Patent Publication Number: US-2018032230-A1

Title: Information processing method and system for executing the information processing method

Description:
RELATED APPLICATIONS 
     The present application claims priority to JP2016-148490 filed Jul. 28, 2016, JP 2016-148491 filed Jul. 28, 2016, JP 2017-006886 filed Jan. 18, 2017 and JP 2016-156006 filed Aug. 8, 2016 the disclosures of which are hereby incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     This disclosure relates to an information processing method and a system for executing the information processing method. 
     BACKGROUND 
     In Non-Patent Document 1, there is described a technology of changing a state of a hand object in a virtual reality (VR) space based on a state (for example, position and inclination) of a hand of a user in a real space, and operating the hand object to exert a predetermined action on a predetermined object in the virtual space. 
     Non-Patent Documents 
     
         
         [Non-Patent Document 1] “Toybox Demo for Oculus Touch”, [online], Oct. 13, 2015, Oculus, [retrieved on Aug. 6, 2016], Internet &lt;https://www.youtube.com/watch?v=iFEMiyGMa58&gt; 
       
    
     SUMMARY 
     In Non-Patent Document 1, there is room for improving a virtual experience in a virtual reality space. 
     At least one embodiment of this disclosure has an object to provide an information processing method and a system for executing the information processing method, which are capable of improving a virtual experience. 
     According to at least one aspect of this disclosure, there is provided an information processing method to be executed by a computer in a system including a head-mounted device and a position sensor configured to detect a position of the head-mounted device and a position of a part of a body other than a head of a user. The information processing method includes generating virtual space data for defining a virtual space that includes an operation object and a target object. The method further includes displaying a visual-field image on the head-mounted device based on the position and an inclination of the head-mounted device. The method further includes identifying a position of the operation object based on the position of the part of the body of the user. The method further includes avoiding causing the operation object to exert a predetermined effect on the target object in response to a determination that a predetermined condition for determining whether or not a collision area of the operation object has touched a collision area of the target object intentionally is not satisfied. 
     According to at least one embodiment of this disclosure, improving the virtual experience in the virtual reality space is possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A schematic diagram of a head-mounted device (HMD) system according to at least one embodiment. 
         FIG. 2  A diagram of a head of a user wearing an HMD according to at least one embodiment. 
         FIG. 3  A diagram of a hardware configuration of a control device according to at least one embodiment. 
         FIG. 4  A diagram of an example of a configuration of an external controller according to at least one embodiment. 
         FIG. 5  A flowchart of a method of displaying a visual-field image on the HMD according to at least one embodiment. 
         FIG. 6  An xyz spatial diagram of an example of a virtual space according to at least one embodiment. 
         FIG. 7A  A yx plane diagram of the virtual space in  FIG. 6  according to at least one embodiment. 
         FIG. 7B  A zx plane diagram of the virtual space in  FIG. 6  according to at least one embodiment. 
         FIG. 8  A diagram of an example of the visual-field image displayed on the HMD according to at least one embodiment. 
         FIG. 9A  A diagram of a user wearing the HMD and the external controller according to at least one embodiment. 
         FIG. 9B  A diagram of the virtual space including a virtual camera, a hand object, and a wall object according to at least one embodiment. 
         FIG. 10  A flowchart of an information processing method according to at least one embodiment of this disclosure. 
         FIG. 11A  A diagram of a state in which a user moves a left-hand external controller greatly forward according to at least one embodiment. 
         FIG. 11B  A diagram of the wall object destroyed by the left hand object under the state in  FIG. 11A  according to at least one embodiment. 
         FIG. 12A  A diagram of a state in which the user moves the left-hand external controller a little forward according to at least one embodiment. 
         FIG. 12B  A diagram of the wall object destroyed by the left hand object under the state in  FIG. 12A  according to at least one embodiment. 
         FIG. 13A  A diagram of a pattern of a collision area of the left hand object and a range of an effect exerted on the wall object according to at least one embodiment. 
         FIG. 13B  A diagram of a pattern of a collision area of the left hand object and the range of an effect exerted on the wall object according to at least one embodiment. 
         FIG. 14  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 15A  A diagram of the user wearing the HMD and the external controller according to at least one embodiment. 
         FIG. 15B  A diagram of the virtual space including the virtual camera, the hand object, and the wall object according to at least one embodiment. 
         FIG. 16A  A diagram of the user wearing the HMD and the external controller according to at least one embodiment. 
         FIG. 16B  A diagram of the virtual space including the virtual camera, the hand object, and the wall object according to at least one embodiment. 
         FIG. 17A  A diagram of the virtual camera before movement, the hand object, and the wall object according to at least one embodiment. 
         FIG. 17B  A diagram of the virtual space including the virtual camera after movement, the hand object, and the wall object according to at least one embodiment. 
         FIG. 18  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 19A  A diagram of how the user moves forward (+w direction) at a speed faster than a predetermined speed according to at least one embodiment. 
         FIG. 19B  A diagram of the wall object destroyed by the left hand object under the state of  FIG. 19A  according to at least one embodiment. 
         FIG. 20A  A diagram of how the user moves forward at a speed slower than the predetermined speed according to at least one embodiment. 
         FIG. 20B  A diagram for illustrating the wall object destroyed by the left hand object under the state in  FIG. 20A  according to at least one embodiment. 
         FIG. 21  A flowchart an information processing method according to at least one embodiment. 
         FIG. 22A  A diagram of a pattern of the collision area of the left hand object and the range of an effect exerted on the wall object according to at least one embodiment. 
         FIG. 22B  A diagram a diagram of a pattern of the collision area of the left hand object and the range of an effect exerted on the wall object according to at least one embodiment. 
         FIG. 23A  A diagram of a real space including the user wearing the HMD and the external controller according to at least one embodiment. 
         FIG. 23B  A diagram of the virtual space including the virtual camera, a right hand object, the left hand object, a block object, and a button object according to at least one embodiment. 
         FIG. 24  A plan-view diagram of the virtual space of how the collision area of the right hand object touches an operation portion of the button object according to at least one embodiment. 
         FIG. 25  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 26  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 27  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 28  A plan-view diagram of the virtual space of a state in which the right hand object and the button object are outside the visual field of the virtual camera according to at least one embodiment. 
         FIG. 29  A flowchart of an information processing method according to at least one embodiment. 
         FIG. 30  A flowchart of an information processing method according to at least one embodiment of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of this disclosure are described below with reference to the drawings. Once a component is described in this description of the embodiments, a description on a component having the same reference number as that of the already described component is omitted for the sake of convenience. 
     First, with reference to  FIG. 1 , a configuration of a head-mounted device (HMD) system  1  is described.  FIG. 1  is a schematic view of the HMD system  1  according to at least one embodiment. In  FIG. 1 , the HMD system  1  includes an HMD  110  worn on a head of a user U, a position sensor  130 , a control device  120 , and an external controller  320 . 
     The HMD  110  includes a display unit  112 , an HMD sensor  114 , and an eye gaze sensor  140 . The display unit  112  includes a non-transmissive display device configured to cover a field of view (visual field) of the user U wearing the HMD  110 . With this, the user U can see a visual-field image displayed on the display unit  112 , and thus the user U can be immersed in a virtual space. The HMD  110  is, for example, a head-mounted display device having the display unit  112  constructed integrally or separately. The display unit  112  may include a left-eye display unit configured to provide an image to a left eye of the user U, and a right-eye display unit configured to provide an image to a right eye of the user U. Further, the HMD  110  may include a transmissive display device. In this case, the transmissive display device may be able to be temporarily configured as the non-transmissive display device by adjusting the transmittance thereof. Further, the visual-field image may include a configuration for presenting a real space in a part of the image forming the virtual space. For example, an image taken by a camera mounted to the HMD  110  may be displayed so as to be superimposed on a part of the visual-field image, or a transmittance of a part of the transmissive display device may be set high to enable the user to visually recognize the real space through a part of the visual-field image. 
     The HMD sensor  114  is mounted near the display unit  112  of the HMD  110 . The HMD sensor  114  includes at least one of a geomagnetic sensor, an acceleration sensor, or an inclination sensor (for example, an angular velocity sensor or a gyro sensor), and can detect various movements of the HMD  110  worn on the head of the user U. 
     The eye gaze sensor  140  has an eye tracking function of detecting a line-of-sight direction of the user U. For example, the eye gaze sensor  140  may include a right-eye gaze sensor and a left-eye gaze sensor. The right-eye gaze sensor may be configured to detect reflective light reflected from the right eye (in particular, the cornea or the iris) of the user U by irradiating the right eye with, for example, infrared light, to thereby acquire information relating to a rotational angle of a right eyeball. Meanwhile, the left-eye gaze sensor may be configured to detect reflective light reflected from the left eye (in particular, the cornea or the iris) of the user U by irradiating the left eye with, for example, infrared light, to thereby acquire information relating to a rotational angle of a left eyeball. 
     The position sensor  130  is constructed of, for example, a position tracking camera, and is configured to detect the positions of the HMD  110  and the external controller  320 . The position sensor  130  is connected to the control device  120  so as to enable communication to/from the control device  120  in a wireless or wired manner. The position sensor  130  is configured to detect information relating to positions, inclinations, or light emitting intensities of a plurality of detection points (not shown) provided in the HMD  110 . Further, the position sensor  130  is configured to detect information relating to positions, inclinations, and/or light emitting intensities of a plurality of detection points  304  (refer to  FIG. 4 ) provided in the external controller  320 . The detection points are, for example, light emitting portions configured to emit infrared light or visible light. Further, the position sensor  130  may include an infrared sensor or a plurality of optical cameras. 
     The control device  120  is capable of acquiring movement information such as the position and the direction of the HMD  110  based on the information acquired from the HMD sensor  114  or the position sensor  130 , and accurately associating a position and a direction of a virtual point of view (virtual camera) in the virtual space with the position and the direction of the user U wearing the HMD  110  in the real space based on the acquired movement information. Further, the control device  120  is capable of acquiring movement information of the external controller  320  based on the information acquired from the position sensor  130 , and accurately associating a position and a direction of a hand object (described later) to be displayed in the virtual space with a relative relationship of the position and the direction between the external controller  320  and the HMD  110  in the real space based on the acquired movement information. Similarly to the HMD sensor  114 , the movement information of the external controller  320  may be obtained from a geomagnetic sensor, an acceleration sensor, an inclination sensor, or other sensors mounted to the external controller  320 . 
     The control device  120  is capable of identifying each of the line of sight of the right eye and the line of sight of the left eye of the user U based on the information transmitted from the eye gaze sensor  140 , to thereby identify a point of gaze being an intersection between the line of sight of the right eye and the line of sight of the left eye. Further, the control device  120  is capable of identifying a line-of-sight direction of the user U based on the identified point of gaze. In this case, the line-of-sight direction of the user U is a line-of-sight direction of both eyes of the user U, and matches with a direction of a straight line passing through the point of gaze and a midpoint of a line segment connecting between the right eye and the left eye of the user U. 
     With reference to  FIG. 2 , a method of acquiring information relating to a position and a direction of the HMD  110  is described.  FIG. 2  is a diagram of the head of the user U wearing the HMD  110  according to at least one embodiment. The information relating to the position and the direction of the HMD  110 , which are synchronized with the movement of the head of the user U wearing the HMD  110 , can be detected by the position sensor  130  and/or the HMD sensor  114  mounted on the HMD  110 . In  FIG. 2 , three-dimensional coordinates (uvw coordinates) are defined about the head of the user U wearing the HMD  110 . A perpendicular direction in which the user U stands upright is defined as a v axis, a direction being orthogonal to the v axis and passing through the center of the HMD  110  is defined as a w axis, and a direction orthogonal to the v axis and the w axis is defined as a u direction. The position sensor  130  and/or the HMD sensor  114  are/is configured to detect angles about the respective uvw axes (that is, inclinations determined by a yaw angle representing the rotation about the v axis, a pitch angle representing the rotation about the u axis, and a roll angle representing the rotation about the w axis). The control device  120  is configured to determine angular information for defining a visual axis from the virtual viewpoint based on the detected change in angles about the respective uvw axes. 
     With reference to  FIG. 3 , a hardware configuration of the control device  120  is described.  FIG. 3  is a diagram of the hardware configuration of the control device  120  according to at least one embodiment. The control device  120  includes a control unit  121 , a storage unit  123 , an input/output (I/O) interface  124 , a communication interface  125 , and a bus  126 . The control unit  121 , the storage unit  123 , the I/O interface  124 , and the communication interface  125  are connected to each other via the bus  126  so as to enable communication therebetween. 
     The control device  120  may be constructed as a personal computer, a tablet computer, or a wearable device separately from the HMD  110 , or may be built into the HMD  110 . Further, a part of the functions of the control device  120  may be mounted to the HMD  110 , and other functions of the control device  120  may be mounted to another device separate from the HMD  110 . 
     The control unit  121  includes a memory and a processor. The memory is constructed of, for example, a read only memory (ROM) having various programs and the like stored therein or a random access memory (RAM) having a plurality of work areas in which various programs to be executed by the processor are stored. The processor is constructed of, for example, a central processing unit (CPU), a micro processing unit (MPU) and/or a graphics processing unit (GPU), and is configured to develop, on the RAM, programs designated by various programs installed into the ROM to execute various types of processing in cooperation with the RAM. 
     The control unit  121  may control various operations of the control device  120  by causing the processor to develop, on the RAM, a program (to be described later) for executing the information processing method on a computer according to at least one embodiment to execute the program in cooperation with the RAM. The control unit  121  executes a predetermined application program (including a game program and an interface program) stored in the memory or the storage unit  123  to display a virtual space (visual-field image) on the display unit  112  of the HMD  110 . With this, the user U can be immersed in the virtual space displayed on the display unit  112 . 
     The storage unit (storage)  123  is a storage device, for example, a hard disk drive (HDD), a solid state drive (SSD), or a USB flash memory, and is configured to store programs and various types of data. The storage unit  123  may store the program for executing the information processing method on a computer according to at least one embodiment. Further, the storage unit  123  may store programs for authentication of the user U and game programs including data relating to various images and objects. Further, a database including tables for managing various types of data may be constructed in the storage unit  123 . 
