Patent Publication Number: US-9424676-B2

Title: Transitioning between top-down maps and local navigation of reconstructed 3-D scenes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/699,896 filed Feb. 4, 2010, now U.S. Pat. No. 8,624,902, entitled “Transitioning Between a Top-Down Map Display and a Local Navigation Display of Reconstructed 3-D Scenes,” which is incorporated herein by reference in its entirely. 
    
    
     BACKGROUND 
     Using the processing power of computers, it is possible to create a visual reconstruction of a scene or structure from a collection of digital photographs (“photographs”) of the scene. The reconstruction may consist of the various perspectives provided by the photographs coupled with a group of three-dimensional (“3-D”) points computed from the photographs. The 3-D points may be computed by locating common features, such as objects or edges, in a number of the photographs, and using the position, perspective, and visibility or obscurity of the features in each photograph to determine a 3-D position of the feature. The visualization of 3-D points computed for the collection of photographs is referred to as a “3-D point cloud.” For example, given a collection of photographs of a cathedral from several points of view, a 3-D point cloud may be computed that represents the cathedral&#39;s geometry. The 3-D point cloud may be utilized to enhance the visualization of the cathedral&#39;s structure when viewing the various photographs in the collection. 
     Current applications may allow a user to navigate a visual reconstruction by moving from one photograph to nearby photographs within the view. For example, to move to a nearby photograph, the user may select a highlighted outline or “quad” representing the nearby photograph within the view. This may result in the view of the scene and accompanying structures being changed to the perspective of the camera position, or “pose,” corresponding to the selected photograph in reference to the 3-D point cloud. This form of navigation is referred to as “local navigation.” 
     Local navigation, however, may be challenging for a user. First, photographs that are not locally accessible or shown as a quad within the view may be difficult to discover. Second, after exploring a reconstruction, the user may not retain an understanding of the environment or spatial context of the captured scene. For example, the user may not appreciate the size of a structure captured in the reconstruction or have a sense of which aspects of the overall scene have been explored. Furthermore, since the photographs likely do not sample the scene at a regular rate, a local navigation from one photograph to the next may result in a small spatial move or a large one, with the difference not being easily discernable by the user. This ambiguity may further reduce the ability of the user to track the global position and orientation of the current view of the reconstruction. 
     It is with respect to these considerations and others that the disclosure made herein is presented. 
     SUMMARY 
     Technologies are described herein for transitioning between a top-down map display of a reconstructed structure within a 3-D scene and an associated local-navigation display. In a display of a visual reconstruction of the 3-D scene, a user may utilize the top-down map display as an alternative means of navigating the photographs within the reconstruction, enhancing the user&#39;s understanding of the environment and spatial context of the scene while improving the discoverability of photographs not easily discovered through local navigation. If the user selects a camera pose, object, point, or other element of the reconstruction on the top-down map display, the display may be transitioned to the local-navigation display showing a representative photograph based on the selected element. Utilizing the technologies described herein, this transition may be performed in such way as to preserve the continuity between the top-down map display and the local-navigation display without causing confusing or visually unpleasant effects like camera spiral or vertigo. 
     According to embodiments, an application transitions between the top-down map display and the local-navigation display by animating a view in a display window over a period of time while interpolating camera parameters from values representing a starting camera view to values representing an ending camera view. In one embodiment, the starting camera view is the top-down map display view and the ending camera view is the camera view associated with a target photograph. In another embodiment, the starting camera view is the camera view associated with a currently-viewed photograph in the local-navigation display and the ending camera view is the top-down map display. In yet another embodiment, the starting camera view is the camera view associated with a currently-viewed photograph in the local-navigation display and the ending camera view is the camera view associated with another photograph within the reconstruction, with the animation moving from the starting camera view to the top-down map display view and then from the top-down map display view to the ending camera view. 
