Patent Publication Number: US-2022229497-A1

Title: Foot-part input system, foot-part position indicating instrument, foot-part position detecting device, indicated position input method using foot-part input system, and image processing system using foot-part input system

Description:
BACKGROUND 
     Technical Field 
     This disclosure relates to a system, a device, and a method for enabling input of information to, for example, an image processing device by use of a foot part of a user. 
     Description of the Related Art 
     In recent years, fields of virtual reality (VR), augmented reality (AR), and mixed reality (MR) have been rapidly developing due to improvement in the performance of computers and displays. In execution environments in these fields, in order to carry out operation of a computer with a feeling similar to one in the real world, not existing input devices such as a mouse, a keyboard, and a game pad but a special hand device that senses motion of a hand or a finger of a user is used in some cases. This can reproduce hand gesture such as grasping and handling an object with a hand in a space created by the computer. Attempts to bring gesture by a hand itself of the user in digital content formed by a computer as above have been being carried out. 
     However, as the reproducibility of operation based on the hand gesture by a hand of the actual user is made higher in the space created by the computer, it become more difficult to carry out operation with use of an operation stick, an operation button, a touch panel, or the like directly operated with a hand. Further, for example, behavior using foots (legs), such as walking movement, is substituted with gesture of a fingertip or the whole of an arm and therefore, using the hand gesture can become a cause of impairing of a sense of immersion as well, which is important in the VR, for example. 
     Thus, input devices that allow input of information by use of a foot (leg) have been considered. For example, in Japanese Patent Laid-open No. Hei 09-198188 (hereinafter, referred to as Patent Document 1), an disclosure relating to an input device of a foot-operated type that allows input through simple operation with only one foot is disclosed. The input device of the foot-operated type allows change in an indicated position through causing rotational movement, by a foot, of a ball disposed on the sole side. In addition, switches operated by a toe of the foot are disposed, and the input device allows operation similar to what is generally called a left click and right click of a mouse. 
     Further, in Japanese Patent Laid-open No. 2016-174699 (hereinafter, referred to as Patent Document 2), an disclosure relating to a game controller that can carry out not only measurement of the weight and the center of gravity but also various kinds of action, such as stepping, walking, jumping, and crouching, is disclosed. The game controller is what detects the pressure distribution of a region of contact by part of the body of a player (user) through movement by the player on a sheet having plural pressure sensors and detects the action of the player based on the shape of the distribution and change in the shape. 
     The disclosure disclosed in Patent Document 1 remains what allows the mouse operated with a hand to be operated with a foot and is not what enables more flexible information input. On the other hand, the disclosure disclosed in Patent Document 2 can detect various action states of the player and therefore, has an effective function as the game controller. However, as a device that carries out information input in a space formed by a computer of the above-described VR, AR, or MR, the state that can be detected is limited, and it is impossible to carry out sufficient input. 
     Further, by using a controller that allows direction input by a lever and is referred to as what is generally called a joystick, a three-dimensional space image can be changed as if the user moved in a virtual three-dimensional space formed by a VR technique. However, in this case, the three-dimensional space image changes although the body of the user does not move. Therefore, a remarkable difference is caused between the three-dimensional space image that changes and a feeling with respect to the motion of the body of the user, and some users experience a symptom referred to as what is generally called VR sickness. 
     Thus, there has also been employed a configuration in which a display of a head wearing type referred to as a head-mounted display or the like is used, the motion of the head of the user is detected by a six-axis sensor and so forth mounted in the head-mounted display, and a display image is changed according to the motion of the head of the user. In this case, in a case of moving the position (point of view) of the user in a three-dimensional space image, making indication input by using a foot part will less readily cause a difference between the three-dimensional space image that changes and a feeling with respect to the motion of the body of the user because the indication input by using a foot part is closer to the actual motion of the body in a case where the user moves. 
     BRIEF SUMMARY 
     In view of the above, this disclosure intends to enable input of various kinds of information to an image processing device by use of a foot part of a user in order not to cause a difference between an image that changes and a feeling with respect to the motion of the body of the user. 
     In order to solve the above-described problem, a foot-part input system including a foot-part position indicating instrument mounted on a foot part of a user and a foot-part position detecting device that detects a position indicated by the foot-part position indicating instrument is provided. The foot-part input system, in operation, supplies, to an image processing device, detection output supplied from the foot-part position detecting device. The foot-part position indicating instrument includes a sole part including a sole front part located at a toe-side part of a sole of a foot and a sole back part located at a heel-side part of the sole of the foot and a position indication signal transmitting part that is disposed at one or both of the sole front part and the sole back part and that, in operation, transmits a position indication signal. The foot-part position detecting device includes a position detecting sensor that includes a plurality of electrodes disposed at predetermined intervals in each of a first direction and a second direction intersecting the first direction and that, in operation, receives the position indication signal from the position indication signal transmitting part, and generates output regarding each of the plurality of electrodes. The foot-part position detecting device includes also a detecting circuit that detects, as forward movement, movement of the sole part in a direction that is a direction along a center axis of the sole part in a longitudinal direction and is an extension direction of a line extended in a direction from the heel-side part toward the toe-side part, and detects, as backward movement, movement of the sole part in the extension direction of a line extended in a direction from the toe-side part toward the heel-side part based on an output signal from the position detecting sensor. 
     According to this foot-part input system, the position indication signal transmitting part that transmits the position indication signal is disposed at one or both of the sole front part and the sole back part of the sole part of the foot-part position indicating instrument. The position detecting sensor of the foot-part position detecting device, in operation, receives the position indication signal from the position indication signal transmitting part and generates output for each of the plural electrodes. The detecting circuit of the foot-part position detecting device, in operation, detects, as forward movement, movement of the sole part in the direction that is the direction along the center axis of the sole part in the longitudinal direction and that is the extension direction of the line extended in the direction from the heel-side part toward the toe-side part, based on the output signal from the position detecting sensor. Further, the detecting circuit of the foot-part position detecting device detects, as backward movement, movement of the sole part in the extension direction of the line extended in the direction from the toe-side part toward the heel-side part. Due to this, the forward movement and the backward movement can easily be indicated to the image processing device by the foot-part input system, and making an instruction to perform processing relating to an image, such as enlargement of the image corresponding to the forward movement and reduction of the image corresponding to the backward movement, is allowed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagram for explaining a use example of a foot-part input system according to a first embodiment of the present disclosure; 
         FIGS. 2A and 2B  each depict a diagram for explaining a configuration example of a foot-part position indicating instrument according to the first embodiment of the present disclosure; 
         FIGS. 3A to 3C  each depict a diagram for explaining a configuration example of the foot-part position indicating instrument according to the first embodiment of the present disclosure; 
         FIG. 4  is a diagram for explaining a configuration example of a foot-part position detecting device according to the first embodiment of the present disclosure; 
         FIGS. 5A and 5B  each depict a diagram for explaining height information and angle information that can be input by the foot-part position indicating instrument according to the first embodiment of the present disclosure; 
         FIGS. 6A and 6B  each depict a diagram for explaining angle information that can be input by the foot-part position indicating instrument according to the first embodiment of the present disclosure; 
         FIG. 7  is a diagram for explaining a use example of a foot-part input system according to a second embodiment of the present disclosure; 
         FIG. 8  is a diagram for explaining the overall configuration of an image processing system configured with use of the foot-part input system according to the second embodiment of the present disclosure; 
         FIGS. 9A and 9B  each depict a diagram for explaining a configuration example of a foot-part position indicating instrument according to the second embodiment of the present disclosure; 
         FIGS. 10A and 10B  each depict a diagram for explaining a configuration example of a foot-part position detecting device according to the second embodiment of the present disclosure; 
         FIGS. 11A to 11C  each depict a diagram for explaining a use example of the foot-part input system according to the second embodiment of the present disclosure; 
         FIGS. 12A to 12C  each depict a diagram for explaining the operation state of the foot-part input system according to the second embodiment of the present disclosure and a display image of a head-mounted display; 
         FIGS. 13A to 13C  each depict a diagram for explaining the operation state of the foot-part input system according to the second embodiment of the present disclosure and the display image of the head-mounted display; 
         FIGS. 14A to 14C  each depict a diagram for explaining the operation state of the foot-part input system according to the second embodiment of the present disclosure and the display image of the head-mounted display; 
         FIG. 15  is a diagram for explaining indication input in the image processing system configured with use of the foot-part input system according to the second embodiment of the present disclosure; 
         FIG. 16  is a diagram for explaining the indication input in the image processing system configured with use of the foot-part input system according to the second embodiment of the present disclosure; 
         FIGS. 17A to 17E  each depict a diagram for explaining how to detect the indication input in the foot-part input system according to the second embodiment of the present disclosure; 
         FIGS. 18A to 18F  are diagrams for explaining variations of setting positions of position indication signal transmitting parts of a foot-part position indicating instrument; 
         FIGS. 19A and 19B  each depict a diagram for explaining a foot-part position indicating instrument configured with use of flat coils; 
         FIG. 20  is a diagram for explaining the foot-part position indicating instrument configured with use of the flat coils; and 
         FIGS. 21A and 21B  are diagrams for explaining use examples of the foot-part position indicating instrument configured with use of the flat coils. 
     
    
    
     DETAILED DESCRIPTION 
     Systems, devices, and methods according to embodiments of this disclosure will be described below with reference to the drawings. 
     First Embodiment 
     Use Example of Foot-Part Input System 
       FIG. 1  is a diagram for explaining a use example of a foot-part input system of a first embodiment. As illustrated in  FIG. 1 , a computer rendering system is composed of a pen tablet device TB, an electronic pen PN, what is generally called a joystick JS, a display DP, and a computer main unit, for example. Although the computer main unit is not illustrated in  FIG. 1 , the pen tablet device TB, the joystick JS, and the display DP are connected to the computer main unit. 
     In a case of carrying out rendering input by using the computer rendering system, the rendering input is carried out to the pen tablet device TB disposed on a desk, by using the electronic pen PN. An image (rendered image) according to the rendering input is displayed on the display DP. The user can rotate the rendered image in various directions by operating what is generally called the joystick JS, and the user can carry out finer rendering input on a target part in the rendered image, by the electronic pen PN through the pen tablet device TB. 
     In a case of the computer rendering system of this embodiment, the foot-part input system is allowed to be further used. The foot-part input system is composed of a foot-part position indicating instrument  100  and a foot-part position detecting device  200 . As illustrated in  FIG. 1 , the foot-part position indicating instrument  100  is configured into a slipper shape and is used in such a manner as to be mounted on a foot part of the user. The foot-part position indicating instrument  100  is a cordless instrument that is not connected to another piece of equipment by a cord. 
     The foot-part position detecting device  200  is a device with a floor mat shape, is located on the lower side of the foot-part position indicating instrument  100 , and implements a function of detecting a position indicated by the foot-part position indicating instrument  100 . The foot-part position detecting device  200  is allowed to be connected to the computer main unit and supply detection output. Further, operation of, for example, movement, enlargement, reduction, and so forth of a rendered image, the operation having been carried out, in the exiting technology, through operation to an icon displayed on the display DP, is allowed to be carried out by using the foot-part input system. 
     Specifically, a rendered image can be moved on a display screen of the display DP by moving the foot-part position indicating instrument  100  on the foot-part position detecting device  200 . Further, enlargement and reduction of a rendered image can be carried out by raising and lowering the toe side of the foot-part position indicating instrument  100  with the heel side thereof kept contact with the foot-part position detecting device  200 . This is one example and various indication inputs can be made through the foot-part input system by a program that runs in the computer rendering system. 
     As above, the foot-part input system is what can function as an input device (input system) of the computer rendering system. In this embodiment, the foot-part input system allows indication of a position through the foot-part position indicating instrument  100  and sensing of a pressure applied to the foot-part position indicating instrument  100  and notification thereof by an electromagnetic induction system also as described later. Configuration examples of the foot-part position indicating instrument  100  and the foot-part position detecting device  200  that configure the foot-part input system will be specifically described below. 
     Configuration Example of Foot-Part Position Indicating Instrument  100   
       FIGS. 2A and 2B  and  FIGS. 3A to 3C  are diagrams for explaining the configuration example of the foot-part position indicating instrument  100  of the first embodiment. As illustrated in  FIG. 2B , the sole of the foot of the user (human) is classified into three parts, that is, a toe-side part, an arch part, and a heel part. As illustrated in  FIG. 2A , the foot-part position indicating instrument  100  includes a sole front part  101  located on the lower side of the toe-side part, a sole back part  103  located on the lower side of the heel part, and a sole central part  102  that is located on the lower side of the arch part and connects the sole front part  101  and the sole back part  103  to each other. 
     At the sole front part  101 , a position indicating unit  101 U including a coil  101 L and a pressure sensor  101 P is disposed. Further, at the sole back part  103 , a position indicating unit  103 U including a coil  103 L and a pressure sensor  103 P is disposed. More specifically, as illustrated in  FIG. 3A , the position indicating unit  101 U is configured through connection of the coil  101 L, a capacitor  101 C, and the pressure sensor  101 P in parallel. Similarly, the position indicating unit  103 U is configured through connection of the coil  103 L, a capacitor  103 C, and the pressure sensor  103 P in parallel. 