     The I/O interface  124  is configured to connect each of the position sensor  130 , the HMD  110 , and the external controller  320  to the control device  120  so as to enable communication therebetween, and is constructed of, for example, a universal serial bus (USB) terminal, a digital visual interface (DVI) terminal, or a High-Definition Multimedia Interface® (HDMI) terminal. The control device  120  may be wirelessly connected to each of the position sensor  130 , the HMD  110 , and the external controller  320 . 
     The communication interface  125  is configured to connect the control device  120  to a communication network  3 , for example, a local area network (LAN), a wide area network (WAN), or the Internet. The communication interface  125  includes various wire connection terminals and various processing circuits for wireless connection for communication to/from an external device on a network via the communication network  3 , and is configured to adapt to communication standards for communication via the communication network  3 . 
     With reference to  FIG. 4 , an example of a specific configuration of the external controller  320  is described. The external controller  320  is used to control a movement of a hand object to be displayed in the virtual space by detecting a movement of a part of a body of the user U other than the head. For example, hand of the user U in at least one embodiment. The external controller  320  includes a right-hand external controller  320 R (hereinafter simply referred to as “controller  320 R”) to be operated by the right hand of the user U, and a left-hand external controller  320 L (hereinafter simply referred to as “controller  320 L”) to be operated by the left hand of the user U. The controller  320 R is a device for representing the position of the right hand and the movement of the fingers of the right hand of the user U. Further, a right hand object  400 R (refer to  FIG. 9 ) present in the virtual space moves based on the movement of the controller  320 R. The controller  320 L is a device for representing the position of the left hand and the movement of the fingers of the left hand of the user U. Further, a left hand object  400 L (refer to  FIG. 9 ) present in the virtual space moves based on the movement of the controller  320 L. The controller  320 R and the controller  320 L substantially have similar configurations, and thus description is given only of the specific configuration of the controller  320 R in the following with reference to  FIG. 4 . In the following description, for the sake of convenience, the controllers  320 L and  320 R are sometimes simply and collectively referred to as “external controller  320 ”. 
     In  FIG. 4 , the controller  320 R includes an operation button  302 , a plurality of detection points  304 , a sensor (not shown), and a transceiver (not shown). Only one of the sensor and the detection points  304  needs to be provided according to at least one embodiment. The operation button  302  includes a plurality of button groups configured to receive operation input from the user U. The operation button  302  includes a push button, a trigger button, and an analog stick. The push button is a button to be operated through a depression motion by the thumb. For example, two push buttons  302   a  and  302   b  are provided on a top surface  322 . The trigger button is a button to be operated through such a motion that the index finger or the middle finger pulls a trigger. For example, a trigger button  302   e  is provided in a front surface part of a grip  324 , and a trigger button  302   f  is provided in a side surface part of the grip  324 . The trigger buttons  302   e  and  302   f  are intended to be operated by the index finger and the middle finger, respectively. The analog stick is a stick button that may be operated by being tilted in an arbitrary direction of 360 degrees from a predetermined neutral position. For example, an analog stick  320   i  is provided on the top surface  322 , and is intended to be operated with use of the thumb. 
     The controller  320 R includes a frame  326  that extends from both side surfaces of the grip  324  in directions opposite to the top surface  322  to form a semicircular ring. The plurality of detection points  304  are embedded in the outer side surface of the frame  326 . The plurality of detection points  304  are, for example, a plurality of infrared LEDs arranged in one row along a circumferential direction of the frame  326 . The position sensor  130  detects information relating to positions, inclinations, and light emitting intensities of the plurality of detection points  304 , and then the control device  120  acquires the movement information including the information relating to the position and the attitude (inclination and direction) of the controller  320 R based on the information detected by the position sensor  130 . 
     The sensor of the controller  320 R may be, for example, any one of a magnetic sensor, an angular velocity sensor, an acceleration sensor, or a combination of those sensors. The sensor outputs a signal (for example, a signal indicating information relating to magnetism, angular velocity, or acceleration) based on the direction and the movement of the controller  320 R when the user U moves the controller  320 R. The control device  120  acquires information relating to the position and the attitude of the controller  320 R based on the signal output from the sensor. 
     The transceiver of the controller  320 R is configured to perform transmission or reception of data between the controller  320 R and the control device  120 . For example, the transceiver may transmit an operation signal corresponding to the operation input of the user U to the control device  120 . Further, the transceiver may receive from the control device  120  an instruction signal for instructing the controller  320 R to cause light emission of the detection points  304 . Further, the transceiver may transmit a signal representing the value detected by the sensor to the control device  120 . 
     With reference to  FIG. 5  to  FIG. 8 , processing for displaying the visual-field image on the HMD  110  is described.  FIG. 5  is a flowchart of processing of displaying the visual-field image on the HMD  110  according to at least one embodiment.  FIG. 6  is an xyz spatial diagram of a virtual space  200  according to at least one embodiment.  FIG. 7A  is a yx plane diagram of the virtual space  200  in  FIG. 6  according to at least one embodiment.  FIG. 7B  is a zx plane diagram of the virtual space  200  in  FIG. 6  according to at least one embodiment.  FIG. 8  is a diagram of an example of a visual-field image M displayed on the HMD  110  according to at least one embodiment. 
     In  FIG. 5 , in Step S 1 , the control unit  121  (refer to  FIG. 3 ) generates virtual space data representing the virtual space  200  including a virtual camera  300  and various objects. In  FIG. 6 , the virtual space  200  is defined as an entire celestial sphere having a center position  21  as the center (in  FIG. 6 , only the upper-half celestial sphere is illustrated). Further, in the virtual space  200 , an xyz coordinate system having the center position  21  as the origin is set. The virtual camera  300  defines a visual axis L for identifying the visual-field image M (refer to  FIG. 8 ) to be displayed on the HMD  110 . The uvw coordinate system that defines the visual field of the virtual camera  300  is determined so as to synchronize with the uvw coordinate system that is defined about the head of the user U in the real space. Further, the control unit  121  may move the virtual camera  300  in the virtual space  200  in synchronization with the movement in the real space of the user U wearing the HMD  110 . Further, the various objects in the virtual space  200  include, for example, the left hand object  400 L, the right hand object  400 R, and a wall object  500  (refer to  FIG. 9 ). 
     In Step S 2 , the control unit  121  identifies a visual field CV (refer to  FIG. 7 ) of the virtual camera  300 . Specifically, the control unit  121  acquires information relating to a position and an inclination of the HMD  110  based on data representing the state of the HMD  110 , which is transmitted from the position sensor  130  and/or the HMD sensor  114 . Next, the control unit  121  identifies the position and the direction of the virtual camera  300  in the virtual space  200  based on the information relating to the position and the inclination of the HMD  110 . Next, the control unit  121  determines the visual axis L of the virtual camera  300  based on the position and the direction of the virtual camera  300 , and identifies the visual field CV of the virtual camera  300  based on the determined visual axis L. In this case, the visual field CV of the virtual camera  300  corresponds to a part of the region of the virtual space  200  that can be visually recognized by the user U wearing the HMD  110 . In other words, the visual field CV corresponds to a part of the region of the virtual space  200  to be displayed on the HMD  110 . Further, the visual field CV has a first region CVa set as an angular range of a polar angle α about the visual axis L in the xy plane in  FIG. 7A , and a second region CVb set as an angular range of an azimuth β about the visual axis L in the xz plane in  FIG. 7B . The control unit  121  may identify the line-of-sight direction of the user U based on data representing the line-of-sight direction of the user U, which is transmitted from the eye gaze sensor  140 , and may determine the direction of the virtual camera  300  based on the line-of-sight direction of the user U. 
     The control unit  121  can identify the visual field CV of the virtual camera  300  based on the data transmitted from the position sensor  130  and/or the HMD sensor  114 . In this case, when the user U wearing the HMD  110  moves, the control unit  121  can change the visual field CV of the virtual camera  300  based on the data representing the movement of the HMD  110 , which is transmitted from the position sensor  130  and/or the HMD sensor  114 . That is, the control unit  121  can change the visual field CV in accordance with the movement of the HMD  110 . Similarly, when the line-of-sight direction of the user U changes, the control unit  121  can move the visual field CV of the virtual camera  300  based on the data representing the line-of-sight direction of the user U, which is transmitted from the eye gaze sensor  140 . That is, the control unit  121  can change the visual field CV in accordance with the change in the line-of-sight direction of the user U. 
     In Step S 3 , the control unit  121  generates visual-field image data representing the visual-field image M to be displayed on the display unit  112  of the HMD  110 . Specifically, the control unit  121  generates the visual-field image data based on the virtual space data defining the virtual space  200  and the visual field CV of the virtual camera  300 . 
     In Step S 4 , the control unit  121  displays the visual-field image M on the display unit  112  of the HMD  110  based on the visual-field image data (refer to  FIGS. 7A and 7B ). As described above, the visual field CV of the virtual camera  300  is updated in accordance with the movement of the user U wearing the HMD  110 , and thus the visual-field image M to be displayed on the display unit  112  of the HMD  110  is updated as well. Thus, the user U can be immersed in the virtual space  200 . 
     The virtual camera  300  may include a left-eye virtual camera and a right-eye virtual camera. In this case, the control unit  121  generates left-eye visual-field image data representing a left-eye visual-field image based on the virtual space data and the visual field of the left-eye virtual camera. Further, the control unit  121  generates right-eye visual-field image data representing a right-eye visual-field image based on the virtual space data and the visual field of the right-eye virtual camera. After that, the control unit  121  displays the left-eye visual-field image and the right-eye visual-field image on the display unit  112  of the HMD  110  based on the left-eye visual-field image data and the right-eye visual-field image data. In this manner, the user U can visually recognize the visual-field image as a three-dimensional image from the left-eye visual-field image and the right-eye visual-field image. In this disclosure, for the sake of convenience in description, the number of the virtual cameras  300  is one. However, at least one embodiment of this disclosure is also applicable to a case in which the number of the virtual cameras is two. 
     Now, a description is given of the left hand object  400 L, the right hand object  400 R, and the wall object  500  included in the virtual space  200  with reference to  FIG. 9 .  FIG. 9A  is a diagram of the user U wearing the HMD  110  and the controllers  320 L and  320 R according to at least one embodiment.  FIG. 9B  is a diagram of the virtual space  200  including the virtual camera  300 , the left hand object  400 L (example of operation object), the right hand object  400 R (example of operation object), and the wall object  500  (example of target object) according to at least one embodiment. 
     In  FIG. 9B , the virtual space  200  includes the virtual camera  300 , the left hand object  400 L, the right hand object  400 R, and the wall object  500 . The control unit  121  generates the virtual space data for defining the virtual space  200  including those objects. As described above, the virtual camera  300  is synchronized with the movement of the HMD  110  worn by the user U. That is, the visual field of the virtual camera  300  is updated based on the movement of the HMD  110 . The left hand object  400 L is an operation object configured to move in accordance with movement of the controller  320 L worn on the left hand of the user U. Similarly, the right hand object  400 R is an operation object configured to move in accordance with movement of the controller  320 R worn on the right hand of the user U. In the following, the left hand object  400 L and the right hand object  400 R may simply be referred to as “hand object  400 ” for the sake of convenience of description. Further, each of the left hand object  400 L and the right hand object  400 R has a collision area CA. The collision area CA is used for determination of a collision (determination of hit) between the hand object  400  and the target object (for example, the wall object  500 ). For example, the collision area CA of the hand object  400  and a collision area of the target object have touched each other so that a predetermined effect is exerted on the target object, for example, the wall object  500 . In  FIG. 9B , the collision area CA may be defined by, for example, a sphere having a center position of the hand object  400  as a center and a diameter R. In the following description, the collision area CA is formed to have a sphere shape having a center position of the hand object  400  and as a center the diameter R. In at least one embodiment, collision area CA has a different shape and or a different positional relationship with respect to the hand object  400 . 
     The wall object  500  is a target object that the left hand object  400 L and the right hand object  400 R exert an effect on. For example, when the left hand object  400 L has touched the wall object  500 , a part of the wall object  500 , which touches the collision area CA of the left hand object  400 L, is destroyed. Further, the wall object  500  also has a collision area, and in at least one embodiment, the collision area of the wall object  500  is the same as the area constructing the wall object  500 . In at least one embodiment, the collision area of the wall object  500  is different from the area constructing the wall object  500 . 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 10  to  FIG. 12 .  FIG. 10  is a flowchart of an information processing method according to at least one embodiment.  FIG. 11A  is a diagram of a state in which the user U moves the controller  320 L greatly forward (+w direction) according to at least one embodiment.  FIG. 11B  is a diagram of the wall object  500  destroyed by the left hand object  400 L under the state of  FIG. 11A  according to at least one embodiment.  FIG. 12A  is a diagram of a state in which the user U moves the controller  320 L a little forward (+w direction) according to at least one embodiment.  FIG. 12B  is a diagram of the wall object  500  destroyed by the left hand object  400 L under the state of  FIG. 12B  according to at least one embodiment. 
     In the information processing method according to at least one embodiment, the control unit  121  is configured to set a collision effect for defining an effect exerted by the collision area associated with left hand object  400 L n the wall object  500 , and to seta collision effect for defining an effect exerted by the a collision area associated with right hand object  400 R the wall object  500 . Meanwhile, the controllers  320 L and  320 R have substantially the same configuration, and thus, in the following, a description is given only of a collision effect for defining an effect exerted by the controller  320 L on the wall object  500  for the sake of convenience of description. In at least one embodiment, a collision effect associated with left hand object  400 L is different from a collision effect associated with right hand object  400 R. Further, the control unit  121  executes processing steps in  FIG. 10  on a frame (still image forming moving image) basis in at least one embodiment. Instead, in at least one embodiment, the control unit  121  may execute the processing steps in  FIG. 10  at predetermined time intervals. 
