Abstract:
One embodiment of the present invention sets forth a technique for providing an end user with a digital pen embedded with a spatially-aware miniature projector for use in a design environment. Paper documents are augmented to allow a user to access additional information and computational tools through projected interfaces. Virtual ink may be managed in single and multi-user environments to enhance collaboration and data management. The spatially-aware projector pen provides end-users with dynamic visual feedback and improved interaction capabilities.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate generally to a dynamic visual display and, more specifically, to a spatially-aware projection pen device. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, digital pens that capture the ink strokes made on physical paper have become widely available. These devices combine the versatility and simplicity of paper with digital enhancements such as the capture and recording of annotations. Special paper that includes pre-printed commands may be used to provide a command interface that allows the pen-user to specify commands that control the digital pen. 
         [0005]    A challenge with such systems is that while the pen provides the end-user with rich and dynamic input capabilities through the creation of ink and command strikes, current digital pen devices have very limited output capabilities. Some digital pens have been enhanced with various forms of feedback including auditory, visual, and haptic feedback. The visual feedback is limited to what can be displayed on the barrel of the pen using colored LEDs or small OLED displays. While such displays may be suitable for basic digital pen operations, e.g. querying simple text, these displays are not well-suited for more complex interactions, e.g., searching for a word or object within a document. 
         [0006]    As the foregoing illustrates, what is needed in the art is a technique for providing end-users with improved visual output in digital pen systems. 
       SUMMARY OF THE INVENTION 
       [0007]    One embodiment of the present invention sets forth a spatially-aware projection pen system. The system includes an input mechanism, a position tracking mechanism, a memory, a projector, a processor, and an enclosure. The input mechanism is configured to be activated and deactivated by a user and the position tracking mechanism is configured to determine a position of the spatially-aware projection pen within a three-dimensional space. The memory is configured to store design data and image data. The projector is configured to display a projected image on a display surface, where the projected image includes at least a portion of the design data and/or at least a portion of the image data. The processor is configured to receive input signals from the input mechanism and the position tracking mechanism and output the projected image to the projector for display based on the input signals and the position of the spatially-aware projection pen. The enclosure is configured to be grasped by a human hand and house the input mechanism, the position tracking mechanism, the memory, the projector, and the processor. 
         [0008]    One advantage of the disclosed method is that it allows an end-user to access additional information and computational tools through projected interfaces when viewing a paper document. Virtual ink may be managed in single and multi-user environments to enhance collaboration and data management. The spatially-aware projector pen provides end-users with dynamic visual feedback and improved interaction capabilities, thereby improving the overall end-user experience. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0010]      FIG. 1  illustrates a spatially-aware projection pen system configured to implement one or more aspects of the present invention; 
           [0011]      FIG. 2A  illustrates a spatially-aware projection pen in an environment, according to one embodiment of the invention; 
           [0012]      FIG. 2B  illustrates a spatially-aware projection pen producing a projected image, according to one embodiment of the invention; 
           [0013]      FIG. 2C  illustrates the different input layer regions in a three-dimensional space that includes the spatially-aware projection pen, according to one embodiment of the invention; 
           [0014]      FIG. 2D  illustrates the different input layers, according to one embodiment of the invention; 
           [0015]      FIG. 3A  illustrates a projected radial menu that is produced by the spatially-aware projection pen, according to one embodiment of the invention; 
           [0016]      FIG. 3B  illustrates a flow diagram of method steps for displaying the projected radial menu, according to one embodiment of the invention; 
           [0017]      FIG. 3C  illustrates a projected radial menu that is locked-onto the display surface, according to one embodiment of the invention; 
           [0018]      FIGS. 3D and 3E  illustrate other flow diagrams of method steps for displaying the projected radial menu, according to one embodiment of the invention; 
           [0019]      FIG. 4A  illustrates a physical layer including a floorplan and a spatially-aware projection pen, according to one embodiment of the invention; 
           [0020]      FIG. 4B  illustrates a physical layer including a floorplan, a spatially-aware projection pen, and a projected image, according to one embodiment of the invention; 
           [0021]      FIG. 4C  illustrates a flow diagram of method steps for displaying overlay data, according to one embodiment of the invention; 
           [0022]      FIG. 4D  illustrates a physical layer including a floorplan, a spatially-aware projection pen, and another projected image, according to one embodiment of the invention; 
           [0023]      FIG. 4E  illustrates a flow diagram of method steps for displaying overlay data for a computation, according to one embodiment of the invention; 
           [0024]      FIG. 5A  illustrates a physical layer including a floorplan with a section line, a spatially-aware projection pen, and a projected image, according to one embodiment of the invention; 
           [0025]      FIG. 5B  illustrates a physical layer including a floorplan with a walk-through path, a spatially-aware projection pen, and a projected image, according to one embodiment of the invention; and 
           [0026]      FIG. 5C  a flow diagram of method steps for rendering and displaying overlay data, according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention. 
