Patent Publication Number: US-2022230391-A1

Title: Display system and display method

Description:
TECHNICAL FIELD 
     The present invention relates to a display system and a display method. 
     Priority is claimed on Japanese Patent Application No. 2019-103166, filed May 31, 2019, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In a case where a work machine is remotely operated, a displayed image is two-dimensional in an operation using an image viewed from an operator of the work machine, and accordingly, the sense of perspective is poor. For this reason, it is difficult to recognize the distance between a work target and the work machine, and there is a possibility that work efficiency is degraded. Even in a case where the operator of the work machine operates work equipment, it may be difficult to recognize the distance between the work equipment and the work target depending on the level of skill of the operator, and there is a possibility that work efficiency is degraded. An example of an image display system for solving such a problem is described in Patent Document 1. The image display system described in Patent Document 1 includes an imaging device that is attached to a work machine provided with work equipment having a work tool, a posture detection device that detects a posture of the work equipment, a distance detection device that obtains information regarding a distance to a work target of the work machine, and a processing device that generates an image of a portion corresponding to the work tool on the work target facing the work tool using information regarding a position of the work tool obtained using the posture of the work equipment and information regarding a position of the work target obtained from information regarding the distance obtained by the distance detection device and combines the generated image with an image of the work target captured by the imaging device to display a combined image on a display device. With the image display system described in Patent Document 1, it is possible to suppress degradation of work efficiency in working using the work machine provided with the work equipment having the work tool. 
     In the image display system described in Patent Document 1, the processing device generates line images along a surface of the work target using information regarding the position of the work target, combines the line images and the image of the work target, and displays a combined image on a display device. Since the line images are displayed along the shape of a terrain (work target) to be worked, a sense of distance on a terrain surface is easily recognized, and a sense of perspective is easily recognized. 
     Patent Document 2 describes a configuration for creating a color elevation map expressed by gradation colors in which a color is allocated to each elevation value such that the color transitions depending on the elevation value. According to the configuration described in Patent Document 2, it is possible to color line images with the gradation colors depending on the elevation. 
     CITATION LIST 
     Patent Documents 
     [Patent Document 1] 
     Japanese Unexamined Patent Application, First Publication No. 2016-160741 
     [Patent Document 2] 
     Japanese Unexamined Patent Application, First Publication No. 2007-048185 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a case where the configuration described in Patent Document 1 and the configuration described in Patent Document 2 are combined, the line images along the surface of the work target can be colored with the gradation colors depending on the elevation, and thus, ruggedness or the like of the surface of the work target is more easily understood. Note that, in a case where change in color is decided with reference to a horizontal plane, for example, as shown in  FIG. 21 , there is a problem in that, while a work machine  400  is climbing a slope ground  401 , ruggedness  402  in the slope ground  401  cannot be color-coded and displayed.  FIG. 21  is a schematic view showing an example of color-coding the slope ground  401 , on which the work machine  400  travels or performs work, depending on an elevation. In  FIG. 21 , change in density of hatching indicates change in coloring. Alternatively, in a case where coloring is changed depending on the elevation, there is a problem in that all small ruggedness are colored with the same color when a difference in elevation of a target range is large. 
     The invention has been accomplished in view of the above-described situation, and an object of the invention is to provide a display system and a display method capable of solving the above-described problem. 
     Solution to Problem 
     To solve the above-described problem, an aspect of the invention provides a display system for a work machine including an acquisition unit configured to acquire three-dimensional data of a plurality of measurement points measured by a distance detection device mounted in a work machine, a conversion unit configured to convert the three-dimensional data into a vehicle body coordinate system defined in association with a vehicle body of the work machine, an image generation unit configured to generate a reference image representing a three-dimensional shape of a terrain based on the three-dimensional data converted into the vehicle body coordinate system, and a display processing unit configured to display the reference image on an image captured by an imaging device in a superimposed manner. The image generation unit decides a display form of the reference image at a position of the reference image corresponding to each measurement point depending on a distance of the measurement point in a normal direction with respect to a ground surface of the work machine. 
     Advantageous Effects of Invention 
     According to the aspect of the invention, since it is possible to change the display form of a target on which the work machine travels or performs work, depending on the distance in the normal direction with respect to the ground surface of the work machine, for example, it is possible to make a display form of ruggedness or the like present on a slope ground different from a display form of a periphery. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing an image display system for a work machine and a remote operation system for a work machine according to an embodiment. 
         FIG. 2  is a side view schematically showing a bulldozer that is the work machine according to the embodiment. 
         FIG. 3  is a diagram showing a control system of a bulldozer that is the work machine according to the embodiment. 
         FIG. 4  is a block diagram showing a functional configuration example of a processing unit  51 P shown in  FIG. 1 . 
         FIG. 5  is a diagram showing a coordinate system in the image display system and the remote operation system according to the embodiment. 
         FIG. 6  is a rear view schematically showing the bulldozer. 
         FIG. 7  is a diagram showing a coordinate system of an imaging device and a distance detection device. 
         FIG. 8  is a flowchart of a control example that is executed by the image display system and the remote operation system. 
         FIG. 9  is a diagram showing processing shown in  FIG. 8 . 
         FIG. 10  is a diagram showing the processing shown in  FIG. 8 . 
         FIG. 11  is a diagram showing the imaging device, the distance detection device, and a work target. 
         FIG. 12  is a diagram showing an occupied area. 
         FIG. 13  is a diagram showing information regarding a shape of the work target with an occupied area removed. 
         FIG. 14  is a diagram showing an image indicating a position of a blade on the work target. 
         FIG. 15  is a diagram showing an image indicating the position of the blade on the work target. 
         FIG. 16  is a diagram showing an image indicating the position of the blade on the work target. 
         FIG. 17  is a diagram showing a lattice image that is a reference image. 
         FIG. 18  is a diagram showing the lattice image as a reference image. 
         FIG. 19  is a diagram showing an image for work. 
         FIG. 20  is a diagram showing an image for work. 
         FIG. 21  is a diagram showing a problem to be solved by the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A mode (embodiment) for carrying out the invention will be described in detail referring to the drawings. In the drawings, the same or corresponding components are represented by the same reference numerals, and description thereof will not be repeated. 
     &lt;Outline of Image Display System of Work Machine and Remote Operation System of Work Machine&gt; 
       FIG. 1  is a diagram showing an image display system  100  for a work machine (display system) and a remote operation system  101  for a work machine according to the embodiment. The image display system  100  for a work machine (hereinafter, appropriately referred to as an image display system  100 ) images a work target of a bulldozer  1100 , and more specifically, a terrain surface as a target of work by work equipment  1130  provided in the bulldozer  1100 , that is, a work target WA and a blade  1132  as a work tool with an imaging device  19  and displays the obtained images on a display device  52  when the operator remotely operates the bulldozer  1100  as the work machine. In this case, the image display system  100  displays an image  69  for work, for example, including an image  68  of the work target WA captured by the imaging device  19 , a lattice image  65 , and an image  60  for indicating a position of the blade  1132  on the work target WA, on the display device  52 . Here, the lattice image  65  is an aspect of an “image representing a three-dimensional shape of a terrain surface (terrain)” (hereinafter, also referred to as a “reference image”). The reference image can be composed using, for example, a plurality of point images, a plurality of line images, a lattice image consisting of plurality of line images, or the like. 