     In  FIG. 10 , in Step S 11 , the control unit  121  identifies a distance D (example of relative relationship) between the HMD  110  and the controller  320 L. Specifically, the control unit  121  acquires position information on the HMD  110  and position information on the controller  320 L based on information acquired from the position sensor  130 , and identifies the distance D between the HMD  110  and the controller  320 L in the w-axis direction of the HMD  110  based on those acquired pieces of position information. In at least one embodiment, the control unit  121  identifies the distance D between the HMD  110  and the controller  320 L in the w-axis direction, but may identify the distance between the HMD  110  and the controller  320 L in a predetermined direction other than the w-axis direction. Further, the control unit  121  may identify a straight distance between the HMD  110  and the controller  320 L. In this case, when the position vector of the HMD  110  is set to PH and the position vector of the controller  320 L is set to PL, the straight distance between the HMD  110  and the controller  320 L is |PH−PL|. 
     Next, in Step S 12 , the control unit  121  identifies a relative speed V of the controller  320 L with respect to the HMD  110 . Specifically, the control unit  121  acquires position information on the HMD  110  and position information on the controller  320 L based on information acquired from the position sensor  130 , and identifies the relative speed V (example of relative relationship) of the controller  320 L with respect to the HMD  110  in the w-axis direction of the HMD  110  based on those acquired pieces of position information. 
     For example, when the distance between the HMD  110  and the controller  320 L in the w-axis direction for an n-th frame (n is an integer of 1 or more) is set to Dn, the distance between the HMD  110  and the controller  320 L in the w-axis direction for an (n+1)-th frame is set to Dn+1, and a time interval between frames is set to ΔT, a relative speed Vn in the w-axis direction for the n-th frame is Vn=(Dn−Dn+1)/ΔT. When the frame rate of the moving image is 90 fps, ΔT is 1/90. 
     Next, in Step S 13 , the control unit  121  determines whether or not the identified distance D is larger than a predetermined distance Dth, and determines whether or not the identified relative speed V is larger than a predetermined relative speed Vth. The predetermined distance Dth and the predetermined relative speed Vth may appropriately be set depending on details of a game. When the control unit  121  determines that the identified distance D is larger than the predetermined distance Dth (D&gt;Dth) and the identified relative speed V is larger than the predetermined relative speed Vth (V&gt;Vth) (YES in Step S 13 ), as in  FIG. 11B , the control unit  121  sets a diameter R of the collision area CA of the left hand object  400 L to a diameter R 2  (Step S 14 ). On the contrary, when the control unit  121  determines that D&gt;Dth or V&gt;Vth is not satisfied (NO in Step S 13 ), as in  FIG. 12B , the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to a diameter R 1  (R 1 &lt;R 2 ) (Step S 15 ). In this manner, the size of the collision area CA is set depending on the distance D between the HMD  110  and the controller  320 L and the relative speed V of the controller  320 L with respect to the HMD  110 . In Step S 14  and Step S 15 , the radius of the collision area CA may be set depending on the distance D and the relative speed V instead of the diameter of the collision area CA. In at least one embodiment predetermined distance D is set based on a distance traveled in real time, e.g., within a refresh rate of the HMD such as 90 frames per second (fps). 
     Next, in Step S 16 , the control unit  121  determines whether or not the wall object  500  touches the collision area CA of the left hand object  400 L. When the control unit  121  determines that the wall object  500  touches the collision area CA of the left hand object  400 L (YES in Step S 16 ), a predetermined effect is exerted on a part of the wall object  500 , which touches the collision area CA (Step S 17 ). For example, the part of the wall object  500 , which touches the collision area CA, may be destroyed, or the wall object  500  may be damaged by a predetermined amount. In  FIG. 11B , the part of the wall object  500 , which touches the collision area CA of the left hand object  400 L, is destroyed. Further, because the collision area CA of the left hand object  400 L in  FIG. 11B  is larger than the collision area CA of the left hand object  400 L in  FIG. 12B  (because R 2 &gt;R 1 ), the wall object  500  is destroyed by the left hand object  400 L by a larger amount in the state in  FIG. 11B  than in the state in  FIG. 12B . 
     On the contrary, when the control unit  121  determines that the wall object  500  does not touch the collision area CA of the left hand object  400 L (NO in Step S 16 ), a predetermined effect is not exerted on the wall object  500 . After that, the control unit  121  updates virtual space data for defining the virtual space including the wall object  500 , and displays a next frame (still image) on the HMD  110  based on the updated virtual space data (Step S 18 ). After that, the processing returns to Step S 11 . 
     In this manner, according to at least one embodiment, the effect (collision effect) of the controller  320 L exerted on the wall object  500  is set depending on the relative relationship (relative positional relationship and relative speed) between the HMD  110  and the controller  320 L, and thus improving the sense of immersion of the user U in the virtual space  200  is possible. In particular, the size (diameter) of the collision area CA of the left hand object  400 L is set depending on the distance D between the HMD  110  and the controller  320 L and the relative speed V of the controller  320 L with respect to the HMD  110 . Further, a predetermined effect is exerted on the wall object  500  depending on the positional relationship between the collision area CA of the left hand object  400 L and the wall object  500 . Therefore, further improvement of the sense of immersion of the user U in the virtual space  200  is possible. 
     More specifically, in  FIG. 11B , the collision area CA of the left hand object  400 L becomes larger as the user U moves the controller  320 L a greater distance and at a higher speed (that is, when the user U moves the controller  320 L such that D&gt;Dth and V&gt;Vth are satisfied), and thus the amount of the wall object  500  destroyed by the left hand object  400 L becomes larger. On the contrary, in  FIG. 12B , when the user U moves the controller  320 L a shorter distance (when the user U moves the controller  320 L so as to satisfy D≦Dth at least), the amount of the wall object  500  destroyed by the left hand object  400 L is smaller, and thus the amount of the wall object  500  destroyed in accordance with movement of the user U changes. Therefore, the user U can be immersed in the virtual space more, and a rich virtual experience is provided. 
     In at least one embodiment, in Step S 13 , whether or not the distance D&gt;Dth and the relative speed V&gt;Vth are satisfied is determined. In at least one embodiment, only whether or not the distance D&gt;Dth is satisfied may be determined. In this case, when the control unit  121  determines that the distance D&gt;Dth is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that the distance D≦Dth is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1 . Further, in at least one embodiment, in Step S 13 , only whether or not the relative speed V&gt;Vth is satisfied may be determined. Also in this case, when the control unit  121  determines that the relative speed V&gt;Vth is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that the relative speed V≦Vth is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1 . 
     Further, in Step S 13 , whether or not a relative acceleration A of the controller  320 L with respect to the HMD  110  is larger than a predetermined relative acceleration Ath (A&gt;Ath) is determined. In this case, the control unit  121  identifies the relative acceleration A (example of relative relationship) of the controller  320 L with respect to the HMD  110  in the w-axis direction before Step S 13 . 
     For example, when the relative speed of the controller  320 L with respect to the HMD  110  in the w-axis direction for an n-th frame (n is an integer of 1 or more) is set to Vn+1, the relative speed of the controller  320 L with respect to the HMD  110  in the w-axis direction for an (n+1)-th frame is set to Vn+1, and a time interval between frames is set to ΔT, a relative acceleration An in the w-axis direction for the n-th frame is Δn=(Vn−Vn+1)/ΔT. 
     In this case, when the control unit  121  determines that the relative acceleration A&gt;Ath is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that the relative acceleration A≦Ath is satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1 . 
     Further, in Step S 13 , it may be determined whether or not the distance D&gt;Dth and the relative acceleration a&gt;ath are satisfied. Also in this case, when the control unit  121  determines that the distance D&gt;Dth and the relative acceleration A&gt;Ath are satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that the distance D&gt;Dth or the relative acceleration A&gt;Ath is not satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1 . 
     Further, in at least one embodiment, when the determination condition defined in Step S 13  is satisfied, the diameter R of the collision area CA of the left hand object  400 L is set to the diameter R 1 . However, when the determination condition is satisfied, the control unit  121  may refer to a table or a function for showing a relationship between the diameter R of the collision area CA and the relative speed V, to thereby change the diameter R (that is, the size of the collision area CA) of the collision area CA in a continuous or stepwise manner depending on the magnitude of the relative speed V. For example, the control unit  121  may increase the diameter R (that is, the size of the collision area CA) of the collision area CA in a continuous or stepwise manner along with increase in relative speed V or relative acceleration A. 
     Similarly, when the determination condition is satisfied, the control unit  121  may refer to a table or a function for showing a relationship between the diameter R of the collision area CA and the distance D, to thereby change the diameter R (that is, the size of the collision area CA) of the collision area CA in a continuous or stepwise manner depending on the magnitude of the distance D. For example, the control unit  121  may increase the diameter R (that is, the size of the collision area CA) of the collision area CA in a continuous or stepwise manner along with increase in distance D. 
     Now, a description is given of an information processing method according to at least one embodiment with reference to  FIG. 10  to  FIG. 13 .  FIGS. 13A and 13B  represent an effect range EA that exerts an effect on the collision area CA of the left hand object  400 L and the wall object  500 . The size (diameter) of the collision area CA in  FIG. 13A  is the same as the size (diameter) of the collision area CA in  FIG. 13B , whereas the size (diameter) of the effect range EA in  FIG. 13A  is smaller than the size (diameter) of the effect range EA in  FIG. 13B . In this case, the effect range EA of the left hand object  400 L is defined as a range of the left hand object  400 L exerting an effect on a target object, for example, the wall object  500 . 
     In the information processing method according to at least one embodiment, when the determination condition defined in Step S 13  illustrated in  FIG. 10  is satisfied (YES in Step S 13 ), the diameter R of the collision area CA is set to the diameter R 2  (Step S 14 ), whereas when the determination condition is not satisfied (NO in Step S 13 ), the diameter R of the collision area CA is set to the diameter R 1  (R 2 &gt;R 1 ) (Step S 15 ). 
     In contrast, in the information processing method according to the modification example, in response to a determination that the condition defined in Step S 13  is satisfied (YES in Step S 13 ), as in  FIG. 13B , the diameter R of the collision area CA is set to the diameter R 1 , whereas the diameter of the effect range EA is set to Rb. On the contrary, when the condition is not satisfied (NO in Step S 13 ), as in  FIG. 13A , the diameter R of the collision area CA is set to the diameter R 1  and the diameter of the effect range EA is set to Ra (Rb&gt;Ra). In this manner, in the information processing method according to at least one embodiment, the diameter of the collision area CA is not changed but the diameter of the effect range EA is changed depending on the determination condition defined in Step S 13 . 
     After that, in Step S 16 , the control unit  121  determines whether or not the wall object  500  touches the collision area CA or the effect range EA of the left hand object  400 L. When the control unit  121  determines that the wall object  500  touches the collision area CA or the effect range EA of the left hand object  400 L (YES in Step S 16 ), a predetermined effect is exerted on apart of the wall object  500 , which touches the collision area CA or the effect range EA (Step S 17 ). For example, as  FIGS. 13A and 13B , the part of the wall object  500 , which touches the collision area CA or the effect range EA, is destroyed. Further, because the effect range EA of the left hand object  400 L in  FIG. 13B  is larger than the effect range EA of the left hand object  400 L in  FIG. 13A  (because Rb&gt;Ra), the wall object  500  is destroyed by the left hand object  400 L by a larger amount in  FIG. 13B  than in of  FIG. 13A . 
     On the contrary, when the control unit  121  determines that the wall object  500  does not touch the collision area CA or the effect range EA of the left hand object  400 L (NO in Step S 16 ), a predetermined effect is not exerted on the wall object  500 . 
     In this manner, according to at least one embodiment, the effect (collision effect) of the controller  320 L exerted on the wall object  500  is set depending on the relative relationship (distance and relative speed) between the HMD  110  and the controller  320 L, and thus improving the sense of immersion of the user U in the virtual space  200  is possible. In particular, the size (diameter) of the effect range EA of the left hand object  400 L is set depending on the determination condition defined in Step S 13 . Further, a predetermined effect is exerted on the wall object  500  depending on the positional relationship between the collision area CA and the effect range EA and the wall object  500 . Therefore, further improvement of the sense of immersion of the user U in the virtual space  200 , and to provide a rich virtual experience is possible. 
     Further, in order to achieve various types of processing to be executed by the control unit  121  with use of software, information processing instructions for a system for executing the information processing method according to at least one embodiment (using a processor) may be installed in advance into the storage unit  123  or the ROM. Alternatively, the information processing instructions may be stored in a computer-readable storage medium, for example, a magnetic disk (HDD or floppy disk), an optical disc (for example, CD-ROM, DVD-ROM, or Blu-ray Disc®), a magneto-optical disk (for example, MO), and a flash memory (for example, SD card, USB memory, or SSD). In this case, the storage medium is connected to the control device  120 , and thus the program stored in the storage medium is installed into the storage unit  123 . Then, the information processing instructions installed in the storage unit  123  is loaded onto the RAM, and the processor executes the loaded program. In this manner, the control unit  121  executes the information processing method according to at least one embodiment. 
     Further, the information processing instructions may be downloaded from a computer on the communication network  3  via the communication interface  125 . Also in this case, the downloaded instructions are similarly installed into the storage unit  123 . 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 14  to  FIG. 17 .  FIG. 14  is a flowchart of the information processing method according to at least one embodiment.  FIG. 15A  is a diagram of how the user U looks forward (+w direction) to move the controller  320 L forward according to at least one embodiment.  FIG. 15B  is a diagram of the wall object  500  destroyed by the left hand object  400 L of  FIG. 15A .  FIG. 16A  corresponds to  FIG. 15A , and includes a positional relationship between the HMD  110  and the controller  320  according to at least one embodiment.  FIG. 16B  includes a change in state of the wall object  500  and the virtual camera  300  when the wall object  500  is destroyed according to at least one embodiment.  FIG. 17A  includes a state after the wall object  500  is destroyed and before the virtual camera  300  is moved from the viewpoint of a Y direction in the virtual space  200  according to at least one embodiment.  FIG. 17B  includes a state after the wall object  500  is destroyed and after the virtual camera  300  is moved from the viewpoint of the Y direction in the virtual space  200  according to at least one embodiment. 
