Abstract:
A system manipulates an object in a three-dimensional graphical scene that includes a graphical camera in a first position and a first orientation. The system receives an object manipulation indication and identifies an improved viewing location of the camera for manipulation the object. The system then moves the camera to a second position and second orientation based on the improved viewing location. Finally, the system receives an end of object manipulation indication and moves the camera back to the first position and first location.

Description:
SUMMARY OF THE INVENTION 
     The present invention is directed to three-dimensional computer graphics. More particularly, the present invention is directed to manipulation objects in a three-dimensional computer graphics scene. 
     BACKGROUND OF THE INVENTION 
     Three-dimensional (“3-D”) computer graphics programs are rapidly increasing in popularity because, for one, they allow graphical scenes to appear more realistic on a two-dimensional (“2-D”) computer display. However, one problem with the typical 3-D computer graphics program is placing and manipulating objects in a 3-D scene. Placement is typically not a problem in 2-D scenes (e.g., drawing programs) because both relevant dimensions are directly visible to the user. Because 3-D scenes are limited to projections of the scene onto a 2-D computer display or screen, direct manipulations of objects is more difficult. Further compounding the difficulty is that most scenes are presented with a perspective projection (making objects in the back appear smaller) to aid in the visual interpretation of the scene. 
     The most common input device for 3-D graphics programs is a computer mouse, which is inherently a 2-D device in spite of the recent addition of a wheel to some models. A common way to map mouse input signals to object movement is to have two or more modes. In one mode, mouse movement maps to movement of the object in a plane parallel to the screen. In another mode (e.g., when a keyboard key is pressed) mouse movement maps to movement in an orthogonal plane (e.g., parallel to the apparent floor of the scene). The mouse movement is always one to one with cursor movement, but the relationship of cursor movement to object movement can be important. A common cursor-object mapping is to interpret a fixed cursor movement with a fixed movement in the scene. 
     Another known method of cursor-object mapping is referred to as “projective mapping”, in which the object position, constrained by the movement plane, stays under the cursor. Typically, a projective mapping also implies that object movement is constrained to planes oriented with the scene rather than to a graphical “camera” that determines the field of view of the user. This mapping is not linear in the 3-D scene (equivalent cursor movements further away give larger object movements than those closer), but gives the user the feeling that the user is actually holding the object, since the object remains under the cursor. 
     One problem with projective mapping occurs when the plane of movement is very nearly parallel to the line between the eye-point, or “camera”, and the object. In this case, very small movements of the cursor result in very large movements of the object. For example, the difference between the object up front versus the object at the back may be only a handful of pixels on the screen, so a very small cursor movement results in a huge object movement. In a severe case, there may be no pixel difference, and the user won&#39;t be able to move the object at all. 
     The common solution to this problem is for the user to move the viewing position to one in which the user has more control over the object. However, this solution generates at least two problems. First, the user must choose and move to an appropriate position for successful object manipulation. Second, the user usually really wanted to be in the original position, so the user is now faced with the job of returning to it after the manipulation. The user often deals with the first problem by making a minimal movement. The user does this because movement in 3-D scenes, especially ones involving changes in viewing angle, are difficult, and therefore the user wants to minimize this difficulty for both the first move and the return. The result of this minimal move is often that it is too minimal, not providing enough control over the object. After losing time trying to make the placement in the first new position, the user moves to a more advantageous location. While this may solve the manipulation problem, the intermediate move wastes time and increases the difficulty associated with returning to the original location. 
     Based on the foregoing, there is a need for an improved apparatus and method for manipulating objects in a 3-D graphical scene. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention is a system for manipulating an object in a three-dimensional graphical scene that includes a graphical camera in a first position and a first orientation. The system receives an object manipulation indication and identifies an improved viewing location of the camera for manipulating the object. The system then moves the camera to a second position and second orientation based on the improved viewing location. Finally, the system receives an end of object manipulation indication and moves the camera back to the first position and first location. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the internal workings of a 3-D computer graphics scene. 
     FIG. 2 is a block diagram of one embodiment of a computer system that can implement the present invention. 
     FIG. 3 illustrates an example of how a camera is moved during object manipulation. 
     FIG. 4 illustrates only the x, z plane of FIG.  3 . 
     FIG. 5 is a flow chart illustrating the steps performed by the computer system in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     One embodiment of the present invention enhances the manipulation of an object in a 3-D computer graphics scene by automatically moving the camera to an improved viewing location, and then moving the camera back to its original location when the manipulation of the object is completed. 