     The image display system  100  includes the imaging device  19 , a posture detection device  32 , a distance detection device  20 , and a processing device  51 . The remote operation system  101  for a work machine (hereinafter, appropriately referred to as a remote operation system  101 ) includes the imaging device  19 , the posture detection device  32 , the distance detection device  20 , a work equipment control device  27 , the display device  52 , the processing device  51 , and an operation device  53 . In the embodiment, the imaging device  19 , the posture detection device  32 , and the distance detection device  20  of the image display system  100  are provided in the bulldozer  1100 , and the processing device  51  is provided in the facility  50 . The facility  50  is a facility that remotely operates the bulldozer  1100  or manages the bulldozer  1100 . In the embodiment, the imaging device  19 , the posture detection device  32 , the distance detection device  20 , and the work equipment control device  27  of the remote operation system  101  are provided in the bulldozer  1100 , and the display device  52 , the processing device  51 , and the operation device  53  are provided in the facility  50 . 
     The processing device  51  of the image display system  100  includes a processing unit  51 P, a storage unit  51 M, and an input-output unit  51 IO. The processing unit  51 P is, for example, a processor, such as a central processing unit (CPU). The storage unit  51 M is, for example, random access memory (RAM), read only memory (ROM), a hard disk drive, a storage device, or a combination thereof. The input-output unit  51 IO is an interface circuit for connecting the processing device  51  and external equipment. In the embodiment, the display device  52 , the operation device  53 , and a communication device  54  as the external equipment are connected to the input-output unit  51 IO. The external equipment that is connected to the input-output unit  51 IO is not limited thereto. 
     The processing device  51  generates the lattice image  65  as the reference image and an image  60  of a portion corresponding to the blade  1132  on the work target WA facing the blade  1132  using information regarding a position of blade  1132  as a work tool obtained using a posture of the work equipment  1130  and information regarding a position of the work target WA obtained from information regarding a distance obtained by the distance detection device  20  with the imaging device  19  as a reference. Then, the processing device  51  combines the generated images  65  and  60  and the image  68  of the work target WA captured by the imaging device  19  and displays a combined image on the display device  52 . The work target WA is a surface on which the work equipment  1130  of the bulldozer  1100  performs work, such as excavation or ground leveling. The display of the image  60  may be omitted. 
     The display device  52  is, for example, but is not limited to, a liquid crystal display or a projector. The communication device  54  is provided with an antenna  54 A. The communication device  54  performs communication with a communication device  25  provided in the bulldozer  1100  to acquire information regarding the bulldozer  1100  or to transmit information to the bulldozer  1100 . 
     The operation device  53  has a left operation lever  53 L that is provided on a left side of the operator, a right operation lever  53 R that is provided on a right side of the operator, and a brake pedal and a decelerator pedal (not shown). The right operation lever  53 R is operated to set a movement amount of a lifting operation or a lowering operation of the blade  1132 . The right operation lever  53 R receives the lowering operation through an operation being tilted forward and receives the lifting operation through an operation being tilted rearward. The left operation lever  53 L is operated to set a moving direction of a traveling device  1120 . The left operation lever  53 L receives a forward movement operation through an operation being tilted forward and receives a rearward movement operation through an operation being tilted rearward. The left operation lever  53 L receives a left swing operation through an operation being tilted to the left and receives a right swing operation through an operation being tilted to the right. The brake pedal (not shown) is operated to brake the traveling device  1120 . The decelerator pedal (not shown) is operated to reduce a rotation speed of the traveling device  1120 . 
     Operation amounts of the left operation lever  53 L and the right operation lever  53 R are detected by, for example, a potentiometer, a Hall IC, or the like, and the processing device  51  generates a control signal for controlling an electromagnetic control valve based on detection values. This signal is sent to the work equipment control device  27  through the communication device  54  of the facility  50  and the communication device  25  of the bulldozer  1100 . The work equipment control device  27  controls the work equipment  1130  by controlling the electromagnetic control valve based on the control signal. The electromagnetic control valve will be described below. 
     The processing device  51  acquires an input on at least one of the left operation lever  53 L and the right operation lever  53 R and generates a command for operating the work equipment  1130  or the like. The processing device  51  transmits the generated command to the communication device  25  of the bulldozer  1100  through the communication device  54 . The work equipment control device  27  provided in the bulldozer  1100  acquires the command from the processing device  51  through the communication device  25  and operates the work equipment  1130  or the like in association with the command. 
     The bulldozer  1100  includes the communication device  25 , the work equipment control device  27 , the posture detection device  32 , the imaging device  19 , the distance detection device  20 , antennas  21  and  22 , and a global position calculation device  23 . The work equipment control device  27  controls the work equipment  1130  or the like. The communication device  25  is connected to an antenna  24  and performs communication with the communication device  54  provided in the facility  50 . The posture detection device  32  detects a posture of at least one of the work equipment  1130  and the bulldozer  1100 . The imaging device  19  is attached to the bulldozer  1100  to image the work target WA. The distance detection device  20  obtains information regarding a distance between a predetermined position of the bulldozer  1100  and the work target WA. The antennas  21  and  22  receive radio waves from positioning satellites  200 . The global position calculation device  23  obtains global positions of the antennas  21  and  22 , that is, positions in global coordinates using radio waves received by the antennas  21  and  22 . 
     &lt;Overall Configuration of Bulldozer  1100 &gt; 
       FIG. 2  is a side view schematically showing the bulldozer  1100  that is the work machine according to the embodiment. The bulldozer  1100  includes a vehicle body  1110 , the traveling device  1120 , the work equipment  1130 , and a cab  1140 . 
     The traveling device  1120  is provided in a lower portion of the vehicle body  1110 . The traveling device  1120  includes crawlers  1121 , sprockets  1122 , and the like. The sprockets  1122  are driven to rotate the crawlers  1121 , and accordingly, the bulldozer  1100  travels. A rotation sensor  1123  is provided in a rotation axis of the sprocket  1122 . The rotation sensor  1123  measures a rotation speed of the sprocket  122 . The rotation speed of the sprocket  122  can be converted into a speed of the traveling device  1120 . 
     An IMU  33  is provided in the vehicle body  1110 . The IMU  33  measures inclination angles in a roll direction and a pitch direction of the vehicle body  1110  and an angle displacement in a yaw direction. 
     The work equipment  1130  is used for excavation and transport of an excavation target, such as earth. The work equipment  1130  is provided in a front portion of the vehicle body  1110 . The work equipment  1130  includes a lift frame  1131 , a blade  1132 , and a lift cylinder  1133 . 
     A proximal end portion of the lift frame  1131  is attached to a side surface of the vehicle body  1110  through a pin extending in a vehicle width direction. A distal end portion of the lift frame  1131  is attached to a back surface of the blade  1132  through a spherical joint. With this, the blade  1132  is supported to be movable in an up-down direction with respect to the vehicle body  1110 . A blade edge  1132   e  is provided in a lower end portion of the blade  1132 . The lift cylinder  1133  is a hydraulic cylinder. A proximal end portion of the lift cylinder  1133  is attached to a side surface of the vehicle body  1110 . A distal end portion of the lift cylinder  1133  is attached to the lift frame  1131 . The lift cylinder  1133  expands and contracts by hydraulic fluid, whereby the lift frame  1131  and the blade  1132  are driven in a lifting direction or a lowering direction. 
     The lift cylinder  1133  is provided with a stroke sensor  1134  that measures a stroke length of the lift cylinder  1133 . The stroke length measured by the stroke sensor  1134  can be converted into a position of the blade edge  1132   e  with the vehicle body  1110  as a reference. Specifically, a rotation angle of the lift frame  1131  is calculated based on the stroke length of the lift cylinder  1133 . Since the shapes of the lift frame  1131  and the blade  1132  are known, it is possible to specify the position of the blade edge  1132   e  of the blade  1132  from the rotation angle of the lift frame  1131 . The bulldozer  1100  according to another embodiment may detect a rotation angle with other sensors, such as an encoder. 
     The cab  1140  is a space where the operator boards and performs an operation of the bulldozer  1100 . The cab  1140  is provided in an upper portion of the vehicle body  1110 . 
