Patent Publication Number: US-10760919-B2

Title: Evaluating line-of-sight measurements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/767,247 entitled “EVALUATING LINE-OF-SIGHT MEASUREMENTS” and filed on Nov. 14, 2018 for Ryan Lamoreaux, which is incorporated here by reference. 
    
    
     FIELD 
     The subject matter disclosed herein relates to evaluating line-of-sight measurements. 
     BACKGROUND 
     Line-of-Sight measurements to known landmarks may be needed to improve navigation information in GPS-denied environments. 
     BRIEF SUMMARY 
     A method for evaluating line-of-sight measurements is disclosed. The method measures a line-of-sight measurement with an imager. The method further calculates an information metric based on the line-of-sight measurement. The information metric as a function of imager pixel measurement noise and a relative position vector for an imager frame aligned with a focal plane frame for the imager. The method evaluates navigation information using the information metric. An apparatus and computer program product also perform the functions of the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only some embodiments and are not therefore to be considered to be limiting of scope, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1A  is a perspective drawing of one embodiment of a vehicle and vehicle frame; 
         FIG. 1B  is a perspective drawing of one embodiment of a vehicle  1  frame; 
         FIG. 1C  is a perspective drawing of one embodiment of a vehicle  2  frame; 
         FIG. 1D  is a perspective drawing of one embodiment of a body frame; 
         FIG. 1E  is a perspective drawing of one embodiment of an imager frame; 
         FIG. 1F  is a perspective drawing of one embodiment of a focal plane and focal plane frame; 
         FIG. 1G  is a schematic block diagram of one embodiment of a navigation device; 
         FIG. 1H  is a perspective drawing of one embodiment of an inertial frame. 
         FIG. 2A  is a perspective drawing of one embodiment of a navigation environment; 
         FIG. 2B  is a perspective drawing of one alternate embodiment of a navigation environment; 
         FIG. 3  is a schematic block diagram of one embodiment of navigation data; 
         FIG. 4  is a schematic block diagram of one embodiment of a computer; 
         FIG. 5  is a schematic flow chart diagram of one embodiment of a line-of-sight measurement evaluation method; 
         FIG. 6A  is a perspective drawing illustrating one embodiment of establishing a landmark; and 
         FIG. 6B  is a perspective drawing illustrating one embodiment of modifying a route. 
     
    
    
