Patent Publication Number: US-11025826-B2

Title: Display system, display device, and control method for display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 15/895,214 filed Feb. 13, 2018, which is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2017-034319 filed on Feb. 27, 2017. The entire contents of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a display system, a display device, and a control method for the display device. 
     2. Related Art 
     There has been known an unmanned aircraft (a so-called Drone) that can be remotely piloted (see, for example, JP-A-2013-144539 (Patent Literature 1)). The unmanned aircraft described in Patent Literature 1 is a quadricopter including a navigation posture control system. The unmanned aircraft receives a piloting command through a wireless link between the unmanned aircraft and a remote control device. The unmanned aircraft described in Patent Literature 1 includes a camera and transmits an image captured by a camera to the remote control device. A user can perform operation such as a turn and raising or lowering of the unmanned aircraft and a change of a direction pointed by the camera. 
     As described in Patent Literature 1, when the camera is provided in the unmanned aircraft to cause the camera to perform imaging, it is conceivable to appropriately display a captured image. Therefore, there has been a demand for a technique for displaying the image captured by the unmanned aircraft using a method with high usefulness. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a display system, a display device, and a control method for the display device capable of effectively displaying an image captured by a mobile body having an imaging function. 
     A display system according to an aspect of the invention includes a first display device and a second display device. The first display device includes: a first display section; a first operation detecting section configured to detect operation; a first mobile-body control section configured to generate, according to the operation detected by the first operation detecting section, a command for operating a first mobile body; a first mobile-body-image-data acquiring section configured to acquire first mobile body image data concerning a captured image captured by the first mobile body; and a first display control section configured to cause the first display section to display an image based on the first mobile body image data acquired by the first mobile-body-image-data acquiring section. The second display device includes: a second display section; a second mobile-body-image-data acquiring section configured to acquire the first mobile body image data concerning the captured image captured by the first mobile body; and a second display control section configured to cause the second display section to display an image based on the first mobile body image data acquired by the second mobile-body-image-data acquiring section. 
     According to the aspect of the invention, since the display device generates the command for operating the first mobile body, it is possible to use, for operation of the first mobile body, the display device that displays an image concerning the captured image captured by the first mobile body. Therefore, it is possible to perform the operation of the first mobile body while viewing the image displayed by the display device. Since it is possible to display, with the second display device, the image concerning the captured image captured by the first mobile body, for example, a person not involved in the operation of the first mobile body can confirm the captured image of the first mobile body. 
     In the configuration described above, the first display section may display the image to enable visual recognition of an outside scene by transmitting external light, and the first display control section may control visibility of the outside scene in the first display section. 
     According to this configuration, the first display device displays, on the first display section that enables the visual recognition of the outside scene, the image concerning the captured image captured by the first mobile body. Consequently, it is possible to visually recognize the first mobile body in a real space, perform operation concerning a motion of the first mobile body, and visually recognize the image concerning the captured image. Therefore, it is possible to confirm the captured image and perform the operation of the first mobile body while viewing the first mobile body in the real space. Since the visibility of the outside scene in the display section can be controlled, for example, it is possible to prioritize the visibility of the first mobile body in the real space over the visibility of the captured image and control the display to facilitate the operation of the first mobile body. 
     In the configuration described above, the first display control section may cause the display section to display a screen for operation concerning processing for generating the command and control the visibility of the outside scene in the first display section according to a display state of the screen for operation. 
     According to this configuration, since it is possible to control the visibility of the outside scene according to the display state of the screen for operation concerning the motion of the first mobile body, for example, it is possible to adjust the visibility of the screen for operation and the visibility of the first mobile body in the real space. Therefore, it is possible to improve easiness of the operation of the first mobile body. 
     In the configuration described above, the first display control section may control the visibility of the outside scene in the first display section according to a display state of the image based on the first mobile body image data. 
     According to this configuration, since the visibility of the outside scene is controlled according to the display state concerning the captured image of the first mobile body, for example, it is possible to adjust the visibility of the first mobile body in the real space and the visibility of the image concerning the captured image. It is possible to achieve further improvement of convenience. 
     In the configuration described above, the first display control section may control the visibility of the outside scene in the first display section on the basis of a state of the first display section or a user who uses the first display section. 
     According to this configuration, since the visibility of the outside scene in the first display section is controlled on the basis of the state of the first display section or the user who uses the first display section, it is possible to control the visibility of the outside scene according to importance of the visibility of the outside scene for the user reflected on the position, the movement, the posture, and the like of the first display section or the user. 
     In the configuration described above, the first display control section may cause the first display section to display an image corresponding to an operation state of the first mobile body. 
     According to this configuration, it is possible to obtain information concerning the operation state of the first mobile body according to the display of the first display section. It is possible to achieve improvement of convenience concerning use of the captured image of the first mobile body. 
     In the configuration described above, the second display section may display the image to enable visual recognition of an outside scene by transmitting external light, and the second display control section may control visibility of the outside scene in the second display section. 
     According to this configuration, in the second display device, it is possible to visually recognize the outside scene and an image concerning the captured image captured by the first mobile body. It is possible to control the visibility of the outside scene. 
     In the configuration described above, the second display control section may control the visibility of the outside scene in the second display section on the basis of a state of the second display section or a user who uses the second display section. 
     According to this configuration, since the visibility of the outside scene in the first display section is controlled on the basis of the state of the second display section or the user who uses the second display section, it is possible to control the visibility of the outside scene according to importance of the visibility of the outside scene for the user reflected on the position, the movement, the posture, and the like of the second display section or the user. 
     In the configuration described above, the second display device may further include: a second operation detecting section configured to detect operation; and a second mobile-body control section configured to generate, according to the operation detected by the second operation detecting section, a command for operating a second mobile body, and the second display control section may cause the display section to display a screen for operation concerning processing for generating the command and control the visibility of the outside scene in the second display section according to a display state of the screen for operation. 
     According to this configuration, the first display device generates the command concerning the operation of the first mobile body and the second display device generates the command concerning the operation of the second mobile body. Therefore, a user who uses the first display device and a user who uses the second display device can respectively perform operation concerning motions of the mobile bodies while visually recognizing the mobile bodies in the real space and visually recognize images concerning captured images captured by the mobile bodies. Consequently, it is possible to provide the display system capable of easily performing the operation of the mobile bodies and use of the captured images captured by the mobile bodies. 
     In the configuration described above, the second mobile-body-image-data acquiring section included in the second display device may acquire second mobile body image data concerning a captured image captured by the second mobile body, and the second display control section may display, on the second display section, an image based on the first mobile body image data acquired by the second mobile-body-image-data acquiring section and an image based on the second mobile body image data acquired by the second mobile-body-image-data acquiring section. 
     According to this configuration, it is possible to display, with the second display device, the images concerning the captured images respectively captured by the first mobile body and the second mobile body. 
     In the configuration described above, the second display control section may control the visibility of the outside scene in the second display section according to a display state of at least either one of the image based on the first mobile body image data acquired by the second mobile-body-image-data acquiring section and the image based on the second mobile body image data acquired by the second mobile-body-image-data acquiring section. 
     According to this configuration, it is possible to control the visibility of the outside scene in displaying the captured images of the first mobile body and/or the second mobile body. Therefore, since it is possible to adjust a balance of the visibilities of the outside scene and the captured images of the first mobile body and/or the second mobile body, for example, when the user of the second display device operates the second display device, it is possible to prioritize the visibility of the second mobile body in the real space and improve operability. 
     In the configuration described above, the second display control section may cause the second display section to display an image corresponding to an operation state of the second mobile body. 
     According to this configuration, it is possible to perform display concerning the operation state of the second mobile body in the second display device. It is possible to further facilitate the operation concerning the motion of the second mobile body and improve the operability. 
     In the configuration described above, the second display control section may cause the second display section to display images corresponding to an operation state of the first mobile body and an operation state of the second mobile body. 
     According to this configuration, it is possible to perform the display concerning the operation states of the first mobile body and the second mobile body in the second display device. Consequently, it is possible to perform operation concerning the motion of the second mobile body while confirming a state of the first mobile body. 
     In the configuration described above, the second display control section may cause the second display section to display an image corresponding to an operation state of the second mobile body in a position corresponding to the second mobile body visually recognized in the outside scene via the second display section. 
     According to this configuration, it is possible to cause the second display section to display, according to a position where the second mobile body in the real space is visually recognized, an image displayed by the second display section concerning the operation state of the second mobile body. Therefore, it is possible to further facilitate the operation concerning the motion of the second mobile body and improve the operability. 
     In the configuration described above, the second display device may further include a position-information acquiring section configured to acquire information concerning a position of the first mobile body and a position of the second mobile body, and the second display control section may cause the second display section to display the information acquired by the position-information acquiring section. 
     According to this configuration, it is possible to perform display concerning the positions of the first mobile body and the second mobile body in the second display device. 
     In the configuration described above, the second mobile-body control section included in the second display device may generate, on the basis of the information acquired by the position-information acquiring section, the command for operating the second mobile body. 
     According to this configuration, it is possible to operate the second mobile body with the second display device according to the positions of the first mobile body and the second mobile body. 
     In the configuration described above, at least either one of the first display section and the second display section may be a head-mounted display section mounted on a head of a user. 
     According to this configuration, with the display device including the head-mounted display section, it is possible to, while visually recognizing the first mobile body or the second mobile body in the real space, perform operation concerning a motion of the mobile body and further view an image concerning a captured image captured by the mobile body. 
     A display device according another aspect of the invention includes: a display section configured to display an image to enable visual recognition of an outside scene by transmitting external light; an operation detecting section configured to detect operation; a mobile-body control section configured to generate, according to the operation detected by the operation detecting section, a command for operating a first mobile body; a mobile-body-image-data acquiring section configured to acquire first mobile body image data concerning a captured image captured by the first mobile body; and a display control section configured to cause the display section to display an image based on the first mobile body image data acquired by the mobile-body-image-data acquiring section. The display control section controls visibility of the outside scene in the display section. 
     According to the aspect of the invention, since an image concerning the captured image captured by the first mobile body is displayed on the display section that enables the visual recognition of the outside scene, it is possible to view the image concerning the captured image while visually recognizing the first mobile body in a real space. Since it is possible to visually recognize the first mobile body in the real space and perform operation while viewing the captured image, it is possible to easily perform both of confirmation of the captured image and the operation of the mobile body. Since it is possible to control the visibility of the outside scene in the display section, for example, it is possible to prioritize the visibility of the first mobile body in the real space over the visibility of the captured image and control display to facilitate the operation of the first mobile body. 
     In the configuration described above, the mobile-body-image-data acquiring section may acquire second mobile body image data concerning a captured image captured by a second mobile body, and the display control section may cause the display section to display an image based on at least either one of the first mobile body image data and the second mobile body image data acquired by the mobile-body-image-data acquiring section and control visibility of the outside scene in the display section according to a display state of at least either one of an image based on the first mobile body image data and an image based on the second mobile body image data. 
     According to this configuration, since it is possible to control the visibility of the outside scene, for example, it is possible to display images related to the captured image of the first mobile body and/or the captured image of the second mobile body and adjust the visibilities of the images and the outside scent. Consequently, it is possible to efficiently use the captured images captured by the mobile bodies. 
     A control method for a display device according to still another aspect of the invention includes a display section configured to display an image to enable visual recognition of an outside scene by transmitting external light, the control method including: detecting operation; generating, according to the detected operation, a command for operating a mobile body; acquiring mobile body image data concerning a captured image captured by the mobile body; and causing the display section to display an image based on the acquired mobile body image data and controlling visibility of the outside scene in the display section. 
     According to the aspect of the invention, since an image concerning the captured image captured by the mobile body is displayed on the display section that enables the visual recognition of the outside scene, it is possible to view the image concerning the captured image while visually recognizing the mobile body in a real space. Since it is possible to visually recognize the mobile body in the real space and perform operation while viewing the captured image, it is possible to easily perform both of confirmation of the captured image and the operation of the mobile body. Since it is possible to control the visibility of the outside scene in the display section, for example, it is possible to prioritize the visibility of the mobile body in the real space over the visibility of the captured image and control display to facilitate the operation of the mobile body. 
     It is possible to realize the invention in various forms other than the display system, the display device, and the control method for the display device explained above. For example, the display system may be a system including the display device and the first mobile body and/or the second mobile body. The invention may be realized as a computer program executed by a control section or a computer in order to execute the control method. The invention can be realized in forms such as a recording medium having the computer program recorded therein, a server apparatus that distributers the computer program, a transmission medium that transmits the computer program, and a data signal obtained by embodying the computer program in a carrier wave. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic configuration diagram of a mobile machine composite control system. 
         FIG. 2  is a functional block diagram of a mobile machine. 
         FIG. 3  is an explanatory diagram showing an exterior configuration of an HMD. 
         FIG. 4  is a diagram showing the configuration of an optical system of an image display section. 
         FIG. 5  is a perspective view showing the configuration of the image display section. 
         FIG. 6  is a schematic diagram showing correspondence between the image display section and an imaging range. 
         FIG. 7  is a block diagram of the HMD. 
         FIG. 8  is a functional block diagram of a control section and a storing section of the HMD. 
         FIG. 9  is a flowchart for explaining the operation of the mobile machine. 
         FIG. 10  is a flowchart for explaining the operation of the HMD. 
         FIG. 11  is a flowchart for explaining the operation of the HMD. 
         FIG. 12  is a sequence chart showing operation related to transmission and reception of data among HMDs. 
         FIG. 13  is a flowchart for explaining the operation of the HMD. 
         FIG. 14  is a diagram showing a display example of the HMD. 
         FIG. 15  is a diagram showing a display example of the HMD. 
         FIG. 16  is a diagram showing a display example of the HMD. 
         FIG. 17  is a diagram showing a display example of the HMD. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  is a schematic configuration diagram of a mobile machine composite control system  1  according to an embodiment applied with the invention. 
     The mobile machine composite control system  1  (a display system) is a display system configured by a mobile machine control system  300  including a mobile machine (a mobile body)  310  and an HMD (Head Mounted Display: a head-mounted display device)  100  worn and used by an operator who pilots the mobile machine  310 . In the mobile machine composite control system  1 , a plurality of operators respectively wear HMDs  100  (display devices) and pilot mobile machines  310 . The mobile machine composite control system  1  includes a plurality of mobile machine control systems  300 . 
     In an example shown in  FIG. 1 , the mobile machine composite control system  1  is configured by three mobile machine control systems  300 A,  300 B, and  300 C. The number of mobile machine control systems  300  configuring the mobile machine composite control system  1 , that is, the number of HMDs  100  and the number of mobile machines  310  are optional and may be two or less or may be four or more. The mobile machine composite control system  1  may include the HMD  100  worn by an operator who does not pilot the mobile machine  310 . 
     In the following explanation, a plurality of HMDs  100  and a plurality of mobile machines  310  are distinguished by signs and described as HMD  100 A,  110 B, and  100 C and mobile machines  310 A,  310 B, and  310 C. When it is necessary to distinguish the respective HMDs  100 , the HMDs  100  are described as HMDs  100 A,  100 B, and  100 C. When the HMDs  100  are not distinguished, the HMDs  100  are described as HMD  100 . Similarly, when it is necessary to distinguish the respective mobile machines  310 , the mobile machines  310  are described as mobile machines  310 A,  310 B, and  310 C. When the mobile machines  310  are not distinguished, the mobile machines  310  are described as mobile machine  310 . 
     Although not shown in the figure, the mobile machine  310 A is piloted by an operator A, the mobile machine  310 B is piloted by an operator B, and the mobile machine  310 C is piloted by an operator C. The operator can be called user. In the following explanation, the operator is referred to as user. 
     In this embodiment, the mobile machine  310  is illustrated as a form of the mobile body according to the invention. The mobile machine  310  is an aerial vehicle that flies according to rotation of four propellers  321 ,  322 ,  323 , and  324 . Alternatively, the mobile machine  310  is a type of a so-called Drone that means an unmanned aerial vehicle (UAV) and can also be called quadricopter. The mobile machine  310  is remotely piloted by the HMD  100 . That is, the mobile machine  310 A is remotely piloted by the HMD  100 A. Similarly, the mobile machine  310 B is piloted by the HMD  100 B and the mobile machine  310 C is piloted by the HMD  100 C. 
     The propellers  321 ,  322 ,  323 , and  324  are respectively driven by flight motors  331 ,  332 ,  333 , and  334  to rotate and lift the mobile machine  310 . A mobile machine camera  335  is provided in the mobile machine  310 . The mobile machine  310  can transmit a captured image captured by the mobile machine camera  335  to the HMD  100 . The mobile machine camera  335  may be directly fixed to a main body of the mobile machine  310  or may be fixed to the main body of the mobile machine  310  via a pedestal such as a Gimbal or a platform. A mechanism for changing and adjusting an imaging direction of the mobile machine camera  335  may be provided in the pedestal of the mobile machine camera  335 . 
     The HMD  100  is a display device including an image display section  20  (a display section) that causes the user to visually recognize a virtual image in a state in which the image display section  20  is worn on the head of the user and a control device  10  that controls the image display section  20 . As explained below with reference to  FIG. 3 , the control device  10  includes a main body having a flat box shape. The control device  10  includes, in the main body, operation sections such as various switches and an operation pad that receive operation by the user. The user operates the operation sections, whereby the control device  10  functions as a control device that controls the HMD  100 . 