         [0028]      FIG. 1  illustrates a spatially-aware projection pen system  100  configured to implement one or more aspects of the present invention. The spatially-aware projection pen system  100  includes, without limitation, a central processing unit (CPU)  130 , a system memory  110 , a graphics processing unit (GPU)  115 , a device/memory bridge  105 , a projector  135 , a camera  140 , a force sensor  120 , a network interface  145 , an input mechanism  125 , and a position tracking mechanism  132 . The various components of the spatially-aware projection pen system  100  are packaged within an enclosure to form a spatially-aware projection pen that is configured to be grasped by the human hand. The CPU  130  communicates with the system memory  110  via the device/memory bridge  105 , which may be, e.g., a Northbridge device or subsystem. System memory  110  is configured to store application programs, as well as data used by or generated by the CPU  130 . In particular, system memory  110  is configured to store design data  150 , such as computer-aided design drawings and information that is accessed by the application program  112 . System memory  110  is also configured to store image data  155  for display by the projector  135 . The image data  155  may be produced by the CPU  130  or a discrete GPU  115  based on design data  150  and/or data received via the camera  140 , position tracking mechanism  132 , force sensor  120 , and/or input mechanism  125 . 
         [0029]    System memory  110  is coupled to the device/memory bridge  105  via a system memory bus  150 . The device/memory bridge  105  may be coupled to the GPU  115  that incorporates real-time image rendering means for rendering both three-dimensional (3D) and two-dimensional (2D) images. The CPU  130  or GPU  115  delivers pixel data to projector  135 . In some embodiments, the integrated circuit implementing the CPU  130  may incorporate additional functional blocks, such as the device/memory bridge  105  and GPU  115 . 
         [0030]    The device/memory bridge  105  is coupled to the network interface  144 , the force sensor  146 , the input mechanism  125 , the position tracking mechanism  132 , the projector  135 , and the camera  140 . The network interface  144  provides network connectivity to other computers in local or remote locations using any suitable technology, preferably a wireless technology. In particular, portions of design data  150  and image data  155  may be output to remote users via the network interface  144 . Similarly, data received from a remote user via the network interface  144  may be displayed and/or stored as design data  150  or image data  155 . 
         [0031]    Other components (not explicitly shown), including USB or other port connections, CD drives, DVD drives, film recording devices, and the like, may also be connected via network interface  145 . Communication paths interconnecting the various components in  FIG. 1  may be implemented using any suitable protocols, such as PCI (Peripheral Component Interconnect), PCI Express (PCI-E), AGP (Accelerated Graphics Port), HyperTransport, Quick Path Interconnect, or any other bus or point-to-point communication protocol(s), and connections between different devices may use different protocols as is known in the art. 
         [0032]    In one embodiment, system memory  110  is configured to store a graphics modeling or authoring application program  112  that is configured to access the design data  150  to provide image data  155  for display via projector  135  and use information acquired by the force sensor  120 , the input mechanism  125 , the position tracking mechanism  132 , and the camera  140  to display a user-interface or image data. The force sensor  120  indicates when a tip of the spatially-aware projection pen is in contact with a physical surface and may be used to record pen strokes. An ink reservoir may be configured to deposit physical ink on the display surface when the tip of the spatially-aware projection pen is in contact with the display surface. The input mechanism  125  may be implemented using a button, wheel, or the like, that is configured to be activated and/or deactivated by a user. The position tracking mechanism  132  indicates the position of the spatially-aware projection pen in three-dimensional space relative to a surface, e.g., paper. The position tracking mechanism  132  may be configured to sense full, six degree-of-freedom information. 
         [0033]    The camera  140  may be used capture pen strokes and/or perform two-dimensional tracking by reading a small high-resolution pattern that is physically printed on the display surface. The use of patterns for two-dimensional orientation and tracking is a technique that is familiar to those skilled in the art. Pen strokes that are captured using any combination of force sensor  120 , the input mechanism  125 , the position tracking mechanism  132 , and the camera  140  may be stored as image data  155  and displayed by projector  135  as virtual ink in real-time. The camera  140  may be used to capture pen strokes that deposit physical ink and store the pen strokes as image data  155 . 
         [0034]      FIG. 2A  illustrates a spatially-aware projection pen  205  in a system  200 , according to one embodiment of the invention. One or more of the elements illustrated in spatially-aware projection pen system  100  are included in the spatially-aware projection pen  205 . In order for the pen projector  225  to display the design data  150  and/or image data  155  as a visual overlay in the context of a paper document, the application program  112  needs to be aware of the spatial location relative to the display surface  201 . Capturing the 3D location of the pen tip on or above the display surface  201  allows the spatially-aware projection pen  205  to display virtual information which is relevant to the existing physical content on the paper. The virtual information may be read from design data  150  or information previously captured by spatially-aware projection pen  205  from pen strokes that is stored as image data  155 . The spatially-aware projection pen  205  increases the user&#39;s ability to work with functionality that requires visual feedback, such as viewing the results of computations, and overlaying contextual information using pen projector  225 . 