     That is, the position indicating unit  101 U configures a resonant circuit through connection of the coil  101 L and the capacitor  101 C in parallel and implements a function of transmitting a position indication signal by cooperating with the foot-part position detecting device  200  to be described later. Further, the pressure sensor  101 P is made into a configuration of a variable-capacitance capacitor and is made into a configuration in which the capacitance changes according to the applied pressure. The pressure sensor  101 P is connected in parallel to the resonant circuit configured by the coil  101 L and the capacitor  101 C to thereby allow change in the phase of the resonant frequency according to the capacitance and transmission of the position indication signal including information on the detected pressure. The position indicating unit  103 U is also what is configured similarly to the position indicating unit  101 U. 
     The foot-part position indicating instrument  100  is made into a slipper shape as illustrated in  FIG. 1  and  FIG. 3B  and includes the sole front part  101  and the sole back part  103  as illustrated in  FIGS. 3B and 3C . Because the position indicating unit  101 U is disposed at the sole front part  101  and the position indicating unit  103 U is disposed at the sole back part  103 , the respective positions thereof can be indicated and the pressures applied to them can be sensed and notified. Further, as described in detail later, it is possible to input not only the position and the pressure but various kinds of information such as the height and the angle at which the position indicating unit  101 U or  103 U is located and the angle when the toe-side part of the foot-part position indicating instrument  100  is pivotally moved with the heel part thereof fixed. 
     In this embodiment, for example, the resonant frequency of the position indicating unit  101 U of the sole front part  101  is a frequency f 1 , and the resonant frequency of the position indicating unit  103 U of the sole back part is a frequency f 2 . As above, the resonant frequencies thereof are made different from each other. This allows the side of the foot-part position detecting device  200  to discriminate and detect the position and the pressure based on the position indication signal from the position indicating unit  101 U and the position and the pressure based on the position indication signal from the position indicating unit  103 U. That is, the position of each of the sole front part  101  and the sole back part  103  and the pressure applied to each of them can be detected with discrimination. 
     Configuration Example of Foot-Part Position Detecting Device  200   
       FIG. 4  is a block diagram for explaining the configuration example of the foot-part position detecting device  200  of this embodiment to which an electromagnetic induction system is applied. The foot-part position detecting device  200  is broadly divided into a position detecting sensor  201  and a position detecting circuit  202 . The position detecting sensor  201  is configured through stacking of an X-axis direction loop coil group  201 X and a Y-axis direction loop coil group  201 Y. Further, as illustrated also in  FIG. 1 , the position detecting sensor  201  is used in such a manner as to be disposed under the foot of the user and be located on the lower side of the foot-part position indicating instrument  100 . 
     Each of the respective loop coils X 1  to X 40  of the X-axis direction loop coil group  201 X and the respective loop coils Y 1  to Y 30  of the Y-axis direction loop coil group  201 Y that configure electrodes of the position detecting sensor  201  is a coil with one turn in some cases and is a coil with two or more plural turns in other cases. Further, the numbers of loop coils of the loop coil groups  201 X and  201 Y can also be set to appropriate numbers according to the size of the position detecting sensor  201 . 
     The position detecting circuit  202  is composed of an oscillator  204 , a current driver  205 , a selection circuit  206 , a switching connection circuit  207 , a receiving amplifier  208 , a position detection circuit  209 , a pressure detection circuit  210 , and a control circuit  211 . The control circuit  211  is configured by a microprocessor. The control circuit  211  controls selection of the loop coil in the selection circuit  206  and switching of the switching connection circuit  207 . In addition, the control circuit  211  controls the processing timing in the position detection circuit  209  and the pressure detection circuit  210 . 
     Further, the X-axis direction loop coil group  201 X and the Y-axis direction loop coil group  201 Y of the position detecting sensor  201  are connected to the selection circuit  206 . The selection circuit  206  sequentially selects one loop coil in the two loop coil groups  201 X and  201 Y. The oscillator  204  generates an alternate current (AC) signal with a frequency f 0 . The oscillator  204  supplies the generated AC signal to the current driver  205  and the pressure detection circuit  210 . The current driver  205  converts the AC signal supplied from the oscillator  204  to a current and sends out the current to the switching connection circuit  207 . 
     The switching connection circuit  207  switches the connection destination (transmission-side terminal T, reception-side terminal R) to which the loop coil selected by the selection circuit  206  is connected, based on control from the control circuit  211 . In these connection destinations, the transmission-side terminal T is connected to the current driver  205 , and the reception-side terminal R is connected to the receiving amplifier  208 . Further, the switching connection circuit  207  is switched to the side of the terminal T in a case of transmitting a signal from the position detecting sensor  201 . Conversely, the switching connection circuit  207  is switched to the side of the terminal R in a case of receiving a signal from the external by the position detecting sensor  201 . 
     Further, when the switching connection circuit  207  is switched to the side of the terminal T, the current from the current driver  205  is supplied to the loop coil selected by the selection circuit  206 . Due to this, a magnetic field is generated in this loop coil and acts on the resonant circuit included in the position indicating unit  101 U or  103 U of the foot-part position indicating instrument  100  opposed to this loop coil to allow transmission of a signal (radio wave). 
     On the other hand, when the switching connection circuit  207  is switched to the side of the terminal R, an induced voltage generated in the loop coil selected by the selection circuit  206  is sent to the receiving amplifier  208  through the selection circuit  206  and the switching connection circuit  207 . The receiving amplifier  208  amplifies the induced voltage supplied from the loop coil and sends out the amplified induced voltage to the position detection circuit  209  and the pressure detection circuit  210 . 
     Specifically, in each loop coil of the X-axis direction loop coil group  201 X and the Y-axis direction loop coil group  201 Y, the induced voltage is generated due to a radio wave (position indication signal) transmitted from the position indicating unit  101 U or  103 U of the foot-part position indicating instrument  100 . The position detection circuit  209  carries out detection of the induced voltage generated in the loop coil, i.e., the received signal, and converts a detection output signal thereof to a digital signal to output it to the control circuit  211 . The control circuit  211  calculates the coordinate values of the indicated position regarding the X-axis direction and the Y-axis direction based on the position indication signal from the position indicating unit  101 U or  103 U, based on the digital signal from the circuit  209  for position detection, i.e., the level of the voltage value of the induced voltage generated in each loop coil. 
     Meanwhile, the pressure detection circuit  210  carries out synchronous detection of the output signal of the receiving amplifier  208  with the AC signal from the oscillator  204  and obtains a signal at a level based on the phase difference (frequency deviation) between them, and converts the signal based on the phase difference (frequency deviation) to a digital signal to output it to the control circuit  211 . The control circuit  211  detects the pressure that is being applied to the pressure sensor  101 P or  103 P of the position indicating unit  101 U or  103 U, based on the digital signal from the pressure detection circuit  210 , i.e., the level of the signal based on the phase difference (frequency deviation) between the transmitted radio wave and the received radio wave. 
       FIGS. 5A and 5B  each depict a diagram for explaining height information and angle information that can be input by the foot-part position indicating instrument  100 . With the foot-part position indicating instrument  100 , as illustrated in  FIG. 5B , it is possible to carry out operation in which the sole front part  101  is raised to be separated from the position detecting sensor  201  with the side of the sole back part  103  kept contact with the position detecting sensor  201 . In this case, the control circuit  211  can also detect the distance (height) h of the position indicating unit  101 U of the foot-part position indicating instrument  100  from the position detecting sensor  201  based on the level of the voltage value of the induced voltage generated in each loop coil. 
     Further, as illustrated in  FIG. 5A , a distance l between the position indicating unit  101 U attached to the sole front part  101  and the position indicating unit  103 U attached to the sole back part  103  is settled at the timing when they are attached. Thus, the control circuit  211  can also obtain an angle θ formed by the position detecting sensor  201  and the bottom surface of the foot-part position indicating instrument  100 , by calculation from “tan θ=h/l.” 
     Moreover, with the foot-part position indicating instrument  100 , conversely to the state illustrated in  FIG. 5B , it is also possible to carry out operation in which the sole back part  103  is raised to be separated from the position detecting sensor  201  with the side of the sole front part  101  kept contact with the position detecting sensor  201 . Also in this case, the height and the angle can be obtained similarly to the case described with use of  FIGS. 5A and 5B . That is, the distance (height) of the position indicating unit  103 U from the position detecting sensor  201  can be detected. In addition, the angle formed by the position detecting sensor  201  and the bottom surface of the foot-part position indicating instrument  100  in the state in which the sole back part  103  is raised can also be obtained from calculation. 
       FIGS. 6A and 6B  is a diagram for explaining angle information that can be input by the foot-part position indicating instrument  100 . With the foot-part position indicating instrument  100 , as illustrated in  FIG. 6A , the sole front part  101  is allowed to rotate in the left direction or the right direction around the side of the sole back part  103  on the position detecting sensor  201 . The control circuit  211  can carry out detection also regarding how far and in which direction the sole front part  101  of the foot-part position indicating instrument  100  is rotated, based on change in the position of the position indicating unit  101 U of the foot-part position indicating instrument  100 . 
     For example, suppose that, as illustrated in  FIG. 6B , the position of the position indicating unit  103 U disposed at the sole back part  103  does not change and the sole front part  101  rotates to the right side as illustrated by an arrow and only the indicated position of the position indicating unit  101 U changes. In this case, the length (distance) l between the position indicating unit  103 U and the position indicating unit  101 U does not change. Therefore, an isosceles triangle in which the position indicating unit  103 U is the vertex and an indicated position P 0  of the position indicating unit  101 U before the rotation and an indication position P 1  of the position indicating unit  101 U after the rotation are both ends of the base is formed. 
     The position indicated by the position indicating unit  103 U and the positions P 0  and P 1  indicated by the position indicating unit  101 U can be detected in the control circuit  211  as described above. Therefore, a length a of the base including the position P 0  and the position P 1  as both ends can also be obtained in the control circuit  211 . Similarly, the distance between the midpoint of the base and the vertex indicated by the position indicating unit  103 U, i.e., a height h of this isosceles triangle, can also be obtained in the control circuit  211 . 
     When the length a of the base and the height h about this isosceles triangle are found out, a base angle θ is obtained based on expression (1) in  FIG. 6B . Thus, as indicated in expression (2) in  FIG. 6B , a vertex angle φ is obtained when the sum of the two base angles is subtracted from 180 degrees, which is the sum of the internal angles of the triangle. This angle φ is information indicating how far the sole front part  101  is rotated to the right side (amount of rotation) in this example. Also when the sole front part  101  rotates to the left side, only the rotation direction changes and calculation of the amount of rotation can be similarly carried out. 
     Further, with the foot-part position indicating instrument  100 , it is also possible to rotate the sole back part  103  in the left direction or the right direction around the side of the sole front part  101  on the position detecting sensor  201 . Also in this case, how far and in which direction of the left and right directions the sole back part  103  is rotationally moved can be detected similarly to the case described with use of  FIGS. 6A and 6B . As above, various kinds of information can be input by the foot-part position indicating instrument  100  and therefore, display control of a rendered image with use of these kinds of input information can be carried out. 
     To cite one example, adjustment of enlargement display of a rendered image can be carried out when the sole front part  101  is raised and lowered without moving the sole back part  103  as described with use of  FIGS. 5A and 5B , and adjustment of reduction display of a rendered image can be carried out when the sole back part  103  is raised and lowered without moving the sole front part  101 . Further, rotation display of a rendered image to the left and right sides can be carried out when the sole front part  101  is rotationally moved to the left and right sides without moving the sole back part  103  as described with use of  FIGS. 6A and 6B . In addition, rotation display of a rendered image to the upper and lower sides can be carried out when the sole back part  103  is rotationally moved to the left and right sides without moving the sole front part  101 . 
     In this case, control can be carried out based on the detected height of the position indicating unit  101 U or  103 U from the position detecting sensor  201  and the detected angle of the whole of the sole of the foot-part position indicating instrument  100  relative to the position detecting sensor  201 . Further, it is also possible to detect the pressure applied to the pressure sensor  101 P mounted at the sole front part  101  and the pressure applied to the pressure sensor  103 P mounted at the sole back part. Thus, control such as enlarging a rendered image according to the strength of pressing-down of the sole front part  101  and reducing the rendered image according to the strength of pressing-down of the sole back part  103  is also possible. Such control is one example and other various kinds of control are allowed to be carried out according to information input by the foot-part input system, based on the processing program of the computer rendering system. 
     In the examples described with use of  FIGS. 5A and 5B  and  FIGS. 6A and 6B , either the sole front part  101  or the sole back part  103  of the foot-part position indicating instrument  100  is made contact with the position detecting sensor  201 . However, the configuration is not limited thereto. For example, when both the sole front part  101  and the sole back part  103  are separated from the position detecting sensor  201  and are raised and lowered, the state can be detected in the foot-part position detecting device  200  and therefore, for example, display control of a rendered image can be carried out according to this state. Further, it is also possible to allow both the sole front part  101  and the sole back part  103  to be separated from the position detecting sensor  201  and be rotated in the left direction and the right direction. Further, in the foot-part position detecting device  200 , the state can also be detected and therefore, for example, display control of a rendered image can also be carried out according to this state. 
     Effects of First Embodiment 
     According to the foot-part input system of the above-described first embodiment, various kinds of detailed information, such as the position, the pressure, the height, and the angle, can be input by using a foot part of the user. These pieces of information are detected in the position detecting circuit  202  of the foot-part position detecting device  200 , and the detected pieces of information are input to the computer main unit that processes image data and can be utilized as parameters of image processing. Due to this, for example, various instructions of enlargement, reduction, rotation, image quality adjustment of a rendered image, the instructions having been made through indication input with use of a hand of the user in the existing technology, can be made by using the foot-part input system. That is, the foot-part input system enables new input operation for multiple use purposes. 