     The bulldozer  1100  may include a traveling device that includes tires instead of the crawlers  1121  and transmits drive power of an engine to the tires through a transmission to travel. The bulldozer  1100  may be, for example, a backhoc loader having a structure in which a traveling device having such tires is provided and work equipment is attached to a vehicle main body (main body portion). That is, the backhoe loader has the work equipment attached to the vehicle main body and includes the traveling device that configures a part of the vehicle main body. 
     In the vehicle body  1110 , a side on which the work equipment  1130  is disposed is a front. A front-rear direction of the vehicle body  1110  is a y-direction. A left side facing the front is a left side of the vehicle body  1110 , and a right side facing the front is a right side of the vehicle body  1110 . A right-left direction of the vehicle body  1110  is also referred to as a width direction or an x-direction. In the bulldozer  1100 , a side of the traveling device  1120  is a lower side with the vehicle body  1110  as a reference, and a side of the vehicle body  1110  is an upper side with the traveling device  1120  as a reference. An up-down direction of the vehicle body  1110  is a z-direction. In a case where the bulldozer  1100  is provided on a horizontal plane, the lower side is a vertical direction, that is, a gravity action direction side, and the upper side is a side opposite to the vertical direction. 
     The antennas  21  and  22  and the antenna  24  are attached to the upper portion of the vehicle body  1110 . The antennas  21  and  22  are used to detect a current position of the bulldozer  1100 . The antennas  21  and  22  are electrically connected to the global position calculation device  23  shown in  FIG. 3 . The global position calculation device  23  is a position detection device that detects a position of the bulldozer  1100 . The global position calculation device  23  detects the current position of the bulldozer  1100  using Real Time Kinematic-Global Navigation Satellite Systems (RTK-GNSS). In the following description, the antennas  21  and  22  are appropriately referred to as GNSS antennas  21  and  22 . Signals corresponding to GNSS radio waves received by the GNSS antennas  21  and  22  are input to the global position calculation device  23 . The global position calculation device  23  obtains installation positions of the GNSS antennas  21  and  22  in a global coordinate system. An example of GNSS is a global positioning system (GPS), but GNSS is not limited thereto. 
     As shown in  FIG. 2 , it is preferable that the GNSS antennas  21  and  22  are provided both end positions separated in the right-left direction of the bulldozer  1100 , that is, in the width direction on the vehicle body  1110 . In the embodiment, the GNSS antennas  21  and  22  are attached to both sides in the width direction of the vehicle body  1110 . The positions where the GNSS antennas  21  and  22  are attached to the vehicle body  1110  are not limited, and it is preferable that the GNSS antennas  21  and  22  are provided at positions separated as much as possible since the detection accuracy of the current position of the bulldozer  1100  is improved. It is preferable that the GNSS antennas  21  and  22  are provided at positions where a visual field of the operator is little obstructed. 
     Since the imaging device  19  images the work target WA shown in  FIG. 1 , and the distance detection device  20  obtains a distance between the distance detection device  20  (a predetermined position of the bulldozer  1100 ) and the work target WA, it is preferable to acquire information from the work target WA as wide as possible. For this reason, in the embodiment, the antenna  24 , the imaging device  19 , and the distance detection device  20  are provided above the cab  1140  of the vehicle body  1110 . The places where the imaging device  19  and the distance detection device  20  are not limited to above the cab  1140 . For example, the imaging device  19  and the distance detection device  20  may be provided inside and above the cab  1140 . 
     The imaging device  19  has an imaging surface  19 L facing the front of the vehicle body  1110 . The distance detection device  20  has a detection surface  20 L facing the front of the vehicle body  1110 . In the embodiment, the imaging device  19  is a monocular camera including an image sensor, such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor. 
     In the embodiment, the distance detection device  20  is a three-dimensional laser range finder, a three-dimensional laser scanner, a three-dimensional distance sensor, or the like. The three-dimensional laser range finder or the like is also referred to as light detection and ranging (LiDAR) or the like, and is a sensor (scanning distance measurement sensor) that performs irradiation of laser beam emitting light in a pulse shape in a plurality of measurement directions over a given range while sequentially scanning the measurement directions, and measures a distance and an orientation based on a time until reflected scattered beam is returned and an irradiation direction. In the embodiment, the distance detection device  20  sequentially stores, updates, and outputs three-dimensional data indicating a measurement result of each measurement point (each reflection point) in every scanning cycle. The three-dimensional data output from the distance detection device  20  is point group data indicating a distance and an orientation to each measurement point or a three-dimensional coordinate value of each measurement point. 
     The imaging device  19  and the distance detection device  20  are not limited thereto. For example, a device that has a function of acquiring the image of the work target WA and a function of obtaining the distance to the work target WA may be used instead of the imaging device  19  and the distance detection device  20 . Examples of such a device include a stereo camera. LiDAR is excellent in longer transmission distance and outdoor application. 
     &lt;Control System of Bulldozer  1100 &gt; 
       FIG. 3  is a diagram showing a control system  1 S of the bulldozer  1100  that is the work machine according to the embodiment. The control system  1 S includes the communication device  25 , a sensor controller  26 , the work equipment control device  27 , the imaging device  19 , the distance detection device  20 , the global position calculation device  23 , the posture detection device  32 , an inertial measurement unit (IMU)  33 , and a hydraulic system  36 . The communication device  25 , the sensor controller  26 , and the work equipment control device  27  are connected by a signal line  35 . With such a structure, the communication device  25 , the sensor controller  26 , and the work equipment control device  27  can exchange information through the signal line  35 . Examples of the signal line that transfers information in the control system  1 S include an in-vehicle signal line, such as a controller area network (CAN). 
     The sensor controller  26  has a processor, such as a central processing unit (CPU), and a storage device, such as RAM and ROM. A detection value of the global position calculation device  23 , information regarding an image captured by the imaging device  19 , a detection value of the distance detection device  20 , a detection value of the posture detection device  32 , and a detection value of the IMU  33  are input to the sensor controller  26 . The sensor controller  26  transmits the input detection values and information regarding the image to the processing device  51  of the facility  50  shown in  FIG. 1  through the signal line  35  and the communication device  25 . 
     The work equipment control device  27  has a processor, such as a CPU, and a storage device, such as a random access memory (RAM) and a read only memory (ROM). The work equipment control device  27  acquires a command for operating at least one of the work equipment  1130  and the vehicle body  1110  generated by the processing device  51  of the facility  50  through the communication device  25 . The work equipment control device  27  controls an electromagnetic control valve  28  of the hydraulic system  36  based on the acquired command. 
     The hydraulic system  36  includes the electromagnetic control valve  28 , a hydraulic pump  29 , and hydraulic actuators, such as the lift cylinder  1133  and a traveling motor  30 . The hydraulic pump  29  is driven by an engine  31  to discharge hydraulic fluid for operating the hydraulic actuators. The work equipment control device  27  controls a flow rate of the hydraulic fluid that is supplied to the lift cylinder  1133 , by controlling the electromagnetic control valve  28 . In this manner, the work equipment control device  27  controls the operations of the lift cylinder  1133  and the like. 
     The sensor controller  26  acquires detection values of the stroke sensor  1134  and the like. The stroke sensor  1134  is provided in the lift cylinder  1133 . In a case where a lift cylinder length is decided, the posture of the work equipment  1130  is decided. Accordingly, the stroke sensor  1134  and the like that detect the lift cylinder length correspond to the posture detection device  32  that detects the posture of the work equipment  1130 . The posture detection device  32  is not limited to the stroke sensor  1134  and the like and may be an angle detector. 