         [0035]    In one embodiment, the pen projector  225  is positioned 1 cm above and 5 cm away from the tip of spatially-aware projection pen  205 . The pen-projector angle  206  is 7 degrees, and the projector field of view angle  208  is 30 degrees with an aspect ratio of 4/3. This configuration creates a 2.5 cm×2.5 cm projected image when the tip of the spatially-aware projection pen  205  is 5 cm above the display surface  201 . In other embodiments, the pen projector  225  position, the projector field of view angle  208 , and/or the pen-projector angle  206  may vary. 
         [0036]    A camera lens  203  is positioned to enable 2D tracking using patterns printed on the display surface  201 . The camera lens  203  may also be used to enable 3D optical tracking using traceable patterns to retrieve camera calibration parameters to determine 3D location and orientation. The patterns may also represent a hierarchical encoding pattern which allows the camera to cover a wide range of distances from the display surface  201 . Additional patterns may be printed on the display surface  201  in infrared ink to be less distracting to the user. 
         [0037]      FIG. 2B  illustrates the spatially-aware projection pen  205  producing a projected image  220  on a display surface  215 , according to one embodiment of the invention. The location of the pen projector  225  should be carefully considered, since the location affects the operation of the overall system in several ways. The location of the pen projector  225  within the spatially-aware projection pen  205  determines the size of the projected image  220  and the center of mass of the spatially-aware projection pen  205 . Furthermore, the pen-projector angle  206  determines where the tip of the spatially-aware projection pen  205  is in reference to the projected image  220 . Hence, any technique that requires the user to rely on visual persistence to interact with virtual imagery, such as tracing, will be affected by the location of the pen projector  225 . The pen-projector angle  206  may also determine if any “finger shadows” exist on the projected image  220 . 
         [0038]    In some embodiments, a laser based projection is used to keep the projected image  220  in constant focus at different distances from the spatially-aware projection pen  205 . The dynamic brightness may also be accommodated, using a projector that modulates the brightness based on the distance of the spatially aware pen  205  from the display surface  215  and rendering software that takes the dynamic dots per inch (DPI) into account. In other embodiments, a separate projector configuration, such as a display surface mounted projector or even a removable “pen cap projector” are used. 
         [0039]    Conventional digital pens without an integrated projector are not able to display query results or other information on the display surface  215  at different sizes and resolution. The size of projected image  220  may vary dynamically, based on the location of spatially-aware projection pen  205  relative to the display surface  215 . Spatially-aware projection pen  205  also provides a direct link between input, e.g., pen strokes, and output, e.g., projected image  220 . This coupling between the input and output enables a variety of different interaction techniques since the input and output features of the spatially-aware projection pen  205  may be used simultaneously. Additionally, multiple users may share the same display surface  215  and collaborate by each providing input via a spatially-aware projection pen  205 . Remote users may also provide input and see the same projected image  220  on a remote display surface  215 . 
         [0040]      FIG. 2C  illustrates the different input layer regions in a three-dimensional space  250  that includes the spatially-aware projection pen  205 , according to one embodiment of the invention. The spatially-aware projection pen  205  enables multiple input and display layers that enable new interaction techniques and provide richer visual feedback compared with interacting with paper. Users may navigate between different virtual ink and content layers, perform operations on physical and virtual content, extract and display different representations of the printed content on the display surface  235 , and access functionality through a menu system that is displayed by the spatially-aware projection pen  205  in the projected image  242 . 
         [0041]    The three-dimensional space  250  is partitioned into multiple input layers and display layers. A surface input layer  238  is located coincident with the display surface  235 , a hover input layer  245  is located just above the display surface  235 , and a spatial input layer  245  exists in the three-dimensional space  250  above the hover input layer  240 . The spatial awareness of the spacially-aware pen  205  enables above-the surface interaction within the spatial input layer  245 . The main use of the spatial input layer  245  is for command input and to position or rescale the projected image  242 . The primary use of the hover input layer  240  is for command input and manipulation of a virtual cursor within the projected image  242 . 
         [0042]    The surface input layer  238  is where the tip of the spatially-aware projection pen  205  is in physical contact with the display surface  235 . The visibility characteristic of the surface input layer  238  indicates whether or not input within the layer will produce a visible trail of ink. With a standard physical pen, this input is visible. However, it may be desirable to provide input on the display surface  235  without leaving a trail of ink. For example, when providing command input, an ink trail which was used for selection is of no use after the menu item is selected. Also, it may be useful to support virtual ink annotations created on top of the original of a physical image, to avoid undesirable clutter, and to preserve the original. Virtual ink can be created by mechanically switching, either manually or electronically, to a pen tip without ink or by placing a transparency on top of the paper. Since the spatially-aware projection pen  205  captures the content that has been created and tracks the position within three-dimensional space  250 , input created in surface input layer  238  can be either high level global system commands, or contextual, acting on the data which is in proximity to the input. 