     Moreover, in the foot-part input system, due to employment of the electromagnetic induction system, a battery-less structure is made, and the foot-part input system is excellent in the durability. In addition, it also becomes possible for the user to move while wearing the foot-part position indicating instrument  100  on the foot part. Thus, handling becomes easy, and an easy-to-use input device can be provided. 
     Further, in use scenes of techniques such as VR, AR, and MR, a new input unit can be provided, and more flexible indication input can be implemented. This can implement more flexible information input in fields of VR, AR, and MR. 
     For example, when a large room is prepared as a VR space and the position detecting sensor  201  is disposed on the whole surface of the room under a user, a large three-dimensional VR object is allowed to be formed in this room, and the user can carry out rendering of the three-dimensional VR object while moving in the room. As above, in use scenes of techniques such as VR, AR, and MR, more flexible indication input is enabled and physical fatigue of the user can be reduced and both fine work and rough work can be carried out, without inhibiting a sense of immersion into the three-dimensional space. 
     Second Embodiment 
     Configuration Examples of Foot-part Input System and Image Processing System  FIG. 7  is a diagram for explaining a use example of a foot-part input system of a second embodiment. The foot-part input system of the second embodiment is composed of a foot-part position indicating instrument  300  mounted on a foot part of a user like footwear and a foot-part position detecting device  400  disposed on the lower side of the foot-part position indicating instrument  300 , similarly to the foot-part input system of the first embodiment. In the second embodiment, as illustrated in  FIG. 7 , the foot-part position detecting device  400 , a head-mounted display (hereinafter, abbreviated as an HMD)  500 , and a game controller  600  are connected to an image processing device  700  to be described in detail later. 
     The foot-part input system composed of the foot-part position indicating instrument  300  and the foot-part position detecting device  400  and the game controller  600  function as input devices that accept indication input made by the user and supply the accepted indication input to the image processing device  700 . The HMD  500  is a display (display device) of a head wearing type and, in this embodiment, is mounted on the head of the user in such a manner as to cover both eyes of the user as illustrated in  FIG. 7 . 
     The image processing device  700  is what can form a three-dimensional space image (three-dimensional modeling image) across 360 degrees around the user as illustrated as a 360-degree image region GA in  FIG. 7  and supply it to the HMD  500 . In this embodiment, the image processing device  700  is what functions as what is generally called a computer game machine that provides a game using the three-dimensional space image to the user. 
       FIG. 8  is a diagram for explaining the overall configuration of an image processing system configured with use of the foot-part input system of the second embodiment. As illustrated in  FIG. 8 , the image processing device  700  includes a three-dimensional image data file  701 , a three-dimensional parts image file  702 , an image processing circuit  703 , communication circuits  704  and  705 , and an interface (I/F)  706 . The communication circuit  704  is for mutually carrying out wireless communication with the HMD  500 . The communication circuit  705  is for receiving instruction input made by the game controller. The I/F  706  is for accepting detection output supplied from the foot-part position detecting device  400  (indication input with use of the foot-part position indicating instrument  300 ). 
     As above, the image processing device  700  and the HMD  500  can bidirectionally communicate wirelessly. Further, the image processing device  700  and the game controller  600  are wirelessly connected, and at least the image processing device  700  can accept instruction input made by the game controller  600 . Further, the image processing device  700  and the foot-part position detecting device  400  are connected in a wired manner, and the image processing device  700  can accept detection output supplied from the foot-part position detecting device  400 . 
     Also regarding the HMD  500  and the game controller  600 , connection to the image processing device  700  in a wired manner is also possible. However, the HMD  500  and the game controller  600  are what are worn or carried by the user who often changes the orientation of the body. Thus, it is desirable that the HMD  500  and the game controller  600  be connected to the image processing device  700  wirelessly, which means free of anxiety that, for example, the body gets tangled in a connection cord. Moreover, it is also possible to wirelessly connect the foot-part position detecting device  400  and the image processing device  700 . However, the foot-part position detecting device  400  does not move in association with movement of the user and therefore, the connection in a wired manner does not cause a problem. 
     The three-dimensional image data file  701  stores and holds three-dimensional image data that forms a three-dimensional space image. The three-dimensional parts image file  702  stores and holds three-dimensional parts image data for forming various three-dimensional parts images, such as avatars, displayed in the three-dimensional space image. The image processing circuit  703  forms three-dimensional space image data to be supplied to the HMD  500 , by using the three-dimensional image data of the three-dimensional image data file  701  and the three-dimensional parts image data of the three-dimensional parts image file  702 , and supplies it to the HMD  500 . 
     The HMD  500  includes a display HDP that displays the three-dimensional space image. In addition, the HMD  500  includes, for example, a six-axis sensor configured by a three-axis gyro sensor and a three-axis angular velocity sensor and can detect the rotation direction and the rotation angle. Due to this, the HMD  500  can display, on the display HDP, the three-dimensional space image based on the three-dimensional image data supplied from the image processing device  700  and transmit the detected rotation direction and rotation angle to the image processing device  700 . Thus, when the user who wears the HMD  500  on the head makes action of rotating the head to orient the head to the left or right, looking up, or looking down, the six-axis sensor mounted in the HMD  500  detects how far and in which direction the HMD  500  rotates and notifies the image processing device  700  of the result of the detection. 
     The image processing circuit  703  of the image processing device  700  identifies which direction both eyes of the user are oriented in based on the detection output that the six-axis sensor of the HMD  500  notifies, and forms three-dimensional space image data of the viewing direction thereof to supply it to the HMD  500 . This allows the user to view a three-dimensional space image according to the direction in which both eyes of the user are oriented through the display HDP of the HMD  500 . 
     Further, the image processing circuit  703  of the image processing device  700  can create, according to instruction input made by the game controller  600 , three-dimensional space image data obtained by addition of a change such as throwing a ball or shooting a gun by an avatar, for example, in the three-dimensional space image displayed on the display of the HMD  500  and supply it to the HMD  500 . In this manner, through the display HDP of the HMD  500 , the three-dimensional space image that changes according to the instruction input made through the game controller  600  can be viewed. 
     Moreover, the image processing circuit  703  of the image processing device  700  can carry out enlargement, reduction, and so forth of the three-dimensional space image displayed on the display of the HMD  500 , according to the detection output supplied from the foot-part position detecting device  400  (indication input with use of the foot-part position indicating instrument  300 ). As described in detail later, by moving the foot-part position indicating instrument  300  mounted on a foot part of the user on the foot-part position detecting device  400 , the three-dimensional space image displayed on the display of the HMD  500  can be enlarged and reduced and the position of the point of view can be shifted to the right side and be shifted to the left side in the three-dimensional space image. 
     Specifically, the image processing device  700  can be instructed to enlarge the three-dimensional space image when the foot-part position indicating instrument  300  is moved by sliding on the foot-part position detecting device  400  in a direction which is the longitudinal direction of the foot part and in which the front of the body is oriented. Conversely, the image processing device  700  can be instructed to reduce the three-dimensional space image when the foot-part position indicating instrument  300  is moved by sliding on the foot-part position detecting device  400  in a direction which is the longitudinal direction of the foot part and in which the back of the body is oriented. 
     Further, suppose that the foot-part position indicating instrument  300  is moved by sliding on the foot-part position detecting device  400  in a direction to the left side of the body, the direction intersecting the longitudinal direction of the foot part. In this case, the position of the point of view can be moved to the left side in the three-dimensional space image, and the three-dimensional space image as viewed from the position after the movement can be displayed. Conversely, suppose that the foot-part position indicating instrument  300  is moved by sliding on the foot-part position detecting device  400  in a direction to the right side of the body, the direction intersecting the longitudinal direction of the foot part. In this case, the position of the point of view can be moved to the right side in the three-dimensional space image, and the three-dimensional space image as viewed from the position after the movement can be displayed. 
     Due to this, as illustrated in  FIG. 7 , the user who wears the HMD  500  on the head, holds the game controller  600  with hands, and puts the right foot on which the foot-part position indicating instrument  300  is mounted on the foot-part position detecting device  400  can enjoy a game using the three-dimensional space image. In this case, the user changes the viewing direction by making action of rotating the head to the left or right, looking up, or looking down and can change the three-dimensional space image displayed on the display of the HMD  500 , according to the change of the viewing direction. 
     Further, by operating the game controller  600 , display of a three-dimensional image object such as an avatar can be changed in the displayed three-dimensional space image. Moreover, by moving the foot-part position indicating instrument on the foot-part position detecting device  400 , enlargement or reduction of the three-dimensional space image or movement of the position of the point of view to the left side or the right side can be carried out. 
     The rotation of the head is not limited to the case of rotating only the head and includes also the case of rotating the whole of the body of the user. Therefore, as illustrated in  FIG. 7 , the user can enjoy the game with utilization of the all-around three-dimensional space image of the 360-degree image region GA while freely making rotational movement such as rotating the whole of the body to greatly change the orientation of user&#39;s own body. In addition, regarding the three-dimensional space image of any direction, enlargement, reduction, movement of the position of the point of view in the three-dimensional space image to the left side or the right side, and so forth can be carried out through the foot-part position indicating instrument  300  and the foot-part position detecting device  400 . As above, the game can be enjoyed in such a manner that the three-dimensional space image is dynamically changed by the rotation of the head and the operation of the foot part. 
     Configuration Example of Foot-Part Position Indicating Instrument 
       FIGS. 9A and 9B  each depict a diagram for explaining a configuration example of the foot-part position indicating instrument  300  of the second embodiment.  FIG. 9A  is a diagram of the front surface side of the foot-part position indicating instrument  300 .  FIG. 9B  is a diagram of the back surface side of the foot-part position indicating instrument  300 . As illustrated in  FIG. 9A , the foot-part position indicating instrument  300  includes one plate-shaped sole part  301  opposed to the whole surface of the sole of the foot of the user. The sole part  301  is composed of a sole front part  301   f  located on the lower side of the toe part of a foot part of the user, a sole back part  301   b  located on the lower side of the heel part of the foot part of the user, and a sole central part  301   c  that connects the sole front part  301   f  and the sole back part  301   b . On the sole front part  301   f , toe-side belt holding parts  301 L and  301 R through which a belt for fixing the foot-part position indicating instrument  300  to the foot part of the user is made to pass and which hold the belt are disposed. 
     A heel-side fixing part  302  is disposed on the side of the sole back part  301   b . In  FIG. 9A , the heel-side fixing part  302  is illustrated in the state of being separated from the sole part  301 , in order to allow viewing of the whole of the configuration on the side of the sole back part  301   b . However, in practice, the heel-side fixing part  302  is formed integrally with a bottom surface part  302   a  that covers the sole back part  301   b  and the sole central part  301   c  of the sole part  301  from the lower side thereof as illustrated in  FIG. 9B . On the upper side of the bottom surface part  302   a  of the heel-side fixing part  302 , as illustrated in  FIG. 9B , the sole back part  301   b  and the sole central part  301   c  of the sole part  301  are placed in such a manner as to be opposed to the bottom surface part  302   a  and are fixed by a sole holding part  302 SL and a sole holding part  302 SR of the bottom surface part  302   a . Needless to say, the bottom surface part  302   a  of the heel-side fixing part  302  and the sole back part  301   b  and the sole central part  301   c  of the sole part  301  may be stuck to each other by an adhesive to be fixed. 
     Further, on the heel-side fixing part  302 , heel-side belt holding parts  302 L and  302 R through which a belt for fixing the foot-part position indicating instrument  300  to the foot part of the user is made to pass and which hold the belt are disposed as illustrated in  FIG. 9A . The toe part of the foot part of the user can be fixed to the sole front part  301   f  of the sole part  301  by causing the toe part of the foot part of the user to be located between the sole front part  301   f  and the belt made to pass through the above-described toe-side belt holding parts  301 L and  301 R. When the heel part of the foot part of the user is put on the sole back part  301   b  and is fastened by the belt made to pass through the heel-side belt holding parts  302 L and  302 R in such a manner that the opposite side to the heel part is covered by the belt, the heel side of the foot part of the user can be fixed to the sole back part  301   b . This can fix the whole of the foot-part position indicating instrument  300  to the foot part of the user. 
     Moreover, in the foot-part position indicating instrument  300  of this embodiment, a left position indicating unit  303 L is disposed on the left end side of the sole back part  301   b , and a right position indicating unit  303 R is disposed on the right end side of the sole back part  301   b . In addition, a back position indicating unit  303 C is disposed at the center on the back end side of the sole back part  301   b . The basic configuration of these three position indicating units  303 L,  303 R, and  303 C is similar to that of the position indicating units  101 U and  103 U described with use of  FIGS. 3A to 3C  and is composed of a coil for signal transmission, a capacitor, and a pressure sensor. In this embodiment, each of the position indicating units  303 L,  303 R, and  303 C is configured to transmit a signal with a different frequency. 