     In  FIG. 14 , in Step S 10 A, a visual-field image to be presented on the HMD  110  is identified. In at least one embodiment, as in  FIG. 15B , the wall object  500  and the hand objects  400 L and  400 R are present forward of the virtual camera  300 . Therefore, as in  FIG. 8 , a counter part  510  of the wall object  500 , which is a surface opposed to the virtual camera  300 , is displayed on the visual-field image M. There are the hand objects  400 L and  400 R between the wall object  500  and the virtual camera  300  in the visual field, and thus the hand objects  400 L and  400 R are displayed on the visual-field image M so as to be superimposed on the counter part  510 . 
     In Step S 11 A, the control unit  121  moves the hand object  400  as described above based on movement of the hand of the user U, which is detected by the controller  320 . 
     In Step S 12 A, the control unit  121  determines whether or not the wall object  500  and the hand object  400  satisfy a predetermined condition. In at least one embodiment, the control unit  121  determines whether or not each hand object  400  has touched the wall object  500  based on the collision area CA set to the left hand object  400 L and the right hand object  400 R. When each hand object  400  has touched the wall object  500 , the processing proceeds to Step S 13 A. When each hand object  400  does not touch the wall object  500 , the control unit  121  waits for information on movement of the hand of the user again, and continues to control movement of the hand object  400 . 
     In Step S 13 A, the control unit  121  changes the position of the counter part  510  of the wall object  500 , which is opposed to the virtual camera  300 , such that the counter part  510  becomes away from the virtual camera  300 . In at least one embodiment, as in  FIG. 15B , the left hand object  400 L touches the wall object  500  based on movement of the left hand of the user U so that a part of the wall object  500  is destroyed as  FIG. 16B . Specifically, a part of the area including the counter part  510  within the wall object  500  is deleted so that the wall object  500  changes to form a new counter part  510  in the visual-axis direction (+w direction) of the virtual camera  300 . With this, the user can get such a virtual experience that a part of the wall object  500  is destroyed by moving his or her left hand. 
     In Step S 14 A, the control unit  121  determines whether or not a position at which the hand object  400  and the wall object  500  have touched each other is located within the visual field of the virtual camera  300 . When the position is located within the visual field, the processing proceeds to Step S 15 A, and the control unit  121  executes processing of moving the virtual camera  300 . When the position is not located within the visual field, the control unit  121  waits for information on movement of the hand of the user again, and continues to control movement of the hand object  400 . 
     In Step S 15 A, the control unit  121  moves the virtual camera  300  without association with movement of the HMD  110 . Specifically, as in  FIG. 16B , the control unit  121  moves the virtual camera  300  forward in the visual-axis direction (+w direction) of the virtual camera  300 , in which the wall object  500  is destroyed. When the user U destroys a first part of the wall object  500 , the user U further takes an action to destroy remain parts of the wall object  500 . In this case, the counterpart  510  moves backward with respect to the virtual camera  300 , and thus the user U needs to move the virtual camera  300  forward because the user U cannot reach the wall object  500  with the hand object  400  even when the user U extends his or her arm. In at least one embodiment, providing an intuitive feeling of operation while reducing the time and effort of the user U without the necessity for the user U to perform an operation of moving the HMD  110  forward is possible, that is, by the user U moving the virtual camera  300  to approach the wall object  500  without association with movement of the HMD  110 . 
     In at least one embodiment, when the virtual camera  300  is moved, the hand object  400  be moved in accordance with movement of the virtual camera  300  so as to reflect a relative positional relationship between the HMD  110  and the hand. For example, as in  FIG. 16A , a distance d 2  between the HMD  110  and the left hand (left hand controller  320 L) in the +w direction and a distance d 1  between the HMD  110  and the right hand (right hand controller  320 R) in the +w direction are assumed in the real space. In this case, as in  FIG. 16B , the distance between the virtual camera  300  and the left hand object  400 L before movement in the +x direction is set to d 2 , and the distance between the virtual camera  300  and the right hand object  400 R before movement in the +x direction is set to d 1 . When a movement vector F, which is defined by the movement direction and the movement amount of the virtual camera as described above, is specified, the hand object  400  is moved in accordance with movement of the virtual camera  300 . In other words, the distance between the virtual camera  300  and the left hand object  400 L after movement in the +x direction is set to d 2 , and the distance between the virtual camera  300  and the right hand object  400 R after movement in the +x direction is set to d 1 . Through such movement of the hand object  400 , the user U can continue to mutually interact with a target object intuitively via the hand object  400  even after movement. The same holds true for the relative positional relationship in directions other than the w direction and the w direction. 
     In at least one embodiment, when the hand object  400  is moved in accordance with movement of the virtual camera  300 , the virtual camera  300  be moved such that the hand object  400  does not touch the wall object  500 . For example, as in  FIG. 16B , the magnitude of the movement vector F is set such that the hand object  400  (and collision area CA thereof) is set so as to be positioned on the front side of the wall object  500  in the +x direction. With this, preventing occurrence of change in the wall object  500  is possible and movement of the virtual camera  300  that are not intended by the user U due to the hand object  400  touching the wall object  500  again and the counter part  510  moving backward again after movement of the virtual camera  300 . 
     Now, a description is given of an example of setting the movement vector F in at least one embodiment with reference to  FIGS. 17A and 17B .  FIGS. 17A and 17B  is a diagram of the state before and after movement of the virtual camera  300  from the viewpoint of the Y direction in the virtual space  200  according to at least one embodiment. In  FIG. 17A , the left hand object  400 L and the wall object  500  have touched each other so that the counter part  510  moved backward. 
     In at least one embodiment, the direction of the movement vector F of the virtual camera  300  be a direction of extension of the visual axis L of the virtual camera  300  at the time when the virtual camera  300  and the left hand object  400 L have touched each other regardless of the positional relationship between the virtual camera  300  and the left hand object  400 L. With this, the virtual camera  300  is moved in the forward direction with respect to the user U, and the user U is more likely to predict the movement direction. As a result, reducing visually induced motion sickness (so-called VR sickness) caused by movement of the virtual camera  300  and suffered by the user U is possible. In at least one embodiment, even when the virtual camera  300  starts to move and the user U moves his or her head before completion of the movement so that the direction of the virtual camera changes, the virtual camera  300  be moved in the direction of extension of the visual axis L of the virtual camera  300  at the time when the virtual camera  300  and the left hand object  400 L have touched each other. With this, the user U is more likely to predict the movement direction, and the VR sickness is reduced. 
     The magnitude of the movement vector F of the virtual camera  300  is set smaller as the position at which the left hand object  400 L and the wall object  500  have touched each other becomes more away from the visual axis L of the virtual camera  300 . With this, even when the virtual camera  300  is moved in the direction of the visual axis L, preventing the left hand object  400 L from touching the wall object  500  again after movement of the virtual camera  300  is possible. 
     In  FIG. 17A , the distance between the position at which the left hand object  400 L and the wall object  500  have touched each other and the visual axis L of the virtual camera  300  may be defined based on an angle θ between the direction from the virtual camera  300  to the left hand object  400 L and the visual axis L. When the distance between the position at which the left hand object  400 L touches the wall object  500  and the position of the virtual camera  300  is set to D, a distance F 1  defined by D*cos θ is obtained. The magnitude of the movement vector F becomes smaller as the position at which the left hand object  400 L touches the wall object  500  becomes more away from the visual axis L of the virtual camera  300  by defining the magnitude of the movement vector F as αD*cos θ (α is a constant of 0&lt;α&lt;1). 
     In Step S 16 A, the control unit  121  updates the visual-field image based on the visual field of the moved virtual camera  300 . The user U can experience movement in the virtual space by being presented with the updated visual-field image on the HMD  110 . 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 18  to  FIG. 20 .  FIG. 18  is a flowchart of the information processing method according to at least one embodiment.  FIG. 19A  is a diagram of how the user U moves forward (+w direction) at an absolute speed S faster than a predetermined speed Sth according to at least one embodiment.  FIG. 19B  is a diagram of the wall object  500  destroyed by the left hand object  400 L in  FIG. 19A  according to at least one embodiment.  FIG. 20A  is a diagram of how the user U moves forward (+w direction) at an absolute speed S slower than the predetermined speed Sth according to at least one embodiment.  FIG. 20B  is a diagram of the wall object  500  destroyed by the left hand object  400 L in  FIG. 20A  according to at least one embodiment. 
     In the information processing method according to at least one embodiment, the control unit  121  is configured to seta collision effect for defining an effect exerted by the controller  320 L on the wall object  500 , and set a collision effect for defining an effect exerted by the controller  320 R on the wall object  500 . Meanwhile, the controllers  320 L and  320 R have substantially the same configuration, and thus, in the following, only the collision effect for defining an effect exerted by the controller  320 L on the wall object  500  is described for the sake of convenience of description. Further, the control unit  121  executes processing steps in  FIG. 18  for each frame (still image constructing moving image). Instead, the control unit  121  may execute the processing steps illustrated in  FIG. 18  at predetermined time intervals. 
     In  FIG. 18 , in Step S 11 B, the control unit  121  identifies an absolute speed S of the HMD  110 . The absolute speed S indicates the speed of the HMD  110  with respect to the position sensor  130  installed at a predetermined position in the real space. Further, the user U wears the HMD  110 , and thus the absolute speed of the HMD  110  corresponds to the absolute speed of the user U. That is, in at least one embodiment, the absolute speed of the user U is identified through identification of the absolute speed of the HMD  110 . 
     Specifically, the control unit  121  acquires the position information on the HMD  110  based on the information acquired from the position sensor  130 , and identifies the absolute speed S of the HMD  110  in the w axis direction of the HMD  110  based on the acquired position information. In at least one embodiment, the control unit  121  identifies the absolute speed S of the HMD  110  in the w axis direction, but may identify the absolute speed S of the HMD  110  in a predetermined direction other than the w axis direction. 
     For example, when the position in the w axis direction of a position Pn of the HMD  110  for an n-th frame (n is an integer of 1 or more) is set to wn, the position in the w axis direction of a position Pn+1 of the HMD  110  for an (n+1)-th frame is set to wn+1, and a time interval between frames is set to ΔT, the absolute speed Sn of the HMD  110  in the w-axis direction for the n-th frame is Vn=(wn+1−wn)/ΔT. When the frame rate of the moving image is 90 fps, AT is 1/90. 
     Next, in Step S 12 B, the control unit  121  determines whether or not the identified absolute speed S of the HMD  110  is larger than the predetermined speed Sth. The predetermined speed Sth may be set appropriately depending on details of a game. When the control unit  121  determines that the identified absolute speed S is larger than the predetermined speed Sth (S&gt;Sth) (YES in Step S 12 B), as in  FIG. 19B , the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2  (Step S 13 B). On the contrary, when the control unit  121  determines that the identified absolute speed S is equal to or smaller than the predetermined speed Sth (S≦Sth) (NO in Step S 12 B), as illustrated in  FIG. 20B , the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1  (R 1 &lt;R 2 ) (Step S 14 B). In this manner, the size of the collision area CA is set depending on the absolute speed S of the HMD  110 . In Step S 13 B and Step S 14 B, the radius of the collision area CA may be set depending on the absolute speed S instead of the diameter of the collision area CA. Further, when the predetermined speed Sth=0 is satisfied, the control unit  121  executes the processing of Step S 13 B when determining that the HMD  110  is moving in the +w direction, whereas the control unit  121  executes the processing of Step S 14 B when determining that the HMD  110  is not moving in the +w direction. 
     Next, in Step S 15 B, the control unit  121  determines whether or not the wall object  500  touches the collision area CA of the left hand object  400 L. When the control unit  121  determines that the wall object  500  touches the collision area CA of the left hand object  400 L (YES in Step S 15 B), a predetermined effect is exerted on a part of the wall object  500 , which touches the collision area CA (Step S 16 B). For example, the part of the wall object  500 , which touches the collision area CA, may be destroyed, or the wall object  500  may be damaged by a predetermined amount. As in  FIG. 19B , the part of the wall object  500 , which touches the collision area CA of the left hand object  400 L, is destroyed. Further, because the collision area CA of the left hand object  400 L in  FIG. 19B  is larger than the collision area CA of the left hand object  400 L in  FIG. 20B  (because R 2 &gt;R 1 ), the wall object  500  is destroyed by the left hand object  400 L by a larger amount in  FIG. 19B  than in  FIG. 20B . 
     On the contrary, when the control unit  121  determines that the wall object  500  does not touch the collision area CA of the left hand object  400 L (NO in Step S 15 B), a predetermined effect is not exerted on the wall object  500 . After that, the control unit  121  updates virtual space data for defining the virtual space including the wall object  500 , and displays a next frame (still image) on the HMD  110  based on the updated virtual space data (Step S 17 B). After that, the processing returns to Step S 11 B. 
     In this manner, according to at least one embodiment, the collision effect for defining an effect exerted by the controller  320 L on the wall object  500  is set depending on the absolute speed S of the HMD  110 . In particular, when the absolute speed S of the HMD  110  is equal to or smaller than the predetermined speed Sth, the collision effect in  FIG. 20B  is obtained, whereas, when the absolute speed S of the HMD  110  is larger than the predetermined speed Sth, the collision effect as in  FIG. 19B  is obtained. In this manner, different collision effects are set depending on the absolute speed S of the HMD  110  (that is, the absolute speed of the user U), and thus improving the sense of immersion of the user U in the virtual space, and to provide a rich virtual experience is possible. 
     More specifically, the collision area CA of the left hand object  400 L is set depending on the absolute speed S of the HMD  110 . In particular, when the absolute speed S of the HMD  110  is equal to or smaller than the predetermined speed Sth, the diameter R of the left hand object  400 L is set to R 1 , whereas, when the absolute speed S of the HMD  110  is larger than the predetermined speed Sth, the diameter R of the left hand object  400 L is set to R 2  (R 1 &lt;R 2 ). Further, a predetermined effect is exerted on the wall object  500  depending on the positional relationship between the collision area CA of the left hand object  400 L and the wall object  500 . Therefore, further improvement of the sense of immersion of the user U in the virtual space  200  is possible. 