     The sensor controller  26  calculates a rotation angle of the lift frame  1131  in a direction (z-axis direction) perpendicular to the horizontal plane in a local coordinate system (vehicle body coordinate system) that is the coordinate system of the bulldozer  1100 , from the lift cylinder length detected by the stroke sensor  1134 . Since the shapes of the lift frame  1131  and the blade  1132  are known, the sensor controller  26  can specify the position of the blade edge  1132   e  of the blade  1132  from the rotation angle of the lift frame  1131 . The sensor controller  26  calculates a rotation angle of the lift frame  1131  or an inclination angle of the blade  1132  from the lift cylinder length detected by the stroke sensor  1134 . The rotation angle of the lift frame  1131  is information indicating the posture of the work equipment  1130 . That is, the sensor controller  26  obtains information indicating the posture of the work equipment  1130 . The sensor controller  26  transmits the calculated inclination angles to the processing device  51  of the facility  50  shown in  FIG. 1  through the signal line  35  and the communication device  25 . 
     The GNSS antenna  21  receives a position P 1  indicating the position of the GNSS antenna  21  from the positioning satellites. The GNSS antenna  22  receives a position P 2  indicating the position of the GNSS antenna  22  from the positioning satellites. The GNSS antennas  21  and  22  receive the positions P 1  and P 2  in a 10 Hz cycle, for example. The positions P 1  and P 2  are information regarding the positions that the GNSS antennas are provided, in the global coordinate system. Signals corresponding to GNSS radio waves received by the GNSS antennas  21  and  22 , that is, the positions P 1  and P 2  are input to the global position calculation device  23 . The GNSS antennas  21  and  22  output the positions P 1  and P 2  to the global position calculation device  23  each time the positions P 1  and P 2  are received. 
     The global position calculation device  23  has a processor, such as a CPU, and a storage device, such as a RAM and a ROM. The global position calculation device  23  detects the positions P 1  and P 2  of the GNSS antennas  21  and  22  in the global coordinate system at a frequency of, for example, 10 Hz and outputs the positions P 1  and P 2  as reference position information Pga 1  and Pga 2  to the sensor controller  26 . In the embodiment, the global position calculation device  23  obtains a yaw angle that is an azimuth angle of the bulldozer  1100 , and more specifically, an azimuth angle of the vehicle body  1110 , from the acquired two positions P 1  and P 2  and outputs the yaw angle to the sensor controller  26 . The sensor controller  26  transmits the acquired reference position information Pga 1  and Pga 2  and the yaw angle to the processing device  51  of the facility  50  shown in  FIG. 1  through the signal line  35  and the communication device  25 . 
     The IMU  33  detects an operation and a posture of the bulldozer  1100 . The operation of the bulldozer  1100  includes at least one of an operation of the vehicle body  1110  and an operation of the traveling device  1120 . The posture of the bulldozer  1100  can be represented by a roll angle, a pitch angle, and the yaw angle of the bulldozer  1100 . In the embodiment, the IMU  33  detects and outputs an angular velocity and an acceleration of the bulldozer  1100 . 
     &lt;Functional Configuration Example of Processing Unit  51 P&gt; 
       FIG. 4  is a block diagram showing a functional configuration example of the processing unit  51 P shown in  FIG. 1 . As shown in  FIG. 4 , the processing unit  51 P of the embodiment has, as functional elements configured with a combination of hardware and software, an acquisition unit  51 P 1 , a conversion unit  51 P 2 , an image generation unit  51 P 3 , and a display processing unit  51 P 4 . The acquisition unit  51 P 1  acquires three-dimensional data of a plurality of measurement points measured by the distance detection device  20  mounted in the bulldozer  1100  (work machine). The conversion unit  51 P 2  converts the three-dimensional data into a local coordinate system (vehicle body coordinate system) defined in association with the vehicle body  1110  of the bulldozer  1100 . The image generation unit  51 P 3  generates a reference image representing a three-dimensional shape of a terrain based on the three-dimensional data converted into the local coordinate system. Then, the display processing unit  51 P 4  displays the reference image on the display device  52  to be superimposed on an image captured by the imaging device  19  (camera). In this case, the image generation unit  51 P 4  decides a display form of the reference image at a position of the reference image corresponding to each measurement point depending on the distance of the measurement point of the three-dimensional data in a normal direction with respect to a ground surface of the bulldozer  1100 . Here, the ground surface is a surface with which the crawlers  1121  are in contact, at a site. The display form is, for example, coloring of the reference image, a thickness of a line or density of lines, or a line type (broken line, a chain line, and the like) in a case where the reference image includes a plurality of line images or a lattice image consisting of a plurality of line images, or the like. According to this configuration, since it is possible to change the display form of a target on which the work machine travels or performs work, depending on the distance in the normal direction with respect to the ground surface of the work machine, for example, it is possible to make a display form of ruggedness or the like present on a slope ground different from a display form of a periphery. 
     &lt;Coordinate System&gt; 
       FIG. 5  is a diagram showing a coordinate system in the image display system  100  and the remote operation system  101  according to the embodiment.  FIG. 6  is a rear view schematically showing the bulldozer  1100 .  FIG. 7  is a diagram showing a coordinate system of the imaging device and the distance detection device. In the image display system  100  and the remote operation system  101 , there are a global coordinate system, a local coordinate system, a coordinate system of the imaging device  19 , and a coordinate system of the distance detection device  20 . In the embodiment, the global coordinate system is, for example, a coordinate system in GNSS. The global coordinate system is a three-dimensional coordinate system indicated by (X, Y, Z) with, for example, a reference position PG of a reference pile  80  to be a reference provided in a work section GA of the bulldozer  1100  as a reference. As shown in  FIG. 5 , the reference position PG is positioned, for example, at a distal end  80 T of the reference pile  80  provided in the work section GA. 
     The local coordinate system is a three-dimensional coordinate system indicated by (x, y, z) with the bulldozer  1100  as a reference. In the embodiment, an origin position PL of the local coordinate system is a predetermined position of the vehicle body  1110 . 
     In the embodiment, as shown in  FIG. 7 , the coordinate system of the imaging device  19  is a three-dimensional coordinate system indicated by (Xc, Yc, Zc) with the center of a light receiving surface  19 P of an imaging element  19 RC as an origin PC. In the embodiment, as shown in  FIG. 7 , the coordinate system of the distance detection device  20  is a three-dimensional coordinate system indicated by (Xd, Yd, Zd) with the center of a light receiving surface  20 P of a distance detection element  20 RC as an origin PD. 
     &lt;Posture of Bulldozer  1100 &gt; 
     As shown in  FIG. 6 , an inclination angle θ 4  of the vehicle body  1110  with respect to the right-left direction, that is, the width direction is the roll angle of the bulldozer  1100 , an inclination angle θ 5  of the vehicle body  1110  with respect to the front-rear direction is the pitch angle of the bulldozer  1100 , and an angle of the vehicle body  1110  around the z-axis is the yaw angle of the bulldozer  1100 . The roll angle is obtained by integrating an angular velocity around the y-axis detected by the IMU  33  with a time, the pitch angle is obtained by integrating an angular velocity around the x-axis detected by the IMU  33  with a time, and the yaw angle is obtained by integrating an angular velocity around the z-axis detected by the IMU  33  with a time. The angular velocity around the z-axis is a swing angular velocity ω of the bulldozer  1100 . That is, the yaw angle of the bulldozer  1100 , and more specifically, the vehicle body  1110  is obtained by integrating the swing angular velocity ω with a time. 
     The acceleration and the angular velocity detected by the IMU  33  are output as operation information to the sensor controller  26 . The sensor controller  26  executes processing, such as filter processing and integration, on the operation information acquired from the IMU  33  to obtain the inclination angle θ 4  as the roll angle, the inclination angle θ 5  as the pitch angle, and the yaw angle. The sensor controller  26  transmits the obtained inclination angle θ 4 , the inclination angle θ 5 , and the yaw angle as information related to the posture of the bulldozer  1100  to the processing device  51  of the facility  50  shown in  FIG. 1  through the signal line  35  and the communication device  25  shown in  FIG. 3 . 