     The position indicating units  303 L,  303 R, and  303 C form, in the bottom surface of the sole back part  301   b , an isosceles triangle in which the left position indicating unit  303 L and the right position indicating unit  303 R are both ends of the base and the back position indicating unit  303 C is the vertex. By the position indicating units  303 L,  303 R, and  303 C disposed in this manner, detection of whether the foot-part position indicating instrument  300  makes forward movement or backward movement is allowed. Regarding the foot-part position indicating instrument  300 , the forward movement means movement in the extension direction of a line extended from the heel part toward the toe part, and the backward movement means movement in the extension direction of a line extended from the toe part toward the heel part. 
     Further, as illustrated in  FIG. 9B , a movable range restricting plate  304  is disposed over the back surface of the sole back part  301   b  with the interposition of the bottom surface part  302   a  of the heel-side fixing part  302 . The movable range restricting plate  304  engages with a ring-shaped protrusion part that surrounds the outer edge of a movable range restriction region made on an operation surface of the foot-part position detecting device  400  to be described later and acts to restrict the movable range of the foot-part position indicating instrument  300  on the foot-part position detecting device  400 . As above, the foot-part position indicating instrument  300  of this embodiment is configured by the sole part  301 , the heel-side fixing part  302 , the position indicating units  303 L,  303 R, and  303 C, and the movable range restricting plate  304 . 
     Configuration Example of Foot-Part Position Detecting Device  400   
       FIGS. 10A and 10B  each depict a diagram for explaining a configuration example of the foot-part position detecting device  400  of the second embodiment. In  FIGS. 10A and 10B ,  FIG. 10A  is a diagram of the front surface side of the foot-part position detecting device  400  and  FIG. 10B  is a diagram illustrating the schematic configuration of the inside of the foot-part position detecting device  400 . The foot-part position detecting device  400  is configured by disposing an operation surface (top plate)  401  that is circular and has a flat plate shape, on the upper side of the foot-part position detecting device  200  described with use of  FIG. 4 . The above-described foot-part position indicating instrument  300  is placed on the operation surface  401  and various operations are carried out. At a central part of the operation surface  401 , by a ring-shaped protrusion part  403  made into a circumferential shape (ring shape), the inside thereof is caused to be a movable range restriction region  402 . 
     Inside the movable range restriction region  402 , the movable range restricting plate  304  of the above-described foot-part position indicating instrument  300  is caused to be located. Due to this, when the foot-part position indicating instrument  300  is greatly moved, the side surface of the movable range restricting plate  304  engages with the ring-shaped protrusion part  403 , and further outward movement is restricted. It is also possible for the movable range restricting plate  304  to move on the operation surface  401  beyond the ring-shaped protrusion part  403  if necessary. 
     As above, the foot-part position indicating instrument  300  is capable of free movement as long as it is on the operation surface  401 . However, normally, various kinds of operation input are allowed by free movement of the movable range restricting plate  304  in the movable range restriction region  402  on the operation surface  401 . In the movable range restriction region  402 , straight line marks are represented in a reference direction K and the direction orthogonal to the reference direction K, and the reference direction and the direction orthogonal thereto are allowed to be recognized visually as well. Further, the intersection of the straight line marks becomes an origin O of a reference coordinate system as described in detail later. 
     Moreover, a groove part  404  for recognition is made at an outer circumferential part of the operation surface  401  represented by the reference direction K. The sole front part  301   f  of the foot-part position indicating instrument  300  is fitted in the groove part  404  for recognition. This allows the user to recognize the initial position and the initial angle of the foot-part position indicating instrument  300  on the operation surface  401 . Specifically, the tip of the sole front part  301   f  abuts against an inner wall part  405  made at an inside opening part of the groove part  404  for recognition. This allows the user to recognize that the foot-part position indicating instrument  300  is located at the inside opening part of the groove part  404  for recognition. That is, the user can recognize that the foot-part position indicating instrument  300  is present at the initial position on the operation surface  401 . 
     If necessary, the sole front part  301   f  of the foot-part position indicating instrument  300  is fitted in such a manner as to ride on the groove part  404  for recognition. This allows the user to grasp the position of the foot-part position indicating instrument  300  on the operation surface  401  more surely due to the fitting of the foot-part position indicating instrument  300  in the groove part  404  for recognition. Thereafter, the foot-part position indicating instrument  300  can be positioned to the initial position on the operation surface  401  by moving the foot-part position indicating instrument  300  backward and causing the tip of the sole front part  301   f  to abut against the inner wall part  405  of the inside opening part of the groove part  404  for recognition. 
     As described above with use of  FIG. 4  and as illustrated in  FIG. 10B , the foot-part position detecting device  400  is composed of the position detecting sensor  201  with a rectangular shape and the position detecting circuit  202 . In  FIG. 10B , as the position detecting circuit  202 , the position detecting circuit  202  described with use of  FIG. 4  is configured in a casing illustrated as the position detecting circuit  202  in  FIG. 10B . In  FIG. 10B , a cable  221  drawn out from the position detecting circuit  202  is connected to the I/F  706  of the image processing device  700 . In this embodiment, the foot-part position detecting device  400  includes a wireless communication part  222  and a battery  223  as illustrated in  FIG. 10B . The wireless communication part  222  is what allows the connection to the image processing device  700  also wirelessly, and the battery  223  is what supplies drive power to the parts of the foot-part position detecting device  400 . 
     In this embodiment, as is understood also from  FIG. 10B , the position detecting sensor  201  is disposed with a tilt to the left by 45 degrees with respect to the reference direction K which is the direction in which the groove part  404  for recognition in the operation surface  401  is made. Due to this, at the initial position and angles in the vicinity thereof, frequent riding of two position indicating units over the same position detecting coil is suppressed, and reduction of what is generally called jitter that is fluctuation of the signal waveform in the time-axis direction, for example, are enabled, so that the accuracy of position detection is improved. 
     Further, in the foot-part position detecting device  400  of this embodiment, the frequency of the signal transmitted from each of the position indicating units  303 L,  303 R, and  303 C disposed in the foot-part position indicating instrument  300  is grasped in a memory disposed in the control circuit  211 , for example. This allows the foot-part position detecting device  400  to detect which position indicating unit is indicating which position. 
     Use Example of Foot-Part Input System 
       FIGS. 11A to 11C  each depict a diagram for explaining a use example of the foot-part input system of the second embodiment. In  FIGS. 11A to 11C ,  FIG. 11A  is a diagram for explaining the positional relation among the three position indicating units  303 L,  303 R, and  303 C disposed at the sole back part  301   b  of the foot-part position indicating instrument  300 . Further,  FIG. 11B  is a diagram illustrating a case in which the foot-part position indicating instrument  300  is placed at the initial position on the operation surface  401  of the foot-part position detecting device  400 . Moreover,  FIG. 11C  is a diagram of a case in which the state illustrated in  FIG. 11B  is viewed from a side surface side of the foot-part position indicating instrument  300  (lateral direction). In  FIG. 11C , only the operation surface  401  of the foot-part position detecting device  400  is illustrated as a circuit and, regarding the foot-part position indicating instrument  300 , the whole as viewed from the side surface side thereof is illustrated. 
     As illustrated in  FIG. 9A , on the sole back part  301   b  of the foot-part position indicating instrument  300  of this embodiment, the left position indicating unit  303 L and the right position indicating unit  303 R are disposed at positions that are close to the sole central part  301   c  and are bilaterally symmetric. Moreover, the back position indicating unit  303 C is disposed at the center on the back end side of the sole back part  301   b . As illustrated in  FIG. 11A , these three position indicating units  303 L,  303 R, and  303 C form a triangle in which each of them is a vertex. 
     In this example, the distance from the left position indicating unit  303 L to the back position indicating unit  303 C is equal to the distance from the right position indicating unit  303 R to the back position indicating unit  303 C. Therefore, an isosceles triangle in which the left position indicating unit  303 L and the right position indicating unit  303 R are both ends of the base and the back position indicating unit  303 C is the vertex is formed. In other words, the line segment that links the left position indicating unit  303 L and the right position indicating unit  303 R is the base, and the line segment that links the back position indicating unit  303 C and the left position indicating unit  303 L and the line segment that links the back position indicating unit  303 C and the right position indicating unit  303 R are the legs. 
     Due to this, as illustrated in  FIG. 11A , a position indication coordinate system (transmission coil coordinate system) defined by the three position indicating units  303 L,  303 R, and  303 C is formed. Specifically, a coordinate system in which a straight line that is parallel to the line segment linking the left position indicating unit  303 L and the right position indicating unit  303 R and that passes through a centroid G is the x-axis and a straight line obtained by drawing a perpendicular line from the back position indicating unit  303 C to the x-axis and further extending the perpendicular line from both ends is the y-axis can be formed. This coordinate system is employed as the position indication coordinate system identified by the three position indicating units. The origin of this position indication coordinate system is the centroid G of the isosceles triangle formed by the three position indicating units  303 L,  303 R, and  303 C. 
     In this embodiment, as the coordinate system to decide the movement direction and the amount of movement regarding the foot-part position indicating instrument  300 , this position indication coordinate system defined by the left position indicating unit  303 L, the right position indicating unit  303 R, and the back position indicating unit  303 C is used as one basis. However, this position indication coordinate system is the coordinate system defined by the three position indicating units  303 L,  303 R, and  303 C disposed in the foot-part position indicating instrument  300 . Therefore, when the foot-part position indicating instrument  300  moves, this coordinate system also moves. 
     Thus, another reference coordinate system is set. In this case, as illustrated in  FIG. 10A , the center O of the movable range restriction region  402  that is set on the operation surface  401  of the foot-part position detecting device  400  and that has a circular shape is employed as the origin O of the reference coordinate system. A straight line that passes through the origin O and is parallel to the x-axis of the position indication coordinate system is employed as the X-axis of the reference coordinate system. Further, a straight line that passes through the origin O and is parallel to the y-axis of the position indication coordinate system is employed as the Y-axis of the reference coordinate system. Change in the position of the origin (centroid) G of the position indication coordinate system in the reference coordinate system defined in this manner becomes indication input in the foot-part input system. 
     The reference coordinate system and the position indication coordinate system will be described below. First, in  FIG. 11A , a point inside the isosceles triangle formed by the three position indicating units  303 L,  303 R, and  303 C represents the centroid G of the isosceles triangle. Suppose that the foot-part position indicating instrument  300  is placed on the operation surface  401  of the foot-part position detecting device  400 . In this case, the position on the position detecting sensor  201  corresponding to the centroid G of the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C is detected as the indicated position of the foot-part position indicating instrument  300  in the foot-part position detecting device  400 . 
     First, a case in which the foot-part position indicating instrument  300  is placed on the operation surface  401  of the foot-part position detecting device  400  as illustrated in  FIG. 11B  will be considered. When the state illustrated in  FIG. 11B  is viewed from just beside the foot-part position indicating instrument  300 , the state illustrated in  FIG. 11C  is obtained. As is understood from  FIGS. 11B and 11C , in the case of this example, the movable range restricting plate  304  disposed on the lower side of the sole back part  301   b  of the foot-part position indicating instrument  300  is located in the movable range restriction region  402  on the operation surface  401  of the foot-part position detecting device  400 . Simultaneously, the tip of the sole front part  301   f  of the foot-part position indicating instrument  300  is opposed to the inner wall part  405  disposed at the inside opening part of the groove part  404  for recognition in the foot-part position detecting device  400 , and abuts against the inner wall part  405  or is in the state of being allowed to immediately abut against it. 
     The state illustrated in  FIGS. 11B and 11C  corresponds to the initial position of the foot-part position indicating instrument  300  placed on the operation surface  401  of the foot-part position detecting device  400 . In this case, the centroid G of the isosceles triangle formed by the left position indicating unit  303 L, the right position indicating unit  303 R, and the back position indicating unit  303 C disposed at the sole back part  301   b  of the foot-part position indicating instrument  300  corresponds with the center of the movable range restriction region  402  on the operation surface  401 . The center of this movable range restriction region becomes the origin O of the reference coordinate system. In practice, it is rare that the centroid (origin) G of the isosceles triangle (position indication coordinate system) completely corresponds with the origin O of the reference coordinate system. Therefore, the foot-part position indicating instrument  300  is allowed to be regarded as being present at the initial position on the foot-part position detecting device  400  when the centroid G is located in a predetermined range centered at the origin O. 
     As above, the origin of the reference coordinate system is the center of the movable range restriction region. However, the orientations of the X-axis and the Y-axis of the reference coordinate system depend on the x-axis and the y-axis of the position indication coordinate system settled according to the orientation of the foot-part position indicating instrument  300 . In other words, the orientation of the position indication coordinate system depends on the orientation of the isosceles triangle formed by the left position indicating unit  303 L, the right position indicating unit  303 R, and the back position indicating unit  303 C disposed in the foot-part position indicating instrument  300 . 
     Thus, whichever orientation the foot-part position indicating instrument  300  placed on the operation surface  401  of the foot-part position detecting device  400  is placed in, movement of the indicated position (centroid G) can be sensed as change in the Y-axis direction of the reference coordinate system, when the foot-part position indicating instrument  300  is moved in the longitudinal direction. Further, whichever orientation the foot-part position indicating instrument  300  placed on the operation surface  401  of the foot-part position detecting device  400  is placed in, movement of the indicated position (centroid G) can be sensed as change in the X-axis direction of the reference coordinate system, when the foot-part position indicating instrument  300  is moved in the direction orthogonal to the longitudinal direction. 
