Patent Publication Number: US-11036217-B2

Title: Controlling a vehicle using a remotely located laser and an on-board camera

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage of International Application No. PCT/IB2019/052884, filed on Apr. 8, 2019, which claims priority to U.S. Provisional Patent Application No. 62/666,197, filed on May 3, 2018, entitled “AN INSTRUMENTED LASER POINTING DEVICE FOR REMOTELY PILOTING AN AUTONOMOUS MOBILE PLATFORM,” and U.S. Provisional Patent Application No. 62/778,075, filed on Dec. 11, 2018, entitled “CONTROLLING A VEHICLE USING A REMOTELY LOCATED LASER AND AN ON-BOARD CAMERA,” the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of the disclosed subject matter relate generally to systems and methods of controlling a vehicle first in a laser guidance mode in which a laser beam is used to determine a set of waypoints to a destination and then switching to a vision-based mode in which a camera of the vehicle is used to move the vehicle into position at the destination. 
     Discussion of the Background 
     Over the past several years, the size and cost of UAVs have decreased while the maneuverability of UAVs has increased. These UAVs typically incorporate cameras, which also continue to decrease in size and cost, while also performing better in terms of specifications and capabilities. Accordingly, UAVs are now being used for wide variety of applications, such as inspecting structures, for example for structural damage, etc. UAVs are particularly useful for inspecting structures that are not easily accessible by people, such as tall structures. For example, industrial facilities typically have portions that are not easily accessible by workers but nonetheless require annual inspection plans for quality control and addressing any potential problems. UAVs can be used to capture images (either still images or video streams), which allow an operator of the UAV to assess the structure and take appropriate actions. 
     There currently are two basic ways of using a UAV to inspect structures. The first is for the UAV to operate completely autonomously so that the UAV is provided with a destination, for example defined using GPS coordinates, then the UAV will calculate the path to the destination and follow the calculated path. This requires a great deal of pre-planning because if there is any error in the information regarding the position of the destination, the UAV will autonomously move to an incorrect position. This is particularly likely to happen when inspecting structures that are not easily accessible because the precise position of these structures may not be known in advance. 
     Another way to use a UAV to inspect structures is by manually controlling the UAV&#39;s path to the destination using a remote controller. This technique requires a trained operator because manual control of a UAV is difficult, and the UAV must be carefully aligned with the destination so that it can capture images of the destination (e.g., the structure). 
     Thus, it would be desirable to provide systems and methods for operating UAVs that do not require a great deal of preplanning and do not require a skilled operator to control the UAV. 
     SUMMARY 
     According to an embodiment, there is a method for guiding a vehicle from an initial position to a target position using a projection of a laser beam on a target. A set of waypoints from the initial position of the vehicle to a position proximate to the target position is determined using an orientation of a laser pointer that projects the laser beam and based on projection of the UAV initial position onto the laser beam pointing at the target. The vehicle is guided along the set of determined waypoints to the position proximate to the target position. The vehicle is guided from the position proximate to the target position using the optical system of the vehicle responsive to detection of a dot of the laser beam on the target by an optical system of the vehicle. 
     According to another embodiment, there is a system. The system includes an unmanned aerial vehicle (UAV), comprising a processor coupled to a wireless communication interface and an optical system comprising an imager. The system also includes a laser pointer comprising a processor coupled to wireless communication interface, a laser emitter, and a pose estimation module. The processor of the UAV is configured to guide the UAV along a set of determined waypoints from an initial position of the UAV to a position proximate to a target position based on a laser beam emitted from the laser emitter. The processor of the UAV is also configured to guide the UAV, responsive to detection of the laser beam impinging on a target using an image captured by the imager, from the position proximate to the target position to the target position using the optical system. 
     According to a further embodiment, there is an unmanned aerial vehicle (UAV), which includes a processor, a wireless communication interface coupled to the processor, and an optical system comprising an imager. The processor is configured to guide the UAV along a set of determined waypoints from an initial position of the UAV to a position proximate to a target position based on a laser beam emitted from a laser emitter of a laser pointer. The processor is also configured to guide the UAV, responsive to detection of the laser beam impinging on a target using an image captured by the imager, from the position proximate to the target position to the target position using the optical system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings: 