     It should be appreciated that the above-described subject matter may be implemented as a computer-controlled apparatus, a computer process, a computing system, or as an article of manufacture such as a computer-readable medium. These and various other features will be apparent from a reading of the following Detailed Description and a review of the associated drawings. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended that this Summary be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing aspects of an illustrative operating environment and several software components provided by the embodiments presented herein; 
         FIG. 2  is a display diagram showing an illustrative user interface for displaying a local-navigation display of a visual reconstruction, according to embodiments presented herein; 
         FIG. 3  is a display diagram showing an illustrative user interface for displaying a top-down map display of the visual reconstruction, according to embodiments presented herein; 
         FIG. 4  is a diagram showing aspects of one technique for transitioning from the local-navigation display to the top-down map display, according to embodiments presented herein; 
         FIG. 5  is a diagram showing aspects of one technique for transitioning from the top-down map display to the local-navigation display, according to embodiments presented herein; 
         FIG. 6  is a flow diagram showing methods for performing the transition from the local-navigation display to the top-down map display, according to embodiments described herein; 
         FIG. 7  is a flow diagram showing methods for performing the transition from the top-down map display to the local-navigation display, according to embodiments described herein; and 
         FIG. 8  is a block diagram showing an illustrative computer hardware and software architecture for a computing system capable of implementing aspects of the embodiments presented herein. 
         FIG. 9  illustrates Table 1 representing a sigmoid function producing an “S-curve.” 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is directed to technologies for transitioning between a top-down map display of a reconstructed structure within a 3-D scene and an associated local-navigation display. While the subject matter described herein is presented in the general context of program modules that execute in conjunction with the execution of an operating system and application programs on a computer system, those skilled in the art will recognize that other implementations may be performed in combination with other types of program modules. Generally, program modules include routines, programs, components, data structures, and other types of structures that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the subject matter described herein may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. 
     In the following detailed description, references are made to the accompanying drawings that form a part hereof and that show, by way of illustration, specific embodiments or examples. In the accompanying drawings, like numerals represent like elements through the several figures. 
       FIG. 1  shows an illustrative operating environment  100  including several software components for transitioning between a top-down map display of a reconstructed structure within a 3-D scene and an associated local navigation display, according to embodiments provided herein. The environment  100  includes a server computer  102 . The server computer  102  shown in  FIG. 1  may represent one or more web servers, application servers, network appliances, dedicated computer hardware devices, personal computers (“PC”), or any combination of these and/or other computing devices known in the art. 
     According to one embodiment, the server computer  102  stores a collection of photographs  104 . The collection of photographs  104  may consist of two or more digital photographs taken by a user of a particular structure or scene, or the collection of photographs may be an aggregation of several digital photographs taken by multiple photographers of the same scene, for example. The digital photographs in the collection of photographs  104  may be acquired using digital cameras, may be digitized from photographs taken with traditional film-based cameras, or may be a combination of both. 
     A spatial processing engine  106  executes on the server computer  102  and is responsible for computing a 3-D point cloud  108  representing the structure or scene from the collection of photographs  104 . The spatial processing engine  106  may compute the 3-D point cloud  108  by locating recognizable features, such as objects or textures, that appear in two or more photographs in the collection of photographs  104 , and calculating the position of the feature in space using the location, perspective, and visibility or obscurity of the features in each photograph. The spatial processing engine  106  may be implemented as hardware, software, or a combination of the two, and may include a number of application program modules and other components on the server computer  102 . 
     A visualization service  110  executes on the server computer  102  that provides services for users to view and navigate visual reconstructions of the scene or structure captured in the collection of photographs  104 . The visualization service  110  may be implemented as hardware, software, or a combination of the two, and may include a number of application program modules and other components on the server computer  102 . 