     Description will be made more specifically.  FIGS. 11B and 11C  illustrate a case in which the foot-part position indicating instrument  300  is present at the initial position on the operation surface  401  of the foot-part position detecting device  400 . In this embodiment, the foot-part position indicating instrument  300  can rotate by 360 degrees around the centroid G of the isosceles triangle formed by the three position indicating units  303 L,  303 R, and  303 C at the sole back part  301   b  on the operation surface  401  which is a circular flat surface. Further, the foot-part position indicating instrument  300  can move in both the forward-backward direction and the left-right direction when the movable range restricting plate  304  of the foot-part position indicating instrument  300  is present in the movable range restriction region  402  of the operation surface  401 . 
     The reference coordinate system in this case corresponds with the position indication coordinate system defined by the three position indicating units  303 L,  303 R, and  303 C at the sole back part  301   b  as described above with use of  FIG. 11A . Therefore, whichever direction the foot-part position indicating instrument  300  is oriented in, the value of the Y-axis of the reference coordinate system becomes larger when the foot-part position indicating instrument  300  is moved forward. Further, the value of the Y-axis of the reference coordinate system becomes smaller when the foot-part position indicating instrument  300  is moved backward. Similarly, the value of the X-axis of the reference coordinate system becomes larger when the foot-part position indicating instrument  300  is moved rightward. In addition, the value of the X-axis of the reference coordinate system becomes smaller when the foot-part position indicating instrument  300  is moved leftward. As illustrated in  FIGS. 9A and 9B , in this embodiment, the left position indicating unit  303 L and the right position indicating unit  303 R are disposed at bilaterally symmetrical positions and closer to the sole central part  301   c . Further, the back position indicating unit  303 C is disposed on the back end side of the sole back part  301   b . Thus, the movement direction can be identified according to whether the back position indicating unit  303 C is moving to follow the left position indicating unit  303 L and the right position indicating unit  303 R or the left position indicating unit  303 L and the right position indicating unit  303 R are moving to follow the back position indicating unit  303 C. 
     Specifically, suppose that the back position indicating unit  303 C is moving to follow the left position indicating unit  303 L and the right position indicating unit  303 R. The following in this case means that the back position indicating unit  303 C moves to the front side on which the left position indicating unit  303 L and the right position indicating unit  303 R have been located, in association with the movement of the left position indicating unit  303 L and the right position indicating unit  303 R. In this case, it is possible to sense that the foot-part position indicating instrument  300  is moving in the forward direction that is the extension direction of a line extended from the heel part toward the toe part as illustrated by an arrow Fd in  FIG. 11A . Further, the distance from the position on the position detecting sensor  201  at which the centroid G before the movement is located to the position on the position detecting sensor  201  at which the centroid G after the movement is located is equivalent to the amount of movement in the forward direction, i.e., the amount of movement in the direction in which the value increases on the y-axis. 
     If the amount of movement is deemed as the amount of movement per unit time in the image processing device  700 , the amount of movement can be regarded as the speed from “speed=distance/time.” Therefore, forward movement is made at a higher speed when the amount of movement is larger. This is also what is generally called joystick-like operation. For example, assuming that the centroid G moves by 10 cm in one second when the unit time is one second, it is deemed that the movement is made at a movement speed of 10 cm per one second, that is, the movement speed is 10 cm/seconds, and this movement speed can be used for processing. 
     Conversely, suppose that the left position indicating unit  303 L and the right position indicating unit  303 R are moving to follow the back position indicating unit  303 C. The following in this case means that the left position indicating unit  303 L and the right position indicating unit  303 R move to the back side on which the back position indicating unit  303 C has been located, in association with the movement of the back position indicating unit  303 C. In this case, it is possible to sense that the foot-part position indicating instrument  300  is moving in the backward direction that is the extension direction of a line extended from the toe part toward the heel part as illustrated by an arrow Bk in  FIG. 11A . Further, the distance from the position on the position detecting sensor  201  at which the centroid G before the movement is located to the position on the position detecting sensor  201  at which the centroid G after the movement is located is equivalent to the amount of movement in the backward direction, i.e., the amount of movement in the direction in which the value decreases on the y-axis. In addition, it is also possible to think of the amount of movement of the centroid G in the backward direction as the movement speed in the backward direction (negative direction on the y-axis) per unit time and use the amount of movement as the movement speed similarly to the case of the movement in the forward direction. 
     Moreover, suppose that the right position indicating unit  303 R is moving to follow the left position indicating unit  303 L. The following in this case means that the right position indicating unit  303 R moves in the left direction in which the left position indicating unit  303 L has been located, in association with the movement of the left position indicating unit  303 L. In this case, it is possible to sense that the foot-part position indicating instrument  300  is moving in the left direction that is a direction intersecting a line extended from the heel part toward the toe part as illustrated by an arrow Lf in  FIG. 11A . Further, the distance from the position on the position detecting sensor  201  at which the centroid G before the movement is located to the position on the position detecting sensor  201  at which the centroid G after the movement is located is equivalent to the amount of movement in the left direction, i.e., the amount of movement in the direction in which the value decreases on the x-axis. In addition, it is also possible to think of the amount of movement of the centroid G in the left direction as the movement speed in the left direction (negative direction on the x-axis) per unit time and use the amount of movement as the movement speed similarly to the case of the movement in the forward direction. 
     Conversely, suppose that the left position indicating unit  303 L is moving to follow the right position indicating unit  303 R. The following in this case means that the left position indicating unit  303 L moves in the right direction in which the right position indicating unit  303 R has been located, in association with the movement of the right position indicating unit  303 R. In this case, it is possible to sense that the foot-part position indicating instrument  300  is moving in the right direction that is a direction intersecting a line extended from the heel part toward the toe part as illustrated by an arrow Rt in  FIG. 11A . Further, the distance from the position on the position detecting sensor  201  at which the centroid G before the movement is located to the position on the position detecting sensor  201  at which the centroid G after the movement is located is equivalent to the amount of movement in the right direction, i.e., the amount of movement in the direction in which the value increases on the x-axis. In addition, it is also possible to think of the amount of movement of the centroid G in the right direction as the movement speed in the right direction (positive direction on the x-axis) per unit time and use the amount of movement as the movement speed similarly to the case of the movement in the forward direction. 
     As above, in the foot-part position detecting device  400  of this embodiment, first, the position indication coordinate system is identified from the positions of the three position indicating units  303 L,  303 R, and  303 C. Next, the center of the movable range restriction region  402  of the operation surface  401  is deemed as the origin O of the reference coordinate system, and the X-axis and the Y-axis of the reference coordinate system are identified based on the x-axis and the y-axis of the position indication coordinate system. In the reference coordinate system identified in this manner, how far and in which direction of the forward direction Fd, the backward direction Bk, the left direction Lf, and the right Rt the foot-part position indicating instrument  300  moves is sensed. The amount of movement in this case is obtained based on how far the centroid G set on the sole back part  301   b  is separate from the origin O of the reference coordinate system. The movement direction and the amount of movement regarding the foot-part position indicating instrument  300  detected in this manner are sent to the image processing device  700 . In another example, it is also possible to interpret (regard) the amount of movement per unit time in each movement direction obtained in the above-described manner as the movement speed per unit time and provide the movement speed to the image processing device  700  to use it. 
     Indication Input Through Foot-Part Input System 
       FIGS. 12A to 12C ,  FIGS. 13A to 13C , and  FIGS. 14A to 14C  are diagrams for explaining the operation state of the foot-part input system of the second embodiment and the display image of the head-mounted display. As described above, in the foot-part input system of this embodiment, when the foot-part position indicating instrument  300  is moved forward, backward, leftward, and rightward on the operation surface  401  of the foot-part position detecting device  400 , the movement direction and the amount of movement are supplied to the image processing device  700 . Thus, in the image processing device  700 , a three-dimensional space image displayed on the display of the HMD  500  can be changed according to the movement direction and the amount of movement from the foot-part position detecting device  400 . 
     In the second embodiment, the amount of movement of the centroid G from the origin O is deemed as the amount of movement per unit time, and the movement speed per unit time identified from this amount of movement per unit time is reflected in the system. To put it simply, the amount of movement (distance) of displacement from the origin is thought of as the movement speed per unit time. Therefore, when the centroid G of the foot-part position indicating instrument  300  is displaced forward by r (+r), the image can be changed in such a manner that forward movement is made at the speed at which the movement is made by the distance r per unit time. Further, when the centroid G is displaced forward by 2r (+2r), the image can be changed in such a manner that forward movement is made at the speed at which the movement is made by the distance 2r per unit time. Moreover, when the centroid G of the foot-part position indicating instrument  300  is returned to the origin O, the movement distance becomes zero and the change in the image stops. 
     Similarly, when the centroid G of the foot-part position indicating instrument  300  is displaced backward by r (−r), the image can be changed in such a manner that backward movement is made at the speed at which the movement is made by the distance r per unit time. Further, when the centroid G of the foot-part position indicating instrument  300  is displaced to the right by l (+l (ell)), the image can be changed with the speed at which movement is made to the right by the distance l per unit time. Moreover, when the centroid G of the foot-part position indicating instrument  300  is displaced to the left by l (−l), the image can be changed with the speed at which movement is made to the left by the distance l per unit time. In this manner, the direction and the speed of changing the image can be varied according to the displacement of the centroid G from the origin O. 
     Suppose that, as illustrated in  FIGS. 12A to 12C , the foot-part position indicating instrument  300  is placed on the operation surface  401  of the foot-part position detecting device  400  and the movable range restricting plate  304  that is present on the back surface of the sole back part  301   b  of the foot-part position indicating instrument  300  is present in the movable range restriction region  402  on the operation surface  401 . Therefore, in all of  FIGS. 12A, 12B, and 12C , the left position indicating unit  303 L, the right position indicating unit  303 R, and the back position indicating unit  303 C disposed in the foot-part position indicating instrument  300  are located in the movable range restriction region  402 . 
       FIG. 12B  illustrates the case in which the foot-part position indicating instrument  300  is present at the initial position (home position) on the operation surface  401 . Therefore,  FIG. 12B  illustrates a case in which the centroid G of the isosceles triangle formed by the three position indicating units  303 L,  303 R, and  303 C disposed at the sole back part  301   b  of the foot-part position indicating instrument  300  substantially corresponds with the center (origin) O of the movable range restriction region  402 . Suppose that, in this state, a three-dimensional space image including a tree and a cloud as the subject is displayed on the display HDP of the HMD  500  mounted on the head of the user, as illustrated in  FIG. 12B . 
     Suppose that, from the state illustrated in  FIG. 12B , the foot-part position indicating instrument  300  is moved forward in the state of being kept contact with the operation surface  401  as illustrated in  FIG. 12C . In this case, the movement direction and the amount of movement based on the centroid G are detected in the position detecting circuit  202  of the foot-part position detecting device  400 , and they are supplied to the image processing device  700 . The movement direction in this case is the forward direction (extension direction of the line extended from the heel toward the toe), and the amount of movement is the distance from the origin O to the centroid G in the positive direction of the Y-axis of the reference coordinate system. Further, as described above, the movement speed per unit time can be grasped from the amount of movement per unit time. Thus, the forward movement is made at the movement speed according to this amount of movement per unit time. 
     In this case, the image processing circuit  703  of the image processing device  700  determines that the forward movement of the foot-part position indicating instrument  300  is indication input of enlargement of the three-dimensional space image, and performs processing to display the three-dimensional space image on the display HDP in such a manner as to continue to enlarge the three-dimensional space image according to the amount of movement or the movement speed. The enlargement of the three-dimensional space image means that, due to gradual forward movement of the point of view, the subject gradually comes closer and comes to look large and change to a more detailed three-dimensional space image is caused. That is, in the enlargement of the image, display processing is executed to provide the following display process, for example. Specifically, a wood seen in the distance gradually comes closer due to the forward movement and trees come to look large. Then, if the forward movement is further continued, the point of view enters the wood and details in the wood become visible. 
     Suppose that, from the state illustrated in  FIG. 12B , the foot-part position indicating instrument  300  is moved backward in the state of being kept contact with the operation surface  401  as illustrated in  FIG. 12A . In this case, the movement direction and the amount of movement based on the centroid G are detected in the position detecting circuit  202  of the foot-part position detecting device  400 , and they are supplied to the image processing device  700 . The movement direction in this case is the backward direction (extension direction of the line extended from the toe toward the heel), and the amount of movement is the distance from the origin O to the centroid G in the negative direction of the Y-axis of the reference coordinate system. Also in this case, the movement speed per unit time can be grasped from the amount of movement per unit time. Thus, the backward movement is made at the movement speed according to this amount of movement per unit time. 
     In this case, the image processing circuit  703  of the image processing device  700  determines that the backward movement of the foot-part position indicating instrument  300  is indication input of reduction of the three-dimensional space image, and performs processing to display the three-dimensional space image on the display HDP in such a manner as to continue to reduce the three-dimensional space image according to the amount of movement or the movement speed. The reduction of the three-dimensional space image means that, conversely to the case of the enlargement, due to gradual backward movement of the point of view, the subject gradually gets farther away and comes to look small and further becomes gradually unidentifiable. That is, in the reduction of the image, display processing is executed to provide the following display process, for example. Specifically, from the state in which the details in the wood are visible, the point of view gets out of the wood and gradually gets farther away from the wood, and woods that looked large thus far come to look small. Finally, the wood and the trees that configure the wood become invisible. 