     As described above, the sensor controller  26  obtains information indicating the posture of the work equipment  1130 . Specifically, information regarding the posture of the work equipment  1130  is an inclination angle θ 1  of the lift frame  1131  with respect to a direction (z-axis direction) perpendicular to the horizontal plane in the local coordinate system, an inclination angle of the blade  1132 , a position of the blade edge  1132   e , or the like. The processing device  51  of the facility  50  shown in  FIG. 1  calculates information indicating the posture of the work equipment  1130  acquired from the sensor controller  26  of the bulldozer  1100 , that is, the inclination angle θ 1  or the position (hereinafter, appropriately referred to as a blade edge position) P 4  of the blade edge  1132   e  of the blade  1132 . 
     The storage unit  51 M of the processing device  51  stores data (hereinafter, appropriately referred to as work equipment data) of the work equipment  1130 . The work equipment data includes data representing the shapes of the lift frame  1131  and the blade  1132 , for example, with the origin position PL of the local coordinate system as a reference. The processing device  51  can obtain the blade edge position P 4  with respect to the origin position PL using the work equipment data and the lift cylinder length detected by the stroke sensor  1134  or the inclination angle θ 1  and the origin position PL. In the embodiment, although the processing device  51  of the facility  50  obtains the blade edge position P 4 , the sensor controller  26  of the bulldozer  1100  may obtain the blade edge position P 4  and may transmit the blade edge position P 4  to the processing device  51  of the facility  50 . 
     &lt;Control Example that is Executed by the Image Display System  100  and the Remote Operation System  101 &gt; 
       FIG. 8  is a flowchart of a control example that is executed by the image display system  100  and the remote operation system  101 .  FIG. 11  is a diagram showing the imaging device  19 , the distance detection device  20 , and the work target WA. 
     In Step S 101 , the sensor controller  26  shown in  FIG. 3  acquires information regarding the bulldozer  1100 . Information regarding the bulldozer  1100  is information obtained from the imaging device  19 , the distance detection device  20 , the global position calculation device  23 , the posture detection device  32 , and the IMU  33 . As shown in  FIG. 11 , the imaging device  19  images the work target WA within an imaging range TA and obtains an image of the work target WA. The distance detection device  20  detects a distance Ld between the distance detection device  20  and the work target WA and other objects within a detection range MA. The global position calculation device  23  obtains the reference position information Pga 1  and Pga 2  corresponding to the positions P 1  and P 2  of the GNSS antennas  21  and  22  in the global coordinate system. The posture detection device  32  detects the lift cylinder length and the like. The IMU  33  detects the posture of the bulldozer  1100 , and more specifically, the roll angle θ 4 , the pitch angle θ 5 , and the yaw angle of the vehicle body  1110 . 
     In Step S 102 , the image display system  100  and the processing device  51  of the remote operation system  101  acquires information regarding the bulldozer  1100  from the sensor controller  26  of the bulldozer  1100  through the communication device  25  of the bulldozer  1100  and the communication device  54  connected to the processing device  51 , with the acquisition unit  51 P 1 . 
     Information regarding the bulldozer  1100  that is acquired from the sensor controller  26  by the processing device  51  includes the image of the work target WA captured by the imaging device  19 , information regarding the distance between the distance detection device  20  and the work target WA detected by the distance detection device  20 , information regarding the posture of the work equipment  1130  provided in the bulldozer  1100  detected by the posture detection device  32 , the reference position information Pga 1  and Pga 2 , and information regarding the posture of the bulldozer  1100 . 
     Information regarding the distance between the distance detection device  20  and the work target WA includes a distance Ld to the work target WA or an object OB within the detection range MA and information regarding an azimuth direction of a position Pd corresponding to the distance Ld.  FIG. 11  shows the distance Ld as the distance to the work target WA. Information regarding the azimuth direction of the position Pd is an azimuth direction of the position Pd with the distance detection device  20  as a reference, and angles with respect to the axes Xd, Yd, and Zd of the coordinate system of the distance detection device  20 . Information regarding the posture of the work equipment  1130  that is acquired by the processing device  51  is the inclination angle θ 1  of the work equipment  1130  obtained by the sensor controller  26  using the lift cylinder length and the like. Information regarding the posture of the bulldozer  1100  is the roll angle θ 4 , the pitch angle θ 5 , and the yaw angle of the bulldozer  1100 , and more specifically, the vehicle body  1110 . 
     The processing device  51  obtains the blade edge position P 4  of the blade  1132  using the inclination angle θ 1  of the work equipment  1130  acquired from the sensor controller  26  and the lift cylinder length and the like stored in the storage unit  51 M, for example, with the conversion unit  51 P 2 . The blade edge position P 4  of the blade  1132  is a set of coordinates in the local coordinate system (x, y, z) of the bulldozer  1100 . 
     The process progresses to Step S 103 , and the processing device  51  obtains the origin of the local coordinate system with the conversion unit  51 P 2 . 
     The process progresses to Step S 104 , and the processing device  51  converts the distance Ld to the work target WA into information regarding a position using information regarding the distance to the work target WA, with the conversion unit  51 P 2 . Information regarding the position is the coordinates of the position Pd in the coordinate system (Xd, Yd, Zd) of the distance detection device  20 . In Step S 104 , all distances Ld detected by the distance detection device  20  within the detection range MA are converted into information regarding the position. The processing device  51  converts the distance Ld into information regarding the position using the distance Ld and information regarding the azimuth direction of the position Pd corresponding to the distance Ld, with the conversion unit  51 P 2 . In Step S 104 , the distance to the object OB within the detection range MA is also converted into information regarding the position similarly to the distance Ld of the work target WA. Through the processing of Step S 104 , information regarding the position of the work target WA within the detection range MA is obtained. It is possible to obtain information regarding a shape of the work target WA from information regarding the position of the work target WA. 
     Information regarding the position and the shape of the work target WA is a set of coordinates of the position Pd in the coordinate system (Xd, Yd, Zd) of the distance detection device  20 . The processing device  51  converts information regarding the shape of the work target WA into a value of the coordinate system (Xc, Yc, Zc) of the imaging device  19 , and then, converts the converted value into a value of the local coordinate system (x, y, z) of the bulldozer  1100 , with the conversion unit  51 P 2 . 
     In Step S 105 , processing device  51  converts information regarding the position of the work target WA, the blade edge position P 4  of the blade  1132 , and the reference position information Pga 1  and Pga 2  acquired from the sensor controller  26  of the bulldozer  1100  into the global coordinate system (X, Y, Z), with the conversion unit  51 P 2 . In the conversion into the global coordinate system (X, Y, Z), the processing device  51  generates a rotation matrix using the roll angle θ 4 , the pitch angle θ 5 , and the yaw angle of the bulldozer  1100  acquired from the sensor controller  26 , with the conversion unit  51 P 2 . The processing device  51  converts information regarding the position of the work target WA, the blade edge position P 4  of the blade  1132 , and the reference position information Pga 1  and Pga 2  into the global coordinate system (X, Y, Z) using the generated rotation matrix, with the conversion unit  51 P 2 . Next, the process progresses to Step S 106 , and the processing device  51  obtains an occupied area with the image generation unit  51 P 3  (or the conversion unit  51 P 2 ). 
       FIG. 12  is a diagram showing an occupied area SA. The occupied area SA is an area occupied by the work equipment  1130  within information regarding the shape of the work target WA. In an example shown in  FIG. 12 , a part of the blade  1132  of the work equipment  1130  enters within the detection range MA of the distance detection device  20  and between the distance detection device  20  and the work target WA. For this reason, in the portion of the occupied area SA, the distance detection device  20  detects a distance to the blade  1132 , instead of the distance to the work target WA. In the embodiment, the processing device  51  removes the portion of the occupied area SA from information regarding the shape of the work target WA obtained in Step S 104 , with the image generation unit  51 P 3 . 