     FIG. 1 illustrates the internal workings of a 3-D computer graphics scene. The 3-D scene of FIG. 1 is intended to be a simulated 3-D graphics that is displayed to a user on a flat, 2-D computer display. 
     The scene includes an eye position or graphical “camera”  10  which determines which objects appear to the user in the 3-D scene. Camera  10  projects out at a field of view, or angle  14 . Angle  14  determines how much area is seen by camera  10 . 
     The scene further includes a near plane  12  and a far plane  16 . Near plane  12  and far plane  16  define an area, referred to as a “viewing frustrum” where objects viewed by camera  10  reside. In FIG. 1, objects  18  (a cube) and  19  (a sphere) are within the viewing frustrum formed by near plane  12  and far plane  16 , but only object  18  is viewable by camera  10  because it falls within angle  14 . Near plane  12  includes a front plane of the frustrum where objects are projected for display on the computer display. Object  18  is projected onto the front plane of the frustrum as object  18 ′. 
     In the 3-D scene of FIG. 1, two types of movement that require user interaction are available. One movement involves changing the location of camera  10  in order to change the view seen by the user on the computer display. Among other things, in changing the location both the position and orientation of the camera can be changed. This is referred to as “navigating” or “moving” camera  10 . Further, the user can move objects  18  and  19 , which is referred to as “manipulating” the objects. In the present invention, objects are manipulated by attaching the cursor to the desired object, and moving the mouse. The selected object tracks the movement of the cursor. 
     FIG. 2 is a block diagram of one embodiment of a computer system that can implement the present invention. Computer system  75  includes a keyboard  54 , a mouse  52 , a system unit  60  and a computer display  50 . System unit  60  includes a processor, memory, and other known computer components. Display  50  displays objects captured by camera  10  of FIG. 1 that appear in the front plane of the frustrum. Therefore, in the example of FIG. 1, display  50  shows object  18 . 
     The present invention automatically moves camera  10  to a more appropriate or improved location when a user desires to manipulate an object. FIG. 3 illustrates an example of how camera  10  is moved during object manipulation. FIG. 3, similar to FIG. 1, shows camera  10  in conjunction with a 3-D object  18 . FIG. 3 does not show near plane  12  or far plane  16 , but does illustrate a “floor”  40  that provides a perspective on the directions object  18  can be manipulated. 
     Object  18  can be manipulated in either an x, y, or z direction relative to floor  40 . Some directions of movement of object  18  can be more easily visualized by a user via computer display  50  depending on the location of camera  10 . For example, when camera  10  is in location A of FIG. 3, the user can easily visualize movement of object  18  in the y and z direction which forms a plane parallel to camera  10 . However, in location A, movement of object  18  in the x direction, which is perpendicular to camera  10 , is more difficult for the user to visualize. Similarly, when camera  10  is in location B of FIG. 3, the user can easily visualize movement of object  18  in the x and y direction, but not in the z direction. 
     Therefore, depending on the direction that the user wishes to move object  18 , the present invention automatically moves camera  10  to an advantageous location for the user. For example, if the user indicates the desire to move object  18  in the x, y direction of floor  40 , camera  10  may be automatically moved to location B. This allows the user to easily visualize the movement of object  18 . When the user is finished manipulating object  18 , camera  10  is then automatically moved back to its original location A. 
     For simplicity purposes, FIG. 4 illustrates only the x, z plane of FIG.  3 . As discussed, the location of camera  10  may be defined by the position of camera  10  and the orientation of camera  10 . In location A, the position of camera  10  is approximately 0 degrees relative to the x/y intersection, and the orientation is along the x axis. In contrast, in location B, the position of camera  10  is approximately 90 degrees away from the position of camera  10  at location A, and the orientation is along the z axis. In location A it is easy to visualize movement along the z axis, but not along the x ax is. In contrast, in location B it is easy to visualize movement along the x axis, but not along the z axis. In a further location shown in FIG. 4, location C, the position of the camera is approximately 30 degrees away from the position of camera  10  at location A. 
     Referring again to FIG. 3, in one embodiment of the present invention, when a user desires to manipulate object  18 , or an other object, the user places a cursor on the object and presses, for example, the left key of mouse  52 . This attaches the cursor to the object and the user can move mouse  52  and simultaneously drag the object to manipulate it. By only pressing the left key of mouse  52 , the object will be dragged perpendicular to floor  40  (i.e., in the y, z plane). However, if the user wishes to drag the object in a direction parallel to floor  40  (i.e., in the x, y plane) or in any other non-y, z plane, the user, in addition to pressing the left key of mouse  52 , presses a designated key on keyboard  54 . In this embodiment, the pressing of the key on keyboard  54  functions as an object manipulation indication and informs computer system  75  that the user is moving the object. Computer system  75  then changes the location of camera  10  from location A to location B to provide the user with an improved viewing location of the object. 