     DETAILED DESCRIPTION 
     As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, method or program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments may take the form of a program product embodied in one or more computer readable storage devices storing machine readable code, computer readable code, and/or program code, referred hereafter as code. The storage devices may be tangible, non-transitory, and/or non-transmission. The storage devices may not embody signals. In a certain embodiment, the storage devices only employ signals for accessing code. 
     Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom Very Large Scale Integration (VLSI) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. 
     Modules may also be implemented in code and/or software for execution by various types of processors. An identified module of code may, for instance, comprise one or more physical or logical blocks of executable code which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module. 
     Indeed, a module of code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different computer readable storage devices. Where a module or portions of a module are implemented in software, the software portions are stored on one or more computer readable storage devices. 
     Any combination of one or more computer readable medium may be utilized. The computer readable medium may be a computer readable storage medium. The computer readable storage medium may be a storage device storing the code. The storage device may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. 
     More specific examples (a non-exhaustive list) of the storage device would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), 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. 
     Code for carrying out operations for embodiments may be written in any combination of one or more programming languages including an object oriented programming language such as Python, Ruby, R, Java, Java Script, Smalltalk, C++, C sharp, Lisp, Clojure, PHP, or the like, and conventional procedural programming languages, such as the “C” programming language, or the like, and/or machine languages such as assembly languages. The 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). 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise. The term “and/or” indicates embodiments of one or more of the listed elements, with “A and/or B” indicating embodiments of element A alone, element B alone, or elements A and B taken together. 
     Furthermore, the described features, structures, or characteristics of the embodiments may be combined in any suitable manner. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of an embodiment. 
     Aspects of the embodiments are described below with reference to schematic flowchart diagrams and/or schematic block diagrams of methods, apparatuses, systems, and program products according to embodiments. It will be understood that each block of the schematic flowchart diagrams and/or schematic block diagrams, and combinations of blocks in the schematic flowchart diagrams and/or schematic block diagrams, can be implemented by code. This code may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks. 
     The code may also be stored in a storage device that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the storage device produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks. 
     The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     The schematic flowchart diagrams and/or schematic block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of apparatuses, systems, methods and program products according to various embodiments. In this regard, each block in the schematic flowchart diagrams and/or schematic block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions of the code 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. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more blocks, or portions thereof, of the illustrated Figures. 
     Although various arrow types and line types may be employed in the flowchart and/or block diagrams, they are understood not to limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and/or flowchart diagrams, and combinations of blocks in the block diagrams and/or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and code. 
     Lamoreaux, Ryan D. “Impacts of Distributions and Trajectories on Navigation Uncertainty Using Line-of-Sight Measurements to Known Landmarks in GPS-Denied Environments” is incorporated herein by reference. 
     The description of elements in each figure may refer to elements of proceeding figures. Like numbers refer to like elements in all figures, including alternate embodiments of like elements. 
       FIG. 1A  is a perspective drawing of one embodiment of a vehicle  100  and vehicle frame  170 . The vehicle  100  may be an autonomous vehicle  100  and/or a piloted vehicle  100 . The vehicle  100  includes one or more imagers  110 . In the depicted embodiment, the vehicle  100  is a flying drone. The vehicle  100  may also be an aircraft, a land vehicle, and/or a water vehicle. The vehicle  100  has a vehicle frame    170 . As used herein, frame refers to a coordinate frame of reference. The vehicle frame  170  includes    171 ,    173  and    175  coordinates. As used herein, relative north is along a positive x-axis, relative east is along a positive y-axis, and relative down is along a positive z-axis. 
     The vehicle  100  may operate in an environment where Global Positioning System (GPS) information is unavailable. As a result, the vehicle  100  may navigate using inertial navigation to generate navigation information. Line-of-sight measurements to known landmarks may be needed to improve the navigation information in GPS-denied environments as the vehicle  100  navigates the environment. The embodiments evaluate navigation information based on line-of-sight measurements. The navigation information may be from inertial navigation and/or from the line-of-sight measurement. In one embodiment, the embodiments calculate an information metric based on the line-of-sight measurement. The information metric may be used to evaluate the navigation information. In addition, the vehicle  100  may enhance the navigation information based on the information metric. As a result, the vehicle  100  may more efficiently use the navigation information and navigate in the environment. 
       FIG. 1B  is a perspective drawing of one embodiment of a vehicle  1  frame    180 . The vehicle  1  frame  180  is the vehicle frame  170  rotated by angle Ψ  177  about the    175  coordinate axis. The vehicle  1  frame  180  includes    181 ,    183  and    185  coordinates. 
       FIG. 1C  is a perspective drawing of one embodiment of a vehicle  2  frame    190 . The vehicle  2  frame  190  is the vehicle  1  frame  180  rotated by angle θ  179  about the    183  coordinate axis. The vehicle  2  frame  190  includes    191 ,    193  and    195  coordinates. 
       FIG. 1D  is a perspective drawing of one embodiment of a body frame B  290 . The body frame  290  is the vehicle  2  frame  190  rotated by angle φ  187  about the    191  coordinate axis. The body frame  290  includes    291 ,    293  and    295  coordinates. 
       FIG. 1E  is a perspective drawing of one embodiment of an imager frame    130 . The imager frame  130  is the body frame  290  rotated by 90 degrees about the    293  coordinate axis. The imager frame  130  includes    131 ,    133  and    135  coordinates. 
       FIG. 1F  is a perspective drawing of one embodiment of a focal plane  140  and focal plane frame    120  for the imager  110 . In the depicted embodiment, the imager frame  130  is located at a focal point  147  for the imager  110 . The focal plane  140  includes an origin  141  a focal length  145  from the focal point  147  along the    131  coordinate axis. The focal plane frame    120  includes a    125  coordinate that is parallel to    131 . In one embodiment,    125  is colinear with    131 . The imager plane  140  is aligned with the focal plane frame    120  for the imager  110 . The imager  110  images a landmark  150  at an imager pixel  143  in the imager plane  140 . A relative position vector {circumflex over (r)}  151  connects the focal point  147  to the landmark  150  via the imager pixel  143 . 
     Equation 1 shows the calculation of angular relationships c 11.33  as functions of angle Ψ  177 , angle θ  179 , and angle φ  187 . 
     