     The processing device  51  stores information regarding at least one of the position and the posture detected by the distance detection device  20  corresponding to at least one of the position and the posture of blade  1132  in, for example, the storage unit  51 M, with the image generation unit  51 P 3 . Such information is included in the posture of the work equipment  1130  of the bulldozer  1100  in the embodiment. The posture of the work equipment  1130  can be obtained using the inclination angle θ 1  of the work equipment  1130 , the lift cylinder length and the like, and the posture of the bulldozer  1100  as needed. Then, the processing device  51  compares data detected by the distance detection device  20  with information stored in the storage unit  51 M and can determine that the blade  1132  is detected in a case where both match, with the image generation unit  51 P 3 . Through such processing using the posture of the work equipment  1130 , since the processing device  51  does not use information regarding the blade  1132  in the occupied area SA in generating the lattice image  65  shown in  FIG. 1 , the processing device  51  can accurately generate the lattice image  65 . 
     To remove the portion of the occupied area SA, the processing using the posture of the work equipment  1130  may be executed by the following method. Information regarding at least one of the position and the posture in the global coordinate system of the blade  1132  included in the posture of the work equipment  1130  is obtained from the inclination angle θ 1  of the work equipment  1130  and the lift cylinder length and the like. In Steps S 104  and S 105 , information regarding the shape of the work target WA in the global coordinate system is obtained. In Step S 107 , the processing device  51  removes an area where the position of blade  1132  is projected onto information regarding the shape of the work target WA, as the occupied area SA from the shape of the work target WA, with the image generation unit  51 P 3 . 
       FIG. 13  is a diagram showing information regarding the shape of the work target WA with the occupied area removed. Information IMWA regarding the shape of the work target WA is a set of coordinates Pgd (X, Y, Z) in the global coordinate system (X, Y, Z). There is no information of coordinates of the occupied area IMBA through the processing of Step S 107 . Next, the process progresses to Step S 108 , and the processing device  51  generates an image indicating the position of blade  1132  with the image generation unit  51 P 3 . The image indicating the position of the blade  1132  is an image of a portion corresponding to the blade  1132  on the work target WA. 
       FIGS. 14 to 16  are diagrams showing an image indicating the position of blade  1132  on the work target WA. In the embodiment, the image indicating the position of blade  1132  is an image indicating the position of the blade edge  1132   e  of the blade  1132  on the work target WA. Hereinafter, the image indicating the position of the blade edge  1132   e  of the blade  1132  is appropriately referred to as a blade edge position image. As shown in  FIG. 14 , the blade edge position image is an image that is defined by a position Pgt (X, Y, Z) of a surface WAP of the work target WA when the blade edge  1132   e  is projected onto the work target WA in a vertical direction, that is, a direction in which gravity acts. The vertical direction is the Z-direction in the global coordinate system (X, Y, Z) and is a direction perpendicular to the X-direction and the Y-direction. 
     As shown in  FIG. 15 , a line image that is formed along the surface WAP of the work target WA between a first position Pgt 1  (X 1 , Y 1 , Z 1 ) and a second position Pgt 2  (X 2 , Y 2 , Z 2 ) of the surface WAP of the work target WA is a blade edge position image  61 . The first position Pgt 1  (X 1 , Y 1 , Z 1 ) is an intersection between a straight line LV 1  extending in the vertical direction from a position Pgb 1  outside the blade edge  1132   e  on one end portion  8 Wt 1  side of the blade  1132  in a width direction Wb and the surface WAP of the work target WA. The second position Pgt 2  (X 2 , Y 2 , Z 2 ) is an intersection between a straight line LV 2  extending in the vertical direction from a position Pgb 2  outside the blade edge  1132   e  on the other end portion  8 Wt 2  side of the blade  1132  in the width direction Wb and the surface WAP of the work target WA. 
     The processing device  51  obtains the straight line V 1  and the straight line LV 2  extending in the vertical direction from the position Pgb 1  and the position Pgb 2  of the blade  1132 , with the image generation unit  51 P 3 . Next, the processing device  51  obtains the first position Pgt 1  (X 1 , Y 1 , Z 1 ) and the second position Pgt 2  (X 2 , Y 2 , Z 2 ) from the obtained straight line LV 1  and straight line LV 2  and information regarding the shape of the work target WA with the image generation unit  51 P 3 . Then, the processing device  51  defines a set of positions Pgt of the surface WAP when a straight line connecting the first position Pgt 1  and the second position Pgt 2  is projected onto the surface WAP of the work target WA, as the blade edge position image  61  with the image generation unit  51 P 3 . 
     In the embodiment, the processing device  51  generates a first straight line image  62  that is an image of the straight line LV 1  connecting the position Pgb 1  and the first position Pgt 1  (X 1 , Y 1 , Z 1 ) and a second straight line image  63  that is an image of the straight line LV 2  connecting the position Pgb 2  and the second position Pgt 2  (X 2 , Y 2 , Z 2 ), with the image generation unit  51 P 3 . Next, the processing device  51  converts the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  into an image with the imaging device  19  as a reference, that is, an image viewed from the imaging device  19 , with the image generation unit  51 P 3 . 
     As shown in  FIG. 16 , the image viewed from the imaging device  19  is an image as the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  are viewed from the origin Pgc (Xc, Yc, Zc) of the imaging device in the global coordinate system (X, Y, Z). The origin Pgc (Xc, Yc, Zc) of the imaging device is coordinates obtained by converting the center of the light receiving surface  19 P of the imaging element  19 RC provided in the imaging device  19 , that is, the origin PC into the global coordinate system (X, Y, Z). 
     While the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  are images in a three-dimensional space, and the image viewed from the imaging device  19  is a two-dimensional image. Accordingly, the processing device  51  executes perspective projection conversion to project the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  defined in the three-dimensional space, that is, in the global coordinate system (X, Y, Z) onto a two-dimensional plane, with the image generation unit  51 P 3 . Hereinafter, the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  converted into the image viewed from the imaging device  19  are appropriately referred to as a work tool guide image  60 . 
     The process progresses to Step S 109 , and the processing device  51  converts the global coordinates into the local coordinate system with the image generation unit  51 P 3 . 
     The process progresses to Step S 110 , and the processing device  51  obtains gradation coloring of the reference image depending on the height of the local coordinate system with the image generation unit  51 P 3 . In Step S 110 , the image generation unit  51 P 3  decides gradation coloring of the reference image at a position of the reference image corresponding to each measurement point depending on a distance of the measurement point of the three-dimensional data in a normal direction with respect to the ground surface of the bulldozer  1100 . For example, the image generation unit  51 P 3  sets the coloring of the reference image to a cold color at a position corresponding to a comparatively low measurement point, sets the coloring of the reference image to a warm color at a position corresponding to a comparatively high measurement point, and sets the coloring of the reference image to a neutral color at a position corresponding to a measurement point having an intermediate height. 
     For example, as shown in  FIG. 9 , in a case where the ground surface of the bulldozer  1100  is a level ground  403 , the processing device  51  obtains the gradation coloring of the reference image depending on the height in the z-direction (in this case, the vertical direction) of the local coordinate system, with the image generation unit  51 P 3 . In an example shown in  FIG. 9 , the processing device  51  obtains the gradation coloring of the reference image with the image generation unit  51 P 3  in the same manner as in a case where the change in color is decided with reference to the horizontal plane described referring to  FIG. 21 .  FIG. 9  is a schematic view showing change in coloring with change in density of hatching. 
