Patent Publication Number: US-10762599-B2

Title: Constrained virtual camera control

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/532,475, filed Sep. 15, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This specification relates to systems and methods for constrained virtual camera control. 
     BACKGROUND OF THE INVENTION 
     Navigating in three-dimensional environments, such as in animation software programs, can be disorienting and difficult for users because of an availability of multiple degrees of freedom in navigation of the environments with respect to common input devices. Some current systems enable users to navigate using a mouse and keyboard. With a mouse, a user has control over two degrees of freedom, namely control over the x and y directions. If a user wants to move in a z-direction (e.g., toward or back from an object in the 3D environment), the user can select a key on the keyboard. The selection of the key may modify the function of the mouse so that a horizontal movement of the mouse (e.g., a movement in the x direction), is mapped to a forward or backward movement (e.g., a movement along the z direction). The mapping of navigations from one degree of freedom to another degree of freedom, however, can be counter-intuitive to users. 
     Other systems may enable a user to navigate using a single device with up to seven degrees of freedom in movement. For example, a 3D motion controller may permit a user to control a virtual camera so that it can move horizontally, move vertically, move forward or backward, pan, tilt, or roll, or zoom. It may be difficult, however, for user to navigate around an object in a 3D environment because the user may have to compensate continually while trying to view objects in the environment. For example, a user may have to keep compensating in the x and y directions while tilting and panning a virtual camera so that an object that the camera is viewing stays within the camera&#39;s view. 
     BRIEF SUMMARY OF THE INVENTION 
     In general, this document describes constraining a virtual camera&#39;s viewpoint. 
     In certain implementations, a method is described for manipulating, in a computer-generated environment, an object relative to a different selected object while maintaining a specified orientation relative to the selected object. The method includes receiving, from a first device, input used to select a first object in a computer-generated environment. The first device has at least two degrees of freedom with which to control the selection of the first object. The method also includes removing, in response to the selection of the first object, at least two degrees of freedom previously available to a second device used to manipulating a second object in the computer-generated environment. The removed degrees of freedom correspond to the at least two degrees of freedom of the first device and specify an orientation of the second object relative to the selected first object. Additionally, the method includes receiving, from the second device, input including movements within the reduced degrees of freedom used to manipulate a position of the second object while maintaining the specified orientation relative to the selected first object. 
     In other implementations, a system for manipulating one object relative to another object in a computer-generated environment is described. The system includes a selection device having at least two degrees of freedom for selecting a first object in a computer-generated environment, a navigation device having at least three degrees of freedom for positioning a second object in the computer-generated environment, and a camera control system for reducing the at least three degrees of freedom of the navigation device by fixing two of the at least three degrees of freedom so that the second object remains in a specified orientation relative to the selected first object, but the second object remains free to be positioned using degrees of freedom that remain unfixed. 
     The systems and techniques described here may provide one or more of the following advantages. First, a system may increase the convenience of maintaining a selected object within the view of a virtual camera during camera repositioning. Second, a system can reduce compensation motions used when a virtual camera is manipulated around an object, which may increase the speed and accuracy of performing the manipulations. Third, a system may provide an intuitive method for navigating around objects in a 3D environment. Fourth, a system may enable a user to switch between a specialized navigation function around an object and conventional navigation functions. Fifth, a system may allow a user to specify 2 dimensional visual relationships in a view of a 3 dimensional scene. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages of the embodiments will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects will now be described in detail with reference to the following drawings. 
         FIGS. 1A and 1B  are illustrative system diagrams showing a system that is capable of displaying and editing three-dimensional (3D) images. 
         FIGS. 2A-2G  are screenshots showing changes on a screen when a camera orbits around and moves towards a 3D object. 
         FIG. 3  is an illustrative flowchart of a method that is capable of providing smooth camera navigation in a three dimensional image. 
         FIGS. 4A-4C  are illustrative diagrams showing direct manipulation of 3D objects using the system of  FIGS. 1A and 1B . 