     When the foot-part position indicating instrument  300  makes neither forward movement nor backward movement on the operation surface  401 , the movement direction and the amount of movement are not detected in the foot-part position detecting device  400  and are not supplied to the image processing device  700 . Thus, as illustrated in  FIGS. 13A to 13C , when the toe side of the foot-part position indicating instrument  300  is rotated, the three-dimensional space image displayed on the display HDP does not change. That is, the three-dimensional space image displayed on the display HDP does not change when the foot-part position indicating instrument  300  is rotated in a counterclockwise manner ( FIG. 13A ) or is rotated in a clockwise manner ( FIG. 13C ) from the state in which the foot-part position indicating instrument  300  is present at the initial position (home position) ( FIG. 13B ). 
     However, even when the foot-part position indicating instrument  300  makes neither forward movement nor backward movement on the operation surface  401 , the three-dimensional space image on the display HDP changes when the HMD  500  mounted on the head of the user rotates in association with rotation of the head. Specifically, as illustrated in  FIGS. 14A to 14C , even when the foot-part position indicating instrument  300  does not move at all, the three-dimensional space image displayed on the display HDP changes when the HMD  500  rotates. In all of  FIGS. 14A, 14B, and 14C , the foot-part position indicating instrument  300  is present at the initial position (home position). 
     When the user rotates the head in a counterclockwise manner by φ degrees (−φ) in this state, the rotation direction and the rotation angle are supplied from the HMD  500  to the image processing device  700 . In response to this, as illustrated in  FIG. 14A , the image processing circuit  703  forms the three-dimensional space image resulting from the rotation in the counterclockwise manner by φ degrees and displays it on the display HDP. Conversely, when the user rotates the head in a clockwise manner by φ degrees (+φ), the rotation direction and the rotation angle are supplied from the HMD  500  to the image processing device  700 . In response to this, as illustrated in  FIG. 14C , the image processing circuit  703  forms the three-dimensional space image resulting from the rotation in the clockwise manner by φ degrees and displays it on the display HDP. 
     Suppose that, in the foot-part input system of this embodiment, the foot-part position indicating instrument  300  is placed on the operation surface  401  of the foot-part position detecting device  400  and leftward movement or rightward movement is carried out with the placed state kept. In this case, the movement direction and the amount of movement are supplied to the image processing device  700 . Due to this, the position of the point of view can be shifted in the left direction or the right direction in the three-dimensional space image that the display HDP of the HMD  500  is caused to display. In this case, shifting the three-dimensional space image in the left direction or the right direction means not shifting the viewing direction as in rotation of the HMD  500  but shifting the position of the point of view of the user in the three-dimensional space image in the left direction or the right direction. 
     For example, suppose that the foot-part position indicating instrument  300  is moved to the left on the operation surface  401 . In this case, the image processing circuit  703  of the image processing device  700  forms the three-dimensional space image seen when the position of the point of view of the user in the three-dimensional space image is moved in the left direction and displays it on the display HDP. Suppose that the foot-part position indicating instrument  300  is moved to the right on the operation surface  401  similarly. In this case, the image processing circuit  703  of the image processing device  700  forms the three-dimensional space image seen when the position of the point of view of the user in the three-dimensional space image is moved in the right direction and displays it on the display HDP. 
       FIG. 15  and  FIG. 16  are diagrams for explaining indication input in the image processing system configured with use of the foot-part input system of the second embodiment. As illustrated also in  FIG. 8 , the image processing device  700  is what can form the three-dimensional space image in the 360-degree image region GA as illustrated in  FIG. 15 . That is, the image processing device  700  can form an image with width, height, and depth (three-dimensional space image) across the circumference of 360 degrees and display it on the display HDP of the HMD  500 . 
     In this case, as illustrated by arrows R 1  and R 2  in  FIG. 15 , the orientation in the 360-degree image region GA can be changed according to the orientation of the HMD  500 . Further, as illustrated by double arrows around the movable range restriction region  402  illustrated in the bottom surface in  FIG. 15 , enlargement and reduction of the three-dimensional space image displayed on the display HDP of the HMD  500  can be carried out by forward movement and backward movement of the foot-part position indicating instrument  300 . 
     For example, a consideration will be made about a case in which, as illustrated in  FIG. 16 , the 360-degree image region GA is divided into, for example, six regions GA 1 , GA 2 , GA 3 , GA 4 , GA 5 , and GA 6 . In this case, which region is employed as the region whose three-dimensional space image is displayed on the display HDP of the HMD  500  can be switched according to the orientation of the HMD  500  as illustrated by arrows on the respective regions. Further, enlargement and reduction of the three-dimensional space image in the displayed region can be carried out by forward movement and backward movement of the foot-part position indicating instrument  300  placed on the operation surface  401  of the foot-part position detecting device  400  as illustrated by double arrows around the movable range restriction region  402  of the foot-part position detecting device  400 . 
     Although diagrammatic representation is not made in  FIG. 15  and  FIG. 16 , the three-dimensional space image formed when the position of the point of view in the three-dimensional space image is moved to the left or right can be formed through leftward movement or rightward movement of the foot-part position indicating instrument  300  placed on the operation surface  401  of the foot-part position detecting device  400 . This three-dimensional space image is formed by the image processing circuit  703  of the image processing device  700 , is supplied to the HMD  500 , and can be caused to be displayed on the display HDP. 
       FIGS. 17A to 17E  is a diagram for explaining how to detect the indication input in the foot-part input system of the second embodiment.  FIGS. 17A, 17C, and 17E  illustrate the operation surface  401  of the foot-part position detecting device  400  and the states of movement of the position indicating units  303 L,  303 R, and  303 C of the foot-part position indicating instrument  300  subjected to movement operation on the operation surface  401 . Further,  FIG. 17B  illustrates the orientation of the foot-part position indicating instrument  300  located on the operation surface  401  in  FIG. 17A .  FIG. 17D  illustrates the orientation of the foot-part position indicating instrument  300  located on the operation surface  401  in  FIGS. 17C and 17E . 
     As described above, in the second embodiment, the reference coordinate system defined on the operation surface  401  of the foot-part position detecting device  400  includes the center of the operation surface  401  as the origin O. Further, the orientation of the X-axis and the Y-axis of the reference coordinate system is settled based on the x-axis and the y-axis of the position indication coordinate system dependent on the three position indicating units  303 L,  303 R, and  303 C of the foot-part position indicating instrument  300 . Thus, when the foot-part position indicating instrument  300  is placed on the operation surface  401  in the form illustrated in  FIG. 17B , the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C is located at a position P 0  in  FIG. 17A . 
     Therefore, the reference coordinate system (origin O, X-axis, Y-axis) corresponds with the position indication coordinate system (origin G, x-axis, y-axis). Suppose that, in this case, the foot-part position indicating instrument  300  is moved forward to move the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C to a position P 1 . Because the movement is the forward movement, it is interpreted that the movement is being made at a speed at which the movement is made by a movement distance+r per unit time, and the three-dimensional space image is continued to be enlarged. Further, suppose that the foot-part position indicating instrument  300  is moved backward to move the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C to a position P 2 . In this case, because the movement is the backward movement, it is interpreted that the movement is being made at a speed at which the movement is made by a movement distance −r per unit time, and the three-dimensional space image is continued to be reduced. 
     Moreover, suppose that the foot-part position indicating instrument  300  is moved to the left to move the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C to a position P 3 . In this case, because the movement is the leftward movement, it is interpreted that the movement is being made at a speed at which the movement is made by a movement distance −l per unit time, and the point of view is continued to be moved to the left side in the three-dimensional space. In addition, suppose that the foot-part position indicating instrument  300  is moved to the right to move the isosceles triangle formed by the position indicating units  303 L,  303 R, and  303 C to a position P 4 . In this case, because the movement is the rightward movement, it is interpreted that the movement is being made at a speed at which the movement is made by a movement distance+l per unit time, and the point of view is continued to be moved to the right side in the three-dimensional space. 
     Further, suppose that the sole front part  301   f  is rotated around the sole back part  301   b  in the foot-part position indicating instrument  300  as illustrated in  FIGS. 17C  and  17 D. In this case, the reference coordinate system (origin O, X-axis, Y-axis) rotates according to the position indication coordinate system (origin G, x-axis, y-axis). Therefore, as illustrated in  FIG. 17C , the reference coordinate system (origin O, X-axis, Y-axis) corresponds with the position indication coordinate system (origin G, x-axis, y-axis). When the foot-part position indicating instrument  300  is moved forward, backward, leftward, or rightward in this state, the indication input similar to that of the case described with  FIGS. 17A and 17B  can be carried out. 
     Moreover, suppose that the centroid G moves to a position separate both from the X-axis and from the Y-axis as illustrated in  FIG. 17E  instead of moving on the X-axis or the Y-axis of the reference coordinate system as described with use of  FIGS. 17A and 17B  or  FIGS. 17C and 17D . A movement distance n from the origin can be grasped as movement by +r in the Y-axis direction and by −l in the X-axis direction on the reference coordinate system in the foot-part position detecting device  400 . In this case, it is possible to execute processing of continuing to enlarge the three-dimensional space image in such a manner that the point of view moves toward the front left side in the image processing device  700 . 
     When what is generally called a joystick used as an input device in the existing technology is tilted toward, for example, the front side, enlarging a display image at a speed according to the tilt angle, for example, is possible. Specifically, the image can be changed in such a manner that the image slowly changes when the joystick is slightly tilted and the image changes fast when the joystick is greatly tilted. Indication input similar to this can be carried out by using the foot-part input system. Needless to say, not only the enlargement but indication input similar to indication input when the display image is changed through tilting the joystick in various directions can be carried out by using the foot-part input system. 
     In the second embodiment, the reference coordinate system defined on the operation surface  401  of the foot-part position detecting device  400  includes the center of the operation surface  401  as the origin O. Further, the orientation of the X-axis and the Y-axis of the reference coordinate system is settled based on the x-axis and the y-axis of the position indication coordinate system dependent on the three position indicating units  303 L,  303 R, and  303 C of the foot-part position indicating instrument  300 . As above, by detecting how the centroid G of the foot-part position indicating instrument  300  moves in the settled reference coordinate system and detecting the movement speed thereof, enlargement and reduction of the three-dimensional space image, movement of the point of view to the left and right, and so forth can be flexibly carried out. 
     Effects of Embodiment 
     In the image processing system of the above-described embodiment, the viewing direction is changed by rotation of the HMD  500 , and the three-dimensional space image can be changed according to this. In addition to this, by using the foot-part input system, enlargement, reduction, leftward movement, and rightward movement of the three-dimensional space image can be implemented through carrying out forward movement, backward movement, leftward movement, and rightward movement of the foot-part position indicating instrument  300  on the operation surface  401  of the foot-part position detecting device  400 . 
     This enables flexible indication input by use of the foot-part input system. Further, the displayed three-dimensional space image can be changed through inputting various kinds of information to the image processing device by using a foot part of the user in order not to cause a difference between the three-dimensional space image that changes and a feeling with respect to the motion of the body of the user. Because it is possible to avoid the occurrence of a difference between the three-dimensional space image that changes and a feeling with respect to the motion of the body of the user as above, causing a symptom such as what is generally called VR sickness in the user can also be suppressed. 
     MODIFICATION EXAMPLES 
     Variations of Setting Positions of Position Indicating Units 
     In the above-described first embodiment, the case in which the position indicating unit  101 U is disposed at the sole front part  101  and the position indicating unit  103 U is disposed at the sole back part  103  has been explained. Further, in the second embodiment, the case in which the left position indicating unit  303 L, the right position indicating unit  303 R, and the back position indicating unit  303 C are disposed at the sole back part  301   b  has been explained. However, the configuration is not limited thereto. The way of disposing the position indicating units has various variations. 
       FIGS. 18A to 18F  are diagrams for explaining variations of the setting positions of the position indicating units (position indication signal transmitting parts) of the foot-part position indicating instrument. The upper side of the diagram is the toe side (sole front part), and the lower side of the diagram is the heel side (sole back part). A foot-part position indicating instrument  300 A of  FIG. 18A  is an instrument in which two position indicating units  303 F and  303 B are disposed for the sole back part in the longitudinal direction. By disposing the two position indicating units  303 F and  303 B in the longitudinal direction of the foot-part position indicating instrument  300 A as above, a position indication coordinate system in which a straight line that connects the two position indicating units  303 F and  303 B is the y-axis and a straight line orthogonal to the y-axis is the x-axis can be formed, and the movement direction can be identified. 
     For the amount of movement, either one of the position indicating unit  303 F and the position indicating unit  303 B is employed as the basis or the midpoint of a line segment that links the position indicating unit  303 F and the position indicating unit  303 B is employed as the basis, and the distance from the origin O can be obtained as the amount of movement. Besides, a position in the foot-part position indicating instrument  300 A identified according to the position of one or both of the position indicating unit  303 F and the position indicating unit  303 B can be employed as the basis when the amount of movement is obtained. 
     A foot-part position indicating instrument  300 B of  FIG. 18B  illustrates a case in which two position indicating units  306 F and  306 B are disposed for the sole front part in the longitudinal direction. Therefore, the foot-part position indicating instrument  300 A of  FIG. 18A  and the foot-part position indicating instrument  300 B of  FIG. 18B  have the difference of whether the positions at which the position indicating units are disposed are on the feel side or the toe side. However, also in the case of the foot-part position indicating instrument  300 B illustrated in  FIG. 18B , the position indication coordinate system can be formed and the movement direction can be identified, and detection of the amount of movement is possible, similarly to the case of the foot-part position indicating instrument  300 A illustrated in  FIG. 18A . 
