Patent Publication Number: US-7724250-B2

Title: Apparatus, method, and program for processing information

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an apparatus, a method, and a program for processing information and, more particularly, to an apparatus, a method, and a program for processing information which allow a user to deal with information associated with 3-dimensional virtual space in an easy and intuitive manner. 
   In recent years, great advances in information processing technology have been achieved, and it has become possible to easily represent and use a 3-dimensional virtual space via computer graphics (CG) using a general-purpose information processing apparatus, such as a personal computer, without necessitating a special computer. 
   Also, in recent years, great advances in information communication technology have been achieved, whereby it has become possible to easily share and/or distribute data among a number of clients (for example, information processing apparatuses) by using a server on a network such as the Internet. 
   Furthermore, in recent years, a combination of information processing technology and information communication technology has made it possible to share data in a 3-dimensional virtual space built on a server by a number of clients (a specific example may be found, for example, in Japanese Unexamined Patent Application Publication No. 2002-279284). Various kinds of service using such a technique are provided. 
   A coordinate system in a 3-dimensional virtual space represented by CG is generally set by a developer who has implemented the 3-dimensional virtual space on a server or the like. When a user manipulates an object in such a 3-dimensional virtual space using a particular input device, the manipulation is performed on the basis of the coordinate system predefined by the developer. 
   However, when the developer sets the coordinate system in the 3-dimensional virtual system, almost nothing associated with a real space, in which the user operates the input device, is taken into account. As a result, the user has to manipulate an object in the 3-dimensional virtual space via an unintuitive interface. This makes it very difficult to manipulate the object. 
   More specifically, when a mouse connected to a personal computer is used as the input device to manipulate the object in the 3-dimensional virtual space, the distance of movement of a mouse pointer (in the 3-dimensional virtual space) displayed on a screen is, in general, very different from the distance by which the mouse is actually moved in the real space. 
   For example, the user cannot intuitively predict how much to move the mouse in the real space in order to move the mouse pointer by a desired distance on the screen (for example from one end of the screen to the opposite end), in the 3-dimensional virtual space. Thus, the user has to learn how much to move the mouse to achieve desired motion of the mouse pointer by trying to move the mouse many times. 
   Besides, because of a difference between a view point in the 3-dimensional virtual space and a view point in the real space (in general, the view point is arbitrarily set in the 3-dimensional virtual space), the user cannot intuitively predict how to move the mouse in order to move the mouse pointer into a desired direction. Thus, the user has to try to move the mouse many times. 
   It is known that human eyes are poor in ability of recognition in a direction (depth direction) directly away from a view point. Therefore, when an image representing a 3-dimensional virtual space is displayed on a 2-dimensional screen of a display such as a CRT (Cathode Ray Tube), it is very difficult for the user to achieve intuitive recognition in a direction directly away from view point in the 3-dimensional virtual space. In other words, it is very difficult to display an image representing a 3-dimensional virtual space on a 2-dimensional screen of a display such that the user can achieve intuitive recognition in a direction away from a view point in the 3-dimensional virtual space. 
   In many cases, in conventional application software based on a 3-dimensional CG model (such as “3ds max” whose description may be found, for example, on Web page “http://www.discreetjp/products/max5/index_max5.htm” (which is accessible as of Nov. 8, 2002)), a 3-dimensional virtual space including an object is displayed via a three-view drawing. That is, the 3-dimensional virtual space including the object is displayed in a front view, a top view, and a side view. This technique allows a user to achieve recognition in a direction away from a view point in the 3-dimensional virtual space. 
   However, in the three-view drawing, it is necessary to display at least three views including the front view, the top view, and the side view on the single screen (that is, the screen is divided into three parts). Such a manner of displaying an object is unnatural. Besides, recognition in a direction away from a view point is not intuitive, although recognition is possible by analyzing all three views. 
   SUMMARY OF THE INVENTION 
   In view of the above, it is an object of the present invention to provide a technique that allows a user to easily and intuitively deal with information in a 3-dimensional virtual space. 
   The present invention provides an information processing apparatus for controlling the display of an image in a 3-dimensional virtual space, which includes a setting part for setting a first coordinate system in a real space including a first real object on the basis of pre-input information associated with the first real object and for setting a second coordinate system in the 3-dimensional virtual space corresponding to the real space on the basis of the first coordinate system, a construction part for constructing the 3-dimensional virtual space using the second coordinate system set by the setting part, and a display control part for controlling the display of an image corresponding to the 3-dimensional virtual space constructed by the construction part. 
   In this information processing apparatus, the first real object may be a real object whose cross-sectional area is greater, at least in a predetermined direction, than a predetermined value. 
   The first real object may be a sheet-shaped real object or a stack of sheet-shaped real objects. 
   The information processing apparatus may further include an input part for inputting specification information specifying the position and the angle of a particular virtual object in the 3-dimensional virtual space, and a determination part for determining the position and the angle, in the second coordinate system, of the virtual object on the basis of the specification information input via the input part, wherein the construction part may construct the 3-dimensional virtual space including the virtual object disposed at the position and the angle in the second coordinate system determined by the determination means. 
   In this information processing apparatus, if a second real object corresponding to the virtual object is placed in the real space, the input part may measure the position and the angle of the second real object in the real space using a third coordinate system different from the first coordinate system and may input the measurement result as the specification information, the determination part may convert the coordinates of the position and the angle, input via the input part, of the second real object from the third coordinate system into the second coordinate system and may employ the position and the angle of the second real object converted in the second coordinate system as the position and the angle of the virtual object in the second coordinate system. 
   The input part may use at least a part of the input part itself as the second real object. 
   The input part may use, as the second real object, a real object having a feature similar to a particular feature of the virtual object. 
   The construction part may construct the 3-dimensional virtual space such that the image displayed under the control of the display control part includes at least a virtual region corresponding to the first real object. 
   The present invention also provides an information processing method for controlling the display of an image in a 3-dimensional virtual space, which includes the steps of setting a first coordinate system in a real space including a real object on the basis of pre-input information associated with the real object and setting a second coordinate system in the 3-dimensional virtual space corresponding to the real space on the basis of the first coordinate system, constructing the 3-dimensional virtual space using the second coordinate system set in the setting step, and controlling the display of an image corresponding to the 3-dimensional virtual space constructed in the constructing step. 