         FIG. 5  is a schematic diagram of an exemplary computing system, according to some embodiments. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1A  shows an illustrative computer system  100  that is capable of displaying and manipulating three-dimensional (3D) graphics. The computer system  100  includes a display  102 , a keyboard  104 , a handheld pointing device  106  (e.g., a mouse), and a motion controller  108 . In this example, the display  102  shows a 3D object  110 . A user, such as a computer aided design (CAD) designer, a 3D animation artist, or other 3D graphics designers, can obtain different views (e.g., a top view, side views from different angles, etc.) of the 3D object  110  by moving a virtual camera around the 3D object  110 . In this example, the user can change from one view to another view of the 3D object  110  by first selecting the 3D object  110  using the handheld pointing device  106 , and second, by navigating the camera around the selected 3D object  110  using the motion controller  108  to orbit around the object. 
     The computer system  100  can be a desktop computer, a handheld computer, a laptop, or another 3D image-displaying device. In some embodiments, the user can have different selecting devices or motion control devices than those depicted in  FIG. 1A . For example, the user can use the keyboard  104  to select the 3D object  110 . In another example, the display  102  can be a touch screen and the user can use his finger to select the 3D object  110 . In other examples, the user can also select the 3D object  110  using a stylus or a touch pad. 
     In some embodiments, the motion controller device  108  can be a gaming controller, such as a joystick or a joypad. In other embodiments, the motion controller device  108  can also be a controller designed specifically for 3D motion control. One example of a 3D motion controller is a SpaceTraveler, developed by 3D connexion Corporation of San Jose, Calif. 
     A virtual camera can navigate in a 3D image using at least seven degrees of freedom, where each of the degrees can specify a position, an orientation, and a field of view of the camera relative to an object in the 3D image. For example, three degrees of freedom may include the ability to move the virtual camera in each of the three dimensions (e.g., x, y, z dimensions defined by corresponding axes). The remaining three degrees of freedom can include the capability to move the camera around the axes that define the first three degrees of freedom (e.g., rotating around each of the x, y, z-axes) while the view from the camera remains focused on the object in the 3D image. More explicitly, the seven degrees of freedom defined in a 3D image can include moving vertically, moving horizontally, moving forward and backward, tilting (which is rotating with respect to the x axis), rolling (which is twisting with respect to the z axis), panning (which is rotating with respect to the y axis), and zooming (which is changing the field of view). 
     In some embodiments, the computer system  100  can represent the position of the camera relative to the seven degrees of freedom using seven coordinates (e.g., x, y, z, t [tilting], r [rolling], p [panning], f [field of view]). A change of one or more of the seven coordinates can change the position or the orientation of the camera, resulting in a change in the camera&#39;s view. 
     As discussed above, the motion controller  108  can be configured to provide at least seven degrees of freedom when manipulating a virtual camera. The motion controller  108  includes a handle  112  that allows a user to control the camera. In some examples, the configuration of the motion controller  108  can be customized. For example, a user can configure the motion controller to orbit the virtual camera in a leftward direction around an object when the user applies a leftward horizontal pressure to the handle  112 . In other configuration examples, when a target object is selected, a user can twist the handle  112  counter-clockwise to orbit the camera around the object in a counter-clockwise rotation. Additionally, in some configurations, moving the handle  112  forward and backwards with horizontal pressure may move the camera toward the object or away from the object, respectively, while remaining centered on the object. Pressing down and lifting up on the handle can move the camera down or up while remaining centered on the selected object. 
     To zoom, a user can press a button on the motion controller simultaneously with applying horizontal pressure on the handle. The zooming can decrease the field of view to focus on a particular selected point on the image. Without the use of the button, horizontal pressure on the handle may return to the previously described function of moving the camera forward and backward relative to the selected object. Of course, the movements of the handle and the corresponding movement of the camera can be mapped in several different ways, and these examples only describe a subset of the possibilities. 
     Using the handheld pointing device  106  and the motion controller  108 , a user can restrain, or fix, one or more of the degrees of freedom and substantially simplify controlling the camera. In some embodiments, the user can select, using the handheld pointing device  106 , a point in the image at which one or more degrees of freedom is restrained. 