         [0043]      FIG. 2D  illustrates the different display and virtual layers, according to one embodiment of the invention. The display layers include the physical display (surface) layer  260  and the virtual display layer(s)  265 . The virtual display layers  268  may include multiple separate virtual layers that are overlaid. Each virtual layer may include one or more of user interface elements  270 , virtual ink  275 , or data content  280 . The physical display layer  260  is the layer which physically exists on the display surface  235  and may include a variety of different elements. Examples of elements include printed content, such as a diagram or two-dimensional building layout, ink created by the user, and user interface elements, such as menus and icons, preprinted on the physical display layer  260 . 
         [0044]    Above the physical display layer  260  are one or more virtual display layers  265  that may be combined to produce the projected image  262 . A variety of display elements may be projected onto the virtual display layers  262 . Two traditional forms of display elements include the user interface elements  270  and the user generated virtual ink  275 . A third form of display element is auxiliary data content  280  stored as part of design data  150 . Auxiliary data content  280  is not explicitly created by the user with the spatially-aware projection pen  205 . Often, only a subset of associated design data  150  and/or image data  155  is transferred to the physical display layer  260  during the printing process. Data content  280  may be useful for displaying aspects of the design data  150  that are not included in the physical display layer  260 . For example, when multivalent documents that consist of multiple abstract layers of distinct, but closely coupled content, are used only some of the abstract layers may be included in physical layer  260 . Multivalent documents are especially prevalent in the application domain of architecture and three-dimensional modeling, e.g., different floor plans, section views, and additional metadata to describe materials and processes. 
         [0045]    The most basic functionality of digital pens and the spatially-aware projection pen  205  is creating virtual and/or physical ink. The spatially-aware projection pen  205  enables users to create and manage virtual ink that users can then make use of in different functions, such as tracing and drawing virtual guides. In some embodiments, the input mechanism  125  is used to change from a pen tip with physical ink to a pen tip using virtual ink that is displayed within the projected image  262 . When virtual ink is enabled, all pen strokes are added to the virtual ink display layer  265 , in the location of the display surface in which they are created. The virtual ink  275  may be stored in image data  155  or design data  150 . By creating the strokes in the surface input layer  238 , the annotations are added to only the virtual display layer  265 . This allows a user to annotate a blueprint without altering the original document. 
         [0046]    Users can trace over both physical and virtual content within projected image  262  to produce trace data that is captured and stored in image data  155 . The trace data may be applied to different special locations within three-dimensional space  250 . Users may also load existing virtual templates to trace out with physical ink input. The resolution and size of the virtual content being traced changes in resolution and size depending on the location of the spatially-aware projection pen  205  relative to the display surface  235 . 
         [0047]    Instead of tracing, virtual guides may be created to aid in generating a physical sketch. Such grids and guides are widely used in image editing applications, but unavailable when working on physical paper. To create a geometric guide, the user can select the line circle, rectangle, or grid menu item. Instead of entering points that define the geometry, the user may draw a similar shape and the spatially-aware projection pen  205  will approximate the selected shape. For example, the user can draw a circle using the spatially-aware projection pen  205  in the three-dimensional space  250 , and the spatially-aware projection pen  205  determines the center point and the radius. In grid mode, users may draw a rectangle that serves as the unit rectangle shape of the grid. Once the spatially-aware projection pen  205  is lifted, the entire virtual layer is covered with a self replicating grid layout. 
         [0048]      FIG. 3A  illustrates a projected radial menu  300  that is produced by the spatially-aware projection pen  205 , according to one embodiment of the invention. The projected radial menu  300  may be implemented using hierarchy to access various functions of the system  200 . The radial distribution of menu items in regions  301 ,  302 ,  303 , and  304  that are separated by region boundaries, e.g., region boundary  305 , simplifies use of the projected radial menu  300  since users only need to remember what direction to move towards. Users can access the projected radial menu  300  by activating the input mechanism  125  on spatially-aware projection pen  205  to cause the top level of the projected radial menu  300  to be displayed in a virtual display player  265 . In contrast, conventional digital pen menu systems rely on menus that are preprinted on the display surface. 
         [0049]    Projected radial menu  300  may be configured to display different levels of hierarchy. The semantic scale of the projected radial menu  300  may vary depending on the position of the spatially-aware projection pen  205  in the three-dimensional space  205 . For example, when the user lifts the spatially-aware projection pen  205  above the hover input layer  240 , two levels of menu items may be shown by subdividing each of the regions  301 ,  302 ,  303 , and  304 , thereby allowing the user to see more items at the same time. Although the projected image  242  appears larger as the spatially-aware projection pen  205  moves further from the display surface  235 , the motor space is smaller, making selection of one of regions  301 ,  302 ,  303 , or  304  more difficult. 