         FIG. 1  is a flowchart of a method for guiding a vehicle from an initial position to a target position using a projection of a laser beam on a target according to an embodiment; 
         FIGS. 2A and 2B  are block diagrams of systems for guiding an unmanned aerial vehicle, UAV, from an initial position to a target position using a projection of a laser beam on a target according to embodiments; 
         FIG. 3  is a block diagram of a laser pointer according to an embodiment; 
         FIGS. 4A and 4B  are block diagrams of specific hardware that can be used for a laser pointer according to embodiments; 
         FIG. 5  is a block diagram of software modules of a laser pointer according to embodiments; 
         FIG. 6  is a block diagram of a UAV according to embodiments; 
         FIG. 7  is a block diagram of specific hardware that can be used for a UAV according to an embodiment; 
         FIGS. 8A and 8B  are block diagrams of software modules for the UAV&#39;s companion computer and flight control unit, respectively, according to embodiments; 
         FIG. 9  is a block diagram of a base station according to embodiments; 
         FIG. 10  is a block diagram of software modules of a base station according to embodiments; 
         FIG. 11  is a flowchart of a method for guiding UAV from an initial position to a target position using a projection of a laser beam on a target according to an embodiment; 
         FIG. 12  is a block diagram of a system for guiding UAV from an initial position to a target position using a projection of a laser beam on a target according to an embodiment; 
         FIG. 13A  illustrate an arrangement of laser emitters in an equilateral triangle according to embodiments; and 
         FIGS. 13B-13D  illustrate different relationships between laser dots impinging on a target according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of unmanned aerial vehicles. However, the embodiments can be employed with any type of vehicle. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
       FIG. 1  is a flowchart of a method for guiding vehicle from an initial position to a target position using a projection of a laser beam on a target according to an embodiment. Initially, a set of waypoints from the UAV initial position to a position proximate to the target position is determined using an orientation of a laser pointer that projects the laser beam and based on projection of the UAV initial position onto the laser beam pointing at the target (step  110 ). The UAV is then guided along the set of determined waypoints to the position proximate to the target position (step  120 ). Finally, responsive to detection of a dot of the laser beam on the target by an optical system of the vehicle, the vehicle is guided from the position proximate to the target position using the optical system of the vehicle (step  130 ). Thus, as will be appreciated, the vehicle initially operates in a laser guidance mode in step  120 , and once the vehicle detects the dot of the laser beam, the vehicle is operated in a vision-based control mode using the optical system of the vehicle. Should the laser dot move when the vehicle is operated in the vision-based control mode, the vehicle&#39;s path will follow the movement of the laser dot because it will be tracking the laser dot using its optical system. 
     The method of  FIG. 1  has been described in connection with a vehicle, which can be a land-, water-, and/or air-based vehicles. For ease of description, embodiments will be described in which the vehicle is an unmanned aerial vehicle (UAV). However, the discussion below applies equally to other types of vehicles. 
       FIGS. 2A and 2B  are block diagrams of two different system configurations for guiding UAV from an initial position to a target position using a projection of a laser beam on a target. The system illustrated in  FIG. 2A  includes a UAV  205 , a laser pointer  210 , which points a laser beam  215  at the destination  220 . In the system illustrated in  FIG. 2A , the UAV  205  and the laser pointer  210  communicate directly with each other using wireless communication. For example, the laser pointer  210  can determine the set of waypoints and communicate the determined set of waypoints to the UAV  205 . Alternatively, or additionally, the laser pointer  210  can provide the UAV  205  with information that the UAV  205  can use to determine the set of waypoints. It should be recognized that direct communication between the UAV  205  and the laser pointer  210  can include one or more signal repeaters between the UAV  205  and the laser pointer  210 . 
     The system illustrated in  FIG. 2B  includes all of the components of the system in  FIG. 2A , and also includes a base station  225 . In one embodiment, base station  225  is interposed in the communication path between the UAV  205  and the laser pointer  210  so that information from the UAV is sent to the laser pointer  210  via base station  225 , and vice-versa. Additionally, or alternatively, the base station can be used to offload processing that is performed by the UAV  205  and/or laser pointer  210 , which will be described in more detail below. For example, the base station  225  can receive information from the laser pointer  210  in order to determine the set of waypoints and the base station  225  can then provide the determined set of waypoints to the UAV  205 . The base station  225  can also include a display, which shows the video captured by the UAV  205 , as well as information about the operation of the UAV  205 , such as flight speed, heading, etc. 