     A foot-part position indicating instrument  300 C of  FIG. 18C  illustrates a case in which three position indicating units  306 L,  306 R, and  306 C are disposed to form an isosceles triangle at the sole front part. Therefore, the foot-part position indicating instrument  300  of the second embodiment described with use of  FIGS. 9A and 9B ,  FIGS. 11A to 11C , and so forth and the foot-part position indicating instrument  300 C of  FIG. 18C  have the difference of whether the positions at which the position indicating units are disposed are on the feel side or the toe side. However, also in the case of the foot-part position indicating instrument  300 C illustrated in  FIG. 18C , the position indication coordinate system can be formed and the movement direction can be identified, and detection of the amount of movement is possible, similarly to the case of the foot-part position indicating instrument  300  of the second embodiment described with use of  FIGS. 9A and 9B ,  FIGS. 11A to 11C , and so forth. 
     A foot-part position indicating instrument  300 D of  FIG. 18D  illustrates a case in which four position indicating units  303 L,  303 R,  303 F, and  303 B are disposed to form a quadrangle at the sole back part. In this case, a position indication coordinate system in which a straight line that connects the position indicating units  303 F and  303 B is the y-axis and a straight line that connects the position indicating units  303 L and  303 R is the x-axis can be formed, and the movement direction can be identified. For the amount of movement in the case of this example, for example, the center of the quadrangle formed by the position indicating units  303 L,  303 R,  303 F, and  303 B is employed as the basis, and the distance from the origin O can be obtained as the amount of movement. Besides, a position in the foot-part position indicating instrument  300 D identified according to one or more positions of the position indicating units  303 L,  303 R,  303 F, and  303 B can be employed as the basis when the amount of movement is obtained. 
     A foot-part position indicating instrument  300 E of  FIG. 18E  illustrates a case in which three position indicating units  303 L,  303 R, and  303 C are disposed to form an isosceles triangle at the sole back part and one position indicating unit  306  is disposed at the sole front part. Further, a foot-part position indicating instrument  300 F of  FIG. 18F  illustrates a case in which three position indicating units  303 L,  303 R, and  303 C are disposed to form an isosceles triangle at the sole back part and two position indicating units  306 L and  306 R are disposed at the sole front part. 
     In the cases of the foot-part position indicating instruments  300 E and  300 F, the position indication coordinate system can be formed and the movement direction can be identified, and detection of the amount of movement is possible, similarly to the case of the foot-part position indicating instrument  300  of the second embodiment described with use of  FIGS. 9A and 9B ,  FIGS. 11A to 11C , and so forth. Moreover, in the cases of the foot-part position indicating instruments  300 E and  300 F, the position indicating units are disposed at the sole back part and the sole front part. 
     Due to this, as described with use of  FIGS. 5A and 5B , when the sole front part (toe side) is raised with the sole back part (heel side) kept contact with the operation surface  401 , it becomes possible to obtain the height h and the angle θ thereof. Conversely to this, when the sole back part (heel side) is raised with the sole front part (toe side) kept contact with the operation surface  401 , it becomes possible to obtain the height h and the angle θ thereof. That is, the height h can be detected according to the voltage level in the position detecting sensor  201  regarding a signal transmitted from the position indicating unit. 
     Further, in the case of the foot-part position indicating instrument  300 E, the angle θ can be obtained based on the obtained height h and the distance l (ell) from the centroid G of the isosceles triangle formed by the three position indicating units disposed at the sole back part to the position indicating unit  306 . Moreover, in the case of the foot-part position indicating instrument  300 F, the angle θ can be obtained based on the obtained height h and the distance l (ell) from the centroid G of the isosceles triangle formed by the three position indicating units disposed at the sole back part to the midpoint between the position indicating units  306 L and  306 R. 
     Supplying the height h and the angle θ obtained in this manner to the image processing device  700  makes it possible to execute various kinds of image processing in the image processing device  700 . For example, it becomes possible to execute enlargement-reduction processing in which enlargement of the three-dimensional space image is carried out when the sole front part is raised and reduction of the three-dimensional space image is carried out when the sole back part is raised. Further, it becomes possible to execute upward-downward movement processing of the position of the point of view in which the position of the point of view in the three-dimensional space image is moved in the upward direction when the sole front part is raised, the position of the point of view in the three-dimensional space image is moved in the downward direction when the sole back part is raised, and the three-dimensional space image in that case is displayed. 
     The latter, i.e., the upward-downward movement processing of the position of the point of view, is what allows ascent and descent in the three-dimensional space image. Therefore, this processing is different from processing of displaying the three-dimensional space image when the viewing direction is changed without changing the position of the point of view through moving the head on which the HMD  500  is mounted in such a manner as to look up or moving the head on which the HMD  500  is mounted in such a manner as to look down. As above, by supplying the image processing device  700  with the height h and the angle θ that can be detected through raising and lowering of the sole front part and the sole back part, new image processing that utilizes this is enabled. 
     Variations of the setting positions of the position indicating units (position indication signal transmitting parts) of the foot-part position indicating instrument are not limited to those illustrated in  FIGS. 18A to 18F . The position indicating units can be disposed in various forms with which the position indication coordinate system composed of the y-axis and the x-axis can be formed and the amount of movement of the foot-part position indicating instrument  300  can be detected. Therefore, the position indicating units may be disposed to form a polygon such as a pentagon or hexagon besides being disposed to form a triangle and being disposed to form a quadrangle. 
     Further, in each of the foot-part position indicating instruments  300 A to  300 F illustrated in  FIGS. 18A to 18F , the respective position indicating units transmit a transmission signal with different frequencies. In this case, the foot-part position detecting device  400  grasps the correspondence between the position at which the position indicating unit is disposed and the frequency of the transmission signal transmitted by this position indicating unit and can discriminate and detect the position indicated by each position indicating unit. 
     Moreover, two position indicating units disposed to form an isosceles triangle may be allowed to transmit a transmission signal with the same frequency. Further, a position may be indicated in such a manner that plural position indicating units are disposed and transmission of the position indication signal is switched in a time-sharing manner in order decided in advance. Therefore, in this case, the frequency of the transmission signal does not need to be changed for each position indicating unit. This is because, in this case, the position indicating units can be recognized as ones located at both ends of the base and the direction in which they are disposed can also be recognized based on the position indicating unit located at the vertex. 
     Continuation of Enlargement or Reduction 
     Further, in the above-described embodiment, it has been explained that enlargement and reduction of the three-dimensional space image are carried out according to the movement direction and the amount of movement. However, it is also possible to carry out enlargement and reduction more flexibly. For example, suppose that the foot-part position indicating instrument  300  is moved forward, the movable range restricting plate  304  of the foot-part position indicating instrument  300  engages with the ring-shaped protrusion part  403  of the operation surface  401 , and the foot-part position indicating instrument  300  becomes incapable of moving. Even in this case, by pressing down the sole back part  301   b , the pressing force can be detected in the position indicating unit and be supplied to the image processing device  700  via the foot-part position detecting device  400 . 
     Thus, in the image processing device  700 , enlargement of the three-dimensional space image can be continued when the pressing force from the foot-part position indicating instrument  300  is equal to or higher than a certain value, and the enlargement of the three-dimensional space image can be stopped when the pressing force has become lower than the certain value. Similarly, suppose that the foot-part position indicating instrument  300  is moved backward, the movable range restricting plate  304  of the foot-part position indicating instrument  300  engages with the ring-shaped protrusion part  403  of the operation surface  401 , and the foot-part position indicating instrument  300  becomes incapable of moving. In this case, in the image processing device  700 , reduction of the three-dimensional space image can be continued when the pressing force from the foot-part position indicating instrument  300  is equal to or higher than a certain value, and the reduction of the three-dimensional space image can be stopped when the pressing force has become lower than the certain value. 
     Although the pressure value from the position indicating unit of the foot-part position indicating instrument  300  is used here, the configuration is not limited thereto. For example, when the foot-part position indicating instrument  300  is moved forward, enlargement of the three-dimensional space image may be continued until the movement turns to backward movement. Similarly, when the foot-part position indicating instrument  300  is moved backward, reduction of the three-dimensional space image may be continued until the movement turns to forward movement. In this case, the foot-part position indicating instrument  300  is moved forward and, when the three-dimensional space image is enlarged to the target state, the foot-part position indicating instrument  300  is slightly moved backward. This can stop the enlargement of the three-dimensional space image. Similarly, the foot-part position indicating instrument  300  is moved backward and, when the three-dimensional space image is reduced to the target state, the foot-part position indicating instrument  300  is slightly moved forward. This can stop the reduction of the three-dimensional space image. 
     Configuration of Foot-Part Position Indicating Instrument 
     Further, the configuration of the foot-part position indicating instrument  300  is also not limited to the above-described configuration. It suffices that the foot-part position indicating instrument  300  be what can be mounted on a foot part of a user similarly to what is generally called footwear such as a slipper, a sandal, and a sneaker and allows mounting (incorporation) of the position indicating unit therein. In this case, it is desirable that the sole central part that connects the sole front part and the sole back part be formed of a material (ingredient) that bends. The purpose thereof is to allow easy execution of operation of raising the toe side with the heel side kept contact with the operation surface  401  or raising the heel side with the toe side kept contact with the operation surface  401 . 
     Further, in the case of the foot-part position indicating instrument  300  of the above-described second embodiment, the foot-part position indicating instrument  300  includes the toe-side belt holding parts  301 L and  301 R and the heel-side belt holding parts  302 L and  302 R and is mounted on a foot part of a user by belts made to pass through them. However, the configuration is not limited thereto. A holding part that covers the upper part of the toe part may be disposed in advance as in a slipper or a sandal, or a holding part that covers side surfaces of the foot part and the upper part of the toe part may be disposed as in a general shoe such as a sneaker. 
     Setting of Mode 
     Moreover, in the above-described embodiment, a mode in which enlargement and reduction of an image and movement of the point of view to the left and right are enabled through forward movement, backward movement, leftward movement, and rightward movement of the foot-part position indicating instrument  300  is defined as a first mode. By changing the three-dimensional space image by operation with the foot part as above, the occurrence of a symptom such as what is generally called VR sickness can be suppressed. In addition, a mode in which only enlargement and reduction of an image are enabled through forward movement and backward movement of the foot-part position indicating instrument  300  is defined as a second mode. In this case, the occurrence of VR sickness can be further suppressed. Therefore, using the mode according to the situation is allowed. For example, a user who is less liable to suffer from VR sickness uses the first mode whereas a user who is more liable to suffer from VR sickness uses the second mode. 
     Use of Flat Coil 
     As the coil for the resonant circuit that can be used for the foot-part position indicating instruments  100  and  300 , there are a cylindrical coil formed into a cylindrical shape through winding an insulated conductor line into a helical shape and a flat coil formed into a thin shape through winding an insulated conductor line into, for example, a spiral shape. The height of the cylindrical coil is equal to or higher than, for example, 10 mm in many cases. Therefore, it is conceivable that the cylindrical coil is disposed along the outer edge of what is generally called the sole (shoe sole) part of the foot-part position indicating instrument  100  or  300 , such as the part at the periphery of the heel of the user of the foot-part position indicating instrument  100  or  300  or the part at the periphery of the toe. This is because the sole becomes thick when disposing the cylindrical coil at the sole-of-foot part of the foot-part position indicating instrument  100  or  300  is attempted. 
     In contrast, in the case of the flat coil, the thickness is as thin as, for example, several millimeters, approximately. Therefore, the thickness of the sole part can be suppressed even when the flat coil is disposed at the sole-of-foot part of the foot-part position indicating instrument. Further, in the case of the flat coil, change in magnetic flux due to tilt is less liable to occur and therefore, it becomes easy to obtain a signal with less variation with respect to physical motion. Thus, as a more specific modification example of the foot-part position indicating instrument, a foot-part position indicating instrument  800  including flat coils disposed at the sole-of-foot part of the sole part will be described. 
       FIGS. 19A and 19B  each depict a diagram for explaining the foot-part position indicating instrument  800  configured with use of flat coils. In  FIGS. 19A and 19B , FIG.  19 A is a diagram of a case where the foot-part position indicating instrument  800  is viewed from an obliquely upper side, and  FIG. 19B  is a diagram of a case where the foot-part position indicating instrument  800  is viewed from an obliquely lower side. As illustrated in  FIG. 19A , the foot-part position indicating instrument  800  includes a sole part  801  with a substantially rectangular shape and belt holding parts  802   a ,  803   a ,  802   b , and  803   b  disposed at the long sides of the sole part  801 . Moreover, a protrusion part  804  for movable range restriction and a board  805  for movable range recognition are disposed on the back surface (lower-side surface) of the sole part  801 . 
     The part composed of the sole part  801 , the belt holding parts  802   a  and  803   a , and the belt holding parts  802   b  and  803   b  is monolithically formed by a material that is flexible and is hard to break, such as a polycarbonate/acrylonitrile butadiene styrene (ABS) resin that is a thermoplastic resin combining characteristics of a polycarbonate resin and an ABS resin, for example. In each of the belt holding parts  802   a  and  803   a  and the belt holding parts  802   b  and  803   b , a triangular opening is a heel fixing band through-hole, and an elongated opening on the lower side thereof is an instep fixing band through-hole. As illustrated in  FIG. 19A , the belt holding part  802   a  and the belt holding part  802   b  are mirror symmetric. Further, the belt holding part  803   a  and the belt holding part  803   b  are mirror symmetric. This allows the foot-part position indicating instrument  800  to be mounted on a foot of a user, irrespective of the front-back/left-right orientation also as described later. 