     In this respect, as in  FIGS. 19A and 19B , when the user U (or the HMD  110 ) moves in thew axis direction such that v&gt;vth is satisfied, the collision area CA of the left hand object  400 L becomes larger, and thus the amount of the wall object  500  destroyed by the left hand object  400 L becomes larger. On the contrary, as in  FIGS. 20A and 20B , when the user U (or the HMD  110 ) moves in the w axis direction such that V≦Vth is satisfied, the collision area CA of the left hand object  400 L becomes smaller, and thus the amount of the wall object  500  destroyed by the left hand object  400 L becomes smaller. As a result, the amount of the wall object  500  destroyed in accordance with movement of the user U changes, and thus the user U can be immersed in the virtual space more. 
     In at least one embodiment, in Step S 12 B, a determination is made whether or not the absolute speed S of the HMD  110  in the w axis direction is larger than the predetermined speed Sth, but in at least one embodiment a determination is made whether or not the absolute speed S of the HMD  110  in the w axis direction is larger than the predetermined speed Sth and the relative speed V of the controller  320 L with respect to the HMD  110  in the movement direction of the HMD  110  (in this example, w axis direction) is larger than the predetermined relative speed Vth. That is, a determination is made whether or not S&gt;Sth and V&gt;Vth are satisfied. The predetermined relative speed Vth may be set appropriately depending on details of a game. 
     In this case, the control unit  121  identifies the relative speed V of the controller  320 L with respect to the HMD  110  in the w axis direction before Step S 12 B. For example, when the distance between the HMD  110  and the controller  320 L in the w axis direction for the n-th frame (n is an integer of 1 or more) is set to Dn, the distance between the HMD  110  and the controller  320 L in the w axis direction for the (n+1)-th frame is set to Dn+1, and a time interval between frames is set to ΔT, the relative speed Vn in the w axis direction for the n-th frame is Vn=(Dn−Dn+1)/ΔT. 
     When the control unit  121  determines that the absolute speed S of the HMD  110  in the w axis direction is larger than the predetermined speed Sth (S&gt;Sth) and the relative speed V of the controller  320 L with respect to the HMD  110  in the movement direction of the HMD  110  (w axis direction) is larger than the predetermined relative speed Vth (V&gt;Vth), the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that v&gt;vth or V&gt;Vth is not satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . In this manner, the collision effect is set depending on the absolute speed S of the HMD  110  and the relative speed V of the controller  320 L with respect to the HMD  110 . Therefore, further improvement the sense of immersion of the user U in the virtual space  200  is possible. 
     Further, in Step S 12 B, a determination is made whether or not the absolute speed S of the HMD  110  in the w axis direction is larger than the predetermined speed Sth and the relative acceleration a of the controller  320 L with respect to the HMD  110  in the movement direction of the HMD  110  (in this example, w axis direction) is larger than the predetermined relative acceleration Ath. 
     In this case, the control unit  121  identifies the relative acceleration A of the controller  320 L with respect to the HMD  110  in the w axis direction before Step S 12 B. For example, when the relative speed of the controller  320 L with respect to the HMD  110  in the w axis direction for the n-th frame (n is an integer of 1 or more) is set to Vn, the relative speed of the controller  320 L with respect to the HMD  110  in thew axis direction for the (n+1)-th frame is set to Vn+1, and a time interval between frames is set to ΔT, the relative acceleration an in the w axis direction for the n-th frame is An=(Vn−Vn+1)/ΔT. 
     When the control unit  121  determines whether or not the absolute speed S of the HMD  110  in the w axis direction is larger than the predetermined speed Sth (S&gt;Sth) and the relative acceleration a of the controller  320 L with respect to the HMD  110  in the movement direction of the HMD  110  (w axis direction) is larger than the predetermined relative acceleration Ath (A&gt;Ath), the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . On the contrary, when the control unit  121  determines that S&gt;Sth or A&gt;Ath is not satisfied, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2 . In this manner, the collision effect is set depending on the absolute speed S of the HMD  110  and the relative speed S of the controller  320 L with respect to the HMD  110 . Therefore, further improvement of the sense of immersion of the user U in the virtual space  200  is possible. 
     Further, when the determination condition defined in Step S 12 B is satisfied, the control unit  121  refers to a table or a function for showing a relationship between the diameter R of the collision area CA and the relative speed V, to thereby change the diameter R of the collision area CA (that is, size of collision area CA) in a continuous or stepwise manner depending on the magnitude of the relative speed V. For example, the control unit  121  may increase the diameter R of the collision area CA (that is, size of collision area CA) in a continuous or stepwise manner along with increase in relative speed V. 
     Next, a description is given of an information processing method according to at least one embodiment with reference to  FIG. 21 .  FIG. 21  is a flowchart of the information processing method according at least one embodiment. In  FIG. 21 , the information processing method according to at least one embodiment is different from the above described information processing method (see  FIG. 18 ) in that the processing of from Step S 22  to Step S 28  is executed instead of the processing of from Step S 12 B to Step S 14 B. The processing of Step S 21  and Step S 29  to Step S 31  in  FIG. 21  is therefore the same as that of Step S 11 B and Step S 15 B to S 17 B in  FIG. 18 , and thus only the processing of from Step S 22  to Step S 28  is described. 
     In Step S 22 , the control unit  121  determines whether or not the absolute speed S of the HMD  110  satisfies 0&lt;S≦S 1 . When the result of determination in Step S 22  is YES, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 1  (Step S 23 ). On the contrary, when the result of determination in Step S 22  is NO, the control unit  121  determines whether or not the absolute speed S of the HMD  110  satisfies S 1 &lt;S≦S 2  (Step S 24 ). When the result of determination in Step S 24  is YES, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to the diameter R 2  (Step S 25 ). On the contrary, when the result of determination in Step S 24  is NO, the control unit  121  determines whether or not the absolute speed S of the HMD  110  satisfies S 2 &lt;S≦S 3  (Step S 26 ). When the result of determination in Step S 26  is YES, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to a diameter R 3  (Step S 27 ). On the contrary, when the result of determination in Step S 26  is NO, the control unit  121  sets the diameter R of the collision area CA of the left hand object  400 L to a diameter R 4  (Step S 28 ). In at least one embodiment, the predetermined speeds S 1 , S 2 , and S 3  are threshold values which satisfy the relationship of 0&lt;S 1 &lt;S 2 &lt;S 3 . Further, in at least one embodiment, the diameters R 1 , R 2 , R 3 , and R 4  of the collision area CA satisfy the relationship of R 1 &lt;R 2 &lt;R 3 &lt;R 4 . 
     According to at least one embodiment, the control unit  121  can refer to a table or a function for showing a relationship between the diameter R of the collision area CA and the absolute speed S, to thereby change the diameter R of the collision area CA of the left hand object  400 L in a stepwise manner depending on the magnitude of the absolute speed S of the HMD  110 . Further, according to at least one embodiment, as the absolute speed S of the HMD  110  becomes larger, the collision area CA of the left hand object  400 L becomes larger in a stepwise manner. In this manner, as the absolute speed S of the HMD  110  (that is, the absolute speed of the user U) becomes larger, the collision area CA of the left hand object  400 L becomes larger. As a result, the collision effect for defining the effect exerted by the left hand object  400 L on the wall object  500  becomes larger. Therefore, improving the sense of immersion of the user U in the virtual space, and to provide a rich virtual experience is possible. 
     The control unit  121  may refer to a table or a function for showing a relationship between the diameter R of the collision area CA and the absolute speed S, to thereby change the diameter R of the collision area CA continuously depending on the magnitude of the relative speed V. Also in this case, further improvement of the sense of immersion of the user U in the virtual space and to provide a rich virtual experience is possible. 
     Next, a description is given of an information processing method according to at least one embodiment with reference to  FIG. 18  and  FIGS. 22A and 22B .  FIGS. 22A and 22B  are diagrams of the collision area CA of the left hand object  400 L and the effect range EA that exerts an effect on the wall object  500 . The size (diameter) of the collision area CA in  FIG. 22A  is the same as the size (diameter) of the collision area CA in  FIG. 22B , whereas the size (diameter) of the effect range EA in  FIG. 22A  is smaller than the size (diameter) of the effect range EA in  FIG. 22B . In this case, the effect range EA of the left hand object  400 L is defined as the range of an effect exerted by the left hand object  400 L on a target object, for example, the wall object  500 . 
     In the information processing method according to at least one embodiment, when the determination condition defined in Step S 12 B illustrated in  FIG. 18  is satisfied (YES in Step S 12 B), the diameter R of the collision area CA is set to the diameter R 2  (Step S 13 B), whereas, when the determination condition is not satisfied (NO in Step S 12 B), the diameter R of the collision area CA is set to the diameter R 1  (R 2 &gt;R 1 ) (Step S 14 B). 
     In contrast, in the information processing method according to at least one embodiment, when the determination condition defined in Step S 12 B is satisfied (YES in Step S 12 B), as in  FIG. 22B , the diameter R of the collision area CA is set to the diameter R 1  and the diameter of the effect range EA is set to Rb. On the contrary, when the determination condition is not satisfied (NO in Step S 12 B), as in  FIG. 22A , the diameter R of the collision area CA is set to the diameter R 1  and the diameter of the effect range EA is set to Ra (Rb&gt;Ra). In this manner, in the information processing method according to at least one embodiment, the diameter of the collision area CA is not changed but the diameter of the effect range EA is changed depending on the determination condition defined in Step S 12 B. 
     Next, in Step S 15 B, the control unit  121  determines whether or not the wall object  500  touches the collision area CA or the effect range EA of the left hand object  400 L. When the control unit  121  determines that the wall object  500  touches the collision area CA or the effect range EA of the left hand object  400 L (YES in Step S 15 B), a predetermined effect is exerted on a part of the wall object  500 , which touches the collision area CA or the effect range EA (Step S 16 B). For example, in  FIGS. 22A and 22B , the part of the wall object  500 , which touches the collision area CA or the effect range EA, is destroyed. Further, because the effect range EA of the left hand object  400 L in  FIG. 22B  is larger than the effect range EA of the left hand object  400 L in  FIG. 22A  (because Rb&gt;Ra), the wall object  500  is destroyed by the left hand object  400 L by a larger amount in  FIG. 22B  than in  FIG. 22A . 
     On the contrary, when the control unit  121  determines that the wall object  500  does not touch the collision area CA or the effect range EA of the left hand object  400 L (NO in Step S 15 B), a predetermined effect is not exerted on the wall object  500 . 
     In this manner, according to at least one embodiment, the effect (collision effect) exerted by the controller  320 L on the wall object  500  is set depending on the absolute speed S of the HMD  110 , and thus further improvement of the sense of immersion of the user U in the virtual space  200  and to provide a rich virtual experience is possible. In particular, the size (diameter) of the effect range EA of the left hand object  400 L is set depending on the determination condition defined in Step S 12 B. Further, a predetermined effect is exerted on the wall object  500  depending on a positional relationship among the collision area CA, the effect range EA, and the wall object  500 . Therefore, further improvement of the sense of immersion of the user U in the virtual space  200 , and to provide a rich virtual experience is possible. 
     Now, with reference to  FIGS. 23A and 23B , a description is given of the left hand object  400 L (example of operation object), the right hand object  400 R (example of operation object), a block object  500  (virtual object), a button object  600  (example of target object being virtual object), which are included in the virtual space  200 .  FIG. 23A  is a diagram of the user U wearing the HMD  110  and the controllers  320 L and  320 R according to at least one embodiment.  FIG. 23B  is a diagram of the virtual space  200  including the virtual camera  300 , the left hand object  400 L, the right hand object  400 R, the block object  500 , and the button object  600  according to at least one embodiment. 
     As described above, the virtual space  200  includes the virtual camera  300 , the left hand object  400 L, the right hand object  400 R, the block object  500 , and the button object  600 . The control unit  121  generates virtual space data for defining the virtual space  200  including those objects. Further, the control unit  121  may update the virtual space data on a frame basis. As described above, the virtual camera  300  moves in accordance with movement of the HMD  110  worn by the user U. That is, the visual field of the virtual camera  300  is updated in accordance with movement of the HMD  110 . 
     The left hand object  400 L moves in accordance with movement of the controller  320 L worn on the left hand of the user U. Similarly, the right hand object  400 R moves in accordance with movement of the controller  320 R worn on the right hand of the user U. In the following, the left hand object  400 L and the right hand object  400 R may simply be referred to as “hand object  400 ” for the sake of convenience of description. 
     Further, the user U can operate the operation button  302  of the external controller  320  to operate each finger of the hand object  400 . That is, the control unit  121  acquires an operation signal corresponding to an input operation for the operation button  302  from the external controller  320 , and controls operation of each finger of the hand object  400  based on the operation signal. For example, the user U can operate the operation button  302  so that the hand object  400  grasps the block object  500 . Further, the hand object  400  and the block object  500  can be moved in accordance with movement of the controller  320  with the hand object  400  holding the block object  500 . In this manner, the control unit  121  is configured to control operation of the hand object  400  in accordance with movement of a finger of the user U. 
     Further, the left hand object  400 L and the right hand object  400 R each include the collision area CA. The collision area CA is used for determination of collision (determination of hit) between the hand object  400  and a virtual object (for example, block object  500  or button object  600 ). The collision area CA of the hand object  400  and the collision area of the block object  500  (button object  600 ) have touched each other so that a predetermined effect (collision effect) is exerted on the block object  500  (button object  600 ). 
     For example, a predetermined damage can be given to the block object  500  by the collision area CA of the hand object  400  and the collision area of the block object  500  touching each other. Further, moving the hand object  400  and the block object  500  in an integrated manner with the hand object  400  holding the block object  500  is possible. 
     In  FIG. 23B , the collision area CA may be defined by, for example, a sphere having the center position of the hand object  400  as a center and the diameter R. In the following description, the collision area CA of the hand object  400  is formed to have a sphere shape having the center position of the hand object  400  as its center and the diameter R. In at least one embodiment, the collision area CA has a different shape and/or a different positional relationship with hand object  400 . 
     The block object  500  is a virtual object that the hand object  400  exerts an effect on. The block object  500  also has the collision area, and in at least one embodiment, the collision area of the block object  500  is the same as the area forming the block object  500  (exterior area of block object  500 ). In at least one embodiment, the collision area of the block object  500  is different from the area forming the block object  500 . 