         [0050]    Different metaphors may be used for displaying the virtual display layers  365  and the projected radial menu  300 . A first metaphor is “content locked on-surface” that displays the content on the display surface  235  and the projected image  242  appears as a peephole through which the content is visible. The content is stationary relative to the spatially-aware projection pen  205  since it is in a position that is locked to the display surface  235 . The virtual content is overlaid in the context of the display surface  235 . For example, ink annotations made by a remote collaborator and captured as virtual ink are positioned on top of the content to which they are referring, or virtual content that augments the physical content may be registered with the printed content and be overlaid on the display surface  235 . 
         [0051]    A second metaphor is “content locked in-hand” that generates projected image  242  without any calibration or transformation. The pen projector  225  does not need to be spatially aware when this display mode is used. This mode is also useful when the user wants to change the position or scale of the content as the spatially-aware projection pen  205  moves. 
         [0052]      FIG. 3B  illustrates a flow diagram of method steps for displaying the projected radial menu  300 , according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 and 2A , persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0053]    The method begins at step  310  where the user activates display of the projected radial menu  300  using the input mechanism  125  on the spatially-aware projection pen  205 , i.e., by pressing and releasing a button. At step  312 , the projected radial menu  300  is output via the pen projector  225  to produce projected image  242 . At step  315 , the projected radial menu  300  is locked in position onto the display surface  235  and a virtual cursor is positioned in the center of the projected radial menu  300 . The virtual cursor is locked to the spatially-aware projection pen  205  and moves with the spatially-aware projection pen  205 . At step  320 , the spatially-aware projection pen  205  determines whether the virtual cursor crosses a region boundary that delineates one of the regions  301 ,  302 ,  303 , and  304  while the spatially-aware projection pen  205  is positioned in the hover input layer  240 . 
         [0054]    The method remains at step  320  when a region boundary is not crossed. Otherwise, at step  322 , the item, specified by the region  301 ,  302 ,  303 , or  304  that is entered when the region boundary is crossed, is selected. At step  324 , the spatially-aware projection pen  205  determines whether another level of hierarchy of the projected radial menu  300  should be displayed. If so, then the method returns to step  312 . Another level of hierarchy should be displayed when the selected item is hierarchical, i.e., includes more than one option. Otherwise, at step  325 , the spatially-aware projection pen  205  ends display of the projected radial menu  300 . The projected image  242  remains locked to the position on the display surface  235  while the projected radial menu  300  is activated and the spatially-aware projection pen  205  is configured in the locked on-surface mode. This allows the user to move the spatially-aware projection pen  205  relative to the regions in order to cross a region boundary and select a particular region. Note that the locked-on surface mode may be selected by navigating the projected radial menu  300 . 
         [0055]      FIG. 3C  illustrates the projected radial menu  300  that is locked-onto the display surface  228 , according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 and 2A , persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. The projected image  327  output by the spatially-aware projection pen  205  provides a peephole into the projected radial menu  300 . As the virtual cursor path  326 , which is controlled by movement of the spatially-aware projection pen  205 , crosses the region boundary that delineates region  303 , the menu item specified by region  303  is selected. The spatially-aware projection pen  205  is then configured for an operation based on the selected menu item. 
         [0056]      FIG. 3D  illustrates another flow diagram of method steps for displaying the projected radial menu  300 , according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 and 2A , persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0057]    The method begins at step  330 , where the user activates display of the projected radial menu  300  using the input mechanism  125 . At step  332 , the projected radial menu  300  is output via the pen projector  225  to produce projected image  242 . At step  335 , the projected radial menu  300  is locked to the position of the spatially-aware projection pen  205 , i.e., the projected radial menu  300  moves with the spatially-aware projection pen  205 . The virtual cursor is also locked to the position of the spatially-aware projection pen  205  and appears at the center of the projected radial menu  300 . Menu items cannot be selected by crossing a region boundary because the virtual cursor remains in the center of the projected radial menu  300  when the user moves the spatially-aware projection pen  205 . 
         [0058]    At step  336 , the spatially-aware projection pen  205  determines whether the input mechanism  125  is activated. If so, then at step  338  the projected image  242  is locked to the display surface  228 . Otherwise, the method remains at step  336 . At step  340 , the spatially-aware projection pen  205  determines whether or not a region boundary that delineates one of the regions  301 ,  302 ,  303 , and  304  is crossed while the spatially-aware projection pen  205  is positioned in the hover input layer  240  and the input mechanism  125  is activated. In other words, to complete steps  336 ,  338 , and  340  the user depresses a button on the spatially-aware projection pen  205  and gestures in the direction of the region that specifies the menu item to be selected. The spatially-aware projection pen  205  remains in step  340  when a region boundary is not crossed. Otherwise, at step  342 , the item, specified by the region  301 ,  302 ,  303 , or  304  that is entered when the region boundary is crossed, is selected. The user may release the button when the menu item is selected. 