     In another embodiment, to manipulate the object in any direction, the user places a cursor on the object and presses, for example, the left key of mouse  52 . The user then moves mouse  52  to drag the object. When the user begins to move mouse  52 , computer system  75  receives and object manipulation indication. Computer system  75  can then move camera  10  to an improved viewing location based on the object selected and the location of the object relative to camera  10 . 
     FIG. 5 is a flow chart illustrating the steps performed by computer system  75  in accordance with one embodiment of the present invention. The steps of FIG. 5 are performed when a user attempts to manipulate object  18  or any other object in a 3-D scene. 
     At step  100 , system  75  waits for an indication that the user desires to manipulate object  18 , or any other objects present in the 3-D scene. As discussed, in one embodiment the user selects the object by using mouse  52  and pressing a designated key on keyboard  54  when on object is to be manipulated, such as a function key. In this embodiment, the user pressed the designated key when the object will be moved in x, y plane parallel to floor  40 . The pressing of the key provides an object manipulation indication. 
     In another embodiment, the user selects the object using mouse  52  and begins to manipulate the object by pressing a mouse button and moving mouse  52 . The movement of mouse  52  provides an object manipulation indication. 
     In still another embodiment, additional input devices or interactions by the user can indicate object manipulation. For example, the user can indicate an object manipulation through a spoken command such as “Move Red Cube” if system unit  60  has voice recognition capability. 
     After system  75  receives an object manipulation indication, step  102  is performed. At step  102 , system  75  identifies an improved viewing location of camera  10  based how the manipulation of object  18  was selected. In one embodiment, the viewing location is always perpendicular to floor  40  (i.e., location B of FIG. 4) as it is assumed that the user desires to move object  18  within the x, y plane. In this embodiment, camera  10  may be backed up to provide a larger area of floor  40  for the user to manipulate object  18 . 
     In another embodiment, system  75  automatically determines the improved location of camera  10  based on the 3-D scene and the current location of object  18  within the scene. In this embodiment, the improved viewing location is located between location A and location B of FIG.  3 . The improved location of camera  10  should result in a reasonable ratio of movement of mouse  52  to the movement of object  18  on computer display  50 , while minimizing the movement of camera  10  to achieve the reasonable ratio. The reasonable ratio allows the user to see the entire potential range of motion of object  18  and gives the user the impression of complete control over the object. 
     One way of determining a reasonable ratio is to predetermine a minimum number of pixels of apparent cursor movement that is required when a selected object is moved from background to foreground, and vice versa. In one embodiment, the minimum number of pixels is 100. The improved location of camera  10  is then calculated as the location that results in the minimum movement of camera  10  from location A that achieves the required number of pixels. 
     In still another embodiment, the improved location is approximately 16-30 degrees above location A of FIG. 4 (e.g., location C of FIG.  4 ). System  75  determines the current angle of camera  10  relative to the plane of the object selected. System  75  then selects 16 degrees or 30 degrees as the improved location depending on which is closest to the current angle. 
     At step  104 , system  75  animates camera  10  to the improved viewing location. This step includes moving camera  10  from its original location (e.g., location A) to the location determined at step  102  (e.g., location B) and, during the movement, constantly displaying the view from camera  10 . This allows the user to visualize the movement of camera  10  and recognize that the viewing location has been changed, thereby orienting the user to the new viewing location. After step  104  is performed, the user may then manipulate object  18  based on the new location of camera  10 . 
     At step  106 , system  75  waits for the end of object manipulation indication. This indication is typically the reverse of the object manipulation indication of step  100 . For example, if a user has pressed a key to indicate object manipulation, system  75  will wait for the key to be released. If the object manipulation indication is based on movement of mouse  52 , system  75  will wait for the button of mouse  52  to be released. Step  108  is then performed. 
     At step  108 , system  75  returns camera  10  to the original location, thus providing the user with the original viewing location. As in step  104 , the movement of camera  10  is also animated so that the user is oriented to the original viewing location. System  75  then returns to step  100  and waits for another object manipulation indication. 
     As described, the present invention automatically moves a camera in a 3-D graphic scene during object manipulation so a user has and improved viewing location. When the user has completed manipulation the object, the present invention automatically returns the camera to its original location. 
     Several embodiments of the present invention are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing form the spirit and intended scope of the invention. 
     For example, the embodiments illustrated use a mouse and a keyboard as input devices. However, the present invention can be practiced with any type of known input device.