     For example, the user can restrain the camera so that it cannot be manipulated in the x or y dimensions relative to a selected point. The user can select the 3D object  110  to be at the center of camera movements, leaving the camera with only four degrees of freedom (e.g., z, t, r, p) relative to the selected object  110 . An animation artist can use the handheld pointing device  106  to select the 3D object  110  and obtain different views of the selected 3D object  110  by navigating the camera around the 3D object  110  using the motion controller  108  to manipulate the unrestrained four degrees of freedom. 
     Restrainment of the degrees of freedom, however, is not limited to eliminating all movement within a dimension, but instead, the restraint may limit permissible movements to a proper subset of movements within a dimension. For example, a user can constrain a camera so that it cannot be manipulated outside of a range of x and y values. The camera, however, can be manipulated in both x and y dimensions (e.g., points on the axes) within the range. Selecting a point on an object with the pointing device  106  (e.g., mouse) while orbiting will still allow the user to move the virtual camera in all dimensions, but only within a restricted combination of translations and orientations. 
     In certain embodiments, the virtual camera is constrained in the following way. Once a point on an object is selected with the pointing device  106 , the selected point can define a 3D ray in space, starting at the camera origin and extending through the selected point on the object. Information associated with the ray, including its orientation with respect to the virtual camera, can be stored. 
     When the motion controller  108  transmits input to manipulate the camera, the virtual camera can be moved incrementally in a direction indicated by the controller (e.g., to the left of the screen). After the potential new camera location and orientation are computed, a new ray may be calculated, where the new ray extends from the virtual camera&#39;s new position to the selected point on the object. The system can compute the rotation required of the virtual camera to align the new ray with the stored ray and apply a corresponding new orientation to the virtual camera. 
     In other embodiments, the virtual camera is constrained by aligning an object ray with a desired ray. For example, a user may be selecting and positioning (e.g., dragging) a selected object in a computer-generated environment, but not manipulating a virtual camera with the motion controller. The user may desire to position and orient the camera so that the user views the object from the camera at a desired perspective. To accomplish this, a “desired” ray is computed, where the desired ray passes through a point on the selected object from an eye of the camera, which is positioned and oriented to obtain the desired perspective. An “object” ray is also calculated, where the object ray originates from current position of the camera and passes through the object. The camera then may be translated so that the object ray aligns with the desired ray. If translation degrees of freedom are removed or restricted for the camera (e.g., the camera is designated as only a pan or tilt camera), then an alignment rotation can be computed instead of computing the translation for the camera. 
       FIG. 1B  shows three exemplary positions  120   a ,  120   b , and  120   c  of a camera&#39;s placement and the corresponding views  122   a ,  122   b , and  122   c  a user would see of a 3D object&#39;s surface  125 . A camera  124  captures the 3D object  110  in the positions  120   a - c . The camera&#39;s field of view is shown by the dashed lines  121 . In the position  120   a , the back of the camera  124  is facing the user. The user perceives the 3D object&#39;s surface  125 , as shown in the image  122   a.    
     To move the camera  124  to a different position relative to the object, the user can use the handheld pointing device  106  to select the 3D object  110  and move the camera  124  while centered on the 3D object  110 . For example, the user can navigate the camera  124  from the position  120   a  to a second position  120   b  by moving the handle  112  of the motion controller  108  to the right, indicated by an arrow  126 . In response, the display  102  can show the corresponding view  122   b , which shows the 3D image rotated to the left. 
     In another example, the user can move the camera  124  from the second position  120   b  to a third position  120   c  by moving a handle of the motion controller  108  forward, indicated by an arrow  128 . In response, the display  102  can show the corresponding view  122   c , which shows a top view of the 3D image. 
       FIGS. 2A-2G  are screenshots  202 ,  204 ,  206 ,  208 ,  210 ,  212 , and  214  that can be viewed in the display  102 . The screenshots  202 ,  204 ,  206 ,  208 ,  210 ,  212 , and  214 , illustrate how a user can manipulate a camera around a 3D object in the display  102  by selecting the 3D object with the pointing device  106  and manipulating the remaining degrees of freedom for the camera using the motion controller  108 . As shown in  FIG. 2A , the user can select a person  216 . The user can make the selection by depressing a mouse button and then releasing it. 
