module  230  may simply provide a binary indicator that specifies a general likelihood of a presence of an occluded object. In either case, the detection module  230  provides the presence factor as an electronic output, which is, for example, communicated to additional aspects of the vehicle  100  as subsequently discussed. 
     At  560 , the detection module  230  controls one or more systems of the vehicle  100 . In one embodiment, the detection module  230  controls the one or more systems  140  by communicating the presence factor to the one or more systems. For example, the detection module  230  communicates the presence factor to an autonomous driving module  160  to adjust path planning of the vehicle  100  to account for the occluded object according to the presence factor. That is, the detection module  230  can adjust how the vehicle  100  is autonomously controlled by providing additional information to the module  160  that affects situational awareness about the surrounding environment. Accordingly, the detection module  230  can cause the module  160  to change a path by informing the module  160  of the likely presence of an occluded object so that the vehicle  100  can improve avoiding collisions or other undesirable maneuvers in relation to the occluded object. Similarly, awareness of the absence of an occluded object can provide for maneuvering into a space that otherwise may be avoided. In general, the detection module  230  provides the presence factor to different systems to improve safety and general operation of the vehicle  100  as realized through improved awareness of the surrounding environment. 
     Further examples of how the object detection system  170  functions will be discussed in relation to  FIG. 6 .  FIG. 6  illustrates an example surrounding environment  600  of the vehicle that includes a plurality of different objects.  FIG. 6  is illustrated from the perspective of what is perceived by the vehicle  100  when using the LIDAR  124  to scan the surrounding environment  600 . Thus, the plurality of concentric rings generally represent scan lines of the LIDAR  124 , and thus sensor data that is acquired by the vehicle  100  through scans of the LIDAR  124 . Moreover, the surrounding environment  600  is an intersection of two roads in an urban location with multiple different pedestrians, vehicles, and other aspects as will now be described. 
     The surrounding environment depicted in  FIG. 6  includes perceived objects  605 ,  610 ,  615 ,  620 ,  625 , and  630 . The perceived objects  605 ,  615 ,  620 ,  625 , and  630  are nearby vehicles whereas the perceived object  610  is a pedestrian. Object  635  is an occluded or at least partially occlude semi-truck as will be discussed further subsequently. In either case, the noted perceived objects cast occluded regions  640 ,  645 ,  650 ,  655 , and  660  as indicated by an absence of scan lines from the LIDAR  124  return. As a further matter, not all of the objects in the surrounding environment  600  are labeled nor are all of the occluded regions. However, it should be appreciated that the disclosed methods still operate on these additional aspects but are not discussed for purposes of brevity. 
     Accordingly, the object detection system  170  acquires the sensor data, which depicts the surrounding environment  600  as illustrated. The monitoring module  220  executes one or more recognition techniques to identify and localize the perceived objects in the surrounding environment from the sensor data. Thereafter, the detection module  230  can determine characteristics of the occluded regions  640 - 660  and generate presence factors for the separate occluded regions using the observation model  250 . As seen in  FIG. 6 , the occluded regions  640 - 660  are of varying sizes depending on a particular pose/orientation of a perceived object, a distance of a perceived object from the vehicle  100 , and so on. Moreover, in various circumstances, two or more perceived objects can form a larger occluded region as seen with vehicles  615  and  625  casting an occluded region that occludes the truck  635 . Accordingly, in further embodiments, the object detection system  170  can account for combined occluded regions cast by multiple objects. Additionally, the occluded region  660  illustrates a circumstance where multiple occluded objects are present within the occluded region  660  generated by the perceived object  630 . Accordingly, the object detection system  170  may account for circumstances where multiple occluded objects are present in a single occluded region as learned through observations over time. 
       FIG. 1  will now be discussed in full detail as an example environment within which the system and methods disclosed herein may operate. In some instances, the vehicle  100  is configured to switch selectively between an autonomous mode, one or more semi-autonomous operational modes, and/or a manual mode. Such switching can be implemented in a suitable manner, now known or later developed. “Manual mode” means that all of or a majority of the navigation and/or maneuvering of the vehicle is performed according to inputs received from a user (e.g., human driver). In one or more arrangements, the vehicle  100  can be a conventional vehicle that is configured to operate in only a manual mode. 