   The present invention also provides a program for causing a computer to execute a process of controlling the display of an image in a 3-dimensional virtual space, the process including the steps of setting a first coordinate system in a real space including a real object on the basis of pre-input information associated with the real object and setting a second coordinate system in the 3-dimensional virtual space corresponding to the real space on the basis of the first coordinate system, constructing the 3-dimensional virtual space using the second coordinate system set in the setting step, and controlling the display of an image corresponding to the 3-dimensional virtual space constructed in the constructing step. 
   In the apparatus, method, and program for processing information according to the present invention, a first coordinate system in a real space including a real object is set on the basis of pre-input information associated with the real object, and a second coordinate system in a 3-dimensional virtual space corresponding to the real space is set on the basis of the first coordinate system. The 3-dimensional virtual space is constructed using the second coordinate system, and an image corresponding to the constructed 3-dimensional virtual space is displayed. 
   The display for displaying the image under the control of the information processing apparatus according to the present invention may be disposed on the information processing apparatus itself or may be disposed separately on the outside of the information processing apparatus. Similarly, the input device for inputting information to the information processing apparatus according to the present invention may be disposed in the information processing apparatus itself or may be disposed separately on the outside of the information processing apparatus. 
   Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a block diagram showing an example of a hardware configuration of an information processing apparatus according to an embodiment of the present invention. 
       FIG. 2  is a diagram showing an example of an outward appearance of the information processing apparatus shown in  FIG. 1 . 
       FIG. 3  is a block diagram showing an example of a software configuration of the information processing apparatus shown in  FIG. 1 . 
       FIG. 4  is a flow chart showing an example of a control process in displaying a 3-dimensional image by the information processing apparatus shown in  FIG. 3 . 
       FIG. 5  is a flow chart showing an example of a control process in displaying a 3-dimensional image by the information processing apparatus shown in  FIG. 3 . 
       FIG. 6  is a diagram showing a coordinate system of a real space defined with reference to a real object by the information processing apparatus shown in  FIG. 3 . 
       FIG. 7  is a diagram showing a coordinate system of a 3-dimensional virtual space defined on the basis of the coordinate system of the real space shown in  FIG. 6  by the information processing apparatus shown in  FIG. 3 . 
       FIG. 8  is a diagram showing an example of a manner in which a 3-dimensional virtual space constructed on the basis of the coordinate system shown in  FIG. 7  is displayed. 
       FIG. 9  is a diagram showing an example of a displayed 3-dimensional virtual space reconstructed by placing an object in the 3-dimensional virtual space shown in  FIG. 8 , wherein an input device corresponding to the object placed in the 3-dimensional virtual space is placed by a user at a particular position with reference to a real object. 
       FIG. 10  is a diagram showing an example of a displayed 3-dimensional virtual space reconstructed by placing an object in the 3-dimensional virtual space shown in  FIG. 8 , wherein the input device is placed by the user at a position different from that shown in  FIG. 9  with reference to a real object. 
       FIG. 11  is a diagram showing an example of a displayed 3-dimensional virtual space constructed by the information processing apparatus shown in  FIG. 3 , wherein a book is used as the real object. 
       FIG. 12  is a diagram showing an example of a displayed 3-dimensional virtual space constructed by the information processing apparatus shown in  FIG. 3 , wherein a combination of a model and a board is used as the real object. 
       FIG. 13  a diagram showing an example of a displayed 3-dimensional virtual space constructed by the information processing apparatus shown in  FIG. 3 , wherein a model is used as the real object. 
       FIG. 14  is a diagram showing another example of the outward appearance of the information processing apparatus shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the hardware construction of an information processing apparatus according to an embodiment of the present invention. 
   As shown in  FIG. 1 , the information processing apparatus  1  includes an input unit  11 , a main controller  12 , and a display  13 . The information processing apparatus  1  is used in conjunction with a real object  14 . 
   In the present embodiment, for example, the main controller  12  constructs a 3-dimensional virtual space on the basis of particular information (for example, information indicating the shape, the position, and/or the angle) of the real object  14  and the main controller  12  displays, on the display  13 , an image corresponding to the constructed 3-dimensional virtual space. When the user operates the input unit  11 , the main controller  12  changes the position and/or the angle of a particular 3-dimensional virtual object (hereinafter, referred to simply as an object) in the 3-dimensional virtual space (that is, the main controller  12  reconstructs the 3-dimensional virtual space) in accordance with the operation performed by the user, and the main controller  12  displays a corresponding image on the display  13 . The purpose or use of the information processing apparatus  1  is not limited to that in the present embodiment, but may be used for various purposes in which a coordinate system of a 3-dimensional virtual space defined in a manner described later is used. 
   The input unit  11  has a first capability, as one of many basic capabilities, of inputting specification information indicating the position and the angle of an object in the 3-dimensional virtual space to the main controller  12 . By using the first capability of the input unit  11 , the user can freely move an object within the 3-dimensional virtual space. 
   In other words, the input unit  11  is not limited to any special type, as long as it has the capability of inputting specification information indicating the position and the angle of an object in the 3-dimensional virtual space to the main controller  12 . For example, the input unit  11  may be embodied as a 3-dimensional position/angle sensor. More specifically, a 3-dimensional position/angle sensor of the magnetic, optical, ultrasonic, or mechanical type can be used as the input unit  11 . As a matter of course, the input unit  11  is not limited to the 3-dimensional position/angle sensor, but another type input device such as an on/off input device (for example, a keyboard or a mouse) or a 2-dimensional position input device may be used. 
   In the present embodiment, as described later, at least two different coordinate systems including a 3-dimensional coordinate system in a real space (for example, a coordinate system (rx, ry, rz) in a real space  31  described later with reference to  FIG. 6 ) and a coordinate system that defines a 3-dimensional virtual space (for example, a coordinate system (vx, vy, vz) in a 3-dimensional virtual space  32  described later with reference to  FIG. 7 ) are used by the information processing apparatus  1 . The correspondence between those two coordinate systems is defined on the basis of particular information (for example, shape, position, angle, etc.) associated with the real object  14 . 
   For the above reason, it is necessary to input the information associated with the real object  14  to the main controller  12  before the two coordinate systems are defined. For the above purpose, the input unit  11  has, in addition to the first capability described above, a second capability of inputting necessary data to the main controller  12  so that the user can input information associated with the real object  14  to the main controller  12  by using the second capability of the input unit  11 . 
   Herein, an input device included in the input unit  11  and having the first capability may further include the second capability described above (that is, the input unit  11  is formed of a single input device) or another input device having the second capability may be disposed in the input unit  11  in addition to the input device having the first capability. More specifically, an imaging device such as a camera can be used as the input device having the second capability. For example, the image of the real object  14  is taken by a camera, and the resultant image data of the real object  14  is processed by the main controller  12  thereby acquiring the information associated with the real object  14 . As described above, the input unit  11  does not necessarily need to be formed of a single input device, but may be arbitrarily configured using an arbitrary number of devices, as long as the first and second capabilities are achieved. 