         [0059]    At step  344 , the spatially-aware projection pen  205  determines whether another level of hierarchy of the projected radial menu  300  should be displayed. If so, then the method returns to step  332 . Otherwise, at step  345 , the spatially-aware projection pen  205  stops displaying the projected radial menu  300 . The projected image  242  remains locked to the position of the display surface  228 . The spatially-aware projection pen  205  is then configured for an operation based on the selected menu item. Note that the locked in-hand mode or the locked to-surface mode may be activated by navigating the projected radial menu  300 . 
         [0060]      FIG. 3E  illustrates another flow diagram of method steps for displaying the projected radial menu  300  using another variation of the locked in-hand mode, according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 and 2A , persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0061]    The method begins at step  360  where the user activates display of the projected radial menu  300  using the input mechanism  125 . At step  362 , the projected radial menu  300  is output via the pen projector  225  to produce projected image  242 . At step  365 , the projected radial menu  300  is locked to the position of the spatially-aware projection pen  205 , i.e., the projected radial menu  300  moves with the spatially-aware projection pen  205 . The virtual cursor is also locked to the position of the spatially-aware projection pen  205  and appears at the center of the projected radial menu  300 . Menu items cannot be selected by crossing a region boundary because the virtual cursor remains in the center of the projected radial menu  300  when the user moves the spatially-aware projection pen  205 . 
         [0062]    At step  370 , the spatially-aware projection pen  205  determines whether a region boundary delineating one of the regions  301 ,  302 ,  303 , and  304  is crossed while the spatially-aware projection pen  205  is positioned in the surface input layer  238 . When this technique of menu item selection is used, ink trails (virtual or physical) may be made on the display surface  235 . The method remains in step  370  when a region boundary is not crossed. Otherwise, at step  372 , the menu item, specified by the region  301 ,  302 ,  303 , or  304  that is entered when the region boundary is crossed, is selected. 
         [0063]    At step  374 , the spatially-aware projection pen  205  determines if the displaying of the projected radial menu  300  should be deactivated. If so, then the method proceeds directly to step  380 . In some embodiments, the user may deactivate the displaying of the projected radial menu  300  by depressing and releasing the input mechanism  125  or by lifting the spatially-aware projection pen  205  above the surface input layer  238 . 
         [0064]    If, at step  374 , the spatially-aware projection pen  205  determines that the displaying of the projected radial menu  300  should not be deactivated, then, at step  376 , the spatially-aware projection pen  205  determines whether another level of hierarchy of the projected radial menu  300  should be displayed. If another level of hierarchy of the projected radial menu  300  should be displayed, then the method returns to step  362 . Otherwise, at step  380 , the spatially-aware projection pen  205  stops displaying the projected radial menu  300 . The spatially-aware projection pen  205  is then configured for an operation based on the selected menu item. The projected image  242  remains locked to the position of the spatially-aware projection pen  205  while the spatially-aware projection pen  205  is configured in the locked in-hand mode. Note that the locked in-hand mode or the locked on-surface mode may be activated by navigating the projected radial menu  300 . 
         [0065]    When the locked in-hand mode is used, it may be desirable to use an image stabilization technique since the projected image  242  moves with any movement of the spatially-aware projection pen  205 . One technique that may be used involves updating the projected image  242  at fixed intervals in time or at discrete intervals, such as when the spacially-aware pen  205  is in a relatively stable position. Once the spatially-aware projection pen  205  begins moving faster than a threshold velocity value, the projected image  242  may fade out, i.e., become increasingly transparent. This introduces a unique interaction characteristic, specifically that the user may be able to see the virtual imagery when holding the spatially-aware projection pen  205  in a stable position, but the user relies on his or her persistence of vision to interact with the projected image  242  when moving the spatially-aware projection pen  205 . 
         [0066]    Professions such as architecture rely on a paper intensive workflow to distribute designs among different parties and to represent the actual contract commitment. While paper drawings are ubiquitous in each stage of architecture practice, the usefulness of paper drawings is somewhat limited. In particular, it is difficult to access additional information related to the paper drawings. During a discussion between architects and their clients in a meeting room, oftentimes the clients want to see a three-dimensional rendering of the design. This normally requires a computer nearby and real-time applications to simulate the walk-through. Another limitation of conventional paper drawings is that levels of detail are spread across many different pages. Manually tracing one layer of information from one page of a paper drawing onto a sheet (typically onionskin paper) and overlaying that sheet on top of another page of a paper drawing is a common practice that architects use to compensate for this limitation. It is also difficult to coordinate different versions of a design document between different service providers and clients as well as between remote collaborators. 
         [0067]    The spatially-aware projection pen is particularly useful for workflows that are paper-based and use complex designs with multiple layers or contexts. In particular, with the spatially-aware projection pen, users can interact with different layers, access design data, and capture design changes and other input. Importantly, users can query and augment physical architectural sketches and collaborate with remote users. Thus, the spatially-aware projection pen addresses many of the problems set forth above that arise from complex, paper-based workflows that include multiple layers or contexts. 