       
         
           
             
                 
             
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       FIG. 1G  is a schematic block diagram of one embodiment of a navigation device  101 . The navigation device  101  may be disposed in the vehicle  100 . In the depicted embodiment, the navigation device  101  includes a computer  105 , the one or more imagers  110 , and an inertial measurement unit  115 . The inertial measurement unit  115  may include one or more accelerometers and/or gyroscopes. The inertial measurement unit  115  may estimate the navigation information and/or a position estimation as a position and/or orientation of the vehicle  100 . 
       FIG. 1H  is a perspective drawing of one embodiment of an inertial frame    160 . The inertial frame    160  is the frame of the inertial measurement unit  115 . The inertial frame    160  includes    161 ,    163  and    165  coordinates. 
       FIG. 2A  is a perspective drawing of one embodiment of a navigation environment  230 . In the depicted embodiment, the navigation device  101  is within buildings  225  of the city. The navigation device  101  may be disposed on the vehicle  101 , although for simplicity the vehicle  101  is not shown. The buildings  225  may block GPS signals, creating a GPS-denied environment. In the depicted embodiment, the navigation device  101  makes a line-of-sight measurement  201  to a landmark  150  on a building  225 . The embodiments evaluate the line-of-sight measurement  201  using the information metric to improve navigation within the environment  230 . For example, the line-of-sight measurement  201  may be used to generate navigation information or correct a position estimate. The information metric may evaluate the navigation information and determine how best to update the position estimate using the navigation information. 
       FIG. 2B  is a perspective drawing of one alternate embodiment of the navigation environment  230 . In the depicted embodiment, the navigation device  101  is flying on the vehicle  110 , not shown, toward a destination within the city  220 . The navigation device  101  makes another line-of-sight measurement  201  to a landmark  150  in order to improve navigation information. The landmark  150  may be a peak of a mountain  235 . Navigation information may be generated from the line-of-sight measurement  201 . The embodiments evaluate the line-of-sight measurement  201  using the information metric to improve navigation within the environment  230 . The information metric may evaluate the navigation information and determine how best to update the position estimate using the navigation information. 
       FIG. 3  is a schematic block diagram of one embodiment of navigation data  300 . The navigation data  300  may be organized as a data structure in a memory. In the depicted embodiment, the navigation data  300  includes the information metric  301 , the navigation information  303 , the measurement criteria  305 , the position estimation  307 , imager pixel measurement noise  309 , and a measurement noise matrix  311 . 
     The navigation information  303  may express the position and/or orientation of the vehicle  100  based on the line-of-sight measurement  201  and/or the position estimation  307 . The navigation information  303  may comprise a position matrix in the vehicle frame    170  and/or inertial frame    160 . The information metric  301  may be used to evaluate the navigation information  303  as will be described hereafter. 
     The measurement criteria  305  may be used to evaluate the information metric  301 . The position estimation  307  may be a position and/or orientation of the vehicle  100  as determined by the inertial measurement unit  115 . The position estimation  307  may comprise a position matrix in the vehicle frame    170  and/or inertial frame    160 . 
     The imager pixel measurement noise σ δλ   309  may specify average pixel measurement noise for the imager  110 . In one embodiment, the measurement noise is assumed to be the same along each coordinate axis  121 / 123 / 125 . The measurement noise matrix    311  may express the imager pixel measurement noise  309  in the focal plane frame  120 . 
       FIG. 4  is a schematic block diagram of one embodiment of the computer  105 . In the depicted embodiment, the computer  105  includes a processor  405 , a memory  410 , and communication hardware  415 . The memory  410  may include a semiconductor storage device, hard disk drive, an optical storage device, a micromechanical storage device, or combinations thereof. The memory  410  may store code. The processor  405  may execute the code. The communication hardware  415  may communicate with other devices. 
       FIG. 5  is a schematic flow chart diagram of one embodiment of a line-of-sight measurement evaluation method  500 . The method  500  evaluates the navigation information  303  using the information metric  301 . The method  500  may be performed by the navigation device  101 , the computer  105 , and/or the processor  405 . 
     The method  500  starts, and in one embodiment, the imager  110  measures  501  the line-of-sight measurement  201  to the landmark  150 . The line-of-sight measurement  201  may be in the imager frame    130 . The line-of-sight measurement  201  may generate the imager pixel  143  representing the landmark  150 . 
     The processor  405  may calculate  503  the information metric  301  based on the line-of-sight measurement  201 . The information metric  301  may be a function of the imager pixel measurement noise  309  and the relative position vector  151 . 
     In one embodiment, the information metric  301  is calculated  503  using Equation 2, wherein σ δλ  is the imager pixel measurement noise  309  of the imager pixel  143 , c 11.33  are from Equation 1, 
               r   ^         T   ℱ     ,   n     𝒥         
is the relative position vector  151  in the relative north direction of the observed landmark  150  with respect to the vehicle  100  expressed in the imager frame    130 ,
 
               r   ^         T   ℱ     ,   e     𝒥         
is the relative position vector  151  in the relative east direction of the observed landmark  150  with respect to the vehicle  100  expressed in the imager frame    130 ,
 
               r   ^         T   ℱ     ,   d     𝒥         
is the relative position vector  151  in the relative down direction of the observed landmark  150  with respect to the vehicle  100  expressed in the imager frame    130 , and d is a distance of the relative position vector  151 .
 