   In a case in which the shape or the like of the real object  14  has already been given, values indicating the shape may be input as the information associated with the real object  14  to the information processing apparatus  1  before the information processing apparatus  1  is used by a user (for example, before the information processing apparatus  1  is shipped). In this case, the input unit  11  does not need to have the second capability of inputting information associated with the real object  14 . In a case in which the information processing apparatus  1  is used only to define the coordinate systems, the first capability is also unnecessary. In this case, the information processing apparatus  1  does not necessarily need to include the input unit  11 . 
   The data that is input using the second capability is not limited to the above-described information associated with the real object  14 . For example, in the present embodiment, and as further described later, an image representing a scene seen from a particular view point in the 3-dimensional virtual space is displayed on the display  13 . Therefore, information indicating the view point may be input to the main controller  12  by using the second capability. 
   The main controller  12  is formed of, for example, a main part of a personal computer (part of a personal computer other than an input device such as a keyboard and an output device such as a display). The main controller  12  performs a transform between different coordinate systems and constructs a 3-dimensional virtual space. The main controller  12  further produces an image signal representing the constructed 3-dimensional virtual space and outputs the resultant image signal to the display  13 . 
   In the main controller  12 , a CPU (Central Processing Unit)  21  performs various kinds of processing in accordance with programs stored in a ROM (Read Only Memory)  22  or programs loaded into a RAM (Random Access Memory)  23  from a storage unit  26 . The RAM  23  is also used to store data used by the CPU  21  in performing various kinds of processing. 
   The CPU  21 , the ROM  22 , and the RAM  23  are connected with each other via a bus  24 . The bus  24  is also connected with an input/output interface  25 . 
   The input unit  11  described above and the display  13  described later are connected with the input/output interface  25 . 
   The input/output interface  25  is also connected with the storage unit  26  including a hard disk or the like and with a communication unit  27  for communication with another information processing apparatus (not shown) via a network such as the Internet. 
   Furthermore, the input/output interface  25  is also connected with a drive  28 , as required. A removable storage medium  29  such as a magnetic disk, an optical disk, a magnetooptical disk, or a semiconductor memory is mounted on the drive  28  as required, and a computer program is read from the removable storage medium  29  and installed into the storage unit  26 , as required. 
   As for the display  13 , a CRT (Cathode Ray Tube) display, a liquid crystal display, or a projector is used. The display  13  is used to display an image corresponding to the 3-dimensional virtual space in accordance with data output from the main controller  12 . 
   The real object  14  serves as a reference object used by the main controller  12  in constructing a 3-dimensional virtual space. The real object  14  is an object that actually exists in the real space. The material of the real object  14  is not limited to a particular one, as long as the real object  14  has a finite area when viewed from above (that is, as long as the real object  14  has a cross section, taken in a horizontal plane, greater than a predetermined area). More specifically, a sheet, a book, or a diorame model may be used as the real object  14 . 
   As described earlier, various coordinate systems are set in accordance with information associated with the real object  14 . Therefore, after the information associated with the real object  14  is been input, it is required that the real object  14  be placed at the position and the angle that are employed when the information associated with the real object  14  is input. 
     FIG. 2  shows an example of a construction of the information processing apparatus  1 . 
   In the example shown in  FIG. 2 , an object in the form of a sheet is employed as the real object  14 . The main part of a desktop personal computer is used as the main controller  12 . The main controller  12  constructs a 3-dimensional virtual space  32  on the basis of pre-input information associated with the real object  14 . A CRT display is used as the display  13 . The display  13  displays an image corresponding to the 3-dimensional virtual space  32  constructed by the main controller  12 . A 3-dimensional position/angle sensor  11 - 1  is used as a part having the first capability included in the input unit  11 . The 3-dimensional position/angle sensor  11 - 1  measures the position and the angle of an object (the 3-dimensional position/angle sensor  11 - 1  itself, in the example shown in  FIG. 2 ) to be measured in the real space  31 , and the 3-dimensional position/angle sensor  11 - 1  supplies the measurement result to the main controller  12 . 
   An object (image)  33  is included in the 3-dimensional virtual space (image)  32  displayed on the display  13 , wherein the object  33  is linked with the 3-dimensional position/angle sensor  11 - 1 . As described earlier, the coordinate system is defined in the 3-dimensional virtual space  32  on the basis of the information associated with the real object  14  and, thus, the real object  14  serves as a reference of the coordinate system of the 3-dimensional virtual space  32 . 
   Therefore, if a user places the 3-dimensional position/angle sensor  11 - 1  at a desired position and angle in the real space  31  with reference to the real object  14 , the result of measurement performed by the 3-dimensional position/angle sensor  11 - 1  (the position and the angle of the 3-dimensional position/angle sensor  11 - 1  itself) is input to the main controller  12  as specification information specifying the position and the angle of the object  33  in the 3-dimensional virtual space  32 . As a result, the object  33  is placed at the specified position and angle (corresponding to the position and angle of the 3-dimensional position/angle sensor  11 - 1 ) in the 3-dimensional virtual space  32 . That is, an image of the 3-dimensional virtual space  32  including the object  33  placed at the position and angle specified by the user is displayed on the display  13 . 
     FIG. 3  shows an example of a software program that implements, of various functions of the main controller  12  ( FIG. 2 ) of the information processing apparatus  1 , functions of defining a coordinate system of a 3-dimensional virtual space, constructing a 3-dimensional virtual space using the defined coordinate system, and controlling the display of an image corresponding to the 3-dimensional virtual space (the image includes an image of the object) (hereinafter, the process of controlling the display of such an image will be referred to as a process of controlling a 3-dimensional image). 
   As shown in  FIG. 3 , the software program includes a number of modules such as a coordinate system setting module  41 , an object position/angle determination module  42 , a virtual space construction module  43  and a display control module  44 . Each of the modules has its own algorithm and performs a specific operation according to the algorithm. Each module is called by the CPU  21  ( FIG. 1 ) and executed, as required. 
   The coordinate system setting module  41  sets a first coordinate system (for example, a coordinate system (rx, ry, rz) of a real space  31  described later with reference to  FIG. 6 ) on the basis of pre-input particular information associated with the real object  14  (for example, the shape, the position, the angle, and/or the like of the real object  14 ) in the real space  31  including the real object  14 . On the basis of the resultant first coordinate system, the coordinate system setting module  41  further sets a second coordinate system (for example, a coordinate system (vx, vy, vz) of a 3-dimensional virtual space  32  described later with reference to  FIG. 7 ) in the 3-dimensional virtual space  32  corresponding to the real space  31 . The coordinate system setting module  41  also calculates a correspondence (a coordinate transform function) between those two coordinate systems. 