         [0068]      FIG. 4A  illustrates a spatially-aware projection pen  400  and a physical layer including a floorplan that is printed on the display surface  408 , according to one embodiment of the invention. Various layers of the design data  150  and/or image data  155  can be overlaid onto the display surface  408  within the projected image  407  that is produced by the spatially-aware projection pen  400 . 
         [0069]      FIG. 4B  illustrates a spatially-aware projection pen  410 , a physical layer including a floorplan that is printed on the display surface  408 , and a projected image  417 , according to one embodiment of the invention. The projected image  417  includes electrical components  415 . Note that the electrical components  415  are only visible within the projected image  417  (the peephole). In other embodiments, the projected image  417  may include additional components or additional layers, e.g., heating, ventilation, mechanical, lighting, and the like. 
         [0070]    The overlaid content or the original physical content may be copied to another location on display surface  418  to be overlaid. The user enters a copying mode using the projected radial menu  300  and indicates an area using the spatially-aware projection pen  410  to specify a contextual parameter of the projected image  417  or the image printed on the display surface  418 . The user then enters a pasting mode using the projected radial menu  300 , and the copied content is displayed using the locked in-hand metaphor and copied when the user engages the input mechanism  125 . 
         [0071]      FIG. 4C  illustrates a flow diagram of method steps for displaying overlay data, according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 ,  2 A,  4 A, and  4 B, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0072]    The method begins with step  420  where the user selects the overlay data to be displayed in the projected image. The data may be selected using the projected radial menu  300 . At step  422 , the overlay data is displayed using the projector within the spatially-aware projection pen. At step  424 , the user activates the copy mode. At step  426 , the user selects a region or an element within the display surface or the projected image. The region or element may be captured using the camera within the spatially-aware projection pen. At step  428  an image of the copied region or element is stored in memory within image data  155 . At step  430  the user selects a paste position within the display surface using the spatially-aware projection pen. At step  432  the overlay image is updated to include the copied region or element. At step  434  the updated overlay image is displayed using the projector within the spatially-aware projection pen. 
         [0073]      FIG. 4D  illustrates a spatially-aware projection pen  440 , a physical layer including a floorplan that is printed on the display surface  448 , and another projected image  447 , according to one embodiment of the invention. The virtual display layer feature of the spatially-aware projection pen enables computations to be performed and the results displayed in the contexts of the user&#39;s workspace. The user may perform a measurement query by selecting a particular element to be measured using the spatially-aware projection pen  440  and engaging a dimension tool to overlay the measurement information. Using the projected radial menu  300 , the user can choose to measure a distance, path length, area, or volume. Alternatively, the user may create a line or bounding box using the spatially-aware projection pen  440 , and the measurements of the line or bounding box is displayed in projected image  447 . The measurement computation is displayed by the projector of the spatially-aware projection pen  440  within the projected image  447 . 
         [0074]    A search command may allow users to search for an element that exists on the display surface  448  (physical display layer). The user can perform the query in two ways. First, they can choose from a list of query elements, e.g., sprinklers, outlets, and the like, in the search menu provided by the projected radial menu  300  using a virtual cursor. Alternately, the user can directly select an instance of an element on display surface  448  or within projected image  447  using the spatially-aware projection pen  440 . For example, the user may perform a query to search for electrical outlets. In response, the outlets, including outlet  445 , that are within projected image  447  are displayed. Halos  442 ,  443 , and  441  correspond to outlets that are nearby, but not within, the projected image  447 . Halos  442 ,  443 , and  441  may guide the user to additional instances of the element that was searched, allowing the user to find elements of interest faster. The user can raise the spatially-aware projection pen  440  to see a larger portion of the display, i.e., to increase the size of projected image  447 , to navigate toward or to display the elements corresponding to one or more of the halos  442 ,  443 , and  441 . 
         [0075]      FIG. 4E  illustrates a flow diagram of method steps for displaying overlay data for a computation, according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 ,  2 A,  4 A, and  4 B, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0076]    The method begins at step  470  where the user selects a region or element on display surface  448  or within projected image  447  using the spatially-aware projection pen  440 . At step  472 , CPU  130  or GPU  115  obtains the data corresponding to the selected region or element. At step  474 , the CPU  130  or GPU  115  performs one or more computations specified by the user. At step  476 , the overlay image is updated to include the computation result. At step  478 , the updated overlay image is displayed using the projector within the spatially-aware projection pen  440 . 