     The HMD  100  executes communication between the HMD  100  and the mobile machine  310 . The HMD  100  receives the image data from the mobile machine  310  and displays, with the image display section  20 , an image based on the received image data. Consequently, the user can visually recognize, with the image display section  20 , a captured image captured by the mobile machine  310 , operate the control device  10 , and pilot the mobile machine  310 . 
     A form of connecting the HMD  100  and the mobile machine  310  is optional. For example, the control device  10  and the mobile machine  310  transmit and receive various data using radio signals having frequencies explained below. 
       FIG. 2  is functional block diagram of the mobile machine  310 . The configuration of a control system of the mobile machine  310  is shown. The configuration is common to the mobile machines  310 A,  310 B, and  310 C. Therefore, the mobile machines  310 A,  310 B, and  310 C are explained without being distinguished. 
     The control system of the mobile machine  310  is configured by a mobile-machine control section  341  that controls the mobile machine  310  and sections connected to the mobile-machine control section  341 . Specifically, the mobile machine  310  includes the mobile-machine control section  341 , a mobile-machine storing section  342 , a mobile-machine communication section  343 , a GPS device  344 , a flight control section  345 , a camera control section  346 , a motor controller  347 , a posture sensor  348  and indicator  349 . Although not shown in the figure, the mobile machine  310  includes a battery that supplies electric power to sections including the flight motors  331 ,  332 ,  333 , and  334  ( FIG. 1 ) and a battery control circuit that controls the power supply by the battery. 
     The mobile-machine control section  341  includes an arithmetic processing device (a processor) such as a CPU (Central Processing Unit) or a microcomputer. The mobile-machine control section  341  controls the mobile machine  310  by executing a computer program. The mobile-machine control section  341  may include a ROM (Read Only Memory), a RAM (Random Access Memory), and other peripheral circuits. 
     The mobile-machine storing section  342  that stores data and the like processed by the mobile-machine control section  341  is connected to the mobile-machine control section  341 . The mobile-machine storing section  342  includes a storage device such as a semiconductor memory element and stores various data concerning the control of the mobile machine  310  and computer programs executed by the mobile-machine control section  341 . 
     The mobile-machine communication section  343  is connected to the mobile-machine control section  341 . The mobile-machine communication section  343  includes an antenna, an RF circuit, a baseband circuit, and a communication control circuit. Alternatively, the mobile-machine communication section  343  is configured by a device obtained by integrating the antenna, the RF circuit, the baseband circuit, the communication control circuit, and the like. The mobile-machine communication section  343  executes wireless communication between the mobile-machine communication section  343  and the HMD  100 . The mobile-machine communication section  343  executes the wireless communication in a 27 MHz band, a 40 MHz band, a 2.4 GHz band, and the like, which are frequencies for radio control. Alternatively, the mobile-machine communication section  343  performs wireless communication conforming to standards such as a Bluetooth (registered trademark) and a wireless LAN (including Wi-Fi (registered trademark)). The mobile-machine communication section  343  executes communication with the HMD  100  according to the control by the mobile-machine control section  341 , receives a command transmitted by the HMD  100 , and outputs the command to the mobile-machine control section  341 . The mobile-machine communication section  343  transmits captured image data of the mobile machine camera  335  to the HMD  100 . 
     The mobile-machine communication section  343  included in the mobile machine  310 A performs communication with the HMD  100 A. Similarly, the mobile-machine communication section  343  of the mobile machine  310 B communicates with the HMD  100 B. The mobile-machine communication section  343  of the mobile machine  310 C communicates with the HMD  100 C. 
     The GPS (Global Positioning System) device  344  is a device that measures (positions) the position of the mobile machine  310  by receiving and analyzing signals transmitted from GPS satellites. The GPS device  344  performs the positioning according to the control by the mobile-machine control section  341  and outputs a positioning result to the mobile-machine control section  341 . The positioning result output by the GPS device  344  includes the latitude and the longitude of the mobile machine  310  and may include the altitude of the mobile machine  310 . 
     The flight control section  345  is connected to the mobile-machine control section  341 . The flight control section  345  is connected to the motor controller  347  and the posture sensor  348 . The motor controller  347  is a circuit that drives the flight motors  331 ,  332 ,  333 , and  334  according to the control by the flight control section  345 . 
     The posture sensor  348  is a sensor that detects the posture and the movement of the mobile machine  310 . For example, the posture sensor  348  can include any one of a gyro sensor, an acceleration sensor, a speed sensor, and an altitude sensor. The posture sensor  348  may include a terrestrial magnetism sensor for detecting the direction of the mobile machine  310 . For example, as the posture sensor  348 , a nine-axis motion sensor unit obtained by integrating a three-axis gyro sensor, a three-axis acceleration sensor, and a three-axis terrestrial magnetism sensor may be used. The altitude sensor may be integrated in the motion sensor unit. The posture sensor  348  outputs a detection value to the flight control section  345  according to the control by the flight control section  345 . The posture sensor  348  may include a wind velocity sensor. 
     The flight control section  345  outputs, to the mobile-machine control section  341 , the detection value detected by the mobile machine  310  with the posture sensor  348  and/or the latitude and the longitude detected by the mobile machine  310  with the GPS device  344 . The mobile-machine control section  341  can transmit a part or all of detection values of the posture sensor  348  and detection results of the GPS device  344  to the HMD  100  with the mobile-machine communication section  343 . Information concerning the position of the mobile machine  310  transmitted to the HMD  100  by the mobile machine  310  is referred to as mobile machine position information. The mobile machine position information includes, for example, the altitude, the latitude, and the longitude of the mobile machine  310  and may include information concerning an external environment such as wind velocity. The mobile machine position information may include information other than the altitude, the latitude, and the longitude as information indicating the position of the mobile machine  310 . For example, the position of the mobile machine  310  may be represented by an address indication, a place name, or a lot number corresponding to a plane position of the mobile machine  310  or a facility name or a building name in the vicinity of or immediately below the mobile machine  310 . The mobile machine position information may include information indicating the position of the mobile machine  310  with a direction and a distance based on a preset landmark. The mobile machine position information may include information concerning an external environment such as wind velocity. 
     The information concerning the position of the mobile machine  310  transmitted to the HMD  100  by the mobile machine  310  may include, besides the mobile machine position information, mobile machine state information concerning an environment and a state of the mobile machine  310 . The mobile machine state information may include information related to the position of the mobile machine  310 . For example, the mobile machine state information may include information concerning a peripheral facility such as a facility name or a building name in the vicinity of or immediately below the mobile machine  310 . The mobile machine state information may include information concerning the environment (weather, temperature, humidity, wind velocity, wind direction, precipitation, etc.) of the mobile machine  310 . 
     The mobile machine  310  may transmit mobile machine position information based on a detection value and/or a detection result acquired at timing designated by the HMD  100  to the HMD  100 . The mobile machine  310  may transmit, at any time, mobile machine position information based on a detection value and/or a detection result acquired after the timing designated by the HMD  100  to the HMD  100 . 
     Note that a component with which the mobile machine  310  detects a position is not limited to the GPS device  344  and the posture sensor  348 . For example, the mobile machine  310  may receive a beacon signal from a wireless beacon transmitter set in advance in an area where the mobile machine  310  flies and detect the position of the mobile machine  310  on the basis of reception intensity and the like of the beacon signal. As the wireless beacon transmitter, an optical beacon device that transmits a beacon signal with light outside a visible region such as infrared light (IR) or a Bluetooth beacon that transmits a beacon signal with the Bluetooth can be used. The position of the mobile machine  310  detected in this case includes an altitude and a relative position with respect to the wireless beacon transmitter. In this case, the mobile-machine control section  341  only has to generate mobile machine position information including the altitude and the relative position with respect to the wireless beacon transmitter and transmit the mobile machine position information to the HMD  100 . 
     The camera control section  346  that controls the flight control section  345  is connected to the mobile-machine control section  341 . The flight control section  345  is set in the main body of the mobile machine  310  as explained above and images a predetermined direction. The flight control section  345  includes an imaging device  336  and a zoom mechanism  337  that moves an imaging lens (not shown in the figure) to adjust a zoom magnification. The imaging device  336  includes, for example, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. 
     The camera control section  346  drives the imaging device  336  and the zoom mechanism  337  according to the control by the mobile-machine control section  341 , performs imaging at a zoom magnification designated by the mobile-machine control section  341 , and outputs captured image data to the mobile-machine control section  341 . The mobile machine  310  executes imaging with the mobile machine camera  335  at a preset sampling cycle and generates captured image data. That is, the mobile machine  310  is considered to capture a moving image. The mobile machine  310  can transmit captured image data captured at timing designated by the HMD  100  to the HMD  100 . In this case, the HMD  100  can acquire captured image data of a still image captured by the mobile machine  310 . The mobile machine  310  can transmit, at any time, captured image data captured after the timing designated by the HMD  100  to the HMD  100 . In this case, the HMD  100  can acquire captured image data of a moving image (a video) captured by the mobile machine  310 . 
     When transmitting the captured image data of the mobile machine camera  335 , the mobile-machine control section  341  may transmit image data generated on the basis of the captured image data. For example, the mobile-machine control section  341  may change resolution and a frame rate of the captured image data of the mobile machine camera  335  to adjust a band and transmit adjusted image data. 
     An indicator  349  is connected to the mobile-machine control section  341 . The indicator  349  includes a light source such as an LED (Light Emitting Diode) and emits light in a light emission color and/or a light emission pattern corresponding to an operation state of the mobile machine  310 . The indicator  349  is disposed in a position visually recognizable from the outside during the flight of the mobile machine  310  such as the lower surface, the front surface, or the rear surface of a housing of the mobile machine  310 . The mobile-machine control section  341  causes the indicator  349  to emit light according to an operation state of the flight control section  345 . For example, the mobile-machine control section  341  causes the indicator  349  to emit light in red when the mobile machine  310  advances and causes the indicator  349  to emit light in green while the mobile machine  310  retracts. The mobile-machine control section  341  may flash the indicator  349  during a turn of the mobile machine  310 . 
       FIG. 3  is an explanatory diagram showing an exterior configuration of the HMD  100 . This configuration is common to the HMDs  100 A,  100 B, and  100 C. Therefore, the HMDs  100 A,  100 B, and  100 C are explained without being distinguished. The same applies to  FIGS. 4, 5, 6, 7, and 8 . 
     As shown in  FIG. 3 , the control device  10  includes a case  10 A (a housing) having a flat box shape. The case  10 A includes various switches, a track pad  14 , and the like that receive operation by the user. The user operates the switches, the track pad  14 , and the like, whereby the control device  10  functions as a control device that controls the HMD  100 . The case  10 A incorporates a functional section that controls the HMD  100 . 
     The image display section  20  is a wearing body worn on the head of the user. In this embodiment, the image display section  20  has an eyeglass shape. The image display section  20  includes a right display unit  22 , a left display unit  24 , a right light guide plate  26 , and a left light guide plate  28  in a main body including a right holding section  21 , a left holding section  23 , and a front frame  27 . 
     The right holding section  21  and the left holding section  23  respectively extend backward from both end portions of the front frame  27  and, like temples of eyeglasses, hold the image display section  20  on the head of the user. Of both the end portions of the front frame  27 , the end portion located on the right side of the user in a worn state of the image display section  20  is represented as an end portion ER and the end portion located on the left side of the user is represented as an end portion EL. The right holding section  21  is provided to extend from the end portion ER of the front frame  27  to a position corresponding to the right temporal region of the user in the worn state of the image display section  20 . The left holding section  23  is provided to extend from the end portion EL to a position corresponding to the left temporal region of the user in the worn state of the image display section  20 . 
     The right light guide plate  26  and the left light guide plate  28  are provided in the front frame  27 . The right light guide plate  26  is located in front of the right eye of the user in the worn state of the image display section  20  and causes the right eye to visually recognize an image. The left light guide plate  28  is located in front of the left eye of the user in the worn state of the image display section  20  and causes the left eye to visually recognize the image. 
     The front frame  27  has a shape obtained by coupling one end of the right light guide plate  26  and one end of the left light guide plate  28  to each other. A position of the coupling corresponds to the middle of the forehead of the user in the worn state in which the user wears the image display section  20 . In the front frame  27 , a nose pad section in contact with the nose of the user in the worn state of the image display section  20  may be provided in the coupling position of the right light guide plate  26  and the left light guide plate  28 . In this case, the image display section  20  can be held on the head of the user by the nose pad section and the right holding section  21  and the left holding section  23 . A belt (not shown in the figure) in contact with the back of the head of the user in the worn state of the image display section  20  may be coupled to the right holding section  21  and the left holding section  23 . In this case, the image display section  20  can be held on the head of the user by the belt. 
     The right display unit  22  is a unit related to display of an image by the right light guide plate  26 . The right display unit  22  is provided in the right holding section  21  and located in the vicinity of the right temporal region of the user in the worn state. The left display unit  24  is a unit related to display of an image by the left light guide plate  28 . The left display unit  24  is provided in the left holding section  23  and located in the vicinity of the left temporal region of the user in the worn state. Note that the right display unit  22  and the left display unit  24  are collectively simply referred to as “display driving section” as well. 
     The right light guide plate  26  and the left light guide plate  28  in this embodiment are optical sections formed of light transmissive resin or the like and are, for example, prisms. The right light guide plate  26  and the left light guide plate  28  guide image lights emitted by the right display unit  22  and the left display unit  24  to the eyes of the user. 
     The image display section  20  guides image lights respectively generated by the right display unit  22  and the left display unit  24  to the right light guide plate  26  and the left light guide plate  28  and displays an image by causing the user to visually recognize a virtual image with the image light. When the external light is transmitted through the right light guide plate  26  and the left light guide plate  28  and made incident on the eyes of the user from the front of the user, the image lights forming the virtual image and the external light are made incident on the eyes of the user. Visibility of the virtual image is affected by the intensity of the external light. Therefore, it is possible to adjust easiness of the visual recognition of the virtual image by, for example, disposing a right electronic shade  227  and a left electronic shade  247  ( FIG. 5 ) in the front frame  27 . 
     An HMD camera  61  is disposed in the front frame  27  of the image display section  20 . The HMD camera  61  desirably images an outside scene direction visually recognized by the user in the state in which the image display section  20  is worn. The HMD camera  61  is provided in a position not blocking the external light transmitted through the right light guide plate  26  and the left light guide plate  28  on the front surface of the front frame  27 . In an example shown in  FIG. 3 , the HMD camera  61  is disposed on the end portion ER side of the front frame  27 . The HMD camera  61  may be disposed on the end portion EL side or may be disposed in the coupling portion of the right light guide plate  26  and the left light guide plate  28 . 
     The HMD camera  61  is a digital camera including an imaging device such as a CCD or a CMOS and an imaging lens. Although the HMD camera  61  in this embodiment is a monocular camera, the HMD camera  61  may be configured by a stereo camera. The HMD camera  61  images at least a part of an outside scene (a real space) in the front side direction of the HMD  100 , in other words, a visual field direction of the user in the state in which the HMD  100  is mounted. In other words, the HMD camera  61  images a range or a direction overlapping the visual field of the user and images a direction gazed by the user. The breadth of an angle of view of the HMD camera  61  can be set as appropriate. However, in this embodiment, as explained below, the angle of view includes an outside world visually recognized by the user through the right light guide plate  26  and the left light guide plate  28 . More desirably, an imaging range of the HMD camera  61  is set such that the entire visual field of the user visually recognizable through the right light guide plate  26  and the left light guide plate  28  can be imaged. 
     The HMD camera  61  executes imaging according to control by an imaging control section  149  included in the HMD control section  141  and outputs captured image data to the imaging control section  149 . 
     The HMD  100  includes distance sensors  64  that detect a distance to a measurement target object located in a preset measurement direction. For example, the distance sensors  64  can be configured to detect a distance to a measurement target object located in front of the user. In this embodiment, the distance sensors  64  are disposed in the coupling portion of the right light guide plate  26  and the left light guide plate  28  in the front frame  27 . In this example, in the worn state of the image display section  20 , the position of the distance sensors  64  is substantially the middle of both the eyes of the user in the horizontal direction and above both the eyes of the user in the vertical direction. The measurement direction of the distance sensors  64  can be set to, for example, the front side direction of the front frame  27 . In other words, the measurement direction is a direction overlapping the imaging direction of the HMD camera  61 . 
     The distance sensors  64  include, for example, light sources such as LEDs or laser diodes and light receiving sections that receive reflected light of light emitted by the light sources and reflected on the measurement target object. The distance sensors  64  only have to execute triangulation processing and distance measurement processing based on a time difference according to the control by the HMD control section  141 . The distance sensors  64  may be configured to include sound sources that emit ultrasound and detecting sections that receive the ultrasound reflected on the measurement target object. In this case, the distance sensors  64  only have to execute the distance measurement processing on the basis of a time difference until the reflection of the ultrasound according to the control by the HMD control section  141 . 
     The control device  10  and the image display section  20  are connected by a connection cable  40 . The connection cable  40  is detachably connected to a connector  42  provided at an end portion of the case  10 A. That is, the connector  42 , into which the connection cable  40  can be inserted and from which the connection cable  40  can be pulled out, is provided in the case  10 A. The connection cable  40  is connected to the connector  42  when the image display section  20  is used. 