     In one or more embodiments, the vehicle  100  is an autonomous vehicle. As used herein, “autonomous vehicle” refers to a vehicle that operates in an autonomous mode. “Autonomous mode” refers to navigating and/or maneuvering the vehicle  100  along a travel route using one or more computing systems to control the vehicle  100  with minimal or no input from a human driver. In one or more embodiments, the vehicle  100  is highly automated or completely automated. In one embodiment, the vehicle  100  is configured with one or more semi-autonomous operational modes in which one or more computing systems perform a portion of the navigation and/or maneuvering of the vehicle along a travel route, and a vehicle operator (i.e., driver) provides inputs to the vehicle to perform a portion of the navigation and/or maneuvering of the vehicle  100  along a travel route. 
     The vehicle  100  can include one or more processors  110 . In one or more arrangements, the processor(s)  110  can be a main processor of the vehicle  100 . For instance, the processor(s)  110  can be an electronic control unit (ECU). The vehicle  100  can include one or more data stores  115  for storing one or more types of data. The data store  115  can include volatile and/or non-volatile memory. Examples of suitable data stores  115  include RAM (Random Access Memory), flash memory, ROM (Read Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof. The data store  115  can be a component of the processor(s)  110 , or the data store  115  can be operatively connected to the processor(s)  110  for use thereby. The term “operatively connected,” as used throughout this description, can include direct or indirect connections, including connections without direct physical contact. 
     In one or more arrangements, the one or more data stores  115  can include map data  116 . The map data  116  can include maps of one or more geographic areas. In some instances, the map data  116  can include information or data on roads, traffic control devices, road markings, structures, features, and/or landmarks in the one or more geographic areas. The map data  116  can be in any suitable form. In some instances, the map data  116  can include aerial views of an area. In some instances, the map data  116  can include ground views of an area, including 360-degree ground views. The map data  116  can include measurements, dimensions, distances, and/or information for one or more items included in the map data  116  and/or relative to other items included in the map data  116 . The map data  116  can include a digital map with information about road geometry. The map data  116  can be high quality and/or highly detailed. 
     In one or more arrangements, the map data  116  can include one or more terrain maps  117 . The terrain map(s)  117  can include information about the ground, terrain, roads, surfaces, and/or other features of one or more geographic areas. The terrain map(s)  117  can include elevation data in the one or more geographic areas. The map data  116  can be high quality and/or highly detailed. The terrain map(s)  117  can define one or more ground surfaces, which can include paved roads, unpaved roads, land, and other things that define a ground surface. 
     In one or more arrangements, the map data  116  can include one or more static obstacle maps  118 . The static obstacle map(s)  118  can include information about one or more static obstacles located within one or more geographic areas. A “static obstacle” is a physical object whose position does not change or substantially change over a period of time and/or whose size does not change or substantially change over a period of time. Examples of static obstacles include trees, buildings, curbs, fences, railings, medians, utility poles, statues, monuments, signs, benches, furniture, mailboxes, large rocks, hills. The static obstacles can be objects that extend above ground level. The one or more static obstacles included in the static obstacle map(s)  118  can have location data, size data, dimension data, material data, and/or other data associated with it. The static obstacle map(s)  118  can include measurements, dimensions, distances, and/or information for one or more static obstacles. The static obstacle map(s)  118  can be high quality and/or highly detailed. The static obstacle map(s)  118  can be updated to reflect changes within a mapped area. 
     The one or more data stores  115  can include sensor data  119 . In this context, “sensor data” means any information about the sensors that the vehicle  100  is equipped with, including the capabilities and other information about such sensors. As will be explained below, the vehicle  100  can include the sensor system  120 . The sensor data  119  can relate to one or more sensors of the sensor system  120 . As an example, in one or more arrangements, the sensor data  119  can include information on one or more LIDAR sensors  124  of the sensor system  120 . 