     The visualization service  110  utilizes the collection of photographs  104  and the computed 3-D point cloud  108  to create a visual reconstruction  112  of the scene or structure, and serves the reconstruction over a network  114  to a visualization client  116  executing on a user computer  118 . The user computer  118  may be a PC, a desktop workstation, a laptop, a notebook, a mobile device, a personal digital assistant (“PDA”), an application server, a Web server hosting Web-based application programs, or any other computing device. The network  114  may be a local-area network (“LAN”), a wide-area network (“WAN”), the Internet, or any other networking topology that connects the user computer  118  to the server computer  102 . It will be appreciated that the server computer  102  and user computer  118  shown in  FIG. 1  may represent the same computing device. 
     The visualization client  116  receives the visual reconstruction  112  from the visualization service  110  and displays the visual reconstruction to a user of the user computer  118  using a display device  120  attached to the computer. The visualization client  116  may be implemented as hardware, software, or a combination of the two, and may include a number of application program modules and other components on the user computer  118 . In one embodiment, the visualization client  116  consists of a web browser application and a plug-in module that allows the user of the user computer  118  to view and navigate the visual reconstruction  112  served by the visualization service  110 . 
       FIG. 2  shows an example of an illustrative user interface  200  displayed by the visualization client  116  allowing a user to locally navigate the photographs in the visual reconstruction  112 . The user interface  200  includes a window  202  in which a local-navigation display  204  is displayed. The local-navigation display  204  shows a currently-viewed photograph  206  from the photographs in the visual reconstruction  112 . The local-navigation display  204  may show the currently-viewed photograph  206  in relation to other photographs and the 3-D point cloud that make-up the visual reconstruction  112 . The visualization client  116  may provide a set of navigation controls  208  that allows the user to pan and zoom the currently-viewed photograph  206  in the local-navigation display  204 , as well as move between the photographs of the visual reconstruction  112 . The set of navigation controls  208  may further contain a particular control  210  to change the display to a top-down map display, as described below. 
     According to embodiments, the visual reconstruction  112  includes a top-down map display. Generally, the top-down map display is a two-dimensional view of the 3-D scene from the top. In one embodiment, the top-down map display is generated by projecting all the points of the 3-D point cloud  108  into the x-y plane. The positions of the identifiable features, or points, computed in the 3-D point cloud  108  may be represented as dots in the top-down map display. The points of the 3-D point cloud  108  shown in the top-down map display may be filtered and/or enhanced to reduce the noise and enhance the top-down visualization, as described in co-pending U.S. patent application Ser. No. 12/699,902 filed concurrently herewith, and entitled “Generating and Displaying Top-Down Maps of Reconstructed 3-D Scenes,” which is incorporated herein by reference in its entirety. 
     In other embodiments, the top-down map display may be a photograph or image of the scene from above, a top view of a 3-D model of the scene, or some other two-dimensional representation of the 3-D scene. Further, the top-down map display may be projected onto a reference plane other than the x-y plane. For example, in a visual reconstruction  112  of a cathedral with a large amount of detail on the façade, the plane of the façade may serve as the reference plane for the top-down map display. In addition, a non-planar reference surface may be utilized. For example, in a visual reconstruction  112  of the interior of a room, a cylinder centered at the center of the room may be utilized as the reference surface, with the details of the room&#39;s walls projected onto the cylindrical surface. 
       FIG. 3  shows an illustrative user interface  300  provided by the visualization client  116  for displaying a top-down map display  302  generated from the 3-D point cloud  108 , as described above. In this example, the top-down map display  302  is displayed separately from the local-navigation display  204 . This view is referred to as the “modal view.” The visualization client  116  may provide a similar set of navigation controls  208  as those described above that allows the user to pan and zoom the top-down map display  302  to reveal the entire scene or structure represented in the visual reconstruction  112 , or to see more detail of a particular section. The user may toggle back and forth between the display of the top-down map display  302  and the local-navigation display  204  using the particular control  210  in the set of navigation controls  208 , for example. 