   The object position/angle determination module  42  determines the position and the angle of the object  33  in the second coordinate system set by the coordinate system setting module  41  in accordance with information input using the above-described first capability of the input unit  11  (hereinafter, the information input using the first capability will be referred to as position/angle information to distinguish it from information input using the second capability of the input unit  11 , wherein, in the example shown in  FIG. 3 , the result of measurement performed by the 3-dimensional position/angle sensor  11 - 1  is the position/angle information). 
   The virtual space construction module  43  produces image data corresponding to a scene, seen from a particular view point (in the example shown in  FIG. 3 , a view point specified by information input via the input unit  11 ), in the 3-dimensional virtual space  32  defined by the second coordinate system set by the coordinate system setting module  41 , and the virtual space construction module  43  supplies the produced image data to the display control module  44 . Hereinafter, producing such image data of the 3-dimensional virtual space  32  will be referred to as “constructing the 3-dimensional virtual space  32 .” 
   When the position and the angle of the object  33  in the second coordinate system are determined by the object position/angle determination module  42 , the virtual space construction module  43  constructs the 3-dimensional virtual space  32  in which the object  33  is placed at the determined position and angle, and the virtual space construction module  43  supplies the data indicating the resultant 3-dimensional virtual space  32  to the display control module  44 . 
   The display control module  44  controls the display  13  so as to display thereon an image corresponding to the 3-dimensional virtual space  32  constructed by the virtual space construction module  43 . More specifically, the display control module  44  converts the image data supplied from the virtual space construction module  43  into an image signal in a format adapted to the display  13  and supplies the resultant image signal to the display  13 . The display  13  displays an image corresponding to the received image signal (an image corresponding to the 3-dimensional virtual space  32 ). 
   Referring to flow charts shown in  FIGS. 4 and 5 , an example of a process performed by the main controller  12  ( FIG. 3 ) of the information processing apparatus  1  to control the display of a 3-dimensional image is described below. 
   In this example, the information processing apparatus  1  is assumed to be configured as shown in  FIG. 2 . That is, the part having the first capability of the input unit  11  is embodied as a 3-dimensional position/angle sensor  11 - 1  of a particular type. In this example, the 3-dimensional position/angle sensor  11 - 1  detects the position and the angle (position/angle information) of the 3-dimensional position/angle sensor  11 - 1  and supplies, to the main controller  12 , the detected position/angle information expressed in a coordinate system (sx, sy, sz) specific to the 3-dimensional position/angle sensor  11 - 1 . An example of the coordinate system (sx, sy, sz) specific to the 3-dimensional position/angle sensor  11 - 1  is shown in  FIG. 6 . 
   First, in step S 1  shown in  FIG. 4 , the coordinate system setting module  41  sets the sensor coordinate system (sx, sy, sz) shown in  FIG. 6 , on the basis of sensor information of the 3-dimensional position/angle sensor  11 - 1 . That is, in an initial setting, the sensor coordinate system (sx, sy, sz) specific to the 3-dimensional position/angle sensor  11 - 1  is registered in preparation for use in the following processes. 
   In step S 2 , the coordinate system setting module  41  sets the first coordinate system (rx, ry, rz) in the real space  31  (hereinafter, such a coordinate system will be referred to as a real object coordinate system (rx, rx, rz) to distinguish it from the sensor coordinate system) on the basis of information associated with the real object  14  (the shape, the position, the angle, and/or the like of the real object  14 ). 
   In the present example, it is assumed that the shape, the position, and the angle of the real object  14  are predetermined and information indicating the shape, the position, and the angle of the real object  14  are pre-input to the main controller  12  (and stored in the storage unit  26  or the like shown in  FIG. 1 ). 
   Note that the information associated with the real object  14  is not limited to such information. For example, in step S 2 , information may be input by a user using the input unit  11  (an input device such as a keyboard different from the 3-dimensional position/angle sensor  11 - 1 ) for use as the information associated with the real object  14 . Alternatively, an image of the real object  14  may be taken by a camera or the like provided as a part of the input unit  11  other than the 3-dimensional position/angle sensor  11 - 1 , and may be subjected to pattern recognition thereby producing information for use as the information associated with the real object  14 . 
   In the present example, it is assumed that the real object coordinate system (rx, ry, rz) is defined (set) as shown in  FIG. 6 . In the real object coordinate system (rx, ry, rz) shown in  FIG. 6 , the sheet surface of the real object  14  is employed as a X-Y plane, and a Z axis is taken in a direction normal to the sheet surface of the real object  14 . The origin (denoted by O in  FIG. 6 ) is taken at a front left corner point (in  FIG. 6 ) of the real object  14 . As a matter of course, the X-Y plane and the Z axis may be defined in a manner different from that shown in  FIG. 6 , and the coordinate system may be defined differently, as long as particular one or more pieces of information associated with the real object  14  are used as the reference. 
   For example, in a case in which the real object  14  is an object in the form of a rectangular sheet, the origin may be taken at one of corner points, and coordinate axes may be taken along sides of the rectangular sheet. When the real object  14  has an arbitrary shape, lines drawn on the real object  14  or boundaries between different colors or the like on the real object  14  may be employed as the reference. 
   This also holds in definition of coordinate systems described later. 
   Referring again to  FIG. 4 , in step S 3 , the coordinate system setting module  41  sets the second coordinate system (vx, vy, vz) in the 3-dimensional virtual space  32  (hereinafter, referred to as the virtual space coordinate system (vx, vy, vz)) on the basis of the real object coordinate system (rx, ry, rz) set using the real object  14 . 
   In the present example, the virtual space coordinate system (vx, vy, vz) is set as shown in  FIG. 7 . More specifically, in the virtual space coordinate system (vx, vy, vz) shown in  FIG. 7 , a virtual region  34  corresponding to the real object  14  shown in  FIG. 6  (corresponding to the region where the sheet-shaped real object  14  is located) is set, and the upper surface (corresponding to the surface of the real object  14 ) of the virtual region  34  is employed as the X-Y plane, and the Z axis is taken in a direction normal to the upper surface of the virtual region  34 . The origin (denoted by O in  FIG. 7 ) is taken at a front left corner point (in  FIG. 7 ) of the upper surface of the virtual region  34 . As a matter of course, the X-Y plane and the Z axis may be defined in a manner different from that shown in  FIG. 6 , and the coordinate system may be defined differently. 
   The user can move the object  33  in the 3-dimensional virtual space  32  by moving the 3-dimensional position/angle sensor  11 - 1  ( FIG. 6 ) with respect to the real object  14  employed as the reference plane. If an image corresponding to the real object  14  is displayed on the display  13 , it becomes easier for the user to intuitively manipulate the object  33 . For the above purpose, it is desirable that the virtual space coordinate system (vx, vy, vz) be set such that the virtual region  34  corresponding to the real object  14  is displayed on the display  13 . As a matter of course, the virtual region may be displayed explicitly (so as to be seen by the user) as a room floor or the like as shown in  FIG. 8  or may be displayed as a transparent region (that cannot be seen by the user). 
   Referring again to  FIG. 4 , in step S 4 , the coordinate system setting module  41  determines coordinate transform functions that define correspondences among the sensor coordinate system (sx, sy, sz), the real object coordinate system (rx, ry, rz), and the virtual space coordinate system (vx, vy, vz) set in steps S 1  to S 3 . 
   That is, the correspondences among those coordinate systems are represented in the form of mathematical expressions by the coordinate transform functions. 
   More specifically, in the present example, coordinate transform functions are given by the following equations (1) and (2). 
   