     The connection cable  40  is connected from the distal end of the left holding section  23  to various circuits provided on the inside of the image display section  20 . The connection cable  40  includes a metal cable or an optical fiber cable for transmitting digital data and may include a metal cable for transmitting an analog signal. A connector  46  is provided halfway in the connection cable  40 . 
     The connector  46  is a jack (an audio connector) to which a stereo mini plug is connected. The connector  46  and the control device  10  are connected by, for example, a line for transmitting an analog sound signal. In a configuration example shown in  FIG. 3 , a head set  30  including a right earphone  32  and a left earphone  34  configuring a stereo headphone and a microphone  63  is connected to the connector  46 . 
     For example, as shown in  FIG. 3 , the microphone  63  is disposed such that a sound collecting section of the microphone  63  faces the line of sight direction of the user. The microphone  63  collects sound and outputs a sound signal to a sound interface  182  ( FIG. 8 ). For example, the microphone  63  may be a monaural microphone or may be a stereo microphone, may be a microphone having directivity, or may be a nondirectional microphone. 
     The control device  10  includes the track pad  14 , an up-down key  15 , an LED display section  17 , and a power switch  18  as operated sections operated by the user. These operated sections are disposed on the surface of the case  10 A. The operated sections are operated by, for example, the fingers of the user. 
     The track pad  14  is a region for the user to perform touch operation for bringing a finger into contact with the track pad  14  on the front surface of the case  10 A. The track pad  14  may be the same plane as the front surface of the case  10 A. However, the track pad  14  is desirably configured to enable the user to distinguish the track pad  14  and regions other than the track pad  14 . For example, a line indicating the edge of the track pad  14  may be formed by printing or unevenness. The track pad  14  may be applied with surface treatment for differentiating a touch of the surface of the track pad  14  from a touch of the regions other than the track pad  14 . 
     The control device  10  can detect, on the front surface of the case  10 A, with a touch sensor  13  ( FIG. 7 ) explained below, touch operation on the track pad  14  by the user. When the touch sensor  13  detects the touch operation, the control device  10  specifies a position where the operation is detected. The track pad  14  can be used for operation for inputting an absolute position or a relative position in the track pad  14 . 
     The LED display section  17  is set on the front surface of the case  10 A. The LED display section  17  is located in the track pad  14 . The surface of the LED display section  17  is not different from other regions on the front surface of the case  10 A. The LED display section  17  includes a transmitting section (not shown in the figure) capable of transmitting light. The LED display section  17  emits light such that one or a plurality of LEDs set immediately under the transmitting section are lit, whereby the user can visually recognize signs and the like. In the example shown in  FIG. 3 , the LEDs of the LED display section  17  are lit, whereby three signs of a triangle, a circle, and a square appear. 
     The control device  10  can detect, with the touch sensor  13 , touch operation of the fingers of the user on the LED display section  17  and specify an operation position. Therefore, for example, the control device  10  can specify which of the signs appearing on the LED display section  17  the operation position corresponds to. Therefore, the LED display section  17  functions as a software button. For example, by associating the signs appearing on the LED display section  17  with the functions of the HMD  100 , it is possible to detect touch operation on the LED display section  17  as operation for the functions. In the HMD  100 , in the example shown in  FIG. 3 , the sign of the circle can be allocated to a home button. In this case, when touch operation is performed in the position of the sign of the circle, the HMD control section  141  detects operation of the home button. The sign of the square can be allocated to a history button. In this case, the HMD control section  141  detects touch operation on the sign of the square as operation of the history button. Similarly, the sign of the triangle can be allocated to a return button. The HMD control section  141  detects touch operation on the sign of the triangle as operation of the return button. 
     The up-down key  15  includes a pair of keys disposed on aside surface of the case  10 A to detect pressing operation. The up-down key  15  is used for an instruction input for an increase or a reduction of sound volume output from the right earphone  32  and the left earphone  34  and an instruction input for an increase or a decrease of the brightness of display of the image display section  20 . 
     The power switch  18  is a switch for switching ON/OFF of a power supply of the HMD  100 . 
     In the case  10 A, a USB connector  188  ( FIG. 7 ) is provided on a side surface on the same side as the power switch  18 . The USB connector  188  is an interface for connecting the control device  10  to an external apparatus. In this embodiment, as an example of the interface, a connector conforming to a USB standard is illustrated. The USB connector  188  is, for example, a connector having a shape and a size matching a micro USB standard. Specifications such as transfer speed are optional. 
     The control device  10  includes a battery  132  ( FIG. 7 ) as explained below. The control device  10  and the image display section  20  operate with electric power supplied by the battery  132 . Charging to the battery  132  can be performed by supplying electric power to the USB connector  188 . In the HMD  100 , charging can be performed by detaching the control device  10  and the image display section  20  and connecting only the control device  10  to a dedicated charging device. 
       FIG. 4  is a main part plan view showing the configuration of an optical system included in the image display section  20 . In  FIG. 4 , a left eye LE and a right eye RE of the user are shown for explanation. 
     As shown in  FIG. 4 , the right display unit  22  and the left display unit  24  are symmetrically configured. As a component for causing the right eye RE of the user to visually recognize an image, the right display unit  22  includes an OLED (Organic Light Emitting Diode) unit  221  that emits image light and a right optical system  251  including a lens group for guiding image light L emitted by the OLED unit  221 . The image light L is guided to the right light guide plate  26  by the right optical system  251 . 
     The OLED unit  221  includes an OLED panel  223  and an OLED driving circuit  225  that drives the OLED panel  223 . The OLED panel  223  is a self-emitting display panel configured by arranging, in a matrix shape, light emitting elements that emit lights with organic electroluminescence and respectively emit color lights of R (red), G (green), and B (blue). The OLED panel  223  includes a plurality of pixels, one pixel of which is a unit including one each of R, G, and B elements. The OLED panel  223  forms an image with the pixels arranged in the matrix shape. The OLED driving circuit  225  executes selection of a light emitting element included in the OLED panel  223  and energization to the light emitting element and causes the light emitting element of the OLED panel  223  to emit light according to the control by the HMD control section  141 . The OLED driving circuit  225  is fixed to the rear side of a rear surface, that is, a light emitting surface of the OLED panel  223  by bonding or the like. The OLED driving circuit  225  may be configured by, for example, a semiconductor device that drives the OLED panel  223  and may be mounted on a substrate (not shown in the figure) fixed to the rear surface of the OLED panel  223 . A temperature sensor  69  ( FIG. 7 ) is mounted on the substrate. 
     Note that the OLED panel  223  may be configured by arranging, in a matrix shape, light emitting elements that emit white light and disposing color filters corresponding to the colors of R, G, and B to be superimposed one on top of another. An OLED panel  223  of a WRGB configuration including a light emitting element that emits W (white) light in addition to the light emitting elements that respectively radiate the color lights of R, G, and B may be used. 
     The right optical system  251  includes a collimate lens that changes the image light L emitted from the OLED panel  223  to a light beam in a parallel state. The image light L changed to the light beam in the parallel state by the collimate lens is made incident on the right light guide plate  26 . A plurality of reflection surfaces that reflect the image light L are formed in an optical path for guiding light on the inside of the right light guide plate  26 . The image light L is guided to the right eye RE side through a plurality of times of reflection on the inside of the right light guide plate  26 . A half mirror  261  (a reflection surface) located in front of the right eye RE is formed on the right light guide plate  26 . The image light L is reflected on the half mirror  261  and emitted from the right light guide plate  26  toward the right eye RE. The image light L forms an image on the retina of the right eye RE and causes the user to visually recognize the image. 
     The left display unit  24  includes, as components for causing the left eye LE of the user to visually recognize an image, an OLED unit  241  that emits image light and a left optical system  252  including a lens group for guiding the image light L emitted by the OLED unit  241 . The image light L is guided to the left light guide plate  28  by the left optical system  252 . 
     The OLED unit  241  includes an OLED panel  243  and an OLED driving circuit  245  that drives the OLED panel  243 . The OLED panel  243  is a self-emitting display panel configured the same as the OLED panel  223 . The OLED driving circuit  245  executes selection of a light emitting element included in the OLED panel  243  and energization to the light emitting element and causes the light emitting element of the OLED panel  243  to emit light according to the control by the HMD control section  141 . The OLED driving circuit  245  is fixed to the rear side of a rear surface, that is, a light emitting surface of the OLED panel  243  by bonding or the like. The OLED driving circuit  245  may be configured by, for example, a semiconductor device that drives the OLED panel  243  and may be mounted on a substrate (not shown in the figure) fixed to the rear surface of the OLED panel  243 . A temperature sensor  239  is mounted on the substrate. 
     The left optical system  252  includes a collimate lens that changes the image light L emitted from the OLED panel  243  to a light beam in a parallel state. The image light L changed to the light beam in the parallel state by the collimate lens is made incident on the left light guide plate  28 . The left light guide plate  28  is an optical element in which a plurality of reflection surfaces that reflect the image light L are formed and is, for example, a prism. The image light L is guided to the left eye LE side through a plurality of times of reflection on the inside of the left light guide plate  28 . A half mirror  281  (a reflection surface) located in front of the left eye LE is formed on the left light guide plate  28 . The image light L is reflected on the half mirror  281  and emitted from the left light guide plate  28  toward the left eye LE. The image light L forms an image on the retina of the left eye LE and causes the user to visually recognize the image. 
     With this configuration, the HMD  100  functions as a see-through type display device. That is, the image light L reflected on the half mirror  261  and external light OL transmitted through the right light guide plate  26  are made incident on the right eye RE of the user. The image light L reflected on the half mirror  281  and the external light OL transmitted through the half mirror  281  are made incident on the left eye LE. In this way, the HMD  100  makes the image light L of the image processed on the inside and the external light OL incident on the eyes of the user to be superimposed one on top of the other. For the user, the outside scene is seen through the right light guide plate  26  and the left light guide plate  28 . An image formed by the image light L is visually recognized over the outside scene. 
     The half mirrors  261  and  281  are image extracting sections that reflect image lights respectively output by the right display unit  22  and the left display unit  24  and extract images. The half mirrors  261  and  281  can be considered display sections. 
     Note that the left optical system  252  and the left light guide plate  28  are collectively referred to as “left light guide section” as well. The right optical system  251  and the right light guide plate  26  are collectively referred to as “right light guide section” as well. The configuration of the right light guide section and the left light guide section is not limited to the example explained above. Any system can be used as long as a virtual image is formed in front of the eyes of the user using the image lights. For example, a diffraction grating may be used or a semitransmitting reflection film may be used. 
     The image display section  20  includes the right electronic shade  227  and the left electronic shade  247 . The right electronic shade  227  includes a shade driving section  228  ( FIG. 6 ) and a liquid crystal panel  229 . The left electronic shade  247  includes a shade driving section  248  ( FIG. 6 ) and a liquid crystal panel  249 . The liquid crystal panels  229  and  249  can be referred to as transmittance adjusting plates as well. 
     The liquid crystal panel  229  of the right electronic shade  227  is provided on the front surface side of the right light guide plate  26 , that is, the opposite side of the side of the head of the user. In  FIG. 2 , a state is shown in which the liquid crystal panel  229  is disposed apart from the right light guide plate  26 . However, the liquid crystal panel  229  is stuck to the surface of the right light guide plate  26 . The liquid crystal panel  229  is disposed to be superimposed on the right light guide plate  26  of the image display section  20 . 
     The liquid crystal panel  249  of the left electronic shade  247  is provided on the front surface side of the left light guide plate  28 , that is, the opposite side of the side of the head of the user. In  FIG. 2 , a state is shown in which the liquid crystal panel  249  is disposed apart from the left light guide plate  28 . However, the liquid crystal panel  249  is stuck to the surface of the left light guide plate  28 . The liquid crystal panel  249  is disposed to be superimposed on the left light guide plate  28  of the image display section  20 . 
     The liquid crystal panels  229  and  249  are transmissive liquid crystal panels in which plurality of pixels are arranged in a matrix shape. The liquid crystal panels  229  and  249  are configured by any liquid crystal among TN (twisted nematic) liquid crystal, guest host liquid crystal, PDLC (Polymer Dispersed Liquid Crystal), electrochromic, and gaschromic. 
     The liquid crystal panels  229  and  249  increase or reduce, in pixel units, the transmittance of external light guided from the outside to the eyes RE of the user according to an increase or a decrease of a supplied voltage. In the right electronic shade  227  and the left electronic shade  247  in this embodiment, the transmittance of the external light is 100% in a state without the supplied voltage and is 0% (the external light is blocked) in a state in which the supplied voltage the maximum. 
       FIGS. 5 and 6  are diagrams showing a main part configuration of the image display section  20 .  FIG. 5  is a main part perspective view of the image display section  20  viewed from the head side of the user. Note that, in  FIG. 5 , illustration of the connection cable  40  is omitted.  FIG. 6  is an explanatory diagram of the angle of view of the HMD camera  61 . 
     In  FIG. 5 , a side in contact with the head of the user of the image display section  20 , in other words, a side visible to the right eye RE and the left eye LE of the user is shown. In other words, the rear side of the right light guide plate  26  and the left light guide plate  28  is visible. 
     In  FIG. 5 , the half mirror  261  for irradiating image light on the right eye RE of the user and the half mirror  281  for irradiating image light on the left eye LE of the user are seen as substantially square regions. The entire right light guide plate  26  and left light guide plate  28  including the half mirrors  261  and  281  transmit external light as explained above. For this reason, for the user, an outside scene is visually recognized through the entire right light guide plate  26  and left light guide plate  28  and rectangular display images are visually recognized in the positions of the half mirrors  261  and  281 . 
     The HMD camera  61  is disposed at the end portion on the right side in the image display section  20  and images a direction that both the eyes of the user face, that is, the front for the user.  FIG. 6  is a diagram schematically showing the position of the HMD camera  61  in plan view together with the right eye RE and the left eye LE of the user. An angle of view (the imaging range) of the HMD camera  61  is indicated by C. Note that, although the angle of view C in the horizontal direction is shown in  FIG. 6 , an actual angle of view of the HMD camera  61  also expands in the up-down direction as in a general digital camera. 
     The optical axis of the HMD camera  61  is set in a direction including line of sight directions of the right eye RE and the left eye LE. An outside scene visually recognizable by the user in a state in which the user wears the HMD  100  is not always infinity. For example, as shown in  FIG. 6 , when the user gazes an object OB with both the eyes, lines of sight of the user are directed to the object OB as indicated by signs RD and LD in the figure. In this case, the distance from the user to the object OB is often approximately 30 cm to 10 m and more often approximately 1 m to 4 m. Therefore, concerning the HMD  100 , standards of an upper limit and a lower limit of the distance from the user to the object OB during a normal use may be set. The standards may be calculated by researches and experiments or the user may set the standards. The optical axis and the angle of view of the HMD camera  61  are desirably set such that the object OB is included in the angle of view when the distance to the object OB during the normal use is equivalent to the set standard of the upper limit and when the distance is equivalent to the set standard of the lower limit. 
     In general, an angular field of view of a human is approximately 200 degrees in the horizontal direction and approximately 125 degrees in the vertical direction. In the angular field of view, an effective field of view excellent in an information reception ability is approximately 30 degrees in the horizontal direction and approximately 20 degrees in the vertical direction. Further, a stable field of fixation in which a gazing point gazed by the human is quickly and stably seen is approximately 60 to 90 degrees in the horizontal direction and approximately 45 to 70 degrees in the vertical direction. In this case, when the gazing point is the object OB shown in  FIG. 6 , a field of view of approximately 30 degree in the horizontal direction and approximately 20 degrees in the vertical direction centering on the lines of sight RD and LD is the effective field of view. A field of view of approximately 60 to 90 degrees in the horizontal direction and approximately 45 to 70 degrees in the vertical direction is the stable field of fixation. A field of view of approximately 200 degrees in the horizontal direction and approximately 125 degrees in the vertical direction is the angular field of view. Further, an actual field of view visually recognized by the user through the image display section  20  and through the right light guide plate  26  and the left light guide plate  28  can be referred to as real field of view (FOV). In the configuration in this embodiment shown in  FIG. 3 , the real field of view is equivalent to an actual field of view visually recognized by the user through the right light guide plate  26  and the left light guide plate  28 . The real field of view is narrower than the angular field of view and the stable field of fixation but is wider than the effective field of view. 
     The angle of view C of the HMD camera  61  desirably enables imaging of a range wider than the field of view of the user. Specifically, the angle of view C is desirably wider than at least the effective field of view of the user. The angle of view C is more desirably wider than the real field of view of the user. The angle of view C is still more desirably wider than the stable field of fixation. The angle of view C is most desirably wider than the angular field of view of both the eyes of the user. 
     The HMD camera  61  may include a so-called wide-angle lens as an imaging lens and may be capable of imaging a wide angle of view. The wide-angle lens may include lenses called super-wide angle lens and semi-wide angle lens. The wide-angle lens may be a single focus lens or may be a zoom lens. The HMD camera  61  may include a lens group including a plurality of lenses. 