     For example, as shown in  FIG. 10 , in a case where the ground surface of the bulldozer  1100  is a slope ground  401 , the processing device  51  obtains the gradation coloring of the reference image depending on the height in the z-direction (in this case, a direction perpendicular to a slope surface of the slope ground  401 ) of the local coordinate system, with the image generation unit  51 P 3 . In an example shown in  FIG. 10 , the processing device  51  obtains the gradation coloring of the reference image with the image generation unit  51 P 3  unlike a case where the change in color is decided with reference to the horizontal plane described referring to  FIG. 21 .  FIG. 10  is a schematic view showing change in coloring with change in density of hatching. In this case, it is possible to set coloring different from the periphery for the ruggedness  402  on the slope ground  401  not color-coded in  FIG. 21 . 
       FIGS. 17 and 18  are diagrams showing the lattice image  65  as a reference image. In a case where the gradation coloring of the reference image is decided in Step S 110 , the process progresses to Step S 111 , and the processing device  51  generates the lattice image  65  as the reference image with the gradation coloring decided in Step S 110 , with the image generation unit  51 P 3 . The lattice image  65  is a line image along the surface WAP of the work target WA using information regarding the position of the work target WA. The lattice image  65  is a lattice including a plurality of first line images  66  and a plurality of second line images  67  intersecting a plurality of first line images  66 . In the embodiment, the first line image  66  is, for example, a line image that extends in parallel with the X-direction in the global coordinate system (X, Y, Z) and is disposed in the Y-direction. In the global coordinate system (X, Y, Z), the first line image  66  may be a line image that extends in parallel with the front-rear direction of the vehicle body  1110  provided in the bulldozer  1100  and is disposed in the width direction of the vehicle body  1110 . 
     The lattice image  65  is generated using information regarding the position of the work target WA, and more specifically, a position Pgg (X, Y, Z) of the surface WAP. An intersection of the first line image  66  and the second line image  67  is the position Pgg (X, Y, Z). As shown in  FIG. 18 , the first line image  66  and the second line image  67  are defined by the global coordinate system (X, Y, Z), and thus, include three-dimensional information. In the embodiment, a plurality of first line images  66  are disposed at equal intervals, and a plurality of second line images  67  are disposed at equal intervals. An interval between adjacent first line images  66  is equal to an interval between adjacent second line images  67 . 
     The lattice image  65  is an image obtained by converting the first line image  66  and the second line image  67  generated using the position Pgg (X, Y, Z) of the surface WAP into the image viewed from the imaging device  19 . The processing device  51  generates the first line image  66  and the second line image  67 , and then, converts these images into the image viewed from the imaging device  19  to generate the lattice image  65 , with the image generation unit  51 P 3 . The first line image  66  and the second line image  67  are converted into the image viewed from the imaging device  19 , whereby the lattice image  65  having an equal interval on the horizontal plane can be deformed and displayed in conformity with the shape of the work target WA to assist an absolute distance of the work target WA. 
     Next, in Step S 112 , the processing device  51  removes the above-described occupied area SA from the generated work tool guide image  60  and the lattice image  65  that is the reference image, with the display processing unit  51 P 4 . In Step S 112 , the processing device  51  converts the occupied area SA into the image viewed from the imaging device  19  and removes the work tool guide image  60  and the lattice image  65  that is the reference image, with the display processing unit  51 P 4 . In the embodiment, the processing device  51  may remove the occupied area SA before being converted into the image viewed from the imaging device  19 , from the blade edge position image  61 , the first straight line image  62 , and the second straight line image  63  before being converted into the image viewed from the imaging device  19 , and the first line image  66  and the second line image  67  before being converted into the image viewed from the imaging device  19 , with the display processing unit  51 P 4 . 
       FIG. 19  is a diagram showing an image  69  for work. In Step S 113 , the processing device  51  combines the work tool guide image  60  with the occupied area SA removed, the lattice image  65 , and the image  68  of the work target WA captured by the imaging device  19  to generate the image  69  for work, with the display processing unit  51 P 4 . In Step S 114 , the processing device  51  displays the generated image  68  for work on the display device  52 , with the display processing unit  51 P 4 . The image  69  for work is an image in which the lattice image  65  and the work tool guide image  60  are displayed on the image  68  of the work target WA. 
     Since the lattice image  65  has a lattice along the surface WAP of the work target WA, the operator of the bulldozer  1100  can recognize the position of the work target WA by referring to the lattice image  65 . For example, the operator can recognize a depth, that is, the position of the vehicle body  1110  provided in the bulldozer  1100  in the front-rear direction with the second line image  67  and can recognize the position of the blade  1132  in the width direction with the first line image  66 . 
       FIG. 20  is a diagram showing another example of an image  69  for work. In  FIG. 20 , the image  69  for work includes a lattice image  65  in which the thickness of a line is different depending on a distance in a normal direction. In the lattice image  65  shown in  FIG. 20 , as the distance is greater, a line diameter is set to be greater. In the example shown in  FIG. 20 , the work machine is a hydraulic excavator or the like. 
     In the embodiment, the lattice image  65  consisting of the first line image  66  and the second line image  67  are color-coded with different colors depending on the height. In this case, in the embodiment, it is possible to change a display form of a target on which the bulldozer  1100  (work machine) travels or performs work depending on a distance in a normal direction with respect to the ground surface of the bulldozer  1100 , and for example, it is possible to make a display form of ruggedness or the like on a slope ground different from a display form of a periphery. That is, in the embodiment, since a color gauge of a height is decided with reference to the ground surface of the crawlers  1121 , for example, it is possible to enable correct recognition of ruggedness on a slope ground during climbing. 
     In the work tool guide image  60 , the blade edge position image  61  is displayed along the surface WAP of the work target WA and the lattice image  65 . In an example shown in  FIG. 19 , an extension line image  61 - 1  and an extension line image  61 - 2  extending from the blade edge position image  61  are also displayed along the surface WAP of the work target WA and the lattice image  65 . For this reason, since the operator can recognize a positional relationship between the blade  1132  and the work target WA with the lattice image  65  and the blade edge position image  61 , work efficiency and work accuracy are improved. In the embodiment, the first straight line image  62  and the second straight line image  63  connect both ends of the blade edge position image  61  from both sides of the blade  1132  in the width direction Wb. The operator can more easily recognize the positional relationship between the blade  1132  and the work target WA with the first straight line image  62  and the second straight line image  63 . Since the lattice image  65  and the blade edge position image  61  are displayed along the shape of a terrain (work target WA) to be worked, a relative positional relationship between the blade  1132  and the work target WA on a terrain surface (two-dimensionally) can be easily recognized. In addition, since the first line images  66  and the second line images  67  that constitute the lattice image  65  are displayed at equal intervals in the global coordinate system, a sense of distance on the terrain surface is easily recognized, and a sense of perspective is easily recognized. 
     In the embodiment, the image  69  for work can include information regarding a distance between the blade edge  1132   e  of the blade  1132  and the work target WA. With such a configuration, there is an advantage in that the operator can recognize an actual distance between the blade edge  1132   e  of the blade  1132  and the work target WA. The distance between the blade edge  1132   e  of the blade  1132  and the work target WA can be a distance between the blade edge  1132   e  at the center of the blade  1132  in the width direction Wb and the surface WAP of the work target WA. 
     Information regarding the distance to the work target WA may be spatial position information regarding the work tool or the work target W, including information, such as information regarding the posture, for example, the angle of the blade  1132 , information indicating a relative distance between the blade  1132  and the work target WA, information indicating a relationship between an orientation of, for example, the blade edge  1132   e  of the blade  1132  and an orientation of the surface of the work target WA, information indicating the position of blade  1132  by coordinates, information indicating the orientation of the surface of the work target WA, and information indicating a distance between the imaging device  19  and the blade edge  1132   e  of the blade  1132  in the y-direction in the local coordinate system, instead of the distance between the blade edge  1132   e  of the blade  1132  and the work target WA or in addition to the distance. 