     The button object  600  is a virtual object that the hand object  400  exerts an effect on, and includes an operation portion  620 . The button object  600  also includes the collision area, and in at least one embodiment, the collision area of the button object  600  is the same as the area forming the button object  600  (exterior area of button object  600 ). In at least one embodiment, the collision area of the operation portion  620  is the same as the exterior area of the operation portion  620 . 
     A predetermined effect is exerted on a predetermined object (not shown) placed in the virtual space  200  when the operation portion  620  of the button object  600  is pressed by the hand object  400 . Specifically, the collision area CA of the hand object  400  and the collision area of the operation portion  620  have touched each other so that the operation portion  620  is pressed by the hand object  400  as the collision effect. Then, the operation portion  620  is pressed so that a predetermined effect is exerted on a predetermined object placed in the virtual space  200 . For example, an object (character object) present in the virtual space  200  may start to move by the operation portion  620  being pressed by the hand object  400 . 
     Next, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 24  to  FIG. 25 .  FIG. 24  is a plan-view diagram of the virtual space  200  of how the collision area CA of the right hand object  400 R touches the operation portion  620  of the button object  600  according to at least one embodiment.  FIG. 25  is a flowchart of the information processing method according to at least one embodiment. In the flowchart of  FIG. 25 , processing of determining whether or not the collision area CA of the right hand object  400 R has touched the collision area of the operation portion  620  (determination processing defined in Step S 13 C) intentionally is executed before determination of hit between the right hand object  400 R and the operation portion  620  (processing defined in Step S 14 C). 
     Further, in description of at least one embodiment, whether or not the right hand object  400 R exerts a predetermined effect on the operation portion  620  of the button object  600  is mentioned for the sake of convenience of description, whereas whether or not the left hand object  400 L exerts a predetermined effect on the operation portion  620  of the button object  600  is not mentioned. Thus, in  FIG. 24 , the left hand object  400 L is omitted. Further, the control unit  121  may execute processing steps in  FIG. 25  on a frame basis repeatedly. Instead, the control unit  121  may execute the processing steps illustrated in  FIG. 25  at predetermined time intervals. 
     In  FIG. 25 , in Step S 10 C, the control unit  121  identifies an absolute speed S (refer to  FIG. 23 ) of the HMD  110 . At this time, the absolute speed S refers to the speed of the HMD  110  with respect to the position sensor  130  installed in a fixed manner at a predetermined position in the real space. Further, the user U wears the HMD  110 , and thus the absolute speed of the HMD  110  corresponds to the absolute speed of the user U. That is, in at least one embodiment, the absolute speed of the HMD  110  is identified to identify the absolute speed of the user U. In  FIG. 24 , when the HMD  110  is moved in the real space, the virtual camera  300  also moves in the virtual space  200 . 
     Specifically, the control unit  121  acquires position information on the HMD  110  based on data acquired by the position sensor  130 , and identifies the absolute speed S of the HMD  110  based on the acquired position information. For example, when the position of the HMD  110  for an n-th frame (n is an integer of 1 or more) is set to Pn, the position of the HMD  110  for an (n+1)-th frame is set to Pn+1, and a time interval between frames is set to ΔT, the absolute speed Sn of the HMD  110  for the n-th frame is Sn=|Pn+1−Pn|/ΔT. When the frame rate of the moving image is 90 fps, the time interval ΔT is 1/90. Further, a position P of the HMD  110  is a position vector that can be displayed in a three-dimensional coordinate system. In this manner, the control unit  121  can acquire the position Pn of the HMD  110  for an n-th frame and the position Pn+1 of the HMD  110  for an (n+1)-th frame to identify the absolute speed Sn for an n-th frame based on the position vectors Pn and Pn+1 and the time interval ΔT. 
     The control unit  121  may identify the absolute speed S of the HMD  110  in the w axis direction, or may identify the absolute speed S of the HMD  110  in a predetermined direction other than the w axis direction. For example, when the position in the w axis direction of the position Pn of the HMD  110  for an n-th frame (n is an integer of 1 or more) is set to wn, the position in the w axis direction of a position Pn+1 of the HMD  110  for an (n+1)-th frame is set to wn+1, and a time interval between frames is set to ΔT, the absolute speed Sn of the HMD  110  in the w-axis direction for the n-th frame is Sn=(wn+1−wn)/ΔT. 
     Next, in Step S 11 C, the control unit  121  identifies the visual field CV of the virtual camera  300 . Specifically, the control unit  121  identifies the position and inclination of the HMD  110  based on data from the position sensor  130  and/or the HMD sensor  114 , and identifies the visual field CV of the virtual camera  300  based on the position and inclination of the HMD  110 . After that, the control unit  121  identifies the position of the right hand object  400 R (Step S 12 C). Specifically, the control unit  121  identifies the position of the controller  320 R in the real space based on data from the position sensor  130  and/or a sensor of the controller  320 R, and identifies the position of the right hand object  400 R based on the position of the controller  320 R in the real space. 
     Next, the control unit  121  determines whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth (S≦Sth) (Step S 13 C). The predetermined value Sth (Sth≧0) may be set appropriately depending on details of content, for example, a game. Further, the determination condition (S≦Sth) defined in Step S 13 C corresponds to a determination condition (first condition) for determining whether or not the collision area CA of the right hand object  400 R (operation object) has touched the collision area of the operation portion  620  of the button object  600  (target object) intentionally. 
     When the control unit  121  determines whether or not the determination condition defined in Step S 13 C is not satisfied (that is, when the absolute speed S is determined to be larger than the predetermined value Sth) (NO in Step S 13 C), the control unit  121  does not execute processing defined in Step S 14 C and Step S 15 C. That is, the control unit  121  does not execute collision determination processing defined in Step S 14 C and processing of causing a collision effect defined in Step S 15 C, and thus the right hand object  400 R does not exert a predetermined effect on the operation portion  620  of the button object  600 . 
     On the contrary, when the control unit  121  determines that the determination condition defined in Step S 13 C is satisfied (that is, when the absolute speed S is determined to be equal to or smaller than the predetermined value Sth) (YES in Step S 13 C), the control unit  121  determines whether or not the collision area of the operation portion  620  of the button object  600  touches the collision area CA of the right hand object  400 R (Step S 14 C). In particular, the control unit  121  determines whether or not the collision area of the operation portion  620  touches the collision area CA of the right hand object  400 R based on the position of the right hand object  400 R and the position of the operation portion  620  of the button object  600 . When the result of determination in Step S 14 C is YES, the control unit  121  exerts a predetermined effect on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 14 C). For example, the control unit  121  may determine that the operation portion  620  is pressed by the right hand object  400 R as an effect of collision between the right hand object  400 R and the operation portion  620 . As a result, a predetermined effect may be exerted on a predetermined object (not shown) placed in the virtual space  200 . Further, a contact surface  620   a  of the operation portion  620  may move in the +X direction as an effect of collision between the right hand object  400 R and the operation portion  620 . On the contrary, when the result of determination in Step S 14 C is NO, an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. 
     According to at least one embodiment, a determination is made whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth as a determination condition for determining whether or not the collision area CA of the right hand object  400 R touches the collision area of the operation portion  620  intentionally. When the absolute speed S is larger than the predetermined value Sth (when the determination condition of Step S 13 C is not satisfied), the processing defined in Step S 14 C and Step S 15 C is not executed. In this manner, when the right hand object  400 R has touched the operation portion  620  with the absolute speed S of the HMD  110  being larger than the predetermined value Sth, the right hand object  400 R is determined to have touched the operation portion  620  unintentionally. Thus, determination of collision between the right hand object  400 R and the operation portion  620  is not executed, and an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. 
     Therefore, a situation is avoided in which, when the right hand object  400 R has touched the operation portion  620  unintentionally, the operation portion  620  is pressed by the right hand object  400 R unintentionally. In this manner, further improvement of the virtual experience of the user is possible. 
     Next, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 26 .  FIG. 26  is a flowchart of an information processing method according to at least one embodiment. In the flowchart of  FIG. 26 , processing of determining whether or not the collision area CA of the right hand object  400 R has touched the collision area of the operation portion  620  intentionally (determination processing defined in Step S 24 C) is executed after determination of hit between the right hand object  400 R and the operation portion  620  (processing defined in Step S 23 C). In this respect, the information processing method in  FIG. 26  and the information processing method in  FIG. 25  are different from each other. In the following, only a difference from the information processing method in  FIG. 25  is described. 
     In  FIG. 26 , the control unit  121  executes processing defined in Step S 20 C to Step S 22 C, and then determines whether or not the collision area of the operation portion  620  of the button object  600  touches the collision area CA of the right hand object  400 R (Step S 23 C). The processing of from Step S 20 C to Step S 22 C corresponds to the processing of from Step S 10 C to Step S 12 C illustrated in  FIG. 25 . 
     When the result of determination in Step S 23 C is NO, the collision area of the operation portion  620  does not touch the collision area CA of the right hand object  400 R, and thus the control unit  121  ends this processing. On the contrary, when the result of determination in Step S 23 C is YES (when it is determined that the collision area of the operation portion  620  touches the collision area CA of the right hand object  400 R), the control unit  121  determines whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth (Step S 24 C). 
     When the control unit  121  determines that the absolute speed S is larger than the predetermined value Sth (NO in Step S 24 C), the control unit  121  ends this processing without executing processing defined in Step S 25 C. On the contrary, when the control unit  121  determines that the absolute speed S is equal to or smaller than the predetermined value Sth (YES in Step S 24 C), the control unit  121  exerts a predetermined effect (collision effect) on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 25 C). 
     In this manner, in response to a determination that the absolute speed S is larger than the predetermined value Sth (when the determination condition of Step S 24 C is not satisfied), the processing defined in Step S 25 C is not executed. In this manner, when the right hand object  400 R has touched the operation portion  620  with the absolute speed S of the HMD  110  being larger than the predetermined value Sth, the right hand object  400 R is determined to have touched the operation portion  620  unintentionally, and thus an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. In this respect, in the information processing method according to at least one embodiment, determination of collision between the right hand object  400 R and the operation portion  620  is executed, whereas an effect of collision between the right hand object  400 R and the operation portion  620  is not caused when the result of determination in Step S 24 C is NO. 
     Therefore, a situation is avoided in which, when the right hand object  400 R has touched the operation portion  620  unintentionally, the operation portion  620  is pressed by the right hand object  400 R unintentionally. In this manner, further improvement of the virtual experience of the user is possible. 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 27  and  FIG. 28 .  FIG. 27  is a flowchart of an information processing method according to at least one embodiment of this embodiment.  FIG. 28  is a plan-view diagram of the virtual space  200  for illustrating a state in which the right hand object  400 R and the button object  600  are outside the visual field CV of the virtual camera  300  according to at least one embodiment. In  FIG. 27 , the information processing method according to at least one embodiment is different from the information processing method in  FIG. 25  in that the information processing method in  FIG. 27  further includes a step defined in Step S 34 C. In the following, a redundant description is not given of matters already described in the above-mentioned description. 
     In  FIG. 27 , the control unit  121  executes processing defined in Step S 30 C to Step S 32 C, and then determines whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth (Step S 33 C). The processing of from Step S 30 C to Step S 32 C corresponds to the processing of from Step S 10 C to Step S 12 C in  FIG. 25 . 
     When the result of determination in Step S 33 C is YES, the control unit  121  determines whether or not the collision area of the operation portion  620  of the button object  600  touches the collision area CA of the right hand object  400 R (Step S 35 C). On the contrary, when the result of determination in Step S 33 C is NO, the control unit  121  determines whether or not the right hand object  400 R is present in the visual field CV of the virtual camera  300  based on the visual field CV of the virtual camera  300  and the position of the right hand object  400 R (Step S 34 C). In  FIG. 28 , when the right hand object  400 R is present outside the visual field CV of the virtual camera  300 , the control unit  121  determines that the determination condition (second condition) defined in Step S 34 C is not satisfied, and ends this processing without executing the processing of Step S 35 C and Step S 36 C. That is, the control unit  121  does not execute collision determination processing defined in Step S 35 C and processing of causing a collision effect defined in Step S 36 C, and thus the right hand object  400 R does not exert a predetermined effect on the operation portion  620  of the button object  600 . The determination condition defined in Step S 34 C corresponds to a determination condition (second condition) for determining whether or not the collision area CA of the right hand object  400 R has touched the collision area of the operation portion  620  intentionally. 
     On the contrary, when the control unit  121  determines that the determination condition defined in Step S 34 C is satisfied (that is, in response to a determination that the right hand object  400 R is present in the visual field CV of the virtual camera  300 ) (YES in Step S 34 C), the control unit  121  executes the determination processing (collision determination processing) of Step S 35 C. When the result of determination in Step S 35 C is YES, the control unit  121  exerts a predetermined effect on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 36 C). On the contrary, when the result of determination in Step S 35 C is NO, the control unit  121  ends this processing without executing the processing of Step S 36 C. 
     According to at least one embodiment, as determination conditions for determining whether or not the collision area CA of the right hand object  400 R touches the collision area of the operation portion  620  intentionally, a determination is made whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Vth (Step S 33 C), and a determination is made whether or not the right hand object  400 R is present in the visual field CV of the virtual camera  300  (Step S 34 C). Further, in response to a determination that none of the determination condition of Step S 33 C and the determination condition of Step S 34 C is satisfied, the right hand object  400 R does not exert a predetermined effect on the operation portion  620 . In this manner, through use of two different determination conditions, whether or not the right hand object  400 R has touched the operation portion  620  unintentionally is more reliably determined. In particular, when the right hand object  400 R has touched the operation portion  620  under a state in which the absolute speed S of the HMD  110  is larger than the predetermined value Sth and the right hand object  400 R is not present in the visual field CV, a determination is made that the right hand object  400 R has touched the operation portion  620  unintentionally, and an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. Therefore, when the right hand object  400 R has touched the operation portion  620  unintentionally, a situation in which the operation portion  620  is pressed by the right hand object  400 R unintentionally can be avoided. In this manner, further improvement of the virtual experience of the user is possible. 