     The distance sensors  64  are disposed to face forward in the center between the right light guide plate  26  and the left light guide plate  28 . For example, the distance sensors  64  are configured, from the center position of the image display section  20 , to be capable of detecting the distance to an object located in the front direction of the user like the object OB shown in  FIG. 6 . The user wearing the HMD  100  turns the head to a gazing direction. Therefore, a gazing target can be considered to be present in the front of the image display section  20 . Therefore, if the front of the image display section  20  is assumed to be a detecting direction  64 A, the distance sensors  64  disposed in the center of the image display section  20  can detect the distance to the target gazed by the user. 
     As shown in  FIG. 5 , inner cameras  68  are disposed on the user side of the image display section  20 . A pair of inner cameras  68  is provided in the center position between the right light guide plate  26  and the left light guide plate  28  to respectively correspond to the right eye RE and the left eye LE of the user. The inner cameras  68  are a pair of cameras that respectively images the right eye RE and the left eye LE of the user. The inner cameras  68  perform the imaging according to the control by the HMD control section  141 . The HMD control section  141  analyzes captured image data of the inner cameras  68 . For example, the HMD control section  141  detects reflected light on the eyeball surfaces of the right eye RE and the left eye LE and an image of the pupils from the captured image data of the inner cameras  68  and specifies a line of sight direction of the user. The HMD control section  141  can calculate a change in the line of sight direction of the user. The HMD control section  141  may detect respective eyeball motions of the right eye RE and the left eye LE. 
     The movement of the line of sight of the user can also be regarded as a movement of an imaginary visual point of the user. 
     The HMD control section  141  may extract an image of the eyelids of the right eye RE and the left eye LE of the user from the captured image data of the inner cameras  68  and detect eyelid motions or detect states of the eyelids. In this embodiment, a configuration is illustrated in which the image display section  20  includes the pair of inner cameras  68 ,  68 . However, for example, one inner camera  68  may be provided in the center position of the image display section  20 . In this case, the one inner camera  68  desirably has an angle of view for enabling imaging of the right eye RE and the left eye LE. However, for example, only one of the right eye RE and the left eye LE may be imaged by the inner camera  68 . That is, the HMD control section  141  may detect a line of sight direction, an eyeball motion, an eyelid motion, a state of the eyelid, and the like of either one of the right eye RE and the left eye LE. 
     When detecting the line of sight directions of the right eye RE and the left eye LE from the captured images of the inner cameras  68 , the HMD control section  141  can calculate an angle of convergence of the right eye RE and the left eye LE. In  FIG. 6 , the angle of convergence is indicated by a sign PA. The angle of convergence PA corresponds to the distance to the object OB gazed by the user. That is, when the user three-dimensionally visually recognizes an image or an object, the angle of convergence of the right eye RE and the left eye LE is decided according to the distance to the visually recognized object. Therefore, it is possible to calculate the distance of the gazing of the user by detecting the angle of convergence. It is possible to induce a stereoscopic vision by displaying an image to induce the angle of convergence of the user. 
     The angle of convergence can be calculated from, for example, the captured image data of the inner cameras  68 . For example, a line of sight direction of the right eye RE is calculated from the captured image data of the inner cameras  68 . An angle LA in the line of sight direction of the right eye RE with respect to the front direction of the right eye RE is calculated from the line of sight direction. Similarly, a line of sight direction of the left eye LE is calculated from the captured image data of the inner cameras  68 . An angle RA in the line of sight direction of the left eye LE with respect to the front direction of the left eye LE is calculated from the line of sight direction. The angle of convergence PA is equal to a sum of the angles LA and RA. It is possible to easily calculate the angle of convergence PA. 
       FIG. 7  is a block diagram showing the configurations of the sections configuring the HMD  100 . 
     The control device  10  includes a main processor  140  that executes a computer program and controls the HMD  100 . A memory  118  and a nonvolatile storing section  121  are connected to the main processor  140 . An operation section  110  is connected to the main processor  140  as an input device. A six-axis sensor  111 , a magnetic sensor  113 , and a GPS  115  are connected to the main processor  140  as sensors. An HMD communication section  117  (a communication section), a sound codec  180 , an external connector  184 , an external memory interface  186 , the USB connector  188 , a sensor hub  192 , and an FPGA  194  are connected to the main processor  140 . These sections function as interfaces with the outside. 
     The main processor  140  is mounted on a controller board  120  incorporated in the control device  10 . The memory  118 , the nonvolatile storing section  121 , and the like may be mounted on the controller board  120  in addition to the main processor  140 . In this embodiment, the six-axis sensor  111 , the magnetic sensor  113 , the GPS  115 , the HMD communication section  117 , the memory  118 , the nonvolatile storing section  121 , the sound coded  180 , and the like are mounted on the controller board  120 . The external connector  184 , the external memory interface  186 , the USB connector  188 , the sensor hub  192 , the FPGA  194 , and an interface  196  may be mounted on the controller board  120 . 
     The memory  118  configures a work area where, when the main processor  140  executes a computer program, the main processor  140  temporarily stores the computer program to be executed and data to be processed. The nonvolatile storing section  121  is configured by a flash memory or an eMMC (embedded Multi Media Card). The nonvolatile storing section  121  stores the computer program to be executed by the main processor  140  and various data to be processed by the main processor  140  executing the computer program. 
     The main processor  140  detects contact operation on the operation surface of the track pad  14  and acquires an operation position on the basis of an operation signal input from the operation section  110 . 
     The operation section  110  includes buttons  11 , a touch sensor  13 , and an LED display section  17 . The touch sensor  13  detects touch operation on the track pad  14  and specifies an operation position of the detected touch operation. In this case, the operation section  110  outputs a control signal including data indicating the touch position on the track pad  14  to the main processor  140 . When operation of the buttons  11  is performed and when the touch sensor  13  detects the touch operation, an operation signal is output from the operation section  110  to the main processor  140 . 
     The LED display section  17  includes an LED (not shown in the figure) disposed immediately below the track pad  14  ( FIG. 3 ) and a driving circuit that lights the LED. The LED display section  17  lights, flashes, and extinguishes the LED according to the control by the main processor  140 . 
     The six-axis sensor  111  is a motion sensor (an inertial sensor) including a three-axis acceleration sensor and a three-axis gyro (angular velocity) sensor. As the six-axis sensor  111 , an IMU (Inertial Measurement Unit) obtained by modularizing the sensors may be adopted. 
     The magnetic sensor  113  is, for example, a three-axis terrestrial magnetism sensor. 
     The GPS (Global Positioning System)  115  includes a not-shown GPS antenna, receives radio signals transmitted from GPS satellites, and detects a coordinate of a present position of the control device  10 . 
     The six-axis sensor  111 , the magnetic sensor  113 , and the GPS  115  output detection values to the main processor  140  according to sampling cycles designated in advance. Alternatively, the six-axis sensor  111 , the magnetic sensor  113 , the GPS  115  output, in response to a request of the main processor  140 , the detection values to the main processor  140  at timing designated by the main processor  140 . 
     The HMD communication section  117  executes wireless communication between the HMD communication section  117  and an external apparatus. In this embodiment, the HMD communication section  117  executes wireless communication with HMD communication sections  117  included in the other HMDs  100 . The HMD communication section  117  includes an antenna, an RF circuit, a baseband circuit, and a communication control circuit. Alternatively, the HMD communication section  117  is configured by a device obtained by integrating the antenna, the RF circuit, the baseband circuit, and the communication control circuit, and the like. The HMD communication section  117  performs wireless communication conforming to the standards such as the Bluetooth and the wireless LAN (including Wi-Fi). 
     The HMD communication section  117  performs the wireless communication with the mobile-machine communication section  343  included in the mobile machine  310 . In this configuration, a frequency band and a communication system used for the communication by the HMD communication section  117  only have to be selected as appropriate such that the HMD communication section  117  can communicate with the mobile-machine communication section  343 . Therefore, like the mobile-machine communication section  343 , the HMD communication section  117  executes the wireless communication in a 27 MHz band, a 40 MHz band, a 2.4 GHz band, and the like, which are frequencies for radio control. Alternatively, the mobile-machine communication section  343  performs the wireless communication conforming to the standards such as the Bluetooth and the wireless LAN (including Wi-Fi). 
     The HMD  100  may include a communication section (not shown in the figure) separate from the HMD communication section  117  and perform communication with the mobile-machine communication section  343  through the communication section. 
     The HMD communication section  117  included in the HMD  100 A executes communication with the mobile machine  310 A. Similarly, the HMD communication section  117  included in the HMD  100 B communicates with the mobile machine  310 B. The HMD communication section  117  included in the HMD  100 C communicates with the mobile machine  310 C. 
     The HMD communication section  117  is also capable of executing communication with the HMD communication sections  117  included in the other HMDs  100 . Therefore, as explained below, the HMDs  100 A,  100 B, and  100 C configuring the mobile-machine composite control system  1  can mutually transmit and receive data. Further, the HMD communication section  117  of the HMD  100 A may be capable of transmitting data including commands not only to the mobile machine  310 A but also to the mobile machines  310 B and  310 C. Similarly, the HMDs  100 B and  100 C may be capable of transmitting data to the mobile machines  310 A,  310 B, and  310 C. In this case, for example, the HMD  100 A may transmit position information of the mobile machine  310 A to the mobile machines  310 B and  310 C and cause the mobile machines  310 B and  310 C to perform operation for avoiding excessive approach. 
     The sound interface  182  is an interface that inputs and outputs sound signals. In this embodiment, the sound interface  182  includes the connector  46  ( FIG. 3 ) provided in the connection cable  40 . The sound codec  180  is connected to the sound interface  182  and performs encoding/decoding of the sound signals input and output via the sound interface  182 . The sound codec  180  may include an A/D converter that performs conversion from an analog sound signal into digital sound data and a D/A converter that performs conversion opposite to the conversion of the A/D converter. For example, the HMD  100  in this embodiment outputs sound with the right earphone  32  and the left earphone  34  and collects sound with the microphone  63 . The sound codec  180  converts digital sound data output by the main processor  140  into an analog sound signal and outputs the analog sound signal via the sound interface  182 . The sound codec  180  converts an analog sound signal input to the sound interface  182  into digital sound data and outputs the digital sound data to the main processor  140 . 
     The external connector  184  is a connector to which an external apparatus communicating with the main processor  140  is connected. The external connector  184  is an interface to which the external apparatus is connected, for example, when the external apparatus is connected to the main processor  140  and debagging of a computer program executed by the main processor  140  and collection of a log of the operation of the HMD  100  are performed. 
     The external memory interface  186  is an interface to which a portable memory device is connectable. The external memory interface  186  includes, for example, a memory card slot, into which a card-type recording medium is inserted to enable reading of data, and an interface circuit. A size, a shape, and a standard of the card-type recording medium in this case are not limited and can be changed as appropriate. 
     The USB connector  188  includes a connector conforming to the USB standard and an interface circuit. A USB memory device, a smartphone, a computer, and the like can be connected to the USB connector  188 . A size and a shape of the USB connector  188  and a version of the USB standard matching the USB connector  188  can be selected and changed as appropriate. 
     The HMD  100  includes a vibrator  19 . The vibrator  19  includes a motor (not shown in the figure) and an eccentric rotor (not shown in the figure). The vibrator  19  generates vibration according to the control by the main processor  140 . For example, when operation on the operation section  110  is detected or when the power supply of the HMD  100  is turned on and off, the HMD  100  generates vibration with the vibrator  19  in a predetermined vibration pattern. 
     The sensor hub  192  and the FPGA  194  are connected to the image display section  20  via the interface (I/F)  196 . The sensor hub  192  acquires detection values of the various sensors included in the image display section  20  and outputs the detection values to the main processor  140 . The FPGA  194  executes processing of data transmitted and received between the main processor  140  and the sections of the image display section  20  and transmission of the data via the interface  196 . 
     The right display unit  22  and the left display unit  24  of the image display section  20  are respectively connected to the control device  10 . As shown in  FIG. 3 , in the HMD  100 , the connection cable  40  is connected to the left holding section  23 . A wire joined to the connection cable  40  is laid on the inside of the image display section  20 . The right display unit  22  and the left display unit  24  are respectively connected to the control device  10 . 
     The right display unit  22  includes a display unit board  210 . An interface (I/F)  211  connected to the interface  196 , a receiving section (Rx)  213  that receives data input from the control device  10  via the interface  211 , and an EEPROM  215  (storing section) are mounted on the display unit board  210 . 
     The interface  211  connects the receiving section  213 , the EEPROM  215 , a temperature sensor  217 , the HMD camera  61 , an illuminance sensor  65 , an LED indicator  67 , and the shade driving section  228  to the control device  10 . 
     The EEPROM (Electrically Erasable Programmable ROM)  215  stores various data to enable the main processor  140  to read the data. The EEPROM  215  stores, for example, data concerning a light emission characteristic and a display characteristic of the OLED units  221  and  241  included in the image display section  20  and data concerning characteristics of the sensors included in the right display unit  22  or the left display unit  24 . Specifically, the EEPROM  215  stores parameters related to gamma correction of the OLED units  221  and  241 , data for compensating for detection values of the temperature sensors  217  and  239 , and the like. These data are generated by a test during factory shipment of the HMD  100  and written in the EEPROM  215 . After the shipment, the main processor  140  can perform processing using the data of the EEPROM  215 . 
     The HMD camera  61  executes imaging according to a signal input via the interface  211  and outputs captured image data or a signal indicating an imaging result to the control device  10 . 
     As shown in  FIG. 3 , the illuminance sensor  65  is provided at the end portion ER of the front frame  27  and disposed to receive external light from the front of the user wearing the image display section  20 . The illuminance sensor  65  outputs a detection value corresponding to a received light amount (light reception intensity). 
     As shown in  FIG. 3 , the LED indicator  67  is disposed near the HMD camera  61  at the end portion ER of the front frame  27 . The LED indicator  67  is lit during execution of imaging by the HMD camera  61  to inform that the imaging is being performed. 
     The temperature sensor  217  detects temperature and outputs a voltage value or a resistance value corresponding to the detected temperature as a detection value. The temperature sensor  217  is mounted on the rear surface side of the OLED panel  223  ( FIG. 4 ). The temperature sensor  217  may be mounted on, for example, the same substrate as the OLED driving circuit  225 . With this configuration, the temperature sensor  217  mainly detects the temperature of the OLED panel  223 . 
     The inner cameras  68  execute imaging according to a signal input from the control device  10  via the interface  211  and output captured image data or signals indicating imaging results to the control device  10 . In  FIG. 7 , one inner camera  68  is shown. However, the pair of inner cameras  68  shown in  FIG. 5  may simultaneously operate. The respective pair of inner cameras  68  may be connected to the interface  211  and independently operate. 
     The distance sensors  64  execute distance detection according to a signal input from the control device  10  via the interface  211  and output signals indicating detection results to the control device  10 . In  FIG. 7 , one distance sensor  64  is shown. However, the pair of distance sensors  64 ,  64  shown in  FIG. 5  may simultaneously operate. The respective pair of distance sensors  64 ,  64  may be connected to the interface  211  and independently operate. 
     The shade driving section  228  controls, according to the main processor  140 , a voltage supplied to the right electronic shade  227  and increases or reduces, in pixel units, the transmittance of external light of the right electronic shade  227 . 
     The receiving section  213  receives data transmitted by the main processor  140  via the interface  211 . When receiving image data of an image displayed by the OLED unit  221 , the receiving section  213  outputs the received image data to the OLED driving circuit  225  ( FIG. 4 ). 
     The left display unit  24  includes a display unit board  210 . An interface (I/F)  231  connected to the interface  196  and a receiving section (Rx)  233  that receives data input from the control device  10  via the interface  231  are mounted on the display unit board  210 . A six-axis sensor  235  (a movement sensor) and a magnetic sensor  237  are mounted on the display unit board  210 . 
     The interface  231  connects the receiving section  233 , the six-axis sensor  235 , the magnetic sensor  237 , the temperature sensor  239 , and the shade driving section  248  to the control device  10 . 
     The six-axis sensor  235  is a motion sensor (an inertial sensor) including a three-axis acceleration sensor and a three-axis gyro (angular velocity) sensor. As the six-axis sensor  235 , an IMU (Inertial Measurement Unit) obtained by modularizing the sensors may be adopted. 
     The magnetic sensor  237  is, for example, a three-axis terrestrial magnetism sensor. 
     The temperature sensor  239  detects temperature and outputs a voltage value or a resistance value corresponding to the detected temperature as a detection value. The temperature sensor  239  is mounted on the rear surface side of the OLED panel  243  ( FIG. 4 ). The temperature sensor  239  may be mounted on, for example, the same substrate as the OLED driving circuit  245 . With this configuration, the temperature sensor  239  mainly detects the temperature of the OLED panel  243 . 
     The temperature sensor  239  may be incorporated in the OLED panel  243  or the OLED driving circuit  245 . The substrate may be a semiconductor substrate. Specifically, when the OLED panel  243  functioning as an Si-OLED is mounted as an integrated circuit on an integrated semiconductor chip together with the OLED driving circuit  245  and the like, the temperature sensor  239  may be mounted on the semiconductor chip. 
     The shade driving section  248  controls, according to the main processor  140 , a voltage supplied to the left electronic shade  247  and increases or reduces, in pixel units, the transmittance of external light of the left electronic shade  247 . 