     The visualization client  116  may further provide a number of techniques allowing the user to interact with the top-down map display  302 , as described in co-pending U.S. patent application Ser. No. 12/699,904 filed concurrently herewith, and entitled “User Interfaces for Interacting with Top-Down Maps of Reconstructed 3-D Scenes,” which is incorporated herein by reference in its entirety. These interactions may include the user selecting camera poses, objects, points, or other elements of the visual reconstruction  112  on the top-down map display  302  in order to view associated representative photographs in the local-navigation display  204 . For example, the user interface  300  may include a selection control  304  that allows the user to select a point or group of points on the top-down map display  302 . The selection control  304  may be a pointer, circle, square, or other iconic indicator that the user may move around the map using a mouse or other input device connected to the user computer  118 . 
     According to one embodiment, if the user hovers the selection control  304  over a point on the top-down map display  302 , the visualization client  116  may display a thumbnail image  306  of a representative photograph at an appropriate position on the corresponding map. In addition to the thumbnail image  306 , the visualization client  116  may further display a view frustum  308  or other indicator on the top-down map display  302  that indicates the position and point-of-view of the camera that captured the representative photograph. Further, if the user selects the point under the selection control  304 , by clicking a button on the mouse, for example, the visualization client  116  may transition the display in the window  202  to the local-navigation display  204  showing the representative photograph. 
     Both the local-navigation display  204  and the top-down map display  302  inform the user about the reconstructed 3D scene. In the local-navigation display  204 , the main benefit is visualization of local details. A user may zoom into the currently-viewed photograph  206  in the local-navigation display  204  to appreciate the finer details of the subject. In contrast, the top-down map display  302  provides a global context of the 3-D scene, providing the user with an understanding of the environment in which the photographs were taken. Connecting the context of the top-down map display  302  to the details of the local-navigation display  204  is important because it enables the user to better explore the 3D scene. 
     In order to preserve the spatial connection between the top-down map display  302  and the local-navigation display  204 , the visualization client  116  may employ a number of techniques to transition between the displays. In the simplest approach, the visualization client  116  toggles instantly between the two displays. However, this approach lacks any continuity between the views and the spatial connection is lost. In another approach, the visualization client  116  fades between the two displays, taking advantage of the user&#39;s ability to retain a temporary visual imprint. This approach is only successful in retaining continuity between the views, however, when the top-down map display  302  and the local-navigation display  204  have related orientations. For example, if the currently-viewed photograph  206  in the local-navigation display  204  was taken from the top of a mountain looking down into a valley, then a fade to a top-down map display  302  of the same valley oriented in a “camera-up” direction may be adequate. If, instead, the currently-viewed photograph  206  was taken in the valley of a store façade, for example, then a fade to a top-down map display  302  of the valley may be discontinuous. 
     Alternatively, the visualization client  116  may transition between the top-down map display  302  and the local-navigation display  204  by animating a smooth interpolation between the views, according to the embodiments described herein. Further, these transitions may be performed in such a way as to preserve the continuity between the two views without causing confusing or visually unpleasant effects like camera spiral or vertigo. Both the top-down map display  302  display and the local-navigation display  204  can be expressed in terms of a “camera view.” Generally, the camera view may comprise a set of seven parameters, grouped into 3 categories: position (x, y, z), orientation (pitch, yaw, roll), and field-of-view. Together, these parameters define the top-down map display  302  and local-navigation display  204  views and how they are rendered by the visualization client  116  in the window  202 . The camera view for the local-navigation display  204  is typically defined by the position and orientation of the camera that took the currently-viewed photograph  206 , while the top-down map display  302  camera view is typically positioned high above the 3-D scene, pointed downward with a small field-of-view. 
     According to embodiments, to perform the animated transition from one display to the other, the visualization client  116  interpolates the parameters between the starting camera view and the ending camera view. In one embodiment, the visualization client  116  linearly interpolates between the start values and end values of the parameters over the time of the transition. For example, the visualization client may employ a formula such as:
 
 P ( t )=(1 −t )* S+t*E  
 
where P(t) is the value of the parameter at time t, t having a value between 0 and 1, S is the start value of the parameter, and E is the end value of the parameter. The linear interpolation provides a constant acceleration, however, which may not provide the most intuitive transition.