     In some instances, at least a portion of the map data  116  and/or the sensor data  119  can be located in one or more data stores  115  located onboard the vehicle  100 . Alternatively, or in addition, at least a portion of the map data  116  and/or the sensor data  119  can be located in one or more data stores  115  that are located remotely from the vehicle  100 . 
     As noted above, the vehicle  100  can include the sensor system  120 . The sensor system  120  can include one or more sensors. “Sensor” means any device, component and/or system that can detect, and/or sense something. The one or more sensors can be configured to detect, and/or sense in real-time. As used herein, the term “real-time” means a level of processing responsiveness that a user or system senses as sufficiently immediate for a particular process or determination to be made, or that enables the processor to keep up with some external process. 
     In arrangements in which the sensor system  120  includes a plurality of sensors, the sensors can work independently from each other. Alternatively, two or more of the sensors can work in combination with each other. In such case, the two or more sensors can form a sensor network. The sensor system  120  and/or the one or more sensors can be operatively connected to the processor(s)  110 , the data store(s)  115 , and/or another element of the vehicle  100  (including any of the elements shown in  FIG. 1 ). The sensor system  120  can acquire data of at least a portion of the external environment of the vehicle  100  (e.g., nearby vehicles). 
     The sensor system  120  can include any suitable type of sensor. Various examples of different types of sensors will be described herein. However, it will be understood that the embodiments are not limited to the particular sensors described. The sensor system  120  can include one or more vehicle sensors  121 . The vehicle sensor(s)  121  can detect, determine, and/or sense information about the vehicle  100  itself. In one or more arrangements, the vehicle sensor(s)  121  can be configured to detect, and/or sense position and orientation changes of the vehicle  100 , such as, for example, based on inertial acceleration. In one or more arrangements, the vehicle sensor(s)  121  can include one or more accelerometers, one or more gyroscopes, an inertial measurement unit (IMU), a dead-reckoning system, a global navigation satellite system (GNSS), a global positioning system (GPS), a navigation system  147 , and/or other suitable sensors. The vehicle sensor(s)  121  can be configured to detect, and/or sense one or more characteristics of the vehicle  100 . In one or more arrangements, the vehicle sensor(s)  121  can include a speedometer to determine a current speed of the vehicle  100 . 
     Alternatively, or in addition, the sensor system  120  can include one or more environment sensors  122  configured to acquire, and/or sense driving environment data. “Driving environment data” includes and data or information about the external environment in which an autonomous vehicle is located or one or more portions thereof. For example, the one or more environment sensors  122  can be configured to detect, quantify and/or sense obstacles in at least a portion of the external environment of the vehicle  100  and/or information/data about such obstacles. Such obstacles may be stationary objects and/or dynamic objects. The one or more environment sensors  122  can be configured to detect, measure, quantify and/or sense other things in the external environment of the vehicle  100 , such as, for example, lane markers, signs, traffic lights, traffic signs, lane lines, crosswalks, curbs proximate the vehicle  100 , off-road objects, etc. 
     Various examples of sensors of the sensor system  120  will be described herein. The example sensors may be part of the one or more environment sensors  122  and/or the one or more vehicle sensors  121 . However, it will be understood that the embodiments are not limited to the particular sensors described. 
     As an example, in one or more arrangements, the sensor system  120  can include one or more radar sensors  123 , one or more LIDAR sensors  124 , one or more sonar sensors  125 , and/or one or more cameras  126 . In one or more arrangements, the one or more cameras  126  can be high dynamic range (HDR) cameras or infrared (IR) cameras. 
     The vehicle  100  can include an input system  130 . An “input system” includes any device, component, system, element or arrangement or groups thereof that enable information/data to be entered into a machine. The input system  130  can receive an input from a vehicle passenger (e.g. a driver or a passenger). The vehicle  100  can include an output system  135 . An “output system” includes any device, component, or arrangement or groups thereof that enable information/data to be presented to a vehicle passenger (e.g. a person, a vehicle passenger, etc.). 