     The HMD camera  61 , the distance sensors  64 , the illuminance sensor  65 , the inner cameras  68 , and the temperature sensor  217  included in the right display unit  22  and the six-axis sensor  235 , the magnetic sensor  237 , and the temperature sensor  239  included in the left display unit  24  are connected to the sensor hub  192 . The sensor hub  192  performs setting and initialization of sampling cycles of the sensors according to the control by the main processor  140 . The sensor hub  192  executes energization to the sensors, transmission of control data, acquisition of detection values, and the like according to the sampling cycles of the sensors. The sensor hub  192  outputs detection values of the sensors included in the right display unit  22  and the left display unit  24  to the main processor  140  at preset timing. The sensor hub  192  may include a function of temporarily retaining the detection values of the sensors according to the timing of the output to the main processor  140 . The sensor hub  192  may include a function of coping with differences in signal formats or data formats of output values of the sensors, converting the output values into data of a standardized data format, and outputting the data to the main processor  140 . 
     The sensor hub  192  starts and stops energization to the LED indicator  67  according to the control by the main processor  140  and lights or flashes the LED indicator  67  according to timings when the HMD camera  61  starts and ends imaging. 
     The control device  10  includes a power supply section  130  and operates with electric power supplied from the power supply section  130 . The power supply section  130  includes a chargeable battery  132  and a power-supply control circuit  134  that performs detection of a residual capacity of the battery  132  and control of charging to the battery  132 . The power-supply control circuit  134  is connected to the main processor  140  and outputs a detection value of the residual capacity of the battery  132  or a detection value of a voltage to the main processor  140 . The control device  10  may supply electric power to the image display section  20  on the basis of the electric power supplied by the power supply section  130 . The main processor  140  may be capable of controlling a supply state of electric power from the power supply section  130  to the sections of the control device  10  and the image display section  20 . 
     The HMD  100  may include an interface (not shown in the figure) that connects various external devices functioning as supply sources of contents. The interface may be an interface adapted to wired connection such as a USB interface, a micro USB interface, or an interface for a memory card or may be configured by a wireless communication interface. An external device in this case is an image supply device that supplies an image to the HMD  100 . A personal computer (PC), a cellular phone terminal, a portable game machine, or the like is used. In this case, the HMD  100  can output an image and sound based on content data input from the external devices. 
       FIG. 8  is a functional block diagram of an HMD storing section  170  and the HMD control section  141  configuring a control system of the control device  10 . The HMD storing section  170  shown in  FIG. 8  is a logical storing section configured by the nonvolatile storing section  121  ( FIG. 7 ). The HMD storing section  170  may include the EEPROM  215 . The main processor  140  executes computer programs, whereby the HMD control section  141  and the various functional sections included in the HMD control section  141  are formed by cooperation of software and hardware. The HMD control section  141  and the functional sections configuring the HMD control section  141  are configured by, for example, the main processor  140 , the memory  118 , and the nonvolatile storing section  121 . 
     The HMD control section  141  executes various kinds of processing using data stored by the HMD storing section  170  and controls the HMD  100 . 
     The HMD storing section  170  stores various data processed by the HMD control section  141 . The HMD storing section  170  stores setting data  171 , display setting data  172 , captured image data  173 , mobile machine identification data  174 , and moving area data  175 . 
     The HMD storing section  170  may store content data including contents including images and videos displayable by the image display section  20 . 
     The setting data  171  includes various set values related to the operation of the HMD  100 . When the HMD control section  141  uses parameters, a determinant, an arithmetic expression, an LUT (Look UP Table), and the like when controlling the HMD  100 , the parameters, the determinant, the arithmetic expression, the LUT (Look UP Table), and the like may be included in the setting data  171 . 
     The display setting data  172  is data concerning an image displayed by the image display section  20 . Specifically, the display setting data  172  includes setting concerning a display form of an image in the case in which the user pilots the mobile machine  310 . 
     The display setting data  172  includes, for example, information such as a display size and a display position in the case in which image data received by the HMD communication section  117  from the mobile machine  310  is displayed on the image display section  20 . The HMD control section  141  is capable of displaying, on the image display section  20 , images and regions allocated with specific functions such as icons, widgets, and a menu screen. The HMD control section  141  can realize a GUI (Graphical User Interface) using the images and the regions. The display setting data  172  may include information concerning necessity of the display, display positions, and the like of the images and the regions or may include image data for displaying the images and the regions. 
     The captured image data  173  is image data received from the mobile machine  310 . The HMD control section  141  causes the HMD storing section  170  to store, as the captured image data  173 , the image data received from the mobile machine  310 . 
     The HMD control section  141  of the HMD  100 A stores, as the captured image data  173 , captured image data received from the mobile machine  310 A. As explained above, the HMDs  100 A,  100 B, and  100 C are capable of mutually performing data communication. For example, the HMDs  100 A,  100 B, and  100 C can transmit and receive captured image data respectively captured by the mobile machines  310 A,  310 B, and  310 C with the mobile machine cameras  335 . In this case, the HMDs  100 A,  100 B, and  100 C store, as the captured image data  173 , captured image data received from the other HMDs  100 . Specifically, when receiving captured image data of the mobile machines  310 B and  310 C from the HMDs  100 B and  100 C, the HMD  100 A stores the captured image data as the captured image data  173 . The same applies to the HMDs  100 B and  100 C. 
     The mobile machine identification data  174  includes information for identifying the mobile machine  310  with which the control device  10  communicates. The mobile machine identification data  174  may include a model name, a model number, a manufacturer name, a manufacturing number, and a peculiar ID set during manufacturing of the mobile machine  310 . Alternatively, the mobile machine identification data  174  may include identification information such as an ID of the mobile machine  310  set by the user. The HMDs  100 A,  100 B, and  100 C can respectively identify the mobile machines  310 A,  310 B, and  310 C using the mobile machine identification data  174 . 
     The mobile machine identification data  174  may include information for authentication used by the HMD  100  to authenticate the mobile machine control system  300 . When the control device  10  communicates with the mobile machine  310  through the HMD communication section  117 , the mobile machine identification data  174  may include information necessary for the communication. Specifically, the mobile machine identification data  174  may include, for example, authentication information for communication such as a network address, a network ID, and a password. 
     The moving area data  175  includes information concerning a moving area set in advance as a region to which the mobile machine  310  is moved (flown). For example, the moving area includes regions (air regions and ground regions) in which the mobile machines  310 A,  310 B, and  310 C move (fly). The moving area data  175  is map data including the air regions and the ground regions. The moving area data  175  is not limited to data concerning plane positions and may include data concerning altitudes. 
     The data included in the moving area data  175  and the positions of the mobile machines  310 A,  310 B, and  310 C can be associated by latitude and longitude capable of indicating absolute positions in the real space. The data included in the moving area data  175  and the positions of the mobile machines  310 A,  310 B, and  310 C may be able to be associated by relative positions with respect to a reference position set in the real space. 
     The HMD control section  141  includes functions of an operating system (OS)  143 , an image processing section  145 , a display control section  147 , an imaging control section  149 , a detection control section  151 , a communication control section  153 , an image-data acquiring section  154 , a position estimating section  155 , a position-information acquiring section  156 , an operation detecting section  157 , and a command generating section  159 . 
     The function of the operating system  143  is a function of a control program stored by the HMD storing section  170 . The other sections of the HMD control section  141  are functions of application programs executed on the operating system  143 . 
     The image processing section  145  generates, on the basis of image data of an image or a video displayed by the image display section  20 , signals transmitted to the right display unit  22  and the left display unit  24 . The signals generated by the image processing section  145  may be a vertical synchronization signal, a horizontal synchronization signal, a clock signal, an analog image signal, and the like. 
     The image processing section  145  may perform, according to necessity, resolution conversion processing for converting the resolution of the image data into resolution suitable for the right display unit  22  and the left display unit  24 . The image processing section  145  may execute, for example, image adjustment processing for adjusting the luminance and the chroma of the image data and 2D/3D conversion processing for creating 2D image data from 3D image data or creating 3D image data from 2D image data. When executing these kinds of image processing, the image processing section  145  generates a signal for displaying an image on the basis of image data after the processing and transmits the signal to the image display section  20  via the connection cable  40 . 
     Besides being realized by the main processor  140  executing a computer program, the image processing section  145  may be configured by hardware (e.g., a DSP (Digital Signal Processor)) separate from the main processor  140 . 
     The display control section  147  generates a control signal for controlling the right display unit  22  and the left display unit  24  and controls, with the control signal, generation and emission of image lights by the right display unit  22  and the left display unit  24 . Specifically, the display control section  147  controls the OLED driving circuits  225  and  245  to execute display of images by the OLED panels  223  and  243 . The display control section  147  performs, for example, control of timing when the OLED driving circuits  225  and  245  perform drawing on the OLED panels  223  and  243  on the basis of signals output by the image processing section  145  and control of the luminance of the OLED panels  223  and  243 . 
     The display control section  147  causes, on the basis of the display setting data  172 , the image display section  20  to display various images. For example, the display control section  147  causes the image display section  20  to display icons, widgets, menus, and the like according to setting of the display setting data  172 . 
     The imaging control section  149  controls the HMD camera  61  to execute imaging, generates captured image data, and temporarily stores the captured image data in the HMD storing section  170 . When the HMD camera  61  is configured as a camera unit including a circuit that generates captured image data, the imaging control section  149  acquires the captured image data from the HMD camera  61  and temporarily stores the captured image data in the HMD storing section  170 . 
     The imaging control section  149  may control the inner cameras  68  to image the right eye RE and the left eye LE of the user. In this case, the HMD control section  141  may analyze captured image data captured by the inner cameras  68  according to the control by the imaging control section  149  and detect motions of the right eye RE and the left eye LE of the user. In this case, the HMD control section  141  may calculate a moving direction, a movement amount, and the like concerning each of or at least either one of the right eye RE and the left eye LE. 
     The detection control section  151  acquires detection values of the various sensors included in the HMD  100 . The sensors controlled by the detection control section  151  includes, for example, the six-axis sensor  111 , the magnetic sensor  113 , the temperature sensor  217 , the six-axis sensor  235 , the magnetic sensor  237 , the distance sensors  64 , and the illuminance sensor  65 . The sensors may include the GPS  115 . 
     The detection control section  151  functions as a receiving section and receives operation on the HMD  100 . The detection control section  151  detects operation on the buttons  11  and the touch sensor  13  included in the control device  10 . The detection control section  151  detects operation by movement of the control device  10  on the basis of detection values and/or changes in the detection values of the six-axis sensor  111  and the magnetic sensor  113  included in the control device  10 . The detection control section  151  detects operation by movement of the image display section  20  on the basis of detection values and/or changes in the detection values of the six-axis sensor  235  and the magnetic sensor  237  included in the image display section  20 . For example, the detection control section  151  detects the operation when the movement of the control device  10  and/or the image display section  20  corresponds to a movement of a preset form. 
     The communication control section  153  controls the HMD communication section  117  to execute communication between the HMD communication section  117  and the mobile machine  310  and the other HMDs  100 . That is, the communication control section  153  of the HMD  100 A executes communication with the mobile machine  310 A and further executes communication with the HMDs  100 B and  100 C through the HMD communication section  117 . 
     The image-data acquiring section  154  receives, using data communication executed according to the control by the communication control section  153 , captured image data transmitted from the mobile machine  310 . For example, the image-data acquiring section  154  extracts data corresponding to the captured image data from data transmitted and received by the HMD communication section  117  according to the control by the communication control section  153 . 
     The image-data acquiring section  154  included in the HMD  100 A may receive captured image data transmitted by the mobile machine  310 A or may receive captured image data transmitted by the mobile machines  310 B and  310 C. When the HMDs  100 B and  100 C transmit captured image data received from the mobile machine  310  to the HMD  100 A, the image-data acquiring section  154  included in the HMD  100 A may receive the transmitted captured image data. These functions are the same in the image-data acquiring sections  154  included in the HMDs  100 B and  100 C. 
     The position estimating section  155  estimates a position of the mobile machine  310 . The position estimating section  155  may specify the position of the mobile machine  310  on the basis of position information of the mobile machine  310 . That is, the position estimating section  155  may estimate the position of the mobile machine  310  on the basis of mobile machine position information acquired by the position-information acquiring section  156  explained below. Alternatively, in a state in which the mobile machine  310  is located in the moving area, the position estimating section  155  performs processing for estimating a position of the mobile machine  310  on the basis of captured image data transmitted by the mobile machine  310 . 
     The position estimating section  155  of the HMD  100 A estimates a position of the mobile machine  310 A. The position estimating section  155  of the HMD  100 A may be capable of estimating positions of the mobile machines  310 B and  310 C on the basis of data received from the HMDs  100 B and  100 C. 
     The position-information acquiring section  156  acquires mobile machine position information of the mobile machine  310  using data communication executed according to the control by the communication control section  153 . For example, the position-information acquiring section  156  extracts data corresponding to the mobile machine position information from various data received by the HMD communication section  117  according to the control by the communication control section  153 . 
     The position-information acquiring section  156  included in the HMD  100 A may receive mobile machine position information transmitted by the mobile machine  310 A or may receive mobile machine position information transmitted by the mobile machines  310 B and  310 C. When the HMDs  100 B and  100 C transmit mobile machine position information received from the mobile machine  310  to the HMD  100 A, the position-information acquiring section  156  included in the HMD  100 A may receive the transmitted mobile machine position information. These functions are the same in the position-information acquiring sections  156  included in the HMDs  100 B and  100 C. 
     The operation detecting section  157  (a position designating section) detects operation by the user wearing the image display section  20  and detects, for example, position indicating operation. The operation detecting section  157  analyzes captured image data captured by the HMD camera  61  according to the control by the imaging control section  149  and extracts an image of a pointer (a finger, a hand, or another part of the body of the user, another object, or the like) from the captured image data. The operation detecting section  157  specifies a position of the image of the pointer in the captured image data and converts the specified position into a relative position with respect to the image display section  20 . The operation detecting section  157  outputs the position after the conversion as an operation position. Consequently, the user wearing the image display section  20  can perform the position indicating operation by locating the pointer in the imaging range of the HMD camera  61  or moving the pointer in the imaging range. 
     The command generating section  159  generates a command according to the operation detected by the detection control section  151  or the operation detected by the operation detecting section  157 . The command generated by the command generating section  159  is a command for operating the mobile machine  310 . The command is, for example, a command for instructing a rise (floating), a fall, an advance (movement), a retraction, a turn (rotation), a reverse turn (reverse rotation), and the like, a command for instructing the mobile machine  310  to perform a routine operation, or a command for instructing the mobile machine  310  to transmit captured image data. The command generated by the command generating section  159  is transmitted to the mobile machine  310  by the HMD communication section  117 . 
     A data format of the command (equivalent to the command according to the invention) generated by the command generating section  159  and a process for processing the command are not particularly limited as long as the command instructs the operation of the mobile machine  310 . Specifically, the command generated by the command generating section  159  may be a command for the mobile-machine control section  341  to control the sections in the mobile machine  310 , that is, an internal command itself of the mobile machine  310  or may be data serving as a source for causing the mobile-machine control section  341  to generate the internal command. For example, the mobile-machine control section  341  may receive a command generated by the command generating section  159  and transmitted by the HMD communication section  117  and generate, on the basis of the command, an internal command for controlling the flight control section  345 , the camera control section  346 , the indicator  349 , and the like. Therefore, the command generating section  159  may have a function of generating an internal command for the mobile-machine control section  341  to control the flight control section  345 , the camera control section  346 , the indicator  349 , and the like or may have a function of generating control data and the like of a format interpretable by the mobile-machine control section  341 . The internal command may include, for example, the routine operation command explained above. 
     The command generating section  159  of the HMD  100 A generates a command corresponding to the mobile machine  310 A piloted using the HMD  100 A. The command corresponding to the mobile machine  310 A generated by the command generating section  159  of the HMD  100 A at least indicates data of a format that the mobile-machine control section  341  can receive, interpret, and process and is not limited to the internal command of the mobile machine  310 A. When at least a part of the mobile machines  310 A,  310 B, and  310 C operate according to a different command, the command generating section  159  of the HMD  100 A only has to be capable of generating a command corresponding to the mobile machine  310 A. The command generating section  159  of the HMD  100 A may be capable of generating commands corresponding to the mobile machines  310 B and  310 C. 
     Further, the command generating section  159  may generate a command on the basis of data received from the other HMDs  100 . 
     For example, the HMD  100 A may generate a command for the mobile machine  310 A according to data received from the HMD  100 B and transmit the command with the HMD communication section  117 . This operation is equivalent to operation of the HMD  100 B for indirectly transmitting the command to the mobile machine  310 A via the HMD  100 A. The HMDs  100 A,  100 B, and  100 C may be capable of mutually executing this operation. In this case, even when commands corresponding to the mobile machines  310 A,  310 B, and  310 C are different, for example, when the mobile machines  310 A,  310 B, and  310 C are different, the commands can be transmitted from one HMD  100  to the respective mobile machines  310 . 