       FIG. 3  is a block diagram of a laser pointer according to an embodiment. The laser pointer  305  includes a processor  310  coupled to a wireless communication interface  315 , a laser emitter  320 , and a pose estimation module  325 . The wireless communication interface  315  can employ any type of wireless communication technique, such as Bluetooth, WiFi, 3G, 4G, 5G, etc. The laser emitter  320  can include any type of emitter that is capable of emitting a laser beam. The pose estimation module  325  estimates the orientation and position of the laser pointer  305 , and as discussed below, can be an inertial measurement unit (IMU). 
       FIGS. 4A and 4B  illustrate specific hardware that can be used for a laser pointer according to embodiments. The hardware arrangement in  FIG. 4A  employs a microcontroller and the hardware arrangement in  FIG. 4B  employs a microprocessor (also referred to as a central processing unit (CPU)). 
     Turning first to  FIG. 4A , the laser pointer includes a microcontroller  405  coupled to a wireless communication interface  410 , an inertial measurement unit (IMU)  415 , and a switched-laser circuit  420 . The microcontroller  405  can be, for example, a 32-bit MCU clocked at 80 MHz and having 2 MB of onboard memory. The wireless communication interface  410  can be, for example, a Wi-Fi communication module, such as an ESP8266 Wi-Fi module, which can communicate with the microcontroller  405  using a serial connection. The inertial measurement unit  415  can be, for example, a 9-axis bno055 inertial measurement unit from Bosch, which can communicate with the microcontroller  405  using an inter-integrated circuit (I2C) bus. The laser emitter is a switched-laser circuit  420 , which can, for example, be an embedded circuit having a laser diode that emits a laser beam and a switch, the actuation of which causes the laser beam to be emitted. As discussed in more detail below, the laser pointer can be implemented using one or multiple laser beams. Implementing the laser pointer with multiple laser beams can involve incorporating multiple laser emitters in the laser pointer. 
     Turning now to  FIG. 4B , this microprocessor implementation of the laser pointer includes a microprocessor-based computer  425 , such as a Raspberry Pi-zero running, for example, a Raspbian Linux operating system (OS), and the robotics operating system (ROS). Those skilled in the art will recognize that ROS has become the standard operating system for robotic systems. The microprocessor-based computer  425  includes a microprocessor (not illustrated), random access memory, and an embedded wireless communication interface, such as a Wi-Fi interface. An inertial measurement unit  430  can be, for example, a 9-axis myAHRS+ inertial measurement unit (IMU), which can communicate with the microcontroller  405  using an inter-integrated circuit (I2C) bus connected to the general-purpose input output (GPIO) of the microprocessor-based computer  425 . The switched-laser circuit  435  can be configured in a similar manner to that discussed above with respect to switched-laser circuit  420 , and can include a single laser diode or multiple laser diodes. 
     It should be recognized that the particular hardware discussed in connection with  FIGS. 4A and 4B  are merely examples of the types of hardware that can be used for the laser pointer. Other types of hardware and configuration of hardware can be employed for the laser pointer so long as the hardware, in connection with software (as applicable), can perform the functions of the laser pointer described herein. 
       FIG. 5  is a block diagram of software modules of a laser pointer according to embodiments. The software modules include three robot operating system (ROS) nodes,  505 ,  510 , and  515 . ROS node  505  handles the inertial measurement unit  120  interface and register reads. ROS  510  handles any necessary data conversion and extraction of physical quantities (e.g., raw measurements and angular rates) and outputs the filtered linear acceleration components of the laser pointer (a x , a y , a z ) and its attitude angles: roll (φ), pitch (θ), and yaw (ψ). ROS node  515  manages the detection of laser switching (i.e., the laser diode being switched on or off) and the feedback laser diode(s). It should be recognized that the software modules illustrated in  FIG. 5  are merely examples of the types of software modules that can be employed and that other software modules can be employed consistent with the present invention. 
       FIG. 6  is a block diagram of a UAV according to embodiments. The UAV  605  includes a processor  610  coupled to a wireless communication interface  615  and an optical system  620 , which includes an imager  625 . The optical system  620  can be any type of optical system, including those operating using stereo imaging, ultrasound imaging, LIDAR imaging, RGBD imaging, and/or the like. The wireless communication interface  615  can employ any type of wireless communication technique, such as Bluetooth, WiFi, 3G, 4G, 5G, etc. 