     
       
         
           
             
               
                 
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     In one embodiment, the information metric  301  is expressed as a trace as shown in Equation 3, wherein the Trace is a sum of diagonal terms, Λ is a partial derivative of the line-of-sight measurement  201  with respect to the line-of-sight measurement  201  and R is the measurement noise matrix  311 .
 
IM=Trace(Λ T   R   −1 Λ)  Equation 3
 
     In one embodiment, if the vehicle  100  has an attitude of zero such as during flat, level flight, and is pointing relative north, the information metric IM  301  may be calculated  503  using Equation 4. 
     
       
         
           
             
               
                 
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     The processor  405  may evaluate  505  the navigation information  303  using the information metric  301 . In one embodiment, the processor  405  compares the information metric  301  to the measurement criteria  305 . 
     The processor  405  further determines  507  whether the information metric  301  satisfies the measurement criteria  305 . If the measurement criteria  305  is satisfied, the processor  405  may update  513  the position estimation  307  with the navigation information  303  from the line-of-sight measurement  201  and the method  500  ends. The line-of-sight measurement  201  and/or navigation information  303  may be applied to the position estimation  307  using an extended Kalman filter. In one embodiment, the information estimate  307  is corrected to conform with the line-of-sight measurement  201 . 
     If the measurement criteria  305  is not satisfied, the processor  405  may enhance  509  the navigation information  303 . In one embodiment, the processor  405  measures additional line-of-sight measurements  201  to the first landmark  150  and/or to other landmarks  150  to enhance  509  the navigation information  303 . 
     In one embodiment, the processor  405  modifies a route of the vehicle  100  to include additional landmarks  150  to enable additional line-of-sight measurements  201  for enhancing the navigation information  303 . For example, the route may be modified to pass nearer to additional landmarks  150  as will be shown hereafter in  FIG. 6B . 
     In one embodiment, the processor  405  may direct establishing  511  a new landmark  150  in response to the information metric  301  not satisfying a not measurement criteria  305  and the method  500  ends. The new landmark  150  may be established at a location such that the line-of-sight measurement  201  of the new landmark  150  generates an enhanced information metric  301  that satisfies the measurement criteria  305 . For example, the processor  405  may calculate where to establish  511  the new landmark  150  so that the line-of-sight measurement  201  to the new landmark  500  results in an information metric  301  that satisfies the measurement criteria  305 . 
       FIG. 6A  is a perspective drawing illustrating one embodiment of establishing a new landmark  150 . In the depicted embodiment, the navigation device  101  measures one or more line-of-sight measurements  201  to at least one landmark  150  in an environment  230 . The processor  405  may further calculate the information metric  301  for each line-of-sight measurement  201 . If the new landmark  150  satisfies the measurement criteria  305 , the processor  405  may record and/or publish the new landmark  150 . The new landmark  150  may subsequently be used for navigation, resulting in improved position estimations  307  from line-of-sight measurements  201  to the new landmark  150 . 
       FIG. 6B  is a perspective drawing illustrating one embodiment of modifying a route  601 . In the depicted embodiment, a first route  601   a  is shown for the vehicle  100 . If an information metric  301  calculated for a first landmark  150   a  does not satisfy the measurement criteria  305 , the first route  601   a  may be modified to a second route  601   b  that passes nearer to additional landmarks  150   b/c  that may be used to generate additional navigation information  303 . As a result, the position estimation  307  for the vehicle  100  may be improved. 
     The embodiments calculate the information metric  301  based on the line-of-sight measurement  201  and evaluate navigation information  303  using the information metrics  301 . As a result, a navigation device  101  may confidently update the position estimation  307  with the line-of-sight measurement  201  if the information metric  301  satisfies the measurement criteria  305 . However, if the information metric  301  does not satisfy the measurement criteria  305 , the navigation device  101  may enhance the navigation information  303 , establish a new landmark  150 , and/or modify a route  601  two include additional landmarks  150 . Thus, the efficiency and efficacy of the navigation device  101  and the computer  105  therein is enhanced. 
     Embodiments may be practiced in other specific forms. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.