     
       
         
           
             
               
                 
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                             33 
                           
                         
                         
                           
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                             34 
                           
                         
                       
                       
                         
                           
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                             33 
                           
                         
                         
                           
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                             34 
                           
                         
                       
                       
                         
                           
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                             42 
                           
                         
                         
                           
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                             43 
                           
                         
                         
                           
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                           rx 
                         
                       
                       
                         
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   Equation (1) represents a function used to transform the sensor coordinate system (sx, sy, sz) to the real object coordinate system (rx, ry, rz). In equation (1), m11 to m44 are elements of a transform matrix by which the sensor coordinate system (sx, sy, sz) is transformed to the real object coordinate system (rx, ry, rz). 
   Equation (2) represents a function used to transform the real object coordinate system (rx, ry, rz) to the virtual space coordinate system (vx, vy, vz). In equation (2), n11 to n44 are elements of a transform matrix by which the real object coordinate system (rx, ry, rz) is transformed to the virtual space coordinate system (vx, vy, vz). 
   More specifically, in the present example, the coordinate system setting module  41  determines the respective values of m11 to m44 and n11 to n44 via, for example, a least squares method thereby determining the coordinate transform functions that define the correspondences among the sensor coordinate system (sx, sy, sz), the real object coordinate system (rx, ry, rz), and the virtual space coordinate system (vx, vy, vz). 
   Note that the coordinate transform functions determined in step S 4  and the method of determining the coordinate transform functions are not limited to those employed in the present example. For example, the coordinate transform functions may be determined by a nonlinear transform using a neural network that simulates functions of a human brain. 
   As described above, the coordinate system setting module  41  defines the virtual space coordinate system (vx, vy, vz) on the basis of the real object  14  by performing the process in steps S 1  to S 4 . 
   In step S 5 , after the virtual space coordinate system (vx, vy, vz) is defined by the coordinate system setting module  41 , the virtual space construction module  43  sets a view point. The view point may be set in an arbitrary manner, and a pre-registered view point may be employed. In this specific example, it is assumed that the view point is set in accordance with information (specific information used in setting the view point) input using the second capability of the input unit  11 . 
   In step S 6 , the virtual space construction module  43  constructs the 3-dimensional virtual space  32  as shown in  FIG. 7  on the basis of the virtual space coordinate system (vx, vy, vz) and the view point set in the previous steps. 
   In step S 7 , the display control module  44  displays an image of the 3-dimensional virtual space  32  constructed in step S 6  by the virtual space construction module  43  on the display  13  as an initial image. 
   Herein, let us assume that the image shown in  FIG. 8  is displayed as the initial image on the display  13 . In the example shown in  FIG. 8 , the 3-dimensional virtual space  32  is constructed in the virtual space coordinate system (vx, vy, vz) defined on the basis of the real object  14  (hereinafter, referred to as a sheet  14 - 1  because the real object  14  is an object in the form of a sheet in this example), and an image corresponding to the constructed 3-dimensional virtual space  32  is displayed as the initial image on the display  13 . 
   In this 3-dimensional virtual space  32 , a room having a floor formed by the virtual region  34  corresponding to the sheet  14 - 1  is expressed. The floor and walls are expressed in the 3-dimensional virtual space  32  simply to indicate a particular region, and they are not necessarily needed to be displayed. 
   However, it is desirable to display the floor because the floor explicitly indicates the virtual region  34  corresponding to the sheet  14 - 1 . As will be described later with reference to  FIGS. 9 and 10 , displaying the floor (virtual region)  34  corresponding to the sheet  14 - 1  makes it possible to easily and intuitively recognize the correspondences between the position and the angle of the object  33  in the virtual space coordinate system (vx, vy, vz) and the position and the angle of the 3-dimensional position/angle sensor  11 - 1  in the real object coordinate system (rx, ry, rz) on the basis of the correspondence between the sheet  14 - 1  and the floor  34  and on the basis of the position and the angle with respect to the sheet  14 - 1  serving as the reference plane. 
   When the user wants to place the object  33  at a desired position and angle in the 3-dimensional virtual space  32 , the user determines the relative position and angle with respect to the floor  34  and simply places the 3-dimensional position/angle sensor  11 - 1  at a relative place and angle, corresponding to the determined position and angle, with respect to the sheet  14 - 1 . As a result, as will be described later, the object  33  is placed at the above-described position and angle with respect to the floor  34  in the 3-dimensional virtual space  32 , wherein the position and angle correspond to the relative position and angle of the 3-dimensional position/angle sensor  11 - 1  with respect to the sheet  14 - 1 . 
   In the example shown in  FIG. 8 , a picture of a chair  51  and a picture of a desk  52  are drawn on the sheet  14 - 1 . A 3-dimensional model of a chair  61  is placed in the virtual space coordinate system (vx, vy, vz) of the 3-dimensional virtual space  32 , at the position corresponding to the position of the picture of the chair  51  in the real object coordinate system (rx, ry, rz). Similarly, a 3-dimensional model  62  is placed in the virtual space coordinate system (vx, vy, vz) of the 3-dimensional virtual space  32 , at the position corresponding to the position of the picture of the desk  52  in the real object coordinate system (rx, ry, rz). 
   In the example shown in  FIG. 8 , in order to make it possible for the user to easily and intuitively recognize the correspondence between the picture of the chair  51  and the picture of the desk  52 , a 3-dimensional model of the chair  61  having a shape similar to that of the picture of the chair  51  and a 3-dimensional model of the desk  62  having a shape similar to that of the picture of the desk  52  are used. If the above purpose is not necessary, simple 3-dimensional models may be placed at the positions where the 3-dimensional model of the chair  61  and the 3-dimensional model of the desk  62  are placed (in the virtual space coordinate system (vx, vy, vz)). That is, the shapes of 3-dimensional models are not limited to those employed in the example shown in  FIG. 8 , but arbitrary shapes may be used. 
   It is necessary that the 3-dimensional model of the chair  61  and the 3-dimensional model of the desk  62  should be input to the main controller  12  beforehand by using an arbitrary input device by an arbitrary method. 
   In the state in which the initial image is displayed on the display  13  (as shown in  FIG. 8  in this specific example), if the 3-dimensional position/angle sensor  11 - 1  ( FIG. 2 ) is moved in the real space  31 , the object  33  ( FIG. 2 ) is also moved in the 3-dimensional virtual space  32  in response to the motion of the 3-dimensional position/angle sensor  11 - 1  as described earlier. The process of moving the object  33  in response to the motion of the 3-dimensional position/angle sensor  11 - 1  (that is, in response to the operation performed by the user) is performed in steps S 8  to S 13  shown in  FIG. 5 . 
   For example, in the state shown in  FIG. 8 , let us assume that the places the 3-dimensional position/angle sensor  11 - 1  on the picture of the desk  52  drawn on the sheet  14 - 1  (that is, the status of the 3-dimensional position/angle sensor  11 - 1  is changed from that shown in  FIG. 8  into a status described later with reference to  FIG. 9 ). 
   In response, in step S 8  in  FIG. 5 , position/angle information (the position and the angle of the 3-dimensional position/angle sensor  11 - 1  expressed in the sensor coordinate system (sx, sy, sz), in this specific example)) is supplied from the 3-dimensional position/angle sensor  11 - 1  to the object position/angle determination module  42 . 
   In step S 9 , the object position/angle determination module  42  converts the received position/angle information from the sensor coordinate system (sx, sy, sz) into the real object coordinate system (rx, ry, rz). More specifically, the coordinates of the position/angle information are converted from the sensor coordinate system (sx, sy, sz) to the real object coordinate system (rx, ry, rz) using equation (1). 
   In step S 10 , the object position/angle determination module  42  further converts the coordinates of the position/angle information from the real object coordinate system (rx, ry, rz) into the virtual space coordinate system (vx, vy, vz). More specifically, the coordinates of the position/angle information are converted from the real object coordinate system (rx, ry, rz) into the virtual space coordinate system (vx, vy, vz) using equation (2). 
   Although in the example shown in  FIG. 5 , steps S 9  and S 10  are performed separately, steps S 9  and S 10  may be performed at the same time. For this purpose, in step S 4  ( FIG. 4 ), a coordinate transform function in the form of equation (3) that is a combination of equations (1) and (2) is determined instead of determining individual coordinate transform functions in the form of equations (1) and (2). 
   