       FIG. 7  is a block diagram of specific hardware that can be used for a UAV according to an embodiment. The UAV includes, as the processor  610 , a flight control unit  705  coupled to the heading and propulsion control systems  710  and coupled to a companion computer  715 . The flight control unit  705  can be, for example, a MindPX controller running PX4 firmware to handle low-level flight management. The companion computer  715  can be, for example, an Odriod XU4 by Hardkernel running a minimum Linux Ubuntu distribution, and performs high-level control of the UAV and onboard vision sensing of the emitting laser beam. Further, the companion computer  715  includes an integrated wireless interface, which for the Odriod XU4 is a Wi-Fi interface. The companion computer  715  is configured to be the ROS master in a network that includes the UAV, the laser pointer, and the base station (if implemented). The companion computer  715  is connected to the flight control unit  705  over a serial connection utilizing the MAVROS package and MAVLINK library. Thus, in the laser guidance mode of operation, the heading and propulsion system  710  and companion computer guide the UAV toward the destination using a set of waypoints calculated using an orientation of the laser dot that projects the laser beam and based on a projection of the UAV initial position onto the laser beam pointing at the target. Once the laser dot is detected by the imager  720 , the UAV switches to a vision-based control mode, as described in more detail below. 
     The imager  720  is coupled to provide captured images to companion computer  715 . The imager  720  can be, for example, Pixy CMUcam5 programmable camera or oCam 1CGN-U global shutter board camera. The Pixy module provides a standalone image processing device with onboard dual-core processor in which pixel coordinates of the detected target can be acquired by the companion computer  715  and then published to other software nodes existing on the companion computer  715  itself or any device in the network, such as the laser pointer or a base station. While this camera offloads the image processing burden from the companion computer  715 , it prevents the utilization of more advance off-the-shelf image processing libraries such as OpenCV. In contrast, the oCam camera does not perform any internal processing but instead passes the image to the companion computer  315  that can handle more complex computer vision processing. 
     It should be recognized that in  FIG. 7  element  710  corresponds to the heading and propulsion system of the UAV and that the flight control unit  705 , companion computer  715 , and imager  720  are part of the UAV (i.e., either integrated within or attached to the UAV body frame). It should also be recognized that the particular hardware described in connection with  FIG. 7  is merely one example and that the UAV can be implemented consistent with the present invention using other types of hardware. 
       FIGS. 8A and 8B  are block diagrams of software modules for the UAV&#39;s companion computer and flight control unit, respectively, according to embodiments. Turning first to  FIG. 8A , the companion computer software includes a planning node  815 , which plans the UAV&#39;s maneuvers in both the laser guidance mode and the vision-based control mode. In the laser guidance mode, the planning is based on a set of waypoints calculated using an orientation of the laser dot that projects the laser beam and based on a projection of the UAV initial position onto the laser beam pointing at the target. Once the image acquisition node  805  detects the dot of the laser in an acquired image, the UAV switches to the vision-based control mode. Specifically, images acquired from an imager by an image acquisition node  805  are provided to an image processing node  810 , which processes the images (as described in more detail below) and passes extracted data from the processed images to the planning node  815 . In the vision-based control mode, the planning node  815  uses the data extracted from the processed images to control the planning of the UAV&#39;s maneuvers to move from the position proximate to the target position into the target position. The UAV can be equipped with a proximity sensor, such as a LIDAR or ultrasound sensor, to assist in the alignment so that the imager is perpendicular to the target. The results of the planning node  815  are passed to an offboard control node  820 , which uses MAVROS  825  to communicate the results of the planning (i.e., the flight maneuvers for the UAV) to the flight control unit  705 . The planning node  815  also plans the UAV&#39;s maneuvers with respect to the waypoints based on information provided by the laser pointer using MAVROS over a wireless communication channel. As indicated by the symbol on the bottom left-hand side of  FIG. 8A , the companion computer can also include a USB interface for communicating with the flight control unit. It should be recognized, however, that other types of interfaces can be used for communication between the companion computer and the flight control unit. 