     The screenshot  202  of  FIG. 2A  shows the camera currently positioned behind the person&#39;s back. The user may use the motion controller  108  and move the camera to the right of the person  216  by applying a rightward pressure to the handle  112 , which moves the camera to a viewpoint illustrated in the screenshot  204  shown in  FIG. 2B . The user may continue hold the handle  112  to the right, which moves the camera to a position illustrated by the screenshot  206  shown in  FIG. 2C . If the user continues to apply rightward pressure to the handle  112 , the camera can continue to rotate around the person  216 , as shown in screenshots  208 ,  210 , and  212 , shown in  FIGS. 2D-2F , respectively. 
     By restraining the degrees of freedom of the virtual camera, the user may smoothly move the virtual camera around a fixed object (e.g., the person  216 ). The system  100  may substantially minimize compensation movements by restraining the camera movements to degrees of freedom relative to the fixed object. For example, if the object was not fixed at an x and y point, a user may have to continually make adjustments to keep the object at the center of the navigation at the same time the user is navigating around the object. Fixing the object around which to navigate, may also increase the accuracy of the movements around the object by substantially eliminating extra compensation movements that might negatively affect navigation around the fixed object (e.g., overshooting compensation may affect the navigation by requiring several additional compensation movements in multiple directions to correct the original overshoot). 
     As illustrated by the screenshots  212  and  214  of  FIGS. 2F and 2G , respectively, the user can move the camera forward toward the person  216 , for example, by pushing the handle  112  forward to move toward the person  216 . Because the person&#39;s head is selected by the pointing device  106 , the camera zooms in along a z-axis intersecting a selected point on the person&#39;s head. 
       FIG. 3  shows an illustrative flowchart of a method  300  that is capable of providing smooth camera navigation around a 3D object. In some embodiments, the method  300  can be performed under the control of a processor or control logic in the computer system  100 . For example, the computer system  100  can include a processor that performs the illustrated operations to navigate the camera around a 3D object. 
     The method  300  begins when the computer system  100  receives, in step  302 , a command to select the 3D object using a first device, such as the handheld pointing device  106 . After the selection, the computer system  100  fixes the selected object as a center point of camera movements (e.g., the camera&#39;s view remains centered on the selected object) in step  304 . When an object is fixed as the center point of the camera&#39;s movement, one or more degrees of freedom for the camera&#39;s movement can be restricted relative to the selected object. For example, x and y movements of the camera can be restricted relative to the selected object. 
     In step  306 , the computer system  100  limits the control of a second device, such as the motion controller  108 , so that the second device controls the degrees of freedom that were not fixed in step  304 . For example, the computer system  100  may restrict camera movements to the four degrees of freedom that remain (movements along the z, t, r, and p-axes) after fixing the x and y movements. 
     The computer system  100  can move the camera in the unrestrained degrees of freedom specified by the user, as shown in step  308 . For example, the user can move the camera horizontally around the selected object, but the camera&#39;s focus remains on the selected object fixed at an x and y point. The user can initiate this movement by manipulating the second device. For example, the computer system  100  may receive signals from the motion controller  108 , as discussed with reference to  FIG. 1 . When the user moves the handle of the motion controller  108  to the left, the computer system  100  may orbit the camera horizontally to the left while the focus of the camera remains centered on the selected object. 
     After the user moves the camera to a desired position, the computer system  100 , in step  310 , can receive a deselection command from the first device. For example, if the user selects the object by moving a cursor over the object and depressing a button on the handheld pointing device  106 , then the user can deselect the object by releasing the button. In another example, the user may select an object by depressing a button on the pointing device  106  and then releasing the button. To deselect the object, the user can depress and release the button again when the pointing device&#39;s cursor is over the selected object. 