     
       
         
           
             
               
                 
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                         vx 
                       
                     
                     
                       
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                               n 
                               11 
                             
                           
                           
                             
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                               41 
                             
                           
                           
                             
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                               14 
                             
                           
                         
                         
                           
                             
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                 ( 
                 3 
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   Equation (3) represents a function used to directly convert coordinates from the sensor coordinate system (sx, sy, sz) into the virtual space coordinate system (vx, vy, vz). In equation (3), m11 to m44 are elements similar to those of the transform matrix in equation (1) by which the sensor coordinate system (sx, sy, sz) is transformed to the real object coordinate system (rx, ry, rz), and n11 to n44 are elements similar to those of the transform matrix in equation (2) by which the real object coordinate system (rx, ry, rz) is transformed to the virtual space coordinate system (vx, vy, vz). 
   The object position/angle determination module  42  performs a process corresponding to the combination of step S 9  and step S 10  to directly (in a single operation) transform the coordinates of the input position/angle information from the sensor coordinate system (sx, sy, sz) into the virtual space coordinate system (vx, vy, vz) using equation (3). 
   In step S 11 , the object position/angle determination module  42  determines the position and the angle of the object  33  on the basis of the position/angle information transformed into the virtual space coordinate system (vx, vy, vz). In this specific example, because the object  33  is linked with the 3-dimensional position/angle sensor  11 - 1 , the position/angle information transformed into the virtual space coordinate system (vx, vy, vz) is directly employed as the position and the angle of the object  33  in the virtual space coordinate system (vx, vy, vz). 
   In step S 12 , the virtual space construction module  43  reconstructs the 3-dimensional virtual space  32  including the object  33  located at the position and the angle (in the virtual space coordinate system (vx, vy, vz)) determined by the object position/angle determination module  42 . 
   In step S 13 , the display control module  44  displays an image of the 3-dimensional virtual space  32  reconstructed in step S 12  by the virtual space construction module  43  on the display  13 . 
   In this specific case, as described above, the 3-dimensional position/angle sensor  11 - 1  is placed on the picture of the desk  52  drawn on the sheet  14 - 1  as shown in  FIG. 9 . That is, the 3-dimensional position/angle sensor  11 - 1  is in contact with the X-Y plane of the real object coordinate system (rx, ry, rz). Therefore, although not shown in  FIG. 9 , the object  33  in the 3-dimensional virtual space  32  is displayed such that the object  33  is in contact with the floor (virtual region)  34  and, thus, the object  33  penetrates the 3-dimensional model of the desk  62 . This manner of displaying the object  33  can be employed without any problem in the case in which the user places the 3-dimensional position/angle sensor  11 - 1  on the picture of the desk  52  drawn on the sheet  14 - 1  in order to simply select the 3-dimensional model of the desk  62  in selection between the 3-dimensional model of the chair  61  and the 3-dimensional model of the desk  62 . 
   However, in the case in which the user places the 3-dimensional position/angle sensor  11 - 1  on the picture of the desk  52  drawn on the sheet  14 - 1  with the intention of placing the object  33  on the 3-dimensional model of the desk  62 , the above manner of displaying the object  33  cannot achieve the intention of the user. 
   In such a case, it is desirable that the virtual space construction module  43  reconstruct the 3-dimensional virtual space  32  after making a judgment as to penetration between 3-dimensional models. An image of the resultant 3-dimensional virtual space  32  reconstructed in such a manner is displayed on the display  13 , for example, as shown in  FIG. 9 . That is, the object  33  in the 3-dimensional virtual space  32  is displayed (on the display  13 ) such that the object  33  is located on the 3-dimensional model of the desk  62  without penetrating the 3-dimensional model of the desk  62 . 
   Referring again to  FIG. 5 , in step S 14 , the display control module  44  determines whether the condition of ending the process is met. 
   The condition of ending the process, which is checked in step S 14 , is not limited to a particular one. For example, inputting of an end command by a user or detection of a particular status of software or hardware such as a shortage of available storage capacity of the storage unit  26  ( FIG. 1 ) can be used as the condition of ending the process. 
   If it is determined in step S 14  that the condition of ending the process is met, the process is ended. 
   However, if it is determined in step S 14  that the condition of ending the process is not met, the process returns to step S 8  to repeat steps from S 8 . 
   Herein, let us assume that the user moves the 3-dimensional position/angle sensor  11 - 1 , for example, from the position on the picture of the desk  52  drawn on the sheet  14 - 1  to the position on the picture of the chair  51  as shown in  FIG. 10 . That is, the status of the 3-dimensional position/angle sensor  11 - 1  is changed from that shown in  FIG. 9  into a status shown in  FIG. 10 . 
   In this case, it is determined in step S 14  that an end command is not issued and, thus, steps S 8  to S 13  are repeated. 
   Thus, the object position/angle determination module  42  again acquires the position/angle information of the 3-dimensional position/angle sensor  11 - 1 , converts the coordinates thereof into the virtual space coordinate system (vx, vy, vz), and employs the resultant position and the angle in the virtual space coordinate system (vx, vy, vz) as the new position and angle of the object  33 . The virtual space construction module  43  then reconstructs the 3-dimensional virtual space  32  including the object  33  located at the newly determined position and angle. The display control module  44  displays an image of the reconstructed 3-dimensional virtual space  32  on the display  13 . 
   More specifically, in this particular case, the image such as that shown in  FIG. 10  is displayed on the display  13 . That is, in the image displayed on the display  13 , the object  33  in the 3-dimensional virtual space  32  is moved from the previous position on the 3-dimensional model of the desk  62  to the new position on the 3-dimensional model of the chair  61 . 
   In the example shown in  FIG. 10 , as in the example shown in  FIG. 9 , the judgment as to the penetration is performed, and the object  33  is placed on the 3-dimensional model of the chair  61  such that no penetration occurs. However, as described earlier, the judgment as to penetration is not necessarily needed. However, if judgment of penetration is not performed, the object  33  is displayed such that it is in contact with the floor (virtual region)  34  and, thus, object  33  penetrates the 3-dimensional model of the chair  61 . 