     Turning now to  FIG. 8B , the flight control unit software includes a firmware node  830 , which can be, for example, PX4 firmware that supports offboard control via MAVLINK node  835 . The offboard control allows the UAV to be guided using control signals sent to it from an external source, which in this embodiment is the flight control unit  705 . The firmware node  830  receives data from a position control node  840 , power management node  845 , and estimation node  850 . The position control node  840  controls the attitude, altitude, and position of the UAV, which can be implemented using, for example, tunable cascaded-PID control. The power management node  845  is responsible for managing power of the UAV. The estimation node  850  uses filtered sensor data to compute the state of the UAV, including position, velocity, and attitude. As indicated by the symbol on the upper left-hand side of  FIG. 8B , the flight control unit includes a USB interface for communicating with the companion computer. Again, the USB interface can be replaced by any other type of interface for communication between the companion computer and the flight control unit. If the system is implemented with a base station, the flight control unit  705  communicates with it through MAVROS on the companion computer  715 . 
     It should be recognized that the particular software modules illustrated in  FIGS. 8A and 8B  are merely examples of software modules and that other software modules can be used consistent with the present invention. 
       FIG. 9  is a block diagram of a base station according to embodiments. The base station  905  includes a processor  910  coupled to a wireless communication interface  915  and an output device  920 . The wireless communication interface  915  operates using the same type of wireless communication protocol as the UAV and the laser pointer. The processor  910  includes memory for running various software nodes, which will be discussed below in connection with  FIG. 10 . The output device  920  can be, for example, a display that can output information about the flight path of the UAV, as well as display images captured by the UAV&#39;s imager. 
       FIG. 10  is a block diagram of software modules of a base station according to embodiments. The base station software includes an image subscriber/display node  1005  arranged to receive a video stream  1010  from the UAV. The base station software also includes a flight monitoring node  1015 , which monitors the UAV&#39;s flight. If the flight monitoring node  1015  determines that there are abnormal conditions (e.g., the UAV is not following the determined path of waypoints or any other deviation), the flight monitoring node  1015  instructs the emergency landing/kill node  1020 , which can either control the UAV to conduct an emergency landing or completely kill the UAV&#39;s power so that it falls to the ground. The flight monitoring node  1015  and the emergency landing/kill node  1020  communicate with the UAV via MAVROS node  1025 . The base station software also includes a repeater node  1030 , which can forward data and signals received from the UAV to the laser pointer and vice-versa. It should be recognized that the particular software modules described in connection with  FIG. 10  are merely examples and that the base station can be implemented using other software modules consistent with the present invention. 
       FIG. 11  is a flowchart of a method for guiding UAV from an initial position to a target position using a projection of a laser beam on a target according to an embodiment, which will be described in connection with  FIG. 12 . As illustrated in  FIG. 12 , this method involves three coordinate frames, an inertial reference frame (x a , y a , z a ), UAV body frame (x q , y q , z q ), and the laser pointer frame (x p , y p , z p ). The inertial reference frame is fixed and follows a global translational convention. The UAV body frame follows the convention of the flight control unit. The laser pointer frame corresponds to the axes of the inertial measurement unit of the laser pointer. The UAV&#39;s imager is active during this method so that once the laser beam dot is detected in images captured by the UAV&#39;s imager, the UAV can switch to the vision-based control mode. 
     Initially, the UAV  1205  is in laser guidance mode, which as discussed in more detail below involves following a set of calculated waypoints from the UAVs initial position  1210  to a position  1215  proximate to the target  1220  at which the laser beam  1225  is impinging (step  1105 ). The UAV  1205  can be set to laser guidance mode, for example, based on a command sent from the laser pointer  1230  or the base station (if one is implemented). Next, the initial positions of the laser pointer  1230  and the UAV  1205  are determined (step  1110 ). This can be achieved, for example, by initially placing the laser pointer  1230  on or in the same position as the UAV  1205  and then moving the laser pointer  1230  to the position from which it will be operated. Data from the inertial measurement unit of the laser pointer can then be used to determine the three-axis change of position of the laser pointer from its initial position on or in the same position as the UAV to the position from which the laser pointer will be operated. The initial pitch angles of the laser pointer and the UAV are assumed to be sufficiently small (i.e., Θ p     i   ˜0, Θ q     i   ˜0) but their initial headings will initially be different. This difference is referred to as the heading offset, which can be represented by the following equation:
 