     In some embodiments, the computer system  100  does not restrain the camera&#39;s degrees of freedom after the deselection. For example, the camera can move in seven degrees of freedom after the deselection, whereas before the deselection, the camera movement was limited to four degrees. After the degrees of freedom are regained, the user may optionally move the camera using all the possible degrees of freedom, as shown in step  312 . 
     In step  314 , the computer system  100  can determine whether the user desires additional camera views relative to an object. If the computer system  100  determines that the user desires additional camera view relative to an object, then the method returns to step  302 . For example, the computer system  100  can determine that the user desires an additional camera view relative to an object when the computer system  100  receives another selection of an object, which may be the same 3D object or a different one. If an additional selection command is not received, the method  300  can end. 
     As shown in  FIGS. 4A-4C , a user, for example, a graphic designer, can use the computer system  100  to manipulate 3D objects in addition to manipulating a virtual camera.  FIG. 4A  shows an exemplary 3D image  402  on the display  102 . The 3D image  402  includes a house  404  and a light  406 . The user can manipulate the 3D image  402  using the handheld pointing device  106  and the motion controller  108 . For example, the user may move the light  406  in the 3D image  402  using the pointing device to select the house  404  and using the motion controller  108  to direct the light  406  to orbit around the house  404 , where a profile of the light that is facing the house remains facing the house as the light orbits. In another example, the user can use the handheld pointing device  106  to select the light  406  and use the motion controller  108  to move the light  406  to the back of the house  404  along the z axis, where the x and y coordinates of the lights  406  are fixed when the light is selected, as shown in an image  408 . 
       FIG. 4B  shows the light  406  in a coordinate system  430  that includes an x-axis  432 , a y-axis  436 , and a z-axis  438 . The position of the light  406  can be specified by a set of coordinates that are relative to the axes  432 ,  436 , and  438 . In some embodiments, the user can use the handheld pointing device  106  to select the light  406 , where the selection fixes the x- and y-coordinates of the light  406 . After the user selects the light  406 , the user can press the handle  112  of the motion controller  108  to change the position of the light  406  along the z-axis  438 . 
     The user can also change the orientation of the light  406 . Two orientations  460  and  480  of the light  406  are shown in  FIG. 4C . After selecting the light  406 , for example, the user may desire to change the orientation of the light  406 . In this example, the light  406  is originally oriented along an x-axis  462  and a y-axis  464 , as shown by the orientation  460 . The user may desire to orient the light  406  along an x new -axis  466  and a y new -axis  468 . To do so, the user can first select the light  406  to fix the x- and y-coordinates of the light  406 . Then, the user can rotate the handle  112  of the motion controller  108 , as indicated by an arrow  470 . The light&#39;s new orientation is shown as the orientation  480 . 
       FIG. 5  is a schematic diagram of an exemplary computing system  500 . The system  500  may be used to perform the method  300  described above, according to some embodiments. The system  500  may be included the computer system  100 , or other computer systems that manipulate camera views of 3D objects. 
     The system  500  includes a processor  510 , a memory  520 , a storage device  530 , and an input/output device  540 . Each of the components  510 ,  520 ,  530 , and  540  are interconnected using a system bus  550 . The processor  510  is capable of processing instructions for execution within the system  500 . In some embodiments, the processor  510  is a single-threaded processor. In some embodiments, the processor  510  may be a multi-threaded processor. The processor  510  is capable of processing instructions stored in the memory  520  or on the storage device  530  to display graphical information for a user interface on the input/output device  540 , such as the display  102 . 
     The memory  520  stores information within the system  500 . In some embodiments, the memory  520  is a computer-readable medium. In some embodiments, the memory  520  is a volatile memory unit. In some embodiments, the memory  520  is a non-volatile memory unit. 
     The storage device  530  is capable of providing mass storage for the system  500 . In some embodiments, the storage device  530  is a computer-readable medium. In various different embodiments, the storage device  530  may be a floppy disk device, a hard disk device, an optical disk device, or a tape device. 
     The input/output device  540  provides input/output operations for the system  500 . In some embodiments, the input/output device  540  can include a keyboard, a pointing device (e.g., a mouse), and a 3D motion controller. In some embodiments, the input/output device  540  includes a display unit, such as the display  102 , for displaying graphical user interfaces. 