     That is, the processing device  51  may obtain at least one of the position of blade  1132  as the work tool, the posture of the blade  1132 , the position of the work target WA, a relative posture of the work target WA, a relative distance between the blade  1132  and the work target WA, and a relative posture of the blade  1132  and the work target WA and may display the obtained information on the display device  52 , with the display processing unit  51 P 4 . 
     As described above, the image display system  100  and the remote operation system  101  displays the work tool guide image  60  and the lattice image  65  generated as viewed from the imaging device  19  on the display device  52  to be superimposed on the image  68  of the actual work target WA captured by the imaging device  19 . Through such processing, the image display system  100  and the remote operation system  101  can be configured such that the operator who remotely operates the bulldozer  1100  using the image of the work target WA displayed on the display device  52  can easily recognize the positional relationship between the position of the blade  1132  and the work target WA, and thus, work efficiency and work accuracy can be improved. Even an inexperienced operator can easily recognize the positional relationship between the position of the blade  1132  and the work target WA using the image display system  100  and the remote operation system  101 . As a result, degradation of work efficiency and work accuracy is suppressed. Furthermore, the image display system  100  and the remote operation system  101  displays the work tool guide image  60 , the lattice image  65 , and the image  68  of the actual work target WA on the display device  52  in a superimposed manner, whereby a single screen to which the operator pays attention during work is required, and work efficiency can be improved. 
     In the lattice image  65 , the interval between adjacent first line images  66  is equal to the interval between adjacent second line images  67 . For this reason, the lattice image  65  and the image  68  of the actual work target WA captured by the imaging device  19  are displayed in a superimposed manner, whereby a work point on the work target WA is easily recognized. The blade edge position image  61  of the work tool guide image  60  and the lattice image  65  are superimposed, whereby the operator easily recognizes a movement distance of the blade  1132 , and thus, work efficiency is improved. 
     Since the occupied area SA that is the area of the work equipment  1130  is removed from the work tool guide image  60  and the lattice image  65 , the work tool guide image  60  and the lattice image  65  can be prevented from being distorted due to the occupied area SA and the work tool guide image  60  and the lattice image  65  can be prevented from being displayed on the work equipment  1130  in a superimposed manner. As a result, the image display system  100  and the remote operation system  101  can display the image  69  for work on the display device  52  in a visible form for the operator. 
     In the embodiment, the work tool guide image  60  may include at least the blade edge position image  61 . The lattice image  65  may include at least a plurality of second line images  67 , that is, a plurality of line images indicating the direction perpendicular to the front-rear direction of the vehicle body  1110  provided in the bulldozer  1100 . The processing device  51  may change the color of the blade edge position image  61  in the work tool guide image  60  depending on the distance between the blade edge  1132   e  of the blade  1132  and the work target WA. With such a configuration, the operator easily recognizes the distance between the position of blade  1132  and the work target WA. 
     In the embodiment, although the processing device  51  converts information regarding the shape of the work target WA into the global coordinate system (X, Y, Z) to generate the work tool guide image  60  and the lattice image  65 , the processing device  51  may not convert information regarding the shape of the work target WA into the global coordinate system (X, Y, Z). In this case, the processing device  51  handles information regarding the shape of the work target WA in the local coordinate system (x, y, z) of the bulldozer  1100  and generates the work tool guide image  60  and the lattice image  65 . In a case where information regarding the shape of the work target WA is handled in the local coordinate system (x, y, z) of the bulldozer  1100 , the GNSS antennas  21  and  22  and the global position calculation device  23  are not required. 
     In the above-described embodiment, a part (for example, the blade  1132  as described above) of the bulldozer  1100  detected by the distance detection device  20  is removed to obtain information (three-dimensional terrain data) regarding the shape of the work target WA. Note that three-dimensional terrain data acquired in the past (for example, several seconds ago) may be stored in the storage unit  51 M of the processing device  51 , and the processing unit  51 P of the processing device  51  may determine whether or not the position of the current work target WA and the position indicated by the stored three-dimensional terrain data are identical, and in a case where both positions are identical, may display the lattice image  65  using past three-dimensional terrain data. That is, even though a terrain is hidden by part of the bulldozer  1100  as viewed from the imaging device  19 , in a case where there is past three-dimensional terrain data, the processing device  51  can display the lattice image  65 . 
     The lattice image  65  may be displayed, for example, using a local coordinate system as a polar coordinate system, instead of displaying the lattice image  65  using the lattice. Specifically, concentric circles at equal intervals depending on a distance from the center of the bulldozer  1100  (for example, the swing center of the vehicle body  1110 ) may be drawn as line images (second line images), and radial line images (first line images) at equal intervals from the swing center may be drawn depending on a swing angle of the vehicle body  1110 . In this case, the second line images that the concentric circle line images intersect the first line image that are the radial line images from the swing center. Such a lattice image is displayed, whereby it is also possible to easily recognize the positional relationship between the position of the blade  1132  and the work target WA at the time of swing or excavation. 
     &lt;Modification Example of Control System of Bulldozer  1100 &gt; 
     Although the image display system  100  and the remote operation system  101  described above remotely operate the bulldozer  1100  using the operation device  53  of the facility  50  shown in  FIG. 1 , the display device  52  may be provided in the cab  1140  shown in  FIG. 2  or the image  69  for work may be displayed on the display device  52  in the cab  1140  to assist the work of the operator for the bulldozer  1100 . In this case, the bulldozer  1100  can be configured such that the operator who operates the bulldozer  1100  using the image of the work target WA displayed on the display device  52  easily recognizes the positional relationship between the position of blade  1132  and the work target WA. As a result, work efficiency and work accuracy can be improved. Furthermore, even an inexperienced operator can easily recognize the positional relationship between the position of blade  1132  and the work target WA. As a result, degradation of work efficiency and work accuracy is suppressed. In addition, in night work or the like, even though the operator hardly sees the actual work target WA, the operator can perform work while viewing the work tool guide image  60  and the lattice image  65  displayed on the display device  52 , and thus, degradation of work efficiency is suppressed. 
     Although the embodiment has been described above, the embodiment is not limited by the content described above. Furthermore, the above-described components include those that can be easily assumed by those skilled in the art, substantially the same one, and so-called equivalents. In addition, the above-described components can be appropriately combined. Moreover, at least one of various omissions, substitutions, and alterations of the components can be performed without departing from the spirit and scope of the embodiment. The work machine is not limited to the bulldozer  1100  and may be other work machines, such as a wheel loader or a hydraulic excavator. Although the blade (work equipment) of the bulldozer has been an exemplary example of the occupied area, a hood of the vehicle body or an exhaust pipe may be added to the occupied area in addition to the work equipment. 
     INDUSTRIAL APPLICABILITY 
     According to the above-described disclosure of the invention, since it is possible to change the display form of a target on which the work machine travels or performs work, depending on the distance in the normal direction with respect to the ground surface of the work machine, for example, it is possible to make a display form of ruggedness or the like present on a slope ground different from a display form of a periphery. 
     REFERENCE SIGNS LIST 
     
         
           1100 : Bulldozer 
           1110 : Vehicle body 
           1120 : Traveling device 
           1130 : Work equipment 
           1132 : Blade 
           1132   e : Blade edge 
           1 S: Control system 
           19 : Imaging device 
           20 : Distance detection device 
           21 ,  22 : Antenna (GNSS antenna) 
           23 : Global position calculation device 
           26 : Sensor controller 
           27 : Work equipment control device 
           32 : Posture detection device 
           33 : IMU 
           50 : Facility 
           51 : Processing device 
           52 : Display device 
           53 : Operation device 
           60 : Work tool guide image (image) 
           61 : Blade edge position image 
           62 : First straight line image 
           63 : Second straight line image 
           65 : Lattice image 
           66 : First line image 
           67 : Second line image 
           68 : Image 
           69 : Image for work 
           100 : Image display system for work machine (display system) 
           101 : Remote operation system for work machine (remote operation system)