     When the command is generated by the command generating section  159  and transmitted to the mobile machine  310  by the HMD communication section  117 , an encrypted command may be transmitted and received between the HMD communication section  117  and the mobile-machine communication section  343  of the mobile machine  310 . For example, the HMD communication section  117  and the mobile-machine communication section  343  may be configured to transmit and receive various data including commands in a packet format. Encryption may be applied to each of packets using a random number and key information. In this case, the command generating section  159  may encrypt a command and cause the HMD communication section  117  to transmit encrypted data. In the mobile machine  310 , the mobile-machine control section  341  may perform processing for decrypting the encrypted data received by the mobile-machine communication section  343 . When the mobile machine  310  transmits data to the HMD  100 , similarly, the mobile machine  310  may transmit, with the mobile-machine communication section  343 , encrypted data encrypted by the mobile-machine control section  341 . The HMD  100  may receive the encrypted data with the HMD communication section  117 . The HMD control section  141  may decrypt the received encrypted data. 
     The HMD control section  141  communicates with the mobile machine  310  through the HMD communication section  117  and receives, with the position-information acquiring section  156 , mobile machine position information transmitted by the mobile machine  310 . The HMD control section  141  receives, with the image-data acquiring section  154 , captured image data transmitted by the mobile machine  310 . The HMD control section  141  may process the mobile machine position information received from the mobile machine  310  and generate, as new mobile machine position information, data indicating the position of the mobile machine  310  generated on the basis of the received mobile machine position information. The HMD control section  141  may process the captured image data received from the mobile machine  310  and generate new image data based on the received captured image data. 
     The HMD  100 A can transmit mobile machine position information and captured image data of the mobile machine  310 A to the HMDs  100 B and  100 C. In this case, the HMD control section  141  of the HMD  100 A can transmit the mobile machine position information and/or the captured image data to the HMDs  100 B and  100 C at designated timing. Similarly, the HMD  100 B can transmit mobile machine position information and captured image data of the mobile machine  310 B to the HMDs  100 A and  100 C. The HMD  100 C can transmit mobile machine position information and captured image data of the mobile machine  310 C to the HMDs  100 A and  100 B. 
     In the mobile machine composite control system  1 , any one of the HMDs  100 A,  100 B, and  100 C corresponds to the first display device and the other HMDs correspond to the second display device. For example, when the HMD  100 A is set as the first display device, the HMDs  100 B and  100 C correspond to the second display device. When the HMD  100 B or  100 C is set as the first display device, similarly, the HMDs  100 A and  100 C or the HMDs  100 A and  100 B correspond to the second display device. The image display section  20  of the first display device is equivalent to the first display section. The image display section  20  of the second display device is equivalent to the second display section. 
     The operation detecting section  157  of the first display device is equivalent to the first operation detecting section and the operation detecting section  157  of the second display device is equivalent to the second operation detecting section. The command generating section  159  of the first display device is equivalent to the first mobile-body control section and the command generating section  159  of the second display device is equivalent to the second mobile-body control section. The image-data acquiring section  154  of the first display device is equivalent to the first mobile-body-image-data acquiring section. The image-data acquiring section  154  of the second display device is equivalent to the second mobile-body-image-data acquiring section. The display control section  147  of the first display device is equivalent to the first display control section and the display control section  147  of the second display device is equivalent to the second display control section. 
     The mobile machines  310 A,  310 B, and  310 C are the mobile bodies. Any one of the mobile machines  310 A,  310 B, and  310 C corresponds to the first mobile body. The other mobile machines correspond to the second mobile body. For example, when the mobile machine  310 A is set as the first mobile body, the mobile machines  310 B and  310 C correspond to the second mobile body. When the mobile machine  310 B or  310 C is set as the first mobile body, similarly, the mobile machines  310 A and  310 C or the mobile machines  310 A and  310 B correspond to the second mobile body. 
     The same applies to a correspondence relation between the first display device and the first mobile body and a correspondence relation between the second display device and the second mobile body. When the HMD  100 A is the first display device, the mobile machine  310 A corresponds to the first mobile body. When the HMD  100 A is the second display device, the mobile machine  310 A corresponds to the second mobile body. The same applies to the HMDs  100 B and  100 C and the mobile machines  310 B and  310 C. 
       FIGS. 9, 10, 11, 12, and 13  are flowcharts for explaining the operations of the sections of the mobile machine composite control system  1 .  FIGS. 14, 15, 16, and 17  are diagrams showing display examples of screens displayed on the image display section  20  according to the operation of the mobile machine composite control system  1 . The operation of the mobile machine composite control system  1  is explained with reference to the figures. 
       FIG. 9  is a flowchart for explaining the operation of the mobile machine  310 . The operation shown in  FIG. 9  is common to the mobile machines  310 A,  310 B, and  310 C. The mobile machines  310 A,  310 B, and  310 C respectively execute the operation shown in  FIG. 9  according to commands transmitted from the HMDs  100 A,  100 B, and  100 C. The operation is explained with reference to the mobile machine  310 A as an example. 
     When a power supply of the mobile machine  310 A is turned on, the mobile-machine control section  341  of the mobile machine  310 A starts the operation and executes initialization of the sections including the motor controller  347  and operation for establishing communication between the mobile machine  310 A and the HMD  100 A (step S 11 ). 
     The mobile-machine control section  341  starts position detection by the GPS device  344  and starts acquisition of position information detected by the GPS device  344  (step S 12 ). The mobile-machine control section  341  controls the camera control section  346  to start imaging by the mobile machine camera  335  (step S 13 ). 
     The mobile-machine control section  341  starts processing for transmitting the position information acquired from the GPS device  344  and captured image data of the mobile machine camera  335  to the HMD  100 A (step S 14 ). The mobile-machine control section  341  may include, in the position information, a detection value of the posture sensor  348  and transmit the detection value. The mobile-machine control section  341  may include, in the position information, control information including, for example, remaining battery power of the mobile machine  310  and transmit the control information. In an operation example shown in  FIG. 9 , the mobile-machine control section  341  continuously executes the transmission of the position information and the captured image data at a preset cycle after step S 14 . 
     The mobile-machine control section  341  determines whether a command is received from the HMD  100 A by the mobile-machine communication section  343  (step S 15 ). When the command is received (Yes in step S 15 ), the mobile-machine control section  341  determines whether the received command is a routine operation command (step S 16 ). When the received command is the routine operation command (Yes in step S 16 ), the mobile-machine control section  341  causes the flight control section  345  to execute a routine operation designated by the received command (step S 17 ) and shifts to step S 19 . When the received command is not the routine operation command (No in step S 16 ), the mobile-machine control section  341  causes the flight control section  345  to execute operation designated by the received command (step S 18 ) and shifts to step S 19 . When a command is not received from the HMD  100 A (No in step S 15 ), the mobile-machine control section  341  shifts to step S 19 . 
     In step S 19 , the mobile-machine control section  341  determines whether to end the operation (step S 19 ). When not ending the operation (No in step S 19 ), the mobile-machine control section  341  returns to step S 15 . 
     The mobile machine  310 B and the mobile machine  310 C execute the operation shown in  FIG. 9  in the same manner as the mobile machine  310 A and respectively execute communication with the HMDs  100 B and  100 C. Consequently, the mobile machine  310 B operates according to a command transmitted by the HMD  100 B and transmits captured image data and position information to the HMD  100 B. The same applies to the mobile machine  310 C and the HMD  100 C. 
       FIG. 10  is a flowchart for explaining the operation of the HMD  100 . The operation shown in  FIG. 10  is common to the HMDs  100 A,  100 B, and  100 C. The operation is explained with reference to the HMD  100 A as an example. 
     The HMD control section  141  of the HMD  100 A starts the operation when the power supply of the HMD  100 A is turned on, performs initialization of the sections of the HMD  100 A, and establishes communication between the HMD  100 A and the mobile machine  310 A (step S 31 ). 
     The HMD control section  141  causes the image display section  20  to display an operation screen (a screen for operation) for performing operation for piloting the mobile machine  310 A (step S 32 ) and starts command generation processing (step S 33 ). The command generation processing is processing for detecting operation with the operation detecting section  157  in a state in which the operation screen is displayed on the image display section  20 , generating, on the basis of the detected operation, with the command generating section  159 , a command for driving the mobile machine  310 A, and transmitting the command. The HMD control section  141  can generate and transmit a command according to operation by the user from the start of the command generation processing in step S 33  until the end of the operation of the HMD control section  141 . The operation detected by the operation detecting section  157  in the command generation processing is, as explained above, the operation in the control device  10  such as the touch operation of the track pad  14 , the operation by the pointer in the imaging range of the HMD camera  61 , and the like. An example of the operation by the pointer is explained below with reference to  FIG. 15 . 
     The HMD control section  141  starts operation for receiving position information from the mobile machine  310 A (step S 34 ). The HMD control section  141  starts acquisition of image data (step S 35 ). The image data acquired in step S 35  may be captured image data of the mobile machine  310 A or may be captured image data of the other mobile machines  310 B and  310 C. 
     The HMD control section  141  determines whether to transmit the position information started to be received in step S 34  and the image data started to be acquired in step S 35  to the other HMDs  100  (step S 36 ). Necessity of the transmission is set in the HMD control section  141  in advance and determined by, for example, a set value included in the setting data  171 . A specific transmission destination is at least either one of the HMD  100 B and the HMD  100 C. The HMD control section  141  performs communication with the other HMDs  100 , that is, the HMDs  100 B and  100 C. When requested to transmit data, the HMD control section  141  may determine to transmit data. 
     When transmitting the data to the HMD  100 B or the HMD  100 C (Yes in step S 36 ), the HMD control section  141  starts data transmission of the image data and the position information (step S 37 ). If the HMD  100 B executes the operation shown in  FIG. 10 , in step S 37 , the HMD control section  141  starts the data transmission to the HMDs  100 A and  100 C. If the HMD  100 C executes the operation shown in  FIG. 10 , in step S 37 , the HMD control section  141  starts the data transmission to the HMDs  100 A and  100 B. 
     Thereafter, the HMD control section  141  determines whether to receive data from the other HMDs  100  (step S 38 ). Necessity of the reception is set in the HMD control section  141  in advance and determined by, for example, a set value included in the setting data  171 . A specific transmission source is at least either one of the HMD  100 B and the HMD  100 C. The HMD control section  141  may perform communication with the other HMDs  100 , that is, the HMDs  100 B and  100 C. When requested to receive data, the HMD control section  141  may determine to receive the data. When determining not to transmit the data to the HMD  100 B or the HMD  100 C (No in step S 36 ), the HMD control section  141  shifts to step S 38 . 
     When receiving data from the HMD  100 B or the HMD  100 C (Yes in step S 38 ), the HMD control section  141  starts reception of image data and data of position information (step S 39 ). If the HMD  100 B executes the operation shown in  FIG. 10 , in step S 39 , the HMD control section  141  starts data reception from the HMDs  100 A and  100 C. If the HMD  100 C executes the operation shown in  FIG. 10 , in step S 39 , the HMD control section  141  starts data reception from the HMDs  100 A and  100 B. 
     The HMD control section  141  starts display position adjustment processing for determining a display position and size of the image data (step S 40 ) and ends the processing. When determining not to receive data from the other HMDs  100  (No in step S 38 ), the HMD control section  141  executes the operation in step S 40  and ends the processing. 
     Display forms of the HMDs  100 A,  100 B, and  100 C are explained. 
       FIG. 14  is a diagram showing a display example of the HMD  100 A. 
     In the figure, a sign VR 1  indicates a field of view of the user wearing the image display section  20  of the HMD  100 A. A sign V 1  indicates a region where it is possible to cause the user to visually recognize an image with the half mirrors  261  and  281 , in other words, a displayable region where the image display section  20  can display an image. The field of view VR 1  indicates a range visually recognized by the user with the external light OL transmitted through the image display section  20  and the image light L output by the image display section  20 . In the example shown in  FIG. 14 , the mobile machine  310 A in the real space is visually recognized in a position overlapping the display region V 1 . 
     An image P 11  functioning as an operation screen is displayed in the center of the display region V 1 . The image P 11  is a screen for piloting the mobile machine  310 A according to operation by the user. For example, display based on position information received by the HMD  100 A from the mobile machine  310 A is performed. Specifically, the latitude, the longitude, the altitude, the remaining battery power, and the like of the mobile machine  310 A are displayed. 
     When transmitting a command to the mobile machine  310 A according to operation by the user, the HMD control section  141  displays content of the transmitted command on the image P 11 . For example, in  FIG. 14 , an operation indication M 11  indicating that a command for instructing an advance is transmitted to the mobile machine  310 A is displayed on the image P 11 . The display of content of the command may be an image like the operation indication M 11  or characters, a figure, or other display objects can be used. 
     An image P 12  indicating the position of the mobile machine  310 A is displayed in the display region V 1 . As the image P 12 , an image indicating the position of the mobile machine  310 A is displayed together with a map. The position of the HMD  100 A may be displayed on the map of the image P 12 . On the map of the image P 12 , the positions of the mobile machines  310 B and  310 C may be displayed and the positions of the HMDs  100 B and  100 C may be displayed. The HMD  100 A can display these positions on the basis of position information received by the HMD  100 A from the HMDs  100 B and  100 C. As the map displayed on the image P 12 , a bird&#39;s-eye view map may be used. Specifically, the map may be a display form functioning as a navigation map corresponding to a situation in which the mobile machine  310 A is flying. 
     In the display region V 1 , images P 13 , P 14 , and P 15  received by the HMD  100 A from the mobile machine  310 A and the HMDs  100 B and  100 C are displayed. The image P 13  is an image displayed on the basis of captured image data received from the mobile machine  310 A. The image P 14  is an image displayed on the basis of image data received by the HMD  100 A from the HMD  100 B. Specifically, the image P 14  is an image based on captured image data of the mobile machine  310 B received by the HMD  100 B from the mobile machine  310 B or an image based on captured image data of the HMD camera  61  included in the HMD  100 B. The image P 15  is an image displayed on the basis of image data received by the HMD  100 A from the HMD  100 C. Specifically, the image P 15  is an image based on captured image data of the mobile machine  310 C received by the HMD  100 C from the mobile machine  310 C or an image based on captured image data of the HMD camera  61  included in the HMD  100 C. 
     In the display region V 1 , an image AR 1  indicating an operation state of the mobile machine  310 A is displayed. The image AR 1  is an image indicating a traveling direction (an advance, a retraction, a turn, a reverse turn, etc.) of the mobile machine  310 A. In this embodiment, the image AR 1  simulating light emission of the indicator  349  ( FIG. 2 ) included in the mobile machine  310 A is displayed. A display position of the image AR 1  is a position overlapping a position where the mobile machine  310 A in the real space is visually recognized. That is, the image AR 1  is so-called augmented reality (AR) display that affects the visibility of the mobile machine  310 A in the real space and additionally displays information. 
     Consequently, even when the user cannot directly visually recognize the indicator  349  of the mobile machine  310 A, the user can grasp an operation state of the mobile machine  310 A in the same manner as when the user can directly visually recognize the indicator  349 . Therefore, the user can learn the traveling direction of the mobile machine  310 A. In display regions V 2  and V 3 , the same image as the image AR 1  may be displayed during the display of the operation screen or in a state in which the mobile machines  310 B and  310 C in the real space can be visually recognized. When the mobile machines  310 B and  310 C in the real space are visually recognized in positions overlapping the display region V 1 , the HMD control section  141  of the HMD  100 A may display the same image as the image AR 1  in the positions where the mobile machines  310 B and  310 C are visually recognized. 
       FIG. 15  is a diagram showing a display example of the HMD  100 A including another example of the operation screen. 
     In the display example shown in  FIG. 15 , an example is shown in which operation by the pointer H is performed in a state in which the mobile machine  310 A in the real space is visually recognized in the field of view VR 1 . The pointer H is a hand of the user in the example shown in  FIG. 15 . However, the pointer H only has to be an electronic device incorporating a light emission circuit, a pointing stick, a pen, or other various objects, which can be imaged by the HMD camera  61 . The HMD control section  141  acquires captured image data of the HMD camera  61  with the imaging control section  149 . The operation detecting section  157  analyzes the captured image data to detect the pointer H. The operation detecting section  157  specifies a relative position of the pointer H with respect to the image display section  20  to thereby specify a position of the pointer H with respect to the field of view VR 1 . This position is detected as an operation position by the pointer H. The HMD control section  141  causes the image display section  20  to display, in a display position inside the display region V 1  corresponding to the operation position, an operation image M 12  indicating that operation by the pointer H is detected. The operation image M 12  is an image for notifying the operation position detected by the HMD control section  141  to the user. Further, the HMD control section  141  causes, on the basis of the position of the pointer H detected by the operation detecting section  157 , the command generating section  159  to generate a command transmitted to the mobile machine  310  and causes the HMD communication section  117  to transmit the command to the mobile machine  310 . Calibration may be executed in advance concerning the position of the pointer H. The HMD  100  may store calibration data including a result of the calibration. In this case, position alignment of the pointer H can be specified according to the calibration data. That is, the user wearing the image display section  20  can instruct driving of the mobile machine  310  by moving the pointer H. The HMD  100  provides a so-called action UI (User Interface). Operation of the action UI by the pointer H is equivalent to the position indicating operation. That is, the position indicating operation is operation for positioning the pointer H in the imaging range of the HMD camera  61  or moving the pointer H in the imaging range. The operation detecting section  157  not only detects the position of the pointer H as the indicating position as in the example shown in  FIG. 15 . The operation detecting section  157  may realize a gesture UI in which, when the pointer H moves in the imaging range of the HMD camera  61 , if the movement corresponds to a gesture set in advance, the operation detecting section  157  detects the movement. If the operation detecting section  157  detects the position or the movement of the pointer H on the basis of a captured image of the HMD camera  61 , the position indicating operation is detected. In this way, the operation detected by the operation detecting section  157  is not limited to the operation on the track pad  14  or the like, which is the operation section of the control device  10 . Operation by the pointer H and operation by the position, the posture, the movement, and the like of the image display section  20  can be included in the operation. The operation detected by the operation detecting section  157  may be applied to not only the operation by the user who uses the HMD  100  in order to pilot the mobile machine  310  but also, for example, control of display of the HMD  100 B operated by a user of the HMD  100 B when the user of the HMD  100 A pilots the mobile machine  310 A. 