Δψ i =ψ p     i   −ψ p     i     (1)
 
     The UAV laser guidance mode involves the calculation of a set of waypoints, which are separated by a step size s. The calculated waypoints define a path that closely follows the laser beam  1225  emitted by the laser pointer  1230  but is offset from the laser beam  1225  by a distance r, which prevents the UAV  1205  from obstructing the laser beam  1225 , which would make it difficult for the operator of the laser pointer  1230  to dot the laser beam  1225  at intended target  1220 . In order to facilitate the calculation of the set of waypoints, five three-dimensional vectors are defined. The first two of the three-dimensional vectors are defined in the inertial global frame (x a , y a , z a ) and are the laser pointer  1230  position (i.e., the position of the operator of the laser pointer  1230 ) {right arrow over (P)} and the UAV position {right arrow over (Q)} in 3D space. Accordingly, part of the determination of the initial positions of the UAV  1205  and the laser pointer  1230  involves calculating the laser pointer  1230  position {right arrow over (P)} and the UAV position {right arrow over (Q)} in 3D space as follows: 
     
       
         
           
             
               
                 
                   
                     
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     The initial UAV position {right arrow over (Q)} can be the position at which the laser pointer  1230  is placed on or in the same position as the UAV  1205  and the initial laser pointer  1230  position {right arrow over (P)} can be calculated using data from the inertial measurement unit of the laser pointer  1230 , which represents the movement of the laser pointer  1230  from the position at which the laser pointer  1230  is placed on or in the same position as the UAV  1205  to the position at which the laser pointer  1230  is operated so as to emit a laser beam  1225  on the target  1220 . 
     The third three-dimensional vector is the laser unit vector {right arrow over (L)}, which is defined in the frame of the laser pointer (x p , y p , z p ) and has a length of one unit. The laser unit vector {right arrow over (L)} always points along the laser beam  1225  towards the target  1220  and is calculated (step  1115 ) using the orientation measurements obtained from the inertial measurement unit embedded in the laser pointer as follows: 
     
       
         
           
             
               
                 
                   
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     In order to calculate the first waypoint, the UAV position is projected onto the laser beam  1225  (step  1120 ), which defines the projected position vector {right arrow over (N)} in the pointing device reference frame (x p , y p , z p ) as follows: 
     
       
         
           
             
               
                 
                   
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     Next, the first waypoint is determined based on the initial positions of the laser pointer  1230  and UAV  1205  and the projection of the UAV position (step  1125 ). Specifically, the laser occlusion offset r is applied to calculate the position vector of the first waypoint {right arrow over (N)} defined as well in the pointing device reference frame as follows: 
     
       
         
           
             
               
                 
                   
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                               P 
                               → 
                             
                             - 
                             
                               N 
                               → 
                             
                           
                           
                              
                             
                               
                                 Q 
                                 → 
                               
                               - 
                               
                                 P 
                                 → 
                               
                               - 
                               
                                 N 
                                 → 
                               
                             
                              
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     The additional waypoints are then determined (step  1130 ). Specifically, each consecutive waypoint is provided by the following equation, which incorporates a simple addition of predefined steps parallel to the laser line.
 
{right arrow over ( W   k )}= {right arrow over (W)}+k s{right arrow over (L)}   (6)
 
     The waypoints are converted to the global inertial frame (x a , y a , z a ), as shown in the following equation.
 
 {right arrow over (W)}   k     global   ={right arrow over ( W   k )}+ {right arrow over (P)}   (7)
 
     The waypoints can be provided to the UAV  1205  all at once or can be provided at a constant frequency to achieve the desired speed until the laser beam impinging on the target or an obstacle has been detected. The determination of the five vectors and the waypoints can be performed by the UAV  1205 , the laser pointer  1230 , and/or the base station (if one is implemented). In one example, the laser pointer  1230  can determine the five vectors and pass this information to the UAV  1205  or the base station (if one is implemented), which then determines the waypoints. If a base station calculates the waypoints, the base station can transmit them directly to the UAV  1205  or to the UAV  1205  via the laser pointer  1230 . In another example, the laser pointer  1230  determines the five vectors and the waypoints and then transmits them to the UAV  1205 , either directly or via the base station (if one is implemented) so that the UAV can determine the set of waypoints using this information. 
     While waypoints are used to control the position of the UAV, its heading command ψ c  is set such that it is pointing toward the target  1220  while compensating for any initial deviation between the UAV heading and that of the pointer, as reflected in the following formula.
 
ψ c =ψ q +ψ p −Δψ i   (8)
 
     Accordingly, the UAV  1205  then moves towards the target  1220  following the determined set of waypoints and the determined heading (step  1135 ). 
     Once the UAV  1205  detects the laser beam dot impinging on the target  1220  using its imager(s), the UAV switches to a vision-based control mode (step  1140 ). This switch occurs in response to detecting the laser beam dot and can occur even if there are additional waypoints that have been provided while in the laser guidance mode. 
     Initially, in the vision-based control mode, the UAV  1205  maintains its current position and starts adjusting its position in body frame (x q ,y q ,z q ) in order to align the camera with so that it can view the laser beam dot impinging on the target  1220  (step  1145 ). This alignment can employ a proximity sensor, such as a LIDAR or ultrasound sensor, so that the camera is perpendicular to the target In inertial frame, the position vector is represented by: 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
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                             a 
                           