   By performing steps S 8  to S 13  repeatedly in the above-described manner, the object  33  in the 3-dimensional virtual space  32  moves from the 3-dimensional model of the desk  62  to the 3-dimensional model of the chair  61  via a path corresponding to a path via which the 3-dimensional position/angle sensor  11 - 1  is moved by the user, with substantially no delay from the movement of the 3-dimensional position/angle sensor  11 - 1 . 
   Although the present invention has been described above with reference to the embodiment of the information processing apparatus  1  configured as shown in  FIG. 2 , the present invention is not limited to the specific embodiment shown in  FIG. 2 , but may be embodied in various manners. 
   For example, the form of the real object  14  used as the reference object in the virtual space coordinate system (vx, vy, vz) is not limited to a particular one such as the sheet  14 - 1  employed above, but the real object  14  may be in an arbitrary form as long as it has an area greater than a predetermined value at least in a predetermined direction. 
   For example, a book  14 - 2  formed of a stack of sheets of paper may be used as the real object  14  as shown in  FIG. 11 . In this case, the main controller  12  ( FIG. 1 ) of the information processing apparatus  1  may define the real object coordinate system (rx, ry, rz) of the real space  31  by employing the surface (printed surface) of a page of the book  14 - 2  as the X-Y plane and taking the Z axis in a direction normal to the surface of the page. Furthermore, the main controller  12  defines the virtual space coordinate system (vx, vy, vz) of the 3-dimensional virtual space  32  with respect to the defined real object coordinate system (rx, ry, rz). As a matter of course, the manner of defining the coordinate systems is not limited to such the manner described above, but the coordinate systems may be defined in various manners. 
   As a result, as shown in  FIG. 11 , the 3-dimensional virtual space  32  is displayed on the display  13  such that a virtual region  34  corresponding to the surface (X-Y plane) of the page of the book  14 - 2  is displayed as a floor. If the 3-dimensional position/angle sensor  11 - 1  is placed on a picture of a desk  52 , the object  33  is placed on the 3-dimensional model of the desk  62  in the 3-dimensional virtual space  32  (in the image displayed on the display  13 ). In the example shown in  FIG. 11 , it is assumed that judgment as to penetration is performed. 
   In the case in which a single sheet  14 - 1  is used as the real object  14 , as is the case in  FIGS. 8 to 10 , only one scene is defined in the 3-dimensional virtual space  32 . In contrast, if a book  14 - 2  formed of a stack of sheets of paper is used as the real object  14  as shown in  FIG. 11 , a large number of different scenes (drawn on respective pages) can be defined in the 3-dimensional virtual space by turning over pages of the book  14 - 2 . 
   As shown in  FIG. 12 , an object  14 - 3  including a board  71  and models  72  and  73  placed on the board  71  may be used as the real object  14 . The material of the board  71  is not limited to paper such as that employed as the material for the sheet  14 - 1  ( FIGS. 8 to 10 ) or for the book  14 - 2  ( FIG. 11 ), but an arbitrary material may be employed as long as it has an area. 
   In this case, as shown in  FIG. 12 , a 3-dimensional virtual space  32  is displayed on the display  13  such that a virtual region  34  corresponding to the board  71  is displayed as the ground. 
   In the case in which the real object  14  includes not only a part (the board  71 , in the example shown in  FIG. 12 ) used to define a coordinate system but also another part (the model  72  and the model  73  in the example shown in  FIG. 12 ) that is not used to define the coordinate system as is the case with the real object  14 - 3  shown in  FIG. 12 , it is desirable that the 3-dimensional virtual space  32  include 3-dimensional models having similar shapes (a 3-dimensional mode of a house  81  corresponding to a model of a house  72 , and a 3-dimensional model of trees  82  corresponding to a model of trees  73 , in the example shown in  FIG. 12 ), because those models make it possible for the user to easily recognize the correspondence between the real space  31  and the 3-dimensional virtual space  32 . That is, those models make it possible for the user to more easily and intuitively perform manipulation in the 3-dimensional virtual space  32  by performing manipulation with respect to the model  72  or  73 . 
   A model  14 - 4  having an arbitrary shape such as that shown in  FIG. 13  also may be used as the real object  14 . Because the real object coordinate system (rx, ry, rz) can be defined in the real space  31  in an arbitrary manner as described earlier, the main controller  12  ( FIG. 1 ) of the information processing apparatus  1  may define the real object coordinate system (rx, ry, rz) with respect to an object having an arbitrary shape such as the model  14 - 4 . In the example shown in  FIG. 13 , the real object coordinate system (rx, ry, rz) of the real space  31  may be defined, for example, by projecting the model  14 - 4  onto the floor surface and employing the resultant projective plane as the X-Y plane. As a manner of course, as described earlier, the manner of defining the X, Y, and Z axes is not limited to that employed herein. 
   In the example shown in  FIG. 13 , the 3-dimensional virtual space  32  (the image of the 3-dimensional virtual space  32 ) is displayed on the display  13  such that the virtual region  34  corresponding to the X-Y plane (the projective plane of the model  14 - 4 ) defined in the real space  31  is displayed at the bottom of the screen of the display  13 . 
   In the example shown in  FIG. 13 , the virtual region  34  is not represented explicitly unlike the previous examples in which the virtual region  34  is explicitly represented by the floor or the ground. In such a case, it is desirable that a 3-dimensional model  91  having a shape similar to that of the model  14 - 4  (used as the reference object) be displayed in the 3-dimensional virtual space  32  as shown in  FIG. 13 . This makes it possible, as with the example shown in  FIG. 12 , for the user to easily recognize the correspondence between the real space  31  and the 3-dimensional virtual space  32 . Thus, as with the previous examples, the user can easily and intuitively perform manipulation in the 3-dimensional virtual space  32  by using the model  14 - 4  as the reference object. 
   Not only the real object  14  but also the input unit  11  having the first capability also may be embodied in various fashions. 
   For example, in the example shown in  FIG. 2 , because the coordinate system (the sensor coordinate system (sx, sy, sz)) used to express the position/angle information output from the 3-dimensional position/angle sensor  11 - 1  is different from the coordinate system (the real object coordinate system (rx, ry, rz)) of the real space  31  defined with respect to the real object  14 , the information processing apparatus  1  transforms the coordinate system from the sensor coordinate system (sx, sy, sz) to the real object coordinate system (rx, ry, rz) via steps S 1  and S 4  in  FIG. 4  and step S 9  in  FIG. 5 . 
   The coordinate system transform makes it possible for the user to easily manipulate the 3-dimensional position/angle sensor  11 - 1  with reference to the real object  14  (using the real space coordinate system (rx, ry, rz)) without awareness of the sensor coordinate system (sx, sy, sz) even when the 3-dimensional position/angle sensor  11 - 1  has its own sensor coordinate system (sx, sy, sz). 