       FIG. 16  is a diagram showing a display example of the HMD  100 B. 
     In the figure, a sign VR 2  indicates a field of view of the user wearing the image display section  20  of the HMD  100 A. A sign V 2  indicates a region where it is possible to cause the user to visually recognize an image with the half mirrors  261  and  281 , in other words, a displayable region where the image display section  20  can display an image. The field of view VR 2  indicates a range visually recognized by the user with the external light OL transmitted through the image display section  20  and the image light L output by the image display section  20 . In the example shown in  FIG. 16 , the mobile machine  310 B in the real space is visually recognized in a position overlapping the display region V 2 . 
     In the display region V 2 , for example, display based on position information received by the HMD  100 B from the mobile machine  310 B may be performed. Specifically, the latitude, the longitude, the altitude, the remaining battery power, and the like of the mobile machine  310 B may be displayed. 
     In the display region V 2 , images P 21 , P 22 , and P 23  received by the HMD  100 B from the mobile machines  310 B and the HMDs  100 A and  100 C are displayed. The image P 21  is an image displayed on the basis of captured image data received from the mobile machine  310 B. The image P 22  is an image displayed on the basis of image data received by the HMD  100 B from the HMD  100 A. Specifically, the image P 22  is an image based on captured image data of the mobile machine  310 A received by the HMD  100 A from the mobile machine  310 A or an image based on captured image data of the HMD camera  61  included in the HMD  100 A. The image P 23  is an image displayed on the basis of image data received by the HMD  100 B from the HMD  100 C. Specifically, the image P 23  is an image based on captured image data of the mobile machine  310 C received by the HMD  100 C from the mobile machine  310 C or an image based on captured image data of the HMD camera  61  included in the HMD  100 C. 
       FIG. 17  is a diagram showing a display example of the HMD  100 C. 
     In the figure, a sign VR 3  indicates a field of view of the user wearing the image display section  20  of the HMD  100 A. A sign V 3  indicates a region where it is possible to cause the user to visually recognize an image with the half mirrors  261  and  281 , in other words, a displayable region where the image display section  20  can display an image. The field of view VR 3  indicates a range visually recognized by the user with the external light OL transmitted through the image display section  20  and the image light L output by the image display section  20 . 
     In the example shown in  FIG. 17 , a scene in the real space, that is, an outside scene is visually recognized through the image display section  20  in a position overlapping the display region V 3  as well. 
     In the display region V 3 , for example, display based on position information received by the HMD  100 C from the mobile machine  310 C may be performed. Specifically, the latitude, the longitude, the altitude, the remaining battery power, and the like of the mobile machine  310 C may be displayed. 
     In the display region V 3 , images P 31  and P 32  received by the HMD  100 C from the mobile machine  310 C and the HMDs  100 A and  100 B are displayed. The image P 31  is an image displayed on the basis of captured image data received from the mobile machine  310 C. The image P 32  is an image displayed on the basis of image data received by the HMD  100 C from the HMD  100 A or the HMD  100 B. Specifically, the image P 32  may be an image based on captured image data of the mobile machine  310 A received by the HMD  100 A from the mobile machine  310 A or an image based on captured image data of the HMD camera  61  included in the HMD  100 A. Alternatively, the image P 32  may be an image based on captured image data of the mobile machine  310 B received by the HMD  100 B from the mobile machine  310 B or an image based on captured image data of the HMD camera  61  included in the HMD  100 B. 
     In the display region V 2  shown in  FIG. 16 , the HMD  100 B may display an operation screen for piloting the mobile machine  310 B. In the display region V 3  shown in  FIG. 17 , the HMD  100 C may display an operation screen for piloting the mobile machine  310 C. 
     The user of the HMD  100 A views the images P 11  to P 15  and the operation indication M 11  displayed in the display region V 1  shown in  FIG. 14  while visually recognizing the mobile machine  310 A in the real space. For example, when piloting of an unmanned aerial vehicle such as the mobile machine  310 A is regulated by laws, ordinances, and other rules to perform the piloting in a visually recognizable range, the user needs to be able to visually recognize the mobile machine  310 A in the real space. On the other hand, importance of visual recognition of the images P 11  to P 15  by the user is not low. For example, when the HMD  100 B transmits captured image data of the mobile machine  310 B, the user of the HMD  100 A can learn the position and the direction of the mobile machine  310 B by visually recognizing the image P 14 . The user can obtain a lot of information concerning an imaging target object imaged by the mobile machine  310 B. For example, when the mobile machines  310 B and  310 C fly in positions away from the user of the HMD  100 A, it is possible to realize provision of information concerning a congested road, guidance of a bypass, provision of information concerning various disaster sites including fire, and information sharing using images based on captured image data of the mobile machines  310 B and  310 C. Note that, in the display examples shown in  FIGS. 14 to 17 , in order to identify a device that captures a displayed image, a frame may be displayed on the image and a display state (a solid line or a broken line, a display color, etc.) of the frame may be changed for each of device models. 
     The HMD control section  141  of the HMD  100 A performs processing for controlling visibility concerning each of the images P 11  to P 15  displayed in the display region V 1 . The processing is shown in  FIG. 11 . 
       FIG. 11  is a flowchart for explaining the operation of the HMD  100 . The operation shown in  FIG. 11  is common to the HMDs  100 A,  100 B, and  100 C. However, the operation is explained with reference to the HMD  100 A as an example. 
     The HMD control section  141  of the HMD  100 A acquires captured image data and position information received from the mobile machine  310 , which is a display target, that is, the mobile machine  310 A (step S 61 ). The captured image data and the position information acquired in step S 61  is, for example, the captured image data and the position information received in the processing shown in  FIG. 10 . However, the captured image data and the position information may be received from the HMDs  100 B and  100 C. 
     The HMD control section  141  acquires position information of the HMD  100 A (step S 62 ). In step S 62 , the HMD control section  141  acquires, for example, position information detected by the GPS  115  ( FIG. 7 ). However, the position information only has to be information capable of specifying the position of the HMD  100 A. 
     The HMD control section  141  performs, on the basis of the information acquired in steps S 61  and S 62 , ranking of importance degrees with respect to image data related to images displayed in the display region V 1  (step S 63 ). The HMD control section  141  determines display positions and display sizes of the images based on the image data according to the ranking of the importance degrees determined in step S 63  (step S 64 ), updates the display (step S 65 ), and ends the processing. 
     In step S 62 , the HMD control section  141  ranks, on the basis of the position of the mobile machine  310 A and the position of the HMD  100 A, importance degrees of the outside scene, the captured image data of the mobile machine  310 A, and the operation screen for piloting the mobile machine  310 A. For example, when the rank of the importance degree of the operation screen (the image P 11  shown in  FIG. 14 ) is high, the HMD control section  141  performs processing to set the visibility of the operation screen higher than the visibilities of the outside scene and the captured image data. That is, the HMD control section  141  may perform highlighted display through enlarged display, blinking, or the like of the operation screen. In order to reduce the light amount of the external light OL, the HMD control section  141  may reduce transmitted light amounts of the right electronic shade  227  and the left electronic shade  247 . The HMD control section  141  may increase the luminance of the operation screen to set the visibility of the operation screen higher than the visibility of the outside scene. In this processing, the HMD control section  141  may perform control according to an external environment obtained from the detection value of the illuminance sensor  65  and the captured image data of the HMD camera  61 . As an example, the HMD control section  141  may control an image in the display region V 1  according to a back ground of the place of the HMD  100 A, that is, a real background (fine weather, rain, evening, night, snow, sea, autumn tints, etc.) affected by weather and time. The HMD control section  141  may adjust a color or a color tone of the operation screen and automatically adjust the operation screen to be capable of maintaining a state distinguishable from sky, clouds, or scenery of the background. When the operation screen looks dark, the HMD control section  141  may add a watermark or a background having a bright color (white, etc.) to the operation screen. 
     Further, when performing the ranking, the HMD control section  141  may change the ranking according to a positional relation among the positions of the other mobile machines, that is, the mobile machines  310 B and  310 C, the position of the mobile machine  310 A, and the position of the HMD  100 A. 
     Concerning the control of the display positions of the image based on the captured image data of the mobile machine  310 A, the operation screen for piloting the mobile machine  310 A, the other images, and the like, the HMD control section  141  may use detection values of various sensors included in the HMD  100 A. For example, the HMD control section  141  may control the display positions using a detection value concerning the position of the image display section  20 . Specifically, with the operation detecting section  157 , the HMD control section  141  may detect a movement of the image display section  20  on the basis of detection values of the six-axis sensor  235  and/or the magnetic sensor  237  and detect the movement of the image display section  20  and a posture of the user as operation. The operation detecting section  157  may detect the movement of the image display section  20  and the posture of the user on the basis of a change in a captured image of the HMD camera  61  and a change in a detection value of the distance sensors  64 . The operation detecting section  157  may detect, as operation, movements and line of sight directions of the right eye RE and/or the left eye LE imaged by the inner cameras  68 . With the function of the display control section  147 , the HMD control section  141  may determine priority of a displayed image according to the operation detected by the operation detecting section  157  and determine a display position. The HMD control section  141  may control display positions and sizes of display areas of images based on captured image data, transmittances of a captured image and an outside scene, transmittance of the display UI for control, and the like in the HMD  100 A, which is the first display device, and the HMDs  100 B and  100 C, which are the second display devices. As an example, when the line of sight of the user or the direction of the head of the user wearing the image display section  20  faces the mobile machine  310 , which is a target of operation, the HMD control section  141  may change the transmittances of the displayed image and the UI for operation such that the user can preferentially visually recognize the outside scene (the real space) visually recognized through the display region V 1 . The HMD control section  141  may perform these kinds of control with an operation state of the mobile machine  310  reflected on the control. For example, when the mobile machine  310  takes off and lands, if the mobile machine  310  is located in a position close to the user, it is possible to extinguish the display of the image based on the captured image data of the mobile machine camera  335  and improve the priority of the display of an image for piloting for operating the mobile machine  310 . Furthermore, when a sudden movement of the head wearing the image display section  20  or sudden fluctuation in a line of sight direction of the right eye RE or the left eye LE is detected by the operation detecting section  157 , the HMD control section  141  may determine that the detection corresponds to occurrence of a priority matter of viewing the outside scene near the user, specifically, determine that the user is walking. In such a case, the HMD control section  141  may retract the display of the image based on the captured image data of the mobile machine camera  335  and the image for piloting of the mobile machine  310  from the center to the periphery of the field of view VR 1  and reduce the display luminance (the brightness) of the images to control the images to set the visibility of the outside scene higher than the visibility of these images. 
       FIG. 12  is a sequence chart showing operation related to transmission and reception of data among the HMDs  100 A,  100 B, and  100 C. 
     In the mobile machine composite control system  1 , the HMDs  100 A,  100 B, and  100 C are capable of mutually transmitting and receiving data. 
     Specifically, the HMD  100 A can transmit captured image data (mobile machine camera image data) of the mobile machine  310 A, position information (mobile machine position information) of the mobile machine  310 A, and captured image data (HMD camera image data) of the HMD camera  61 . The HMD  100 A can perform both of operation for transmitting the data to the HMD  100 B (step SA 1 ) and operation for transmitting the data to the HMD  100 C (step SA 2 ). 
     Similarly, the HMD  100 B can transmit mobile machine camera image data of the mobile machine  310 B, mobile machine position information of the mobile machine  310 B, and HMD camera image data captured by the HMD  100 B. As a transmission destination, both of the HMD  100 A (step SB 1 ) and the HMD  100 C (step SB 2 ) can be selected. The HMD  100 C can transmit mobile machine camera image data of the mobile machine  310 C, mobile machine position information of the mobile machine  310 C, and HMD camera image data captured by the HMD  100 C. As a transmission destination, both of the HMD  100 A (step SC 1 ) and the HMD  100 B (step SC 2 ) can be selected. 
     In this way, in the mobile machine composite control system  1 , the HMDs  100 A,  100 B, and  100 C can mutually transmit and receive data and mutually acquire captured image data and position information of the mobile machines  310 A,  310 B, and  310 C. It is possible to perform alternation (handover) of the piloting of the mobile machine  310  making use of this configuration. 
     For example, the mobile machine  310 A moves to an A point according to the piloting by the HMD  100 A and executes hovering at the A point. The HMD  100 B communicates with the HMD  100 A. The HMD  100 B and the HMD  100 A mutually perform authentication. After succeeding in the authentication, the HMD  100 A transmits data for identifying the HMD  100 B to the mobile machine  310 A. The mobile machine  310 A communicates and performs authentication with the HMD  100 B on the basis of the data. Thereafter, the mobile machine  310 A shifts from a state in which the mobile machine  310 A performs the hovering at the A point to a state in which the mobile machine  310 A moves according to a command transmitted by the HMD  100 B. According to this procedure, it is possible to hand over the piloting of the mobile machine  310 A from the user of the HMD  100 A to the user of the HMD  100 B. Before and after the handover, an image based on captured image data of the mobile machine  310 A displayed by the HMDs  100 A and  100 B or an AR image displayed over the mobile machine  310 A in the real space may be changed. A display color of the AR display or a color of a display frame of the image based on the captured image data may be changed between during piloting of the mobile machine  310 A by the HMD  100 A and during piloting of the mobile machine  310 A by the HMD  100 B. 
       FIG. 13  is a flowchart for explaining the operation of the HMD  100 . 
     The operation shown in  FIG. 13  is operation concerning display of an AR image (e.g., the image AR 1  shown in  FIG. 14  displayed by the HMD  100 A) corresponding to the mobile machine  310 . The HMDs  100 B and  100 C may execute the operation shown in  FIG. 13 . An example is explained in which the HMD  100 A executes the operation. 
     The HMD control section  141  of the HMD  100 A acquires captured image data of the HMD camera  61  (step S 81 ). The HMD control section  141  extracts an image of the mobile machine  310 A from the captured image data and detects relative positions of the extracted image and the display region V 1  (step S 82 ). The detected position is equivalent to a position of the mobile machine  310 A with respect to the field of view VR 1  transmitted through the image display section  20  and is a condition for determining a display position of the image AR 1 . 
     The HMD control section  141  specifies a moving direction of the mobile machine  310 A (step S 83 ). The moving direction of the mobile machine  310 A can be specified on the basis of a command transmitted to the mobile machine  310 A by the HMD  100 A, position information transmitted to the HMD  100 A by the mobile machine  310 A, and the like. 
     The HMD control section  141  generates, on the basis of the specified moving direction, the image AR 1  corresponding to the display of the indicator  349  and displays the image AR 1  in the display region V 1  (step S 84 ). 
     The HMD control section  141  detects or acquires a visual recognition state of the indicator  349  included in the mobile machine  310 A (step S 85 ). That is, the HMD control section  141  can detect, from the position detected in step S 82  and the altitude, the angle, and the like of the mobile machine  310 A, a visual recognition state including, for example, whether the user of the HMD  100 A can visually recognize the indicator  349 . For example, the user can input the visual recognition state by operating the control device  10 . In this case, the HMD control section  141  acquires the visual recognition state input by the user. 
     The HMD control section  141  adjusts, according to the visual recognition state detected or acquired in step S 85 , a display state of the image AR 1  started to be displayed in step S 84  (step S 86 ). For example, when the user can satisfactorily visually recognize the indicator  349 , the HMD control section  141  reduces the display luminance of the image AR 1  or stops the display. When it is difficult for the user to visually recognize the indicator  349 , the HMD control section  141  improves the display luminance of the image AR 1 . 
     As explained above, the mobile machine composite control system  1  in the embodiment applied with the invention is the display system including the HMD  100  functioning as the first display device and the HMD  100  functioning as the second display device. The HMD  100  functioning as the first display device includes the image display section  20  and the operation detecting section  157  that detects operation. The HMD  100  functioning as the first display device includes the command generating section  159  that generates, according to the operation detected by the operation detecting section  157 , a command for operating the mobile machine  310  functioning as the first mobile body. The HMD  100  functioning as the first display device includes the image-data acquiring section  154  that acquires captured image data concerning a captured image captured by the mobile machine  310  functioning as the first mobile body. The HMD  100  functioning as the first display device includes the display control section  147  that causes the image display section  20  to display an image based on the captured image data acquired by the image-data acquiring section  154 . The HMD  100  functioning as the second display device includes the image display section  20  and the image-data acquiring section  154  that acquires captured image data concerning a captured image captured by the mobile machine  310  functioning as the first mobile body. The HMD  100  functioning as the second display device includes the display control section  147  that causes the image display section  20  to display an image based on the captured image data acquired by the image-data acquiring section  154 . 