     In at least one embodiment, in Step S 34 C, the control unit  121  determines whether or not the right hand object  400 R is present in the visual field CV. Instead, the control unit  121  may determine whether or not at least one of the right hand object  400 R and the button object  600  is present in the visual field CV. In this case, when the right hand object  400 R has touched the operation portion  620  under a state in which the absolute speed S of the HMD  110  is larger than the predetermined value Vth and the right hand object  400 R and the button object  600  are both not present in the visual field CV, a determination is made that the right hand object  400 R has touched the operation portion  620  unintentionally, and an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 29 .  FIG. 29  is a flowchart of an information processing method according to at least one embodiment. In  FIG. 29 , processing of determining whether or not the collision area CA of the right hand object  400 R has touched the collision area of the operation portion  620  intentionally (determination processing defined in Step S 44  and Step S 45 ) is executed after determination of hit between the right hand object  400 R and the operation portion  620  (processing defined in Step S 43 C). In this respect, the information processing method in  FIG. 29  and the information processing method in  FIG. 27  are different from each other. In the following, only a difference from the information processing method in  FIG. 27  is described. 
     In  FIG. 29 , the control unit  121  executes processing defined in Step S 40  to Step S 42 , and then determines whether or not the collision area of the operation portion  620  of the button object  600  touches the collision area CA of the right hand object  400 R (Step S 43 ). 
     When the result of determination in Step S 43  is NO, the collision area of the operation portion  620  does not touch the collision area CA of the right hand object  400 R, and thus the control unit  121  ends this processing. On the contrary, when the result of determination in Step S 43  is YES (when the collision area of the operation portion  620  touches the collision area CA of the right hand object  400 R), the control unit  121  determines whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth (Step S 44 ). 
     When the control unit  121  determines that the absolute speed S is larger than the predetermined value Sth (NO in Step S 44 ), the control unit  121  executes determination processing defined in Step S 45 . On the contrary, when the control unit  121  determines that the absolute speed S is equal to or smaller than the predetermined value Sth (YES in Step S 44 ), the control unit  121  exerts a predetermined effect (collision effect) on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 46 ). 
     When the control unit  121  determines that the right hand object  400 R is present in the visual field CV of the virtual camera  300  (YES in Step S 45 ), the control unit  121  exerts a predetermined effect (collision effect) on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 46 ). On the contrary, when the result of determination in Step S 45  is NO, the control unit  121  ends this processing without executing the processing of Step S 46 . 
     In the information processing method according to at least one embodiment, determination of collision between the right hand object  400 R and the operation portion  620  is executed, but when none of the determination condition of Step S 44  and the determination condition of Step S 45  is satisfied, an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. 
     Therefore, a situation is avoided in which, when the right hand object  400 R has touched the operation portion  620  unintentionally, the operation portion  620  is pressed by the right hand object  400 R unintentionally. In this manner, further improvement of the virtual experience of the user is possible. 
     Now, a description is given of an information processing method according to at least one embodiment of this disclosure with reference to  FIG. 30 .  FIG. 30  is a flowchart of an information processing method according at least one embodiment of this disclosure. In  FIG. 30 , the information processing method according to at least one embodiment is different from the information processing method in  FIG. 25  in that the information processing method according to at least one embodiment further includes steps defined in Step S 51  and Step S 55 . In the following, a redundant description is not given of matters that are already described. 
     In  FIG. 30 , the control unit  121  executes processing defined in Step S 50 , and then identifies the relative speed v (refer to  FIG. 23 ) of the controller  320 R (right hand of user U) with respect to the HMD  110  (Step S 51 ). For example, as described above, the position of the HMD  110  for an n-th frame (n is an integer of 1 or more) is set to Pn, the position of the HMD  110  for an (n+1)-th frame is set to Pn+1, and a time interval between frames is set to ΔT, the absolute speed Sn of the HMD  110  for the n-th frame is Sn=|Pn+1−Pn|/ΔT. Further, when the position of the controller  320 R for an n-th frame is set to P′n, the position of the controller  320 R for an (n+1)-th frame is set to P′n+1, and a time interval between frames is set to ΔT, an absolute speed S′n of the controller  320 R for the n-th frame is S′n=|P′n+1−P′n|/ΔT. Thus, the relative speed Vn of the controller  320 R with respect to the HMD  110  for the n-th frame is Vn=S′n−Sn. In this manner, the control unit  121  can identify the relative speed Vn for an n-th frame based on the absolute speed Sn of the HMD  110  and the absolute speed S′n of the controller  320 R for an n-th frame. The control unit  121  may identify the relative speed V in the w axis direction, or may identify the relative speed V in a predetermined direction other than the w axis direction. 
     Next, the control unit  121  executes processing defined in Step S 52  and Step S 53 , and then determines whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth (Step S 54 ). 
     When the result of determination in Step S 54  is YES, the control unit  121  determines whether or not the collision area of the operation portion  620  of the button object  600  touches the collision area CA of the right hand object  400 R (Step S 56 ). On the contrary, when the result of determination in Step S 54  is NO, the control unit  121  determines whether or not the relative speed V of the controller  320 R with respect to the HMD  110  is larger than the predetermined value Vth (Step S 55 ). The predetermined value Vth (Vth≧0) can be set appropriately depending on details of content, for example, a game. When the result of determination in Step S 55  is NO, the control unit  121  ends this processing without executing processing of Step S 56  and Step S 57 . That is, the control unit  121  does not execute collision determination processing defined in Step S 56  and processing of causing a collision effect defined in Step S 57 , and thus the right hand object  400 R does not exert a predetermined effect on the operation portion  620  of the button object  600 . The determination condition defined in Step S 55  corresponds to a determination condition (second condition) for determining whether or not the collision area CA of the right hand object  400 R has touched the collision area of the operation portion  620  intentionally. 
     On the contrary, when the control unit  121  determines that the determination condition defined in Step S 55  is satisfied (that is, when it is determined that the relative speed V is larger than the predetermined value Vth) (YES in Step S 55 ), the control unit  121  executes the determination processing (collision determination processing) of Step S 56 . When the result of determination in Step S 56  is YES, the control unit  121  exerts a predetermined effect on the operation portion  620  touching the collision area CA of the right hand object  400 R (Step S 57 ). On the contrary, when the result of determination in Step S 56  is NO, the control unit  121  ends this processing without executing the processing of Step S 57 . 
     According to at least one embodiment, as determination conditions for determining whether or not the collision area CA of the right hand object  400 R touches the collision area of the operation portion  620  intentionally, whether or not the absolute speed S of the HMD  110  is equal to or smaller than the predetermined value Sth is determined (Step S 54 ), and whether or not the relative speed V of the controller  320 R with respect to the HMD  110  is larger than the predetermined value Vth is determined (Step S 55 ). Further, in response to a determination that none of the determination condition of Step S 54  and the determination condition of Step S 55  is satisfied, the right hand object  400 R does not exert a predetermined effect on the operation portion  620 . In this manner, through use of two different determination conditions, it is possible to more reliably determine whether or not the right hand object  400 R has touched the operation portion  620  unintentionally. In particular, when the right hand object  400 R has touched the operation portion  620  under a state in which the absolute speed S of the HMD  110  is larger than the predetermined value Vth and the relative speed v of the controller  320 R with respect to the HMD  110  is larger than the predetermined value Vth, the right hand object  400 R is determined to have touched the operation portion  620  unintentionally, and an effect of collision between the right hand object  400 R and the operation portion  620  is not caused. Therefore, when the right hand object  400 R has touched the operation portion  620  unintentionally, a situation in which the operation portion  620  is pressed by the right hand object  400 R unintentionally can be avoided. In this manner, further improvement of the virtual experience of the user is possible. 
     The above description of embodiments is not to be read as a restrictive interpretation of the technical scope of this disclosure. The embodiments are merely given as an example, and is to be understood by a person skilled in the art that various modifications can be made to the embodiments within the scope of this disclosure set forth in the appended claims. Thus, the technical scope of this disclosure is to be defined based on the scope of this disclosure set forth in the appended claims and an equivalent scope thereof. 
     In the above described embodiments, the movement of the hand object is controlled based on the movement of the external controller  320  representing the movement of the hand of the user U, but the movement of the hand object in the virtual space may be controlled based on the movement amount of the hand of the user U. For example, instead of using the external controller, a glove-type device or a ring-type device to be worn on the hand or fingers of the user may be used. With this, the position sensor  130  can detect the position and the movement amount of the hand of the user U, and can detect the movement and the state of the hand and fingers of the user U. Further, the position sensor  130  may be a camera configured to take an image of the hand (including the fingers) of the user U. In this case, by taking an image of the hand of the user with use of a camera, the position and the movement amount of the hand of the user U can be detected, and the movement and the state of the hand and fingers of the user U can be detected based on data of the image in which the hand of the user is displayed, without wearing any kind of device directly on the hand or fingers of the user. 
     Further, in the above described embodiments, there is set a collision effect for defining the effect to be exerted on the wall object by the hand object based on the position and/or movement of the hand, which is a part of the body of the user U other than the head, but the embodiments are not limited thereto. For example, there may be set a collision effect for defining, based on a position and/or movement of a foot of the user U being a part of the body of the user U other than the head, an effect to be exerted on a target object by a foot object (example of operation object), which is synchronized with the movement of the foot of the user U. As described above, in the embodiments, there may be set a collision effect for identifying a relative relationship (distance and relative speed) between the HMD  110  and a part of the body of the user U, and defining the effect to be exerted on a target object by the operation object, which is synchronized with the part of the body of the user U, based on the identified relative relationship. 
     Further, in the above described embodiments, the wall object  500  is described as an example of a target object that the hand object exerts a predetermined effect on, but the attribute of a target object is not particularly limited. Further, an appropriate condition may be set as a condition for moving the virtual camera  300  other than a condition on collision between the hand object  400  and the wall object  500 . For example, when a predetermined finger of the hand object  400  is directed to the wall object  500  for a predetermined period of time, the virtual camera  300  may be moved as well as the counter part  510  of the wall object  500 . In this case, as in  FIG. 2 , through setting of three axes for the hand of the user U as well and definition of the roll axis as a finger pointing direction, providing the user U with an intuitive object operation and a moving experience in the VR space is possible. 
     In Non-Patent Document 1, there is no disclosure of setting a predetermined effect that is exerted on a predetermined object in the VR space in accordance with movement of the user in the real space. In particular, in Non-Patent Document 1, there is no disclosure of changing an effect (hereinafter referred to as “collision effect”) for defining an effect that is exerted on a virtual object (target object) by a hand object due to collision between the hand object and the virtual object in accordance with movement of the hand of the user. Therefore, there is room for improvement of experience in a VR space, an augmented reality (AR) space, and a mixed reality (MR) space of the user by improving the effect that is exerted on the virtual object in accordance with movement of the user. 
     (1) An information processing method to be executed in a system including a head-mounted device and a position sensor configured to detect a position of the head-mounted device and a position of a part of a body other than a head of a user. The information processing method includes generating virtual space data for defining a virtual space that includes a virtual camera, an operation object, and a target object. The method further includes updating a visual field of the virtual camera in accordance with movement of the head-mounted device. The method further includes generating visual-field image data based on the visual field of the virtual camera and the virtual space data. The method further includes displaying a visual-field image on the head-mounted device based on the visual-field image data. The method further includes moving the operation object in accordance with movement of the part of the body of the user. The method further includes identifying a relative relationship between the head-mounted device and the part of the body of the user. The method further includes setting a collision effect for defining an effect that is exerted by the operation object on the target object depending on the identified relative relationship. 
     According to the above-mentioned method, the collision effect is set depending on the relative relationship between the head-mounted device and the part (excluding the head of the user) of the body of the user, and thus further improvement of the experience (hereinafter referred to as “virtual experience”) of the user for the virtual object (target object) is possible. 
     (2) An information processing method according to Item (1), in which the setting of the collision effect includes setting a size of a collision area of the operation object depending on the identified relative relationship. The setting of the collision effect further includes exerting an effect on the target object depending on a positional relationship between the collision area of the operation object and the target object. 
     According to the above-mentioned method, the size of the collision area of the operation object is set depending on the relative relationship between the head-mounted device and the part (excluding the head of the user) of the body of the user, and in addition, an effect is exerted on the target object depending on the positional relationship between the collision area of the operation object and the target object. In this manner, further improvement of the virtual experience is possible. 
     (3) An information processing method according to Item (1) or (2), in which the identifying of the relative relationship includes a step of identifying a relative positional relationship between the head-mounted device and the part of the body of the user. The setting of the collision effect includes setting the collision effect depending on the identified relative positional relationship. 
     According to the above-mentioned method, the collision effect is set depending on the relative relationship between the head-mounted device and the part (excluding the head of the user) of the body of the user, and thus further improvement of the virtual experience is possible. 
     (4) An information processing method according to Item (3), 
     in which the identifying of the relative relationship includes a step of identifying a distance between the head-mounted device and the part of the body of the user. The setting of the collision effect includes setting the collision effect depending on the identified distance. 
     According to the above-mentioned method, the collision effect is set depending on the distance between the head-mounted device and the part (excluding the head of the user) of the body of the user, and thus further improvement of the virtual experience is possible. 
     (5) An information processing method according to Item (1) or (2), 
     in which the identifying of the relative relationship includes a step of identifying a relative speed of the part of the body of the user with respect to the head-mounted device. The setting of the collision effect includes setting the collision effect depending on the identified relative speed. 
     According to the above-mentioned method, the collision effect is set depending on the relative speed of the part (excluding the head of the user) of the body of the user with respect to the head-mounted device, and thus further improvement of the virtual experience is possible. 
     (6) An information processing method according to Item (4), 
     in which the identifying of the relative relationship includes a step of identifying a relative speed of the part of the body of the user with respect to the head-mounted device. The setting of the collision effect includes setting the collision effect depending on the identified distance and the identified relative speed. 
     According to the above-mentioned method, the collision effect is set depending on the distance between the head-mounted device and the part (excluding the head of the user) of the body of the user and the relative speed of the part of the body of the user with respect to the head-mounted device, and thus further improvement of the virtual experience is possible. 