     The vehicle  100  can include one or more vehicle systems  140 . Various examples of the one or more vehicle systems  140  are shown in  FIG. 1 . However, the vehicle  100  can include more, fewer, or different vehicle systems. It should be appreciated that although particular vehicle systems are separately defined, each or any of the systems or portions thereof may be otherwise combined or segregated via hardware and/or software within the vehicle  100 . The vehicle  100  can include a propulsion system  141 , a braking system  142 , a steering system  143 , throttle system  144 , a transmission system  145 , a signaling system  146 , and/or a navigation system  147 . Each of these systems can include one or more devices, components, and/or combination thereof, now known or later developed. 
     The navigation system  147  can include one or more devices, applications, and/or combinations thereof, now known or later developed, configured to determine the geographic location of the vehicle  100  and/or to determine a travel route for the vehicle  100 . The navigation system  147  can include one or more mapping applications to determine a travel route for the vehicle  100 . The navigation system  147  can include a global positioning system, a local positioning system or a geolocation system. 
     The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  can be operatively connected to communicate with the various vehicle systems  140  and/or individual components thereof. For example, returning to  FIG. 1 , the processor(s)  110  and/or the autonomous driving module(s)  160  can be in communication to send and/or receive information from the various vehicle systems  140  to control the movement, speed, maneuvering, heading, direction, etc. of the vehicle  100 . The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  may control some or all of these vehicle systems  140  and, thus, may be partially or fully autonomous. 
     The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  can be operatively connected to communicate with the various vehicle systems  140  and/or individual components thereof. For example, returning to  FIG. 1 , the processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  can be in communication to send and/or receive information from the various vehicle systems  140  to control the movement, speed, maneuvering, heading, direction, etc. of the vehicle  100 . The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  may control some or all of these vehicle systems  140 . 
     The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  may be operable to control the navigation and/or maneuvering of the vehicle  100  by controlling one or more of the vehicle systems  140  and/or components thereof. For instance, when operating in an autonomous mode, the processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  can control the direction and/or speed of the vehicle  100 . The processor(s)  110 , the object detection system  170 , and/or the autonomous driving module(s)  160  can cause the vehicle  100  to accelerate (e.g., by increasing the supply of fuel provided to the engine), decelerate (e.g., by decreasing the supply of fuel to the engine and/or by applying brakes) and/or change direction (e.g., by turning the front two wheels). As used herein, “cause” or “causing” means to make, force, compel, direct, command, instruct, and/or enable an event or action to occur or at least be in a state where such event or action may occur, either in a direct or indirect manner. 
     The vehicle  100  can include one or more actuators  150 . The actuators  150  can be any element or combination of elements operable to modify, adjust and/or alter one or more of the vehicle systems  140  or components thereof to responsive to receiving signals or other inputs from the processor(s)  110  and/or the autonomous driving module(s)  160 . Any suitable actuator can be used. For instance, the one or more actuators  150  can include motors, pneumatic actuators, hydraulic pistons, relays, solenoids, and/or piezoelectric actuators, just to name a few possibilities. 
     The vehicle  100  can include one or more modules, at least some of which are described herein. The modules can be implemented as computer-readable program code that, when executed by a processor  110 , implement one or more of the various processes described herein. One or more of the modules can be a component of the processor(s)  110 , or one or more of the modules can be executed on and/or distributed among other processing systems to which the processor(s)  110  is operatively connected. The modules can include instructions (e.g., program logic) executable by one or more processor(s)  110 . Alternatively, or in addition, one or more data store  115  may contain such instructions. 
     In one or more arrangements, one or more of the modules described herein can include artificial or computational intelligence elements, e.g., neural network, fuzzy logic or other machine learning algorithms. Further, in one or more arrangements, one or more of the modules can be distributed among a plurality of the modules described herein. In one or more arrangements, two or more of the modules described herein can be combined into a single module. 