     With the mobile machine composite control system  1 , the HMD  100 , and the control method for the HMD  100  applied with the invention, the HMD  100  generates a command for operating the mobile machine  310 . Consequently, the HMD  100  that displays an image concerning a captured image captured by the mobile machine  310  can be used for operation of the mobile machine  310 . Therefore, it is possible to perform the operation of the mobile machine  310  while viewing an image displayed by the display device. Since it is possible to display, with the HMD  100  functioning as the second display device, the image concerning the captured image captured by the mobile machine  310 , for example, a person not involved in the operation of the mobile machine  310  can confirm the captured image of the mobile machine  310 . For example, when the user wearing the HMD  100 A pilots the mobile machine  310 A, in the HMD  100 B or the HMD  100 C used by a user not piloting the mobile machine  310 A, it is possible to display an image based on captured image data of the mobile machine  310 A. In this case, it is possible to share the image based on the captured image data of the mobile machine  310 A between the HMD  100 A and the HMDs  100 B and  100 C not piloting the mobile machine  310 A. Not only the sharing of the image, for example, at timing when the image based on the captured image data of the mobile machine  310 A is not displayed in the HMD  100 A, the image based on the captured image data of the mobile machine  310 A may be displayed by the HMDs  100 B and  100 C not piloting the mobile machine  310 A. 
     The image display section  20  displays an image to enable visual recognition of an outside scene by transmitting external light. The display control section  147  controls the visibility of the outside scene in the image display section  20 . Therefore, the HMD  100  functioning as the first display device displays, on the image display section  20  that enables the visual recognition of the outside scene, the image concerning the captured image captured by the mobile machine  310 . Consequently, it is possible to visually recognize the mobile machine  310  in the real space, perform operation concerning the motion of the mobile machine  310 , and visually recognize the image concerning the captured image. Therefore, it is possible to confirm the captured image and perform the operation of the mobile machine  310  while viewing the mobile machine  310  in the real space. Since the visibility of the outside scene in the image display section  20  can be controlled, for example, it is possible to prioritize the visibility of the mobile machine  310  in the real space over the visibility of the captured image and control the display to facilitate the operation of the mobile machine  310 . 
     The display control section  147  causes the image display section  20  to display an operation screen concerning processing for generating a command and controls the visibility of the outside scene in the image display section  20  according to a display state of the operation screen. Consequently, since it is possible to control the visibility of the outside scene according to the display state of the operation screen, for example, it is possible to adjust the visibility of the operation screen and the visibility of the mobile machine  310  in the real space. Therefore, it is possible to improve easiness of the operation of the mobile machine  310 . 
     The display control section  147  controls the visibility of the outside scene in the image display section  20  according to a display state of an image based on captured image data. Consequently, since the visibility of the outside scene is controlled according to a display state concerning a captured image of the mobile machine  310 , for example, it is possible to adjust the visibility of the mobile machine  310  in the real space and the visibility of the image concerning the captured image. It is possible to achieve further improvement of the convenience. 
     The HMD control section  141  of the HMD  100  may control the visibility of the outside scene in the image display section  20  on the basis of a state of the image display section  20  or the user who uses the image display section  20 . This operation can be applied in all of the HMDs  100 A,  100 B, and  100 C functioning as the first display device and the HMDs  100 A,  100 B, and  100 C functioning as the second display device. Therefore, it is possible to control the visibility of the outside scene according to importance of the visibility of the outside scene for the user reflected on the position, the movement, the posture, and the like of the image display section  20  or the user. 
     The display control section  147  causes the image display section  20  to display an image corresponding to an operation state of the mobile machine  310 . Consequently, it is possible to obtain information concerning the operation state of the mobile machine  310  according to the display of the image display section  20 . It is possible to achieve improvement of convenience concerning the operation of the mobile machine  310  and use of a captured image of the mobile machine  310 . 
     In the HMD  100  functioning as the second display device, the image display section  20  displays an image to enable visual recognition of an outside scene by transmitting external light. The display control section  147  controls the visibility of the outside scene in the image display section  20 . Consequently, in the HMD  100  functioning as the second display device, it is possible to visually recognize the outside scene and an image concerning a captured image captured by the mobile machine  310 . It is possible to control the visibility of the outside scene. 
     The HMD  100  functioning as the second display device includes the operation detecting section  157  that detects operation and the command generating section  159  that generates, according to the operation detected by the operation detecting section  157 , a command for operating the mobile machine  310 . The display control section  147  causes the image display section  20  to display an operation screen concerning processing for generating a command and controls the visibility of the outside scene in the image display section  20  according to a display state of the control screen. In this configuration, the HMD  100  functioning as the first display device generates a command concerning the operation of the mobile machine  310  and the HMD  100  functioning as the second display device generates a command concerning the operation of the mobile machine  310 . Therefore, the user who uses the HMD  100  functioning as the first display device and the user who uses the HMD  100  functioning as the second display device can respectively perform operation concerning the motion of the mobile machine  310  while visually recognizing the mobile machine  310  in the real space. Further, it is possible to visually recognize an image concerning a captured image captured by the mobile machine  310 . Consequently, it is possible to provide the mobile machine composite control system  1  capable of easily performing the operation of the plurality of mobile machines  310 A,  310 B, and  310 C and use of captured images captured by the mobile machines  310 A,  310 B, and  310 C. 
     The image-data acquiring section  154  included in the HMD  100  functioning as the second display device acquires image data of the mobile machine  310  concerning a captured image captured by the mobile machine  310 . The display control section  147  displays, on the image display section  20 , an image based on captured image data acquired by the image-data acquiring section  154  and the image based on the image data of the mobile machine  310 . Consequently, it is possible to display, with the HMD  100  functioning as the second display device, images concerning captured images respectively captured by the mobile machines  310 . 
     The display control section  147  controls the visibility of the outside scene in the image display section  20  according to a display state of at least any one of the image based on the captured image data acquired by the image-data acquiring section  154  and the image based on the image data of the mobile machine  310 . Consequently, it is possible to control the visibility of the outside scene in the case in which a captured image of at least any one of the mobile machines  310 A,  310 B, and  310 C is displayed. Therefore, it is possible to adjust a balance of the visibilities of the outside scene and the captured images of the mobile machines  310 A,  310 B, and  310 C. For example, when the user of the HMD  100  functioning as the second display device operates (pilots) the HMD  100 , it is possible to prioritize the visibility of the mobile machine  310  in the real space and improve operability. 
     The display control section  147  causes the image display section  20  to display an image corresponding to an operation state of the mobile machine  310 . Consequently, it is possible to perform display concerning the operation state of the mobile machine  310  in the HMD  100  functioning as the second display device. It is possible to further facilitate the operation concerning the motion of the mobile machine  310  and improve the operability. 
     The display control section  147  causes the image display section  20  to display images corresponding to operation states of the mobile machines  310 . Consequently, it is possible to perform the display concerning the operation states of the mobile machines  310  in the HMD  100  functioning as the second display device. Consequently, it is possible to perform operation concerning the motion of the mobile machine  310  while confirming a state of the mobile machine  310 . 
     The display control section  147  causes the image display section  20  to display an image corresponding to an operation state of the mobile machine  310  in a position corresponding to the mobile machine  310  visually recognized in the outside scene via the image display section  20 . Consequently, it is possible to cause the image display section  20  to display, according to a position where the mobile machine  310  in the real space is visually recognized, an image displayed by the image display section  20  concerning the operation state of the mobile machine  310 . It is possible to obtain information concerning the operation state of the mobile machine  310  while viewing the mobile machine  310  in the real space. Therefore, it is possible to further facilitate the operation concerning the motion of the mobile machine  310  and improve the operability. 
     The HMD  100  acquires, with the position-information acquiring section  156 , information concerning the position of at least any one of the mobile machines  310 A,  310 B, and  310 C. The display control section  147  causes the image display section  20  to display the information acquired by the position-information acquiring section  156 . Consequently, it is possible to perform display concerning the positions of the mobile machines  310 A,  310 B, and  310 C in the HMD  100 . 
     The command generating section  159  generates, on the basis of the position information of the mobile machine  310  acquired by the position-information acquiring section  156 , a command for operating the mobile machine  310 . Consequently, it is possible to operate the mobile machine  310  according to the position of the mobile machine  310 . 
     The image display section  20  is a head-mounted display section mounted on the head of the user. Consequently, with the display device including the head-mounted display section, it is possible to perform operation concerning the motion of the mobile machine  310  while visually recognizing the mobile machine  310  in the real space and further view an image concerning a captured image captured by the mobile machine  310 . 
     The information concerning the position of the mobile machine  310  may include the mobile machine position information explained above and may include, besides the mobile machine position information, mobile machine state information concerning an environment and a state of the mobile machine  310 . The mobile machine state information may include information related to the position of the mobile machine  310 . For example, the mobile machine state information may include information concerning a peripheral facility such as a facility name or a building name in the vicinity of or immediately below the mobile machine  310 . The mobile machine state information may include information concerning the environment (weather, temperature, humidity, wind velocity, wind direction, precipitation, etc.) of the mobile machine  310 . 
     Note that the invention is not limited to the configuration of the embodiment explained above and can be carried out in various forms without departing from the spirit of the invention. 
     For example, the mobile machine camera  335  of the mobile machine  310  is not limited to a camera that performs imaging with visible light and may be a component that performs imaging with invisible light such as infrared light or a sensor that uses ultrasound or the like. For example, a light source that irradiates infrared light may be mounted on the mobile machine  310 . Consequently, it is possible to detect sugar contents of agricultural products using the captured image data of the mobile machine  310 . When a construction is inspected, for example, it is possible to perform flaw examination of the target construction and perform measurement of temperature using a thermography technique. 
     As still another application example of the mobile machine composite control system  1 , there is a use in which, in a large facility including a large number of seats such as a stadium, a congestion degree in each place is determined using the captured image data of the mobile machine  310  or a state of congestion in a road is determined using the captured image data of the mobile machine  310 . 
     In the embodiment explained above, the operation detecting section  157  is capable of detecting the movement of the image display section  20  or the operation on the image display section  20  and generating, according to the operation, a command generated by the command generating section  159  for instructing the routine operation. The operation detecting section  157  may detect operation by a device other than the HMD  100 . For example, the user uses an operation device of a finger ring type worn on a finger. For example, the user uses an operation device of a wristwatch type worn on an arm. Each of the operation devices may include the movement sensors such as the six-axis sensor  235  and the magnetic sensor  237  and a transmitting section that transmits detection values of the movement sensors to the HMD  100 . In this case, if the operation device and the HMD communication section  117  are capable of communicating with each other through the Bluetooth, the operation detecting section  157  can detect operation for moving the operation device. In this case, when the movement of the operation device is a preset form, the operation detecting section  157  may generate a command for instructing the routine operation. 
     The operation detecting section  157  may detect a command instruction by voice collected by the microphone  63 . That is, when a pattern of voice detected by the sound interface  182  corresponds to a preset pattern, the detection control section  151  may generate a command for instructing the routine operation. 
     Like the pointer H shown in the figures, besides a finger, a hand, and the like of a human, a pointer may be a remote control device that remotely operates the HMD  100 , a pointing stick, a pen, or the like. The detection control section  151  may detect operation of a device such as an air mouse. As detecting means, a captured image of the HMD camera  61  can be used. A device including a light emitting body such as an LED can also be used as the pointer. 
     For example, in the embodiment, the configuration is illustrated in which the control device  10  is connected to the image display section  20  by wire. However, the invention is not limited to this. A configuration may be adopted in which the image display section  20  is connected to the control device  10  by radio. As a wireless communication scheme in this case, a scheme illustrated as a communication scheme to which the HMD communication section  117  is adapted may be adopted. Other communication schemes may be adopted. 
     A part of the functions of the control device  10  may be provided in the image display section  20 . The control device  10  may be realized by a plurality of devices. For example, instead of the control device  10 , a wearable device attachable to the body or clothes of the user or an ornament worn by the user may be used. The wearable device in this case may be, for example, a watch-type device, a finger ring-type device, a laser pointer, a mouse, an air mouse, a game controller, or a pen-type device. 
     Further, in the embodiment, the configuration is illustrated in which the image display section  20  and the control device  10  are separated and connected via the connection cable  40 . The invention is not limited to this. A configuration may be adopted in which the control device  10  and the image display section  20  are integrated and worn on the head of the user. 
     In the embodiment, the configuration in which the user visually recognizes the outside scene through the display section is not limited to the configuration in which the right light guide plate  26  and the left light guide plate  28  transmit the external light. For example, the invention can also be applied to a display device that displays an image in a state in which the outside scene cannot be visually recognized. Specifically, the invention can be applied to a display device that displays, for example, a captured image of the HMD camera  61 , an image and a CG generated on the basis of the captured image, and a video based on video data stored in advance and video data input from the outside. The display device of this type can include a display device of a so-called closed type that cannot visually recognize the outside scene. For example, if a configuration is adopted in which a combined image obtained by combining an image of an outside scene imaged by the HMD camera  61  and a displayed image is displayed by the image display section  20 , even if the image display section  20  does not transmit the external light, it is possible to visually recognizably display the outside scene and the image to the user. The invention can be naturally applied to such a display device of a so-called video see-through type. 
     In the embodiment, as an example of the mobile body, the mobile machine  310 , which is the unmanned aerial vehicle and the quadricopter, is explained. The mobile body is not limited to this. The mobile body can also be applied to various unmanned mobile bodies, which are remotely operated and automatically driven, such as an automobile, a ship, a robot, and toys of the automobile, the ship, and the robot. The mobile body in this case only has to include a camera that captures an image. Examples of the mobile body include mobile bodies such as a helicopter, an airplane, a rocket, a submarine, an artificial satellite, a vehicle such as a bus, and a railroad vehicle. The mobile body may be manned or unmanned and may be loaded with a cargo. The mobile body may be an apparatus piloted and operated in an unmanned state and may be configured to transport people. The mobile body may be an additional apparatus such as a crane unit incidental to a truck (an automobile for cargo transportation). The mobile body can be applied to apparatuses used in the agriculture, the forestry, the fishery, the mining industry, and the like such as vehicles for work and apparatuses for work (e.g., for construction sites) such as a power shovel, a snowplow, a lawn mower, a tractor, a bulldozer, a combine harvester, a cultivator, a rice planting machine, a crop-dusting machine. These mobile bodies may be apparatuses remotely operated and used or may be apparatuses that a person rides and operates. 
     The invention can also be applied to a display device that does not perform processing such as the AR display for displaying an image to be superimposed on the real space as explained in the embodiment, MR (Mixed Reality) display for combining a captured image in the real space and a virtual image, or VR (Virtual Reality) display for displaying a virtual image. For example, a display device that displays video data or an analog video signal input from the outside is naturally included as an application target of the invention. 
     For example, instead of the image display section  20 , an image display section of another system such as an image display system worn like a cap may be adopted. The image display section only has to include a display section that displays an image corresponding to the left eye LE of the user and a display section that displays an image corresponding to the right eye RE of the user. The display device according to the invention may be configured as a head mounted display mounted on a vehicle such as an automobile or a plane. For example, the display device may be configured as a head mounted display incorporated in a body protector such as a helmet. In this case, a portion for positioning a position with respect to the body of a user and a portion positioned with respect to the portion can be set as wearing sections. 
     In the embodiment, the configuration in which a virtual image is formed by the half mirrors  261  and  281  in a part of the right light guide plate  26  and the left light guide plate  28  is illustrated as the optical system that guides image light to the eyes of the user. The invention is not limited to this. A configuration may be adopted in which an image is displayed in a display region having an area occupying the entire or most of the right light guide plate  26  and the left light guide plate  28 . In this case, processing for reducing the image may be included in operation for changing a display position of the image. 
     Further, the optical elements according to the invention are not limited to the right light guide plate  26  and the left light guide plate  28  including the half mirrors  261  and  281  and only have to be optical components that make image light incident on the eyes of the user. Specifically, a diffraction grating, a prism, and a holography display section may be used. 
     At least a part of the functional blocks shown in  FIGS. 2, 7, 8 , and the like may be realized by hardware or may be realized by cooperation of hardware and software and are not limited to the configuration in which the independent hardware resources are disposed as shown in the figures. The computer programs to be executed by the HMD control section  141  may be stored in the nonvolatile storing section  121  or other storage devices (not shown in the figure) in the control device  10 . The HMD control section  141  may acquire computer programs stored in an external device via the HMD communication section  117  and the external connector  184  and execute the computer programs. Among the components formed in the control device  10 , the operation section  110  may be formed as a user interface (UI). The components formed in the control device  10  may be redundantly formed in the image display section  20 . For example, a processor similar to the main processor  140  may be disposed in the image display section  20 . The main processor  140  included in the control device  10  and the processor of the image display section  20  may execute separately divided functions. 
     The entire disclosure of Japanese Patent Application No. 2017-034319, filed Feb. 27, 2017 is expressly incorporated by reference herein.