     In  FIG. 19A , the protrusion part  804  for movable range restriction and the board  805  for movable range recognition that have not yet been attached to the sole part  801  are illustrated. They are what are attached to the back surface of the sole part  801  also as described later. The protrusion part  804  for movable range restriction and the board  805  for movable range recognition are formed by using a material having favorable wear resistance and slipperiness, such as a polyacetal (POM) resin. As illustrated in  FIG. 19A , the board  805  for movable range recognition has a predetermined thickness and has inside thereof two coil-and-others fixing recesses each composed of a circular recess and a rectangular recess. 
     A flat coil  806   a  and a circuit substrate  807   a  are fitted in one coil-and-others fixing recess of the board  805  for movable range recognition, and a flat coil  806   b  and a circuit substrate  807   b  are fitted in the other coil-and-others fixing recess. Circuit components such as a capacitor are mounted in each of the circuit substrates  807   a  and  807   b . One resonant circuit is configured by the flat coil  806   a  and the circuit substrate  807   a , and another resonant circuit is configured by the flat coil  806   b  and the circuit substrate  807   b . Due to this, two resonant circuits are mounted in the board  805  for movable range recognition. The resonant frequency is different between the resonant circuit configured by the flat coil  806   a  and the circuit substrate  807   a  and the resonant circuit configured by the flat coil  806   b  and the circuit substrate  807   b.    
     As illustrated in  FIG. 19B , the protrusion part  804  for movable range restriction is fixed to one end part of the back surface of the sole part  801 , and the board  805  for movable range recognition is fixed to the other end part of the back surface of the sole part  801 . The protrusion part  804  for movable range restriction is, for example, what engages with the outer edge of the operation surface of the foot-part position detecting device  400  and allows recognition of the range of the operation surface  401  of the foot-part position detecting device  400 . The resonant circuits mounted inside the board  805  for movable range recognition function as position indicating units, and the board  805  for movable range recognition implements a function of carrying out position indication to the foot-part position detecting device  400 . 
       FIG. 20  is a diagram for explaining the foot-part position indicating instrument  800  configured with use of the flat coils and illustrates a case in which the foot-part position indicating instrument  800  is viewed from the upper surface (front surface) side. Thus, the protrusion part  804  for movable range restriction, the board  805  for movable range recognition, and so forth attached to the back surface of the sole part  801  are illustrated by dotted lines. In the foot-part position indicating instrument  800 , the center of each of the flat coils  806   a  and  806   b  is disposed to be located on the center line of the sole part  801  illustrated by a dotted line given arrows. This arrangement corresponds to the arrangement illustrated in  FIGS. 18A and 18B . 
     Due to this, when the foot-part position indicating instrument  800  is moved forward, backward, leftward, and rightward on the foot-part position detecting device  400 , the position according to the movement can be indicated by carrying out transmission and reception of a magnetic field between the flat coils  806   a  and  806   b  and the foot-part position detecting device  400 . Therefore, the foot-part position indicating instrument  800  can be used on the foot-part position detecting device  400  similarly to the foot-part position indicating instrument  300  of the above-described second embodiment. 
       FIGS. 21A and 21B  are diagrams for explaining the forms of attaching of the foot-part position indicating instrument  800  to a foot part of a user. As illustrated in  FIG. 19A  and  FIG. 20  and also as described above, the belt holding part  802   a  and the belt holding part  803   a  are mirror symmetric, and the belt holding part  802   b  and the belt holding part  803   b  are mirror symmetric. Thus, the foot-part position indicating instrument  800  can be fixed to a foot part of a user, irrespective of the front-back/left-right orientation of the foot part of the user. 
     Specifically, as illustrated in  FIG. 21A , the foot-part position indicating instrument  800  can be fixed to the foot part of the user in such a manner that the protrusion part  804  for movable range restriction is set on the toe side and the board  805  for movable range recognition is set on the heel side. Further, as illustrated in  FIG. 21B , the foot-part position indicating instrument  800  can be fixed to the foot part of the user in such a manner that the protrusion part  804  for movable range restriction is set on the heel side and the board  805  for movable range recognition is set on the toe side. Moreover, the foot-part position indicating instrument  800  can be similarly fixed to the foot part of either side of the left and right sides of the user. 
     As described with use of  FIGS. 21A and 21B , the foot-part position indicating instrument  800  can be mounted on a foot part of a user with different orientations. In this case, the orientation of the foot-part position indicating instrument  800 , i.e., which of the flat coil  806   a  and the flat coil  806  is located on the front side (toe side) and which of them is located on the back side (heel side) with respect to the foot part of the user, is set on software. Simply, when the board  805  for movable range recognition is located on the toe side, the setting can be made in such a manner that the flat coil  806   b  is located on the front side and the flat coil  806   a  is located on the back side with respect to the foot part. Further, when the board  805  for movable range recognition is located on the heel side, the setting can be made in such a manner that the flat coil  806   b  is located on the back side and the flat coil  806   a  is located on the front side with respect to the foot part. 
     Moreover, as described with use of  FIG. 20 , the flat coils  806   a  and  806   b  are each disposed in such a manner that the center is located on the center line of the sole part  801 . That is, the flat coils  806   a  and  806   b  are disposed at the front and back with respect to the longitudinal direction of the sole part  801 . For example, suppose that the toe is raised without separating the heel side from on the operation surface  401  of the foot-part position detecting device  400  in the case in which the foot-part position indicating instrument  800  is mounted in such a manner that the board  805  for movable range recognition is located on the heel side of a foot part of a user as illustrated in  FIG. 21A . 
     In this case, the magnetic field (signal) from the flat coil  806   b  located closer to the back side of the foot part remains strong whereas the magnetic field (signal) from the flat coil  806   a  located closer to the front side of the foot part becomes weak or the magnetic field (signal) becomes undetectable. Such strength or undetectability of the magnetic field can be sensed on the side of the foot-part position detecting device  400  and therefore, this can be applied to input action of a button switch function, for example. Specifically, when the foot-part position indicating instrument  800  is mounted on the foot part of the user in the form illustrated in  FIG. 21A , processing according to action, such as switch-on when the toe is raised and switch-off when the toe is lowered, becomes possible. More specifically, processing according to action, such as making a jump when the toe is raised, becomes possible. 
     Similarly, suppose that the heel is raised without separating the toe side from on the operation surface  401  of the foot-part position detecting device  400  in the case in which the foot-part position indicating instrument  800  is mounted in such a manner that the board  805  for movable range recognition is located on the toe side of a foot part of a user as illustrated in  FIG. 21B . In this case, the magnetic field (signal) from the flat coil  806   b  located closer to the front side of the foot part remains strong whereas the magnetic field (signal) from the flat coil  806   a  located closer to the back side of the foot part becomes weak or the magnetic field becomes undetectable. Thus, when the foot-part position indicating instrument  800  is mounted on the foot part of the user in the form illustrated in  FIG. 21B , processing according to action, such as switch-on when the heel is raised and switch-off when the heel is lowered, becomes possible. More specifically, processing according to action, such as making a jump when the heel is raised (user stands on tiptoe), becomes possible. 
     Further, it is also possible to execute processing in which how much the toe or heel is raised is estimated according to the difference in the strength of the magnetic field (signal) between the flat coil  806   a  and the flat coil  806   b , the angle of depression of the angle of elevation is settled, and a display image is changed. In addition, also in the case of using flat coils, it is also possible to dispose the flat coils in not only the form illustrated in  FIGS. 18A and 18B  but also the forms illustrated in  FIGS. 18C to 18F . 
     Moreover, it has been explained that the resonant circuits are configured by connecting a capacitor to each of the flat coils  806   a  and  806   b  in the case of the foot-part position indicating instrument  800  described with use of  FIGS. 19A to 21B . However, the configuration is not limited thereto. In addition, needless to say, it is also possible to further connect a pressure sensor in parallel to the resonant circuit configured by the flat coil and the capacitor to configure the position indicating unit with the form described with use of  FIGS. 3A to 3C  and use it. 
     Further, in the case of the above-described foot-part position indicating instrument  800 , the configuration in which two resonant circuits with different resonant frequencies are mounted is made and therefore, the number of resonant frequencies for which the side of the foot-part position detecting device  400  is caused to make a scan can be set to two. That is, the number of resonant frequencies that should be detected can be made smaller than with the foot-part position indicating instrument in which three or more resonant circuits with different resonant frequencies are mounted. Therefore, the scan rate is improved, and higher frequent acquisition of indicated-position information is enabled. 
     Moreover, it is also possible to adjust the positions, relative to the sole of the foot part of the user, of the protrusion part  804  for movable range restriction and the board  805  for movable range recognition, by adjusting the length of the belts made to pass through the belt holding parts  802   a  and  802   b  and the belt holding parts  803   a  and  803   b . This makes it possible to mount the foot-part position indicating instrument  800  on the foot part in a form with which ease of use is felt for each user. That is, the usability of the foot-part position indicating instrument can be improved for each user. 
     There may be employed configuration that is obtained by removing the toe side including the belt holding parts  802  of the foot-part position indicating instrument  800  and disposing a heel part configured by the belt holding parts  803  and the board  805  for movable range recognition on the arch of the sole of the foot. That is, it is also possible to make the foot-part position indicating instrument into more simplified one configured by the belt holding parts  803  and the board  805  for movable range recognition. 
     OTHER MODIFICATION EXAMPLES 
     In the case of the second embodiment, an instruction is issued to the image processing device  700  to change a three-dimensional space image displayed on the HMD  500 . However, the configuration is not limited thereto. It is also possible to use the foot-part input system composed of the foot-part position indicating instrument  300  and the foot-part position detecting device  400  of the second embodiment also in the case of changing an image displayed on the display DP as in the case of the first embodiment. 
     It has been explained that, as illustrated in  FIG. 10A , the origin O of the reference coordinate system is fixed at the center of the circular movable range restriction region  402  set on the operation surface  401  of the foot-part position detecting device  400 . However, the configuration is not limited thereto. For example, a consideration will be made by taking as an example the case of using the foot-part input system composed of the foot-part position indicating instrument  300  and the foot-part position detecting device  400  of the above-described second embodiment. 
     The position indication coordinate system in this case is identified according to the positions of the position indicating units  303 L,  303 R, and  303 C as described above. Further, the position of the centroid G when the sole back part  301   b  is pressed and a pressure equal to or higher than a predetermined value is detected by one or more of the position indicating units  303 L,  303 R, and  303 C is defined as the origin O. Thereafter, when the pressure relating to the position indicating units  303 L,  303 R, and  303 C lowers and forward movement, backward movement, leftward movement, or rightward movement is made, sensing of how far and in which direction the centroid G moves from the identified origin O in the identified position indication coordinate system is allowed. Therefore, in the case of this example, the position of the centroid G can be defined as the origin O every time the sole back part  301   b  is pressed and a pressure equal to or higher than a predetermined value is detected by one or more of the position indicating units  303 L,  303 R, and  303 C. 
     Further, in the above-described second embodiment, the HMD  500  has been explained as what includes the display HDP and the six-axis sensor. However, the HMD  500  is not limited thereto. The HMD  500  may have a camera function and may photograph an image in the direction in which the user who wears the HMD  500  on the head is oriented, to supply the image to the image processing device  700 . In this case, three-dimensional space image data obtained by executing image processing such as addition of an image of an avatar or the like for the photographed image supplied from the HMD  500  can be formed in the image processing device  700 , and it can be supplied to the HMD  500  and be displayed. As above, it is also possible to display, on the HMD  500 , a three-dimensional space image according to three-dimensional image data formed through adding processing to an image photographed in real time through the camera mounted in the HMD  500 . 
     Others 
     As is understood also from the explanation of the above-described embodiment, functions of the foot-part position indicating instrument in the claims are implemented by the foot-part position indicating instrument  300  and so forth of the embodiment. Further, functions of the sole part, the sole front part, and the sole back part of the claims are implemented by the sole part  301 , the sole front part  301   f , and the sole back part  301   b  of the embodiment. Moreover, functions of the position indication signal transmitting part of the claims are implemented by the position indicating units  303 L,  303 R, and  303 C and so forth of the embodiment. 
     Further, functions of the foot-part position detecting device of the claims are implemented by the foot-part position detecting device  400  and so forth of the embodiment. Moreover, functions of the position detecting sensor of the claims are implemented by the position detecting sensor  201  of the embodiment, and functions of the detecting circuit of the claims are implemented by the position detecting circuit  202  of the embodiment. Further, functions of the operation surface in the claims are implemented by the operation surface  401  of the embodiment. Functions of the mounting component in the claims are implemented by the belts attached to the belt holding parts  301 L,  301 R,  302 L, and  302 R in the embodiment. 
     A series of methods in which the direction of movement carried out in the foot-part input system composed of the foot-part position indicating instrument  300  and the foot-part position detecting device  400  of the above-described second embodiment is detected and is supplied to the image processing device  700  is one embodiment of the indicated position input method using a foot-part input system. 
     It is to be noted that the embodiment of the present disclosure is not limited to the foregoing embodiments, and that various changes can be made without departing from the spirit of the present disclosure. 
     The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.