 
     To achieve a smoother result, the visualization client  116  employs a sigmoid function to perform the interpolations, according to another embodiment. A sigmoid function is defined as: 
               F   ⁡     (   t   )       =     1     1   +     ⅇ     -   t                 
This function produces an “S-curve,” such as that shown in Table 1 of  FIG. 9 . Utilizing the sigmoid function allows the animation of the transition between the views to initially progress slowly, accelerate to a maximum at the center, and decelerate at the end.
 
     The simplicity and smoothness properties of the S-curve make it ideal for user interactions when smooth motion is required. Integrating the sigmoid function into the interpolation function yields:
 
 P ( t )=(1 −F ( t ))* S+F ( t )* E  
 
The visualization client  116  may utilize such a function to perform the interpolations of the parameters for the transition between the camera views. It will be appreciated that the visualization client  116  may utilize a combination of both the linear and sigmoid-based interpolation functions described above, or it may utilize any general function known in the art for interpolating the parameters for the transition between the views, as described below.
 
       FIG. 4  illustrates one method of transitioning the display from the local-navigation display  204  to the top-down map display  302  utilizing the interpolation techniques described above, according to one embodiment. This transition may be performed when the user selects the specific control  210  in the set of navigation controls  208  to toggle the display from the local-navigation display  204  to the top-down map display  302 , for example. In one embodiment, the visualization client  116  may perform the transition between the local-navigation display  204  and the top-down map display  302  in stages, in order to reduce confusing or visually unpleasant effects like camera spiral or vertigo. It will be appreciated that the transition between stages may be performed in a smooth fashion as to position and speed, such that a user may not notice that the overall motion is composed of separate stages. The transition from local-navigation display  204  to the top-down map display  302  may occur in two stages: 1) transition the position and pitch of the camera view to that of the top-down map display, and 2) transition the field-of-view. 
     As shown in  FIG. 4 , in the first stage, the camera view transitions from the starting camera view  402  of the currently-viewed photograph  206  to a position high above the 3D scene, and is pointed downward. Adjusting the pitch enables the camera view to point downward. Note that the camera view does not transition into the last viewed orientation (roll) of the top-down map display  302  display. Instead, the transition results in a “camera-up” orientation of the top-down map display  302  in respect to the currently-viewed photograph  206 . This results in a transition without spiral effect as the camera transitions through the first stage. 
     Once the camera view is positioned and oriented, the second stage transitions the field-of-view from that of the currently-viewed photograph  206  to that of the ending camera view  404  of the top-down map display  302 . Typically, the top-down map display&#39;s field-of-view is small, e.g. about 1 degree, creating a near-orthographic projection. The local-navigation display  204 , however, may have a more typical photographic field-of-view, such as 45 degrees. The visual effect of transitioning between these two fields-of-view is that walls and vertical structures visualized in the top-down map display  302  will appear to bend inward until they become lines. 
     One reason for separating the transition of the position and orientation of the camera view from the transition of the field-of-view is that the combination of the two transitions could produce unwanted visual effects. For example, adjusting the position and pitch of the camera view while adjusting the field-of-view could result in vertigo, or the 3D scene may appear to throb back and forth if the field-of-view shrinks more rapidly than the movement of the camera view  402 . In addition, if the field-of-view decreases rapidly, the camera view  402  approach a near-orthographic projection before completion of the camera movement, resulting in a loss of all perspective cues, referred to as “foreshortening.” 