   In the case in which an input device used as the input unit  11  having the first capability outputs position/angle information expressed in a coordinate system (the sensor coordinate system (sx, sy, sz)) that is the same as the coordinate system (real object coordinate system (rx, ry, rz)) of the real space  31 , the coordinate transform from the sensor coordinate system (sx, sy, sz) to the real object coordinate system (rx, ry, rz) is not necessary. 
   As shown in  FIG. 14 , an arbitrary real object  101  independent of the 3-dimensional position/angle sensor may be used as the real object linked with an object  33 , and the position and the angle of the real object  101  in the real space  31  may be input using a camera  11 - 2  or the like. That is, in the example shown in  FIG. 14 , the camera  11 - 2  serves as the input unit  11  having the first capability, and the main controller  12  detects the position and the angle of the real object  101  in the real space  31  by performing image processing on the image of the real object  101  taken by the camera  11 - 2 . 
   Although an arbitrary real object can be used as the real object  101 , it is desirable to use a real object that reminds the user of the object  33 , because the real object  101  is linked with the object  33 . That is, it is desirable that the real object  101  have a feature similar to that of the object  33 . In the example shown in  FIG. 14 , in view of the above, an object having a shape similar to that of the object  33  is used as the real object  101 . The features of the object  33  can include not only the shape but also other features such as a color or a relative size in the 3-dimensional virtual space  32 , and, thus, an object having a feature similar to one of those features of the object  33  may be used as the real object  101 . 
   In other words, although the real object  101  by itself does not have a particular function in the information processing apparatus  1 , the similarity in feature with the object  33  reminds the user of the object  33 . If the user changes the position or the angle of the real object  101  in the real space  31 , the position or the angle of the object  33  in the 3-dimensional virtual space  32  is changed in response to the change in the position or the angle of the real object  101  and, thus, the real object  101  can function, in effect, as an input device (that can be used instead of the 3-dimensional position/angle sensor  11 - 1 ) that works in conjunction with the camera  11 - 2 . In this case, of the input unit  11 , the part having the first capability is embodied not only by the camera  11 - 2  but by a combination of the camera  11 - 2  and the real object  101 . 
   As described above, in the information processing apparatus according to the present invention, a first coordinate system (for example, the real object coordinate system (rx, ry, rz)) is defined in the real space with reference to a particular real object, and a second coordinate system (for example, the virtual space coordinate system (vx, vy, vz)) is defined in the 3-dimensional virtual space on the basis of the first coordinate system, so that a user can easily and intuitively manipulate an object in the 3-dimensional virtual space by using the real object as a reference object. This is very useful, in particular, in that the user can get ability of perception in a direction away from a view point, which could otherwise not be obtained. 
   In the conventional techniques, an input device manipulated by a user has a third coordinate system (for example, the sensor coordinate system (sx, sy, sz) in the case in which a 3-dimensional position/angle sensor is used as the input device) that is specific to the input device and is not related with the second coordinate system in the 3-dimensional virtual space and, thus, the user cannot intuitively manipulate the input device. This makes it very difficult for the user to manipulate an object in the 3-dimensional virtual space. 
   In contrast, in the present invention, the first coordinate system is defined with reference to a real object, and the second coordinate system is defined in the 3-dimensional virtual space with reference to the first coordinate system. Therefore, the 3-dimensional virtual space expressed in the second coordinate system and the real space expressed in the first coordinate system correspond with each other. In this case, the position and the angle of the input device manipulated are expressed in the first coordinate system directly related with the second coordinate system. As such, the user can easily and intuitively manipulate an object in the 3-dimensional virtual space expressed in the second coordinate system (even in the case in which the input device has a third coordinate system as in the conventional technique, the user can manipulate the input device without awareness of the third coordinate system, because the coordinate system is transformed). 
   When the processing sequence is executed by software, a program forming the software may be installed from a storage medium or via a network onto a computer which is provided as dedicated hardware or may be installed onto a general-purpose computer capable of performing various processes in accordance with various programs installed thereon. 
   Specific examples of storage media usable for the above purpose include, as shown in  FIG. 1 , a removable storage medium (package medium)  29 , such as a magnetic disk (for example, a floppy disk), an optical disk (for example, a CD-ROM (Compact Disk-Read Only Memory) or a DVD (Digital Versatile Disk)), a magnetooptical disk (for example, a MD (Mini-Disk)), and a semiconductor memory, on which a program is stored and which is supplied to a user separately from a computer. A program also may be supplied to a user by preinstalling it on a built-in ROM  22  or a storage unit  26  such as a hard disk disposed in a computer. 
   The coordinate system setting module  41 , the object position/angle determination module  42 , the virtual space construction module  43 , and the display control module  44 , shown in  FIG. 3 , are not limited to particular types, as long as their functions are achieved. For example, those modules may be implemented via hardware. In the case in which the modules are implemented via hardware, a manufacturer may produce hardware parts corresponding to the coordinate system setting module  41 , the object position/angle determination module  42 , the virtual space construction module  43 , and the display control module  44 , and connect them with one another as shown in  FIG. 3  thereby essentially embodying the information processing apparatus  1  according to the present invention, in a different manner from that shown in  FIG. 1 . 
   The modules described above are not limited to those shown in  FIG. 3 , but they may be configured in different manners (they may be divided into sub modules) as long as they can perform, as a whole, the process corresponding to the flow charts shown in  FIGS. 4 and 5 . Alternatively, the modules may be combined into a single software program having a single algorithm. 
   In the present description, the steps described in the program stored in the storage medium may be performed either in time sequence in accordance with the order described in the program or in a parallel or separate fashion. 
   As can be understood from the above description, the present invention makes it possible to construct a 3-dimensional virtual space and display an image corresponding to the constructed 3-dimensional virtual space. A user can easily and intuitively manipulate information in the 3-dimensional virtual space. 
   Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the present invention as set forth in the hereafter appended claims.