     The vehicle  100  can include one or more autonomous driving modules  160 . The autonomous driving module(s)  160  can be configured to receive data from the sensor system  120  and/or any other type of system capable of capturing information relating to the vehicle  100  and/or the external environment of the vehicle  100 . In one or more arrangements, the autonomous driving module(s)  160  can use such data to generate one or more driving scene models. The autonomous driving module(s)  160  can determine position and velocity of the vehicle  100 . The autonomous driving module(s)  160  can determine the location of obstacles, obstacles, or other environmental features including traffic signs, trees, shrubs, neighboring vehicles, pedestrians, etc. 
     The autonomous driving module(s)  160  can be configured to receive, and/or determine location information for obstacles within the external environment of the vehicle  100  for use by the processor(s)  110 , and/or one or more of the modules described herein to estimate position and orientation of the vehicle  100 , vehicle position in global coordinates based on signals from a plurality of satellites, or any other data and/or signals that could be used to determine the current state of the vehicle  100  or determine the position of the vehicle  100  with respect to its environment for use in either creating a map or determining the position of the vehicle  100  in respect to map data. 
     The autonomous driving module(s)  160  either independently or in combination with the object detection system  170  can be configured to determine travel path(s), current autonomous driving maneuvers for the vehicle  100 , future autonomous driving maneuvers and/or modifications to current autonomous driving maneuvers based on data acquired by the sensor system  120 , driving scene models, and/or data from any other suitable source such as determinations from the observation model  250  as implemented by the detection module  230 . “Driving maneuver” means one or more actions that affect the movement of a vehicle. Examples of driving maneuvers include: accelerating, decelerating, braking, turning, moving in a lateral direction of the vehicle  100 , changing travel lanes, merging into a travel lane, and/or reversing, just to name a few possibilities. The autonomous driving module(s)  160  can be configured to implement determined driving maneuvers. The autonomous driving module(s)  160  can cause, directly or indirectly, such autonomous driving maneuvers to be implemented. As used herein, “cause” or “causing” means to make, command, instruct, and/or enable an event or action to occur or at least be in a state where such event or action may occur, either in a direct or indirect manner. The autonomous driving module(s)  160  can be configured to execute various vehicle functions and/or to transmit data to, receive data from, interact with, and/or control the vehicle  100  or one or more systems thereof (e.g. one or more of vehicle systems  140 ). 
     Detailed embodiments are disclosed herein. However, it is to be understood that the disclosed embodiments are intended only as examples. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the aspects herein in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of possible implementations. Various embodiments are shown in  FIGS. 1-6 , but the embodiments are not limited to the illustrated structure or application. 
     The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. 
     The systems, components and/or processes described above can be realized in hardware or a combination of hardware and software and can be realized in a centralized fashion in one processing system or in a distributed fashion where different elements are spread across several interconnected processing systems. Any kind of processing system or another apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software can be a processing system with computer-usable program code that, when being loaded and executed, controls the processing system such that it carries out the methods described herein. The systems, components and/or processes also can be embedded in a computer-readable storage, such as a computer program product or other data programs storage device, readable by a machine, tangibly embodying a program of instructions executable by the machine to perform methods and processes described herein. These elements also can be embedded in an application product which comprises all the features enabling the implementation of the methods described herein and, which when loaded in a processing system, is able to carry out these methods. 
     Furthermore, arrangements described herein may take the form of a computer program product embodied in one or more computer-readable media having computer-readable program code embodied, e.g., stored, thereon. Any combination of one or more computer-readable media may be utilized. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The phrase “computer-readable storage medium” means a non-transitory storage medium. A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: a portable computer diskette, a hard disk drive (HDD), a solid-state drive (SSD), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer-readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber, cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present arrangements may be written in any combination of one or more programming languages, including an object-oriented programming language such as Java™ Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer, or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     The terms “a” and “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e. open language). The phrase “at least one of . . . and . . . ” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. As an example, the phrase “at least one of A, B, and C” includes A only, B only, C only, or any combination thereof (e.g. AB, AC, BC or ABC). 
     Aspects herein can be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope hereof.