                         
                       
                       
                         
                           
                             y 
                             a 
                           
                         
                       
                       
                         
                           
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                             a 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 
                                   ψ 
                                   q 
                                 
                                 ) 
                               
                             
                           
                           
                             
                               - 
                               
                                 sin 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     ψ 
                                     q 
                                   
                                   ) 
                                 
                               
                             
                           
                           
                             0 
                           
                         
                         
                           
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 
                                   ψ 
                                   q 
                                 
                                 ) 
                               
                             
                           
                           
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 
                                   ψ 
                                   q 
                                 
                                 ) 
                               
                             
                           
                           
                             0 
                           
                         
                         
                           
                             0 
                           
                           
                             0 
                           
                           
                             1 
                           
                         
                       
                       ] 
                     
                     ⁡ 
                     
                       [ 
                       
                         
                           
                             
                               x 
                               q 
                             
                           
                         
                         
                           
                             
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                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     During vision-based alignment control, the UAV  1205  remains in its current position θ q ˜0 and φ q ˜0. After the alignment control is completed, the UAV  1205  is moved towards the laser beam dot according to the vision-based control mode. Specifically, using the processed images of the detected laser beam dot, the UAV calculates the data that is used to command the UAV&#39;s translational motion in three-dimensional space and rotational motion in the yaw direction. The roll and pitch of the UAV are automatically handled by the UAV to stay level. 
     In order to assist with the movement of the UAV  1205 , along the path of waypoints and during the vision-based control mode, the UAV  1205  can include an onboard obstacle avoidance sensing and mechanism, such as a stereo vision or ultrasound system. If, during the vision-based control mode, the UAV  1205  does not sense the laser beam  1225  impinging on the target  1220 , the UAV  1205  can, for example, return to a home position or maintain its current position until detecting the laser beam  1225  impinging on the target  1220 . Similarly, if the waypoints are provided to the UAV  1205  at a constant frequency to achieve the desired speed and the UAV  1205  is at the most recently received waypoint and has not received information related to the next waypoint, the UAV  1205  can, for example, return to a home position or maintain its current position until the UAV  1205  receives the next waypoint. 
     The detection of the dot of the laser beam  1225  impinging on the target  1220  involves a three-stage sensing technique. The first stage is to set the exposure of the imager. In order to detect the laser beam, the UAV&#39;s imager is configured to capture with low exposure settings, which reduces reflections and focuses the image on shiny elements. The imager&#39;s exposure can be experimentally adjusted based on the particular imager used in case the initial exposure setting is so low that the UAV cannot distinguish the reflection of the laser beam  1225  on the target  1220  from other light sources in the environment. 
     The second stage involves applying an RGB filter to one or more images captured by the UAV&#39;s imager using a range that differentiates color of the reflection of the laser beam  1225  from target  1220  from surfaces with different colors and finishes. The filtered image includes the laser dot and some light reflection noise depending on the target orientation. The third stage involves applying a Hough circle transform to the filtered image to search for and detect the correct circle. The range of circle radii can be computed offline and mapped to a lookup table that is a function of the estimated distance between the source and the target. If the laser pointer includes multiple laser emitters, the UAV can include a single imager to control the movement during the vision-based control mode. If the laser pointer includes only a single laser emitter, the UAV can have two imagers (i.e., a stereo imager) in order to control the movement during the vision-based control mode. Alternatively, data from one imager can be fused with a proximity measurement from the target and the pose estimation node to align with the target. As a further alternative, when there is a single laser emitter, a single imager can be used to control the movement during the vision-based control mode. 