     The features described in this disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in a machine-readable storage device, for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described embodiments by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. 
     Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard or keypad and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. 
     The features can be implemented in a computer system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include, e.g., a LAN, a WAN, and the computers and networks forming the Internet. 
     The computer system can include clients and servers. A client and server are generally remote from each other and typically interact through a network, such as the described one. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. For example, the use of the system  100  is not limited to graphical design, but it can be used to navigate other digital settings including video game environments. 
     Additionally, the selected object does not need to be stationary as the virtual camera is navigated around it. For example, a user could select the person  216  and drag the person across the display  102  using the mouse. At substantially the same time, the user could be manipulating the virtual camera around the person  216 . The user can move the camera to keep the selected object at the desired angle or framing from the point of view of the virtual camera. 
     The degrees of freedom described above are only examples of the possible degrees of freedom that the devices may control. For example, additional degrees of freedom can include movement along an axis that permits an image panel (e.g., the entire screen shot of  FIG. 2 ) to slide in horizontal or vertical directions. In another example, the degrees of freedom can include rotating images within the image panels (e.g., a billboard image within a screenshot) around an axis. 
     In another embodiment, the motion controller  108  controls an object&#39;s degrees of freedom and the pointing device  106  similarly constrains an aspect of the object&#39;s motion. For example, the pointing device can hold down the corner of a cube so that it temporarily pivots about the corner. The user may use the motion controller  108  to control how the cube to pivots around the selected point on the cube. 
     In yet other embodiments, a user may position the manipulated object (e.g., a virtual camera) in any fixed orientation relative to the selected object (e.g., a scene element). For example, a user may position a virtual camera so that it remains pointing directly away from a car object that is selected from the scene. When a user manipulates the virtual camera, the camera remains facing away from the car regardless of where the camera is located using the motion controller  108 . 
     A manipulated object may be used as a virtual camera, where the user “sees” from a viewpoint of the manipulated object. For example, a computer-generated scene may include two cubes. A user can select one cube and manipulate another cube relative to the selected cube. The manipulated cube can be treated as a virtual camera, where a simulated viewpoint of the manipulated cube is displayed to the user. 
     In certain embodiments, either the selected object or the manipulated object (e.g., a virtual camera) are driven by procedural input, such as software, rather than directly by user input. For example, the movement of a virtual camera may be re-recorded or can be generated in real time (e.g., such as in a video game), and a user can use the pointing device to supplement, override, or fine-tune the movement of the camera. The user can select an object and the virtual camera can focus on the object as it is following the movements associated with the procedural input. 
     In another example, the operation of the pointing device is generated using procedural input and a user (e.g., animation artist) uses the controller to manipulate an object, such as a virtual camera. The user can position a selected object in the computer-generated environment, “mark” the constraining point, and then later manipulate the virtual camera as if the user was currently restraining the selected object. The saved “mark” acts as a procedural input that simulates user input from the pointing device, and the user is free to manipulate a second object relative to the selected object. 
     In other embodiments, different users can operate the pointing device and the motion controller. For example, one user can direct a virtual camera using the motion controller, while a remote user can select an object on which the camera should focus. 
     Although mentioned in the context of controlling objects and cameras in computer-generated environments, in other implementations, the described systems and techniques can be applied to any user input situation having multiple degrees of freedom, where constraining one or more of those degrees of freedom could improve user&#39;s ability to provide precise and controlled input. For example, the system and techniques can be applied in situations, such as PC or console video gaming, remote piloting of land/sea/air/spacecraft, endoscopy, arthroscopy, or generally surgery using electronically controlled instruments, etc. 
     Also, the logic flow depicted in  FIG. 3  does not require the particular order shown, or sequential order, to achieve desirable results. In addition, although some acts may have been identified expressly as optional, other steps could also be added or removed as appropriate. Also, other steps may be provided, or steps may be eliminated, from the described flow, and other components may be added to, or removed from, the described systems. Accordingly, other embodiments are within the scope of the following claims.