     (7) An information processing method according to Item (1) or (2), 
     in which the identifying of the relative relationship further includes a step of identifying a relative acceleration of the part of the body of the user with respect to the head-mounted device. The setting of the collision effect includes setting the collision effect depending on the identified relative acceleration. 
     According to the above-mentioned method, the collision effect is set depending on the relative acceleration of the part (excluding the head of the user) of the body of the user with respect to the head-mounted device, and thus further improvement of the virtual experience is possible. 
     (8) An information processing method according to Item (4), 
     in which the identifying of the relative relationship further includes a step of identifying a relative acceleration of the part of the body of the user with respect to the head-mounted device. The setting of the collision condition includes setting the collision effect depending on the identified distance and the identified relative acceleration. 
     According to the above-mentioned method, the collision effect is set depending on the distance between the head-mounted device and the part (excluding the head of the user) of the body of the user and the relative acceleration of the part of the body of the user with respect to the head-mounted device, and thus further improvement of the virtual experience is possible. 
     (9) A system for executing the information processing method of any one of Items (1) to (8). 
     Providing a system capable of further improving the virtual experience is possible. 
     In Non-Patent Document 1, there is no disclosure of setting a predetermined effect that is exerted on a predetermined object in the VR space in accordance with movement of the user in the real space. In particular, in Non-Patent Document 1, there is no disclosure of changing an effect (hereinafter referred to as “collision effect”) for defining an effect that is exerted on a virtual object (target object) by a hand object due to collision between the hand object and the virtual object in accordance with movement of the hand of the user. Therefore, there is room for improvement of experience in the VR space, the augmented reality (AR) space, and the mixed reality (MR) space of the user by improving the effect that is exerted on the virtual object in accordance with movement of the user. 
     (10) An information processing method to be executed in a system including a head-mounted device and a position sensor configured to detect a position of the head-mounted device and a position of a part of a body other than a head of a user. The information processing method includes generating virtual space data for defining a virtual space that includes a virtual camera, an operation object, and a target object. The method further includes updating a visual field of the virtual camera in accordance with movement of the head-mounted device. The method further includes generating visual-field image data based on the visual field of the virtual camera and the virtual space data. The method further includes displaying a visual-field image on the head-mounted device based on the visual-field image data. The method further includes moving the operation object in accordance with movement of the part of the body of the user. The method further includes setting a collision effect for defining an effect that is exerted by the operation object on the target object depending on an absolute speed of the head-mounted device. Setting the collision effect includes setting the collision effect as a first collision effect when the absolute speed of the head-mounted device is equal to or smaller than a predetermined value. Setting the collision effect further includes setting the collision effect as a second collision effect different from the first collision effect when the absolute speed of the head-mounted device is larger than the predetermined value. 
     According to the above-mentioned method, the collision effect is set depending on the absolute speed of the head-mounted device. In particular, when the absolute speed of the head-mounted device is equal to or smaller than the predetermined value, the collision effect is set as the first collision effect, whereas when the absolute speed of the head-mounted device is larger than the predetermined value, the collision effect is set as the second collision effect. In this manner, further improvement of the experience (hereinafter referred to as “virtual experience”) of the user for the virtual object (target object) is possible. 
     (11) An information processing method according to Item 10, wherein setting the collision effect as the first collision effect includes setting, when the absolute speed of the head-mounted device is equal to or smaller than the predetermined value, a size of a collision area of the operation object to a first size. Setting the collision effect as the first collision effect includes exerting an effect on the target object depending on a positional relationship between the collision area of the operation object and the target object. Setting the collision effect as the second collision effect includes setting, when the absolute speed of the head-mounted device is larger than the predetermined value, the size of the collision area of the operation object to a second size different from the first size. Setting the collision effect as the second collision includes exerting an effect on the target object depending on the positional relationship between the collision area of the operation object and the target object. 
     According to the above-mentioned method, the size of the collision area of the operation object is set depending on the absolute speed of the head-mounted device. In particular, when the absolute speed of the head-mounted device is equal to or smaller than the predetermined value, the size of the collision area of the operation object is set to the first size. On the contrary, when the absolute speed of the head-mounted device is larger than the predetermined value, the size of the collision area of the operation object is set to the second size. Further, an effect is exerted on the target object depending on the positional relationship between the collision area of the operation object and the target object. In this manner, further improvement of the virtual experience is possible. 
     (12) An information processing method according to Item (10) or (11), further including identifying a relative speed of the part of the body of the user with respect to the head-mounted device. The setting of the collision effect includes setting the collision effect depending on the identified absolute speed of the head-mounted device and the identified relative speed. 
     According to the above-mentioned method, the collision effect is set depending on the absolute speed of the head-mounted device and the relative speed of the part (excluding the head of the user) of the body of the user with respect to the head-mounted device, and thus further improvement of the virtual experience is possible. 
     (13) An information processing method according to Item (10) or (11), further including identifying a relative acceleration of the part of the body of the user with respect to the head-mounted device. The setting of the collision effect includes setting the collision effect depending on the identified absolute speed of the head-mounted device and the identified relative acceleration. 
     According to the above-mentioned method, the collision effect is set depending on the absolute speed of the head-mounted device and the relative acceleration of the part (excluding the head of the user) of the body of the user with respect to the head-mounted device, and thus it is possible to further improve the virtual experience. 
     (14) A system for executing the information processing method of any one of Items (10) to (13). 
     Providing a system capable of further improving the virtual experience is possible. 
     In Non-Patent Document 1, the visual-field image presented on the HMD changes in accordance with movement of the head-mounted device in the real space. In this case, the user needs to move in the real space or perform input for designating a movement destination on a device, for example, a controller, in order for the user to reach a desired object in the VR space. 
     (20) 
     An information processing method to be executed by a computer configured to control a system including a head-mounted device and a position sensor configured to detect a position of the head-mounted device and a position of a part of a body other than a head of a user. The information processing method includes identifying virtual space data for defining a virtual space that includes a virtual camera, an operation object, and a target object. The method further includes moving the virtual camera in accordance with movement of the head-mounted device. The method further includes moving the operation object in accordance with movement of the part of the body. The method further includes moving the virtual camera without association with movement of the head-mounted device when the operation object and the target object satisfy a predetermined condition. The method further includes defining a visual field of the virtual camera based on movement of the virtual camera and generating visual-field image data based on the visual field and the virtual space data. The method further includes displaying a visual-field image on the head-mounted device based on the visual-field image data. 
     According to the information processing method of this item, when the operation object and the target object, which move in accordance with movement of the part of the body of the user, satisfy the predetermined condition, automatically moving the virtual camera is possible. With this, the user can recognize movement in the VR space that conforms to the intention of the user, and the virtual experience can be improved. 
     (Item 21) 
     A method according to Item 20, in which the moving of the virtual camera includes moving the operation object in accordance with movement of the virtual camera so that a relative positional relationship between the head-mounted device and the part of the body is maintained. 
     According to the information processing method of this item, the user can continue virtual experience using the operation object without feeling strange also after movement. With this, the virtual experience can be improved. 
     (Item 22) 
     A method according to Item 20 or 21, in which the predetermined condition includes touch between the operation object and the target object. 
     According to the information processing method of this item, the user can move in the VR space in accordance with the intention of the user. 
     (Item 23) 
     A method according to Item 22, 
     in which the moving of the virtual camera includes a step of processing a counter part of the target object, which is opposed to the virtual camera, based on the touch so that the counter part becomes away from the virtual camera. The method further includes moving the virtual camera so that the virtual camera approaches the counter part and the operation object does not touch the target object when the operation object is moved in accordance with movement of the virtual camera so as to keep a relative positional relationship between the head-mounted device and the part of the body. 
     According to the information processing method of this item, preventing occurrence of movement in the VR space that is not intended by the user due to the fact that the operation object has touched the target object after movement is possible. 
     (Item 24) 
     A method according to Item 22 or 23, in which the moving of the virtual camera includes moving the virtual camera in a direction of extension of a visual axis of the virtual camera at a time when the operation object and the target object have touched each other. 
     According to the information processing method of this item, the virtual camera is moved in a front direction of the user in the VR space, and thus preventing visually induced motion sickness (so-called VR sickness), which may be caused at the time of movement of the virtual camera is possible. 
     (Item 25) 
     A method according to Item 24, further including reducing a distance for which the virtual camera is moved as a position at which the operation object and the target object have touched each other becomes more away from the visual axis of the virtual camera. 
     According to the information processing method of this item, preventing occurrence of movement in the VR space that is not intended by the user due to the fact that the operation object has touched the target object after movement is possible. 
     (Item 26) 
     A method according to anyone of Items 22 to 25, further including avoiding moving the virtual camera when the position at which the operation object and the target object have touched each other is outside the visual field of the virtual camera. 
     According to the information processing method of this item, preventing occurrence of movement in the VR space that is not intended by the user is possible. 
     (Item 27) 
     A system for executing the method of any one of Items 20 to 26. 
     In the VR game disclosed in Non-Patent Document 1, an object may operate erroneously due to the hand object touching the object unintentionally during an operation of the hand object. 
     (30) An information processing method to be executed by a computer in a system including a head-mounted device and a position sensor configured to detect a position of the head-mounted device and a position of a part of a body other than a head of a user. The information processing method includes generating virtual space data for defining a virtual space that includes a virtual camera, an operation object, and a target object. The method further includes identifying a visual field of the virtual camera based on a position and an inclination of the head-mounted device. The method further includes displaying a visual-field image on the head-mounted device based on the visual field of the virtual camera and the virtual space data. The method further includes identifying a position of the operation object based on the position of the part of the body of the user. The method further includes avoiding causing the operation object to exert a predetermined effect on the target object when a predetermined condition for determining whether or not a collision area of the operation object has touched a collision area of the target object intentionally is not satisfied. 
     According to the above-mentioned method, when the predetermined condition for determining whether or not the collision area of the operation object has touched the collision area of the target object intentionally is not satisfied, the operation object does not exert a predetermined effect on the target object. In this manner, when the operation object is determined to have been touched the target object unintentionally, an effect of collision between the operation object and the target object does not occur. For example, a situation is avoided in which, when the hand object (example of operation object) has touched the button object (example of target object) unintentionally, the button object is pressed by the hand object unintentionally. Therefore, providing the information processing method capable of further improving the virtual experience of the user is possible. 
     (31) An information processing method according to Item (30), further including identifying an absolute speed of the head-mounted device, in which the predetermined condition specifies that the absolute speed of the head-mounted device is equal to or smaller than a predetermined value. 
     According to the above-mentioned method, when the absolute speed of the head-mounted device (HMD) is not equal to or smaller than the predetermined value (that is, absolute speed of HMD is larger than predetermined value), the operation object does not exert a predetermined effect on the target object. In this manner, when the operation object has touched the target object with the absolute speed of the HMD being larger than the predetermined value, the operation object is determined to have touched the target object unintentionally, and an effect of collision between the operation object and the target object does not occur. 
     (32) An information processing method according to Item (30) or (31), in which the predetermined condition includes a first condition and a second condition. The first condition is a condition on the head-mounted device. The second condition is a condition different from the first condition. The information processing method further includes avoiding causing the operation object to exert the predetermined effect on the target object when the first condition and the second condition are not satisfied. 
     According to the above-mentioned method, when the first condition and the second condition for determining whether or not the collision area of the operation object has touched the collision area of the target object intentionally are not satisfied, the operation object does not exert a predetermined effect on the target object. In this manner, reliably determining whether or not the operation object has touched the target object unintentionally by using two determination conditions different from each other is possible. 
     (33) An information processing method according to Item (32), further including identifying an absolute speed of the head-mounted device. The first condition specifies that the absolute speed of the head-mounted device is equal to or smaller than a predetermined value. The second condition specifies that the operation object is in the visual field of the virtual camera. 
     According to the above-mentioned method, when the absolute speed of the head-mounted device (HMD) is not equal to or smaller than the predetermined value (that is, absolute speed of HMD is larger than predetermined value) and that the operation object is outside the visual field of the virtual camera, the operation object does not exert a predetermined effect on the target object. In this manner, when the operation object has touched the target object with the absolute speed of the HMD being larger than the predetermined value and with the operation object being outside the visual field of the virtual camera, the operation object is determined to have touched the target object unintentionally, and an effect of collision between the operation object and the target object does not occur. 
     (34) An information processing method according to Item (32), further including identifying an absolute speed of the head-mounted device. The first condition specifies that the absolute speed of the head-mounted device is equal to or smaller than a predetermined value. The second condition specifies that at least one of the operation object and the target object is in the visual field of the virtual camera. 
     According to the above-mentioned method, when the absolute speed of the head-mounted device (HMD) is not equal to or smaller than the predetermined value (that is, absolute speed of HMD is larger than predetermined value) and that both of the operation object and the target object are outside the visual field of the virtual camera, the operation object does not exert a predetermined effect on the target object. In this manner, when the operation object has touched the target object with the absolute speed of the HMD being larger than the predetermined value and with both of the operation object and the target object being outside the visual field of the virtual camera, the operation object is determined to have touched the target object unintentionally, and an effect of collision between the operation object and the target object does not occur. 
     (35) An information processing method according to Item (32), further including identifying an absolute speed of the head-mounted device. The method further includes identifying a relative speed of the part of the body of the user with respect to the head-mounted device. The first condition specifies that the absolute speed of the head-mounted device is equal to or smaller than a predetermined value. The second condition specifies that the relative speed is larger than a predetermined value. 
     According to the above-mentioned method, the operation object does not exert a predetermined effect on the target object when the absolute speed of the head-mounted device (HMD) is not equal to or smaller than the predetermined value (that is, absolute speed of HMD is larger than predetermined value) and that the relative speed of the part of the body of the user with respect to the HMD is not larger than the predetermined value (that is, relative speed of part of body of user with respect to HMD is equal to or smaller than predetermined value). In this manner, when the operation object has touched the target object with the absolute speed of the HMD being larger than the predetermined value and with the relative speed of the part of the body of the user being equal to or smaller than the predetermined value, the operation object is determined to have touched the target object unintentionally, and an effect of collision between the operation object and the target object does not occur. 
     (36) A system for executing the information processing method of any one of Items (30) to (35). 
     According to the above-mentioned system, further improvement of the virtual experience of the user is possible.