     Implementing the laser pointer so that it emits multiple laser beams can improve the operation of the UAV  1205  in the vision-based control mode. For example, the laser pointer can include three laser emitters that are spaced apart in an equilateral triangle and configured so that the corresponding emitted laser beams propagate through space in a parallel arrangement. Assuming the laser pointer is perpendicular to the target, the spots on the target from the three laser beams will form an equilateral triangle having approximately the same spacing between the laser points as the spacing between the laser emitters in the laser pointer. The UAV can then use a single imager to control both its orientation with respect to the target and distance from the target by correlating a number of pixels between the laser dots to an actual distance between the laser dots. In this case, the UAV&#39;s processor can include a correlation value between distance between adjacent pixels and actual distance in a captured image, which can be configured, for example, prior to implementation of the UAV in the system. 
     Specifically, referring now to  FIGS. 13A-13D , assume that the laser pointer includes three laser emitters separated by a distance D 1 , as illustrated in  FIG. 13A . When the UAV is perpendicularly facing the target, the imager of the UAV should capture an image with the three laser dots being separated by the same number of pixels in the captured image. If, however, the UAV is not perpendicularly facing the target, the three laser dots will not form an equilateral triangle and will not be separated by the same number of pixels, as illustrated in the examples of  FIGS. 13B and 13C . 
     In  FIG. 13B , the distance D 1  between the laser dots  1320  and  1325  is the same as the distance D 1  between the corresponding laser emitters  1305  and  1310 . However, the distance D 2  between laser dots  1320  and  1330  is greater than the distance D 1  between laser emitters  1305  and  1315 , and the distance D 3  between laser dots  1325  and  1330  is less than the distance D 1  between laser emitters  1310  and  1315 , which indicates that the UAV&#39;s imager is not perpendicular to the target, i.e., the left side of the imager is farther from the target than the right side of the imager. In  FIG. 13C , the distance D 1  between the laser dots  1320  and  1325  is the same as the distance D 1  between the corresponding laser emitters  1305  and  1310 . However, the distance D 4  between laser dots  1320  and  1330  is less than the distance D 1  between laser emitters  1305  and  1315 , and the distance D 5  between laser dots  1325  and  1330  is greater than the distance D 1  between laser emitters  1310  and  1315 , which indicates that the UAV&#39;s imager is not perpendicular to the target, i.e., the right side of the imager is farther from the target than the left side of the imager. The UAV&#39;s processor can use this information to adjust its orientation (i.e., heading) with respect to the target so that the three laser dots form an equilateral triangle, which results in the UAV&#39;s imager being perpendicular to the target. 
     Turning now to  FIG. 13D , which illustrates the laser dots  1320 - 1330  being arranged in an equal lateral triangle having sides with a distance between the laser dots of D 6 . Because the UAV&#39;s imager captures an image in which the three laser dots form an equilateral triangle, the UAV&#39;s imager is oriented perpendicular to the target. In this example, however, the distances D 6  between the laser dots is smaller than the distances D 1  between the laser emitters. This indicates that the UAV&#39;s imager is farther away from the target than desired because when the UAV&#39;s imager is at the correct target position, the number of pixels for each side of the equilateral triangle formed by laser dots  1320 - 1330  should approximately correlate to the same as between the laser emitters  1305 - 1315 . It should be recognized that in practice the distances D 6  will be slightly less than the distances D 1  so that there is sufficient spacing between the target and the UAV&#39;s imager. Determining the amount of spacing that is sufficient can involve, for example, the minimum focal distance of the UAV&#39;s imager (the sufficient spacing should not be less than the minimum focal distance of the UAV&#39;s imager), a distance that ensures that the UAV does not touch the target (because the distance between the UAV&#39;s imager and portions of the UAV&#39;s body can be different), etc. 
     If the laser pointer is not oriented perpendicular to the target, the laser pointer can determine the angle between the laser emitters and the target and convey this information to the UAV. The UAV&#39;s processor can then use this angular information to determine the length of the sides of the triangle formed by the laser dots  1320 - 1330  when the UAV&#39;s imager is perpendicular to the target and use this information to adjust the orientation of the UAVs imager with respect to the target. The UAV can include an onboard proximity sensor to assist in determining the nominal reflected pattern from the target, which should be the final view when the UAV reaches its final position. 
     Accordingly, once the UAV  1205  confirms that it is in the correct position, based on the three-stage sensing technique, the UAV  1205  continues to capture images of the target  1220 , which can be used for a variety of purposes, such as inspecting the target. 
     In the discussion above, the laser beam forms a dot on the target. The term dot is intended to cover various shapes of the laser beam impinging upon the target or any other surface. Thus, for example, laser beam shaping can be implemented so that the laser beam impinging on the target forms a particular shape, such as a cross-hair. The skew in the particular shape can be used to infer direction similar to the three laser embodiment described above. 
     It should be recognized that the various devices of the system can include additional hardware than what was discussed above. Further, it should be recognized that the software of the various devices can include additional software than what was described above. 
     Although exemplary embodiments have been illustrated in connection with a UAV using a copter-based system for movement, the present invention can employ a UAV having any type of system for moving the UAV as disclosed herein. 
     The disclosed embodiments provide systems and methods for guiding UAV from an initial position to a target position using a projection of a laser beam on a target according to an embodiment. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
     Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
     This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.