         [0077]    The printed content that is visible on the display surface is only one abstract view of a larger electronic file that is stored in the design data  150  within system memory  110 . For example, when a two-dimensional floor plan is printed on the display surface, the spatially-aware projection pen  440  may directly access a highly detailed three-dimensional model that is stored as the design data  150  or image  155  or generated by the CPU  130  or GPU  115  using the design data  150 . A view of the three-dimensional model may be displayed within the projected image that is output by the projector within the spatially-aware projection pen  440 . Note that the projected image may be displayed on a display surface, such as a printed floor plan or on a blank surface. 
         [0078]      FIG. 5A  illustrates a physical layer including a two-dimensional floorplan that is printed on the display surface  508 , a spatially-aware projection pen  500 , and a projected image  507 , according to one embodiment of the invention. When a two-dimensional section view mode is engaged, the user may draw the section line  510  on display surface  508  using the spatially-aware projection pen  500  to define a cutting surface that is used to extract a two-dimensional section of the current three-dimensional model. A two-dimensional section view is generated based on the position and orientation of the section line  510  and displayed in the projected image  507 . The two-dimensional section is locked in-hand and may be locked to a position on the display surface  508  using the input mechanism  125  on the spatially-aware projection pen  500 . 
         [0079]    Users can use the spatial input layer feature of the spatially-aware projection pen  500  to extract a three-dimensional snapshot of the current three-dimensional mode. When choosing this operation, the user may use the location and direction of the spatially-aware projection pen  500  in reference to the display surface  508  to specify the camera location and the viewing vector into the three-dimensional model. Varying the height of the spatially-aware projection pen  500  relative to the display surface  508  determines the view that is captured, e.g., the interior view (when the spatially-aware projection pen  500  is near to the display surface  508 ) or the exterior view (when the spatially-aware projection pen  500  is high above the display surface  508 ). As with the section view, the three-dimensional snapshot may be displayed in the projected image  507  and locked onto the display surface  508  or a blank surface. 
         [0080]    In addition to computing and displaying two-dimensional and three-dimensional section views, the spatially-aware projection pen  500  may be used to create a two-dimensional walk-through of a three-dimensional mode.  FIG. 5B  illustrates a physical layer including a floorplan that is printed on the display surface  568 , a spatially-aware projection pen  560 , and a projected image  567 , according to one embodiment of the invention. The user may draw a path, such as walk-through path  565 , on the display surface  568  with the spatially-aware projection pen  560 . Frames of the two-dimensional walk-through represented as pixel data, as viewed from a viewpoint moving along the walk-through path  565 , are generated by the CPU  160  or the GPU  115  and stored in the image data  155  for playback as a walk-through animation. When a pen-up event is detected, the projected image  567  is locked in-hand. When the user activates the input mechanism  125 , the spatially-aware projection pen  560  displays the walk-through animation in the projected image  567  and locks the projected image  567  to the display surface  568 . As the frames are being displayed in the projected image  567 , the walk-through position  562  indicates the position along the walk-through path  565  that corresponds to the current frame that is displayed. 
         [0081]      FIG. 5C  a flow diagram of method steps for rendering and displaying overlay data, according to one embodiment of the invention. Although the method steps are described in conjunction with  FIGS. 1 ,  2 A,  5 A, and  5 B, persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
         [0082]    The method begins at step  570  when the user defines a path or section cut on display surface  568  or within projected image  567  using the spatially-aware projection pen  560 . At step  572 , CPU  130  or GPU  115  obtains the data corresponding to the defined path or section cut. At step  574 , the CPU  130  or GPU  115  renders one or more frames of pixel data to produce two-dimensional view(s) of the three-dimensional model. At step  576 , the rendered frames are stored in image data  155 . At step  578 , the updated overlay image, including the rendered frames, is displayed using the projector within the spatially-aware projection pen  560 . 
         [0083]    In sum, the spatially-aware projection pen enables the use of virtual ink in addition to conventional physical ink. The virtual ink may be used to capture commands, annotate an existing design, and communicate with a remote user. The virtual ink may be displayed as a projected image on a display surface by the spatially-aware projection pen. Auxiliary design information and rendered images may also be displayed in the projected image. The spatially-aware feature of the projection pen allows for gestures to be interpreted differently based on the position of the spatially-aware projection pen in three-dimensional space. 
         [0084]    Unlike a conventional digital pen, the interaction space available to the user of the spatially-aware projection pen is not merely located to the surface input layer, but extends to the space above the display surface. The integrated projector allows a user to visibly correlate information that is stored inside the pen or on any connected resource with the information illustrated on the display surface. As a result, paper is no longer just a static source of data, but it is also used as the display surface and a dynamic workspace. Virtual ink benefits the user by providing visual feedback without permanently modifying the physical display surface. The spatially-aware projection pen enables a user to interact with the design more efficiently and intuitively. 
         [0085]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, aspects of the present invention may be implemented in hardware or software or in a combination of hardware and software. One embodiment of the invention may be implemented as a program product for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein) and can be contained on a variety of computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the present invention, are embodiments of the present invention. 
         [0086]    In view of the foregoing, the scope of the present invention is determined by the claims that follow.