       FIG. 5  illustrates one method of transitioning from the top-down map display  302  display to a target photograph  406  in the local-navigation display  204 , according to another embodiment. This transition may be performed when the user selects a point or group of points on the top-down map display  302  in order to view a corresponding representative photograph containing the points in the local-navigation display  204 , for example. Similar to the method described above in regard to  FIG. 4 , the transition from top-down map display  302  to local-navigation display  204  may occur in stages to avoid spiraling, vertigo, and non-perspective effects. Specifically, the transition may occur in four stages: 1) rotate the top-down map display view, 2) transition the field-of-view, 3) transition the position and pitch of the camera view from high above the scene to ground level, and 4) approach the ending camera view  404  of the target photograph  406  on the ground level. 
     As shown in  FIG. 5 , in the first stage, the top-down map display  302  is rotated to a camera-up orientation for the map in respect to the target photograph  406  by adjusting the roll parameter of the starting camera view  402 . This avoids any spiraling effects during the transition since the remaining stages only require the camera to “swoop” downward in a straightforward manner. In the second stage, the field-of-view transitions from the starting camera view  402  to that of the target photograph  406 . Decoupling the field-of-view transition from any position or orientation transitions may remove visually unpleasant effects due to vertigo and throbbing, as described above. 
     In the third stage, the position of the camera view is transitioned from high above the top-down map display  302  to an interim camera position  408  approximately at ground level while adjusting the pitch to that of the target photograph  406 . This provides the effect of the camera flying down to ground level at a position slightly behind the ending camera view  404  of the target photograph  406 . In the last stage, the position of the camera view is transitioned from the interim camera position  408  so that the camera approaches the ending camera view  404  for the target photograph  406  in local-navigation display  204 . To avoid visual artifacts that may occur from neighboring photos in the local-navigation display  204 , only the target photograph  406  may be displayed initially as the transition is still distant from the ending camera view  404  position and orientation. As the transition approaches the target photograph  406 , however, neighboring photos may be faded-in. 
     It is possible that before the transition between the displays, the user may have changed the zoom level of the starting camera view. For example, the user may have zoomed-in to the currently-viewed photograph  206  in the local-navigation display  204  to examine more detail, or zoomed-out of the top-down map display  302  display to get a bigger picture of the 3-D scene. In either case, the zooming can cause problems with the transition because the context may be lost. There are two options for transitions in this case: perform the transition starting from the zoomed view, or first transition to a canonical view, then transition into the target view. In the former option, the transition is fast, but if the 3-D scene is sparse (e.g. a sparse 3D point cloud), then the user may lose context in the transition. In the latter option, the disadvantage is that there is an added transition to the canonical view, but the transitions between the views remains consistent and context may be maintained. 
     It will be appreciated that the transitions from the top-down map display  302  display to the local-navigation display  204  or from the local-navigation display to the top-down map display may be accomplished in any number of stages performed in any order, beyond that described above in regard to  FIGS. 4 and 5 . Further the various interpolations of position, orientation, and field-of-view parameters may be performed using linear interpolation functions, sigmoid-based interpolation functions, or any combination of these and other functions known in the art for interpolating the parameters between camera views. It is intended that this application include all such transitional stages and interpolation functions. 
     According to further embodiments, other transitions beyond the transitions from the top-down map display  302  view to the local-navigation display  204  or from the local-navigation display to the top-down map display  302  may be performed using the same approach as described above. For example, while viewing the currently-viewed photograph  206  in the local-navigation display  204 , the user may select another photograph to view from a list of highlighted photographs in the visual reconstruction  112 . Further, the selected photograph may be visually distant from the currently-viewed photograph  206  in the 3-D scene, or may not have a discernable visual connection to the currently-viewed photograph. 
     Simply transitioning the camera view  402  along the ground between the currently-viewed photograph  206  and the target photograph  406  may be confusing. In this case, the visualization client  116  may transition the camera view  402  from that of the currently-viewed photograph  206  in the local-navigation display  204  to the top-down map display  302  using the approach described above in regard to  FIG. 4 , then transition from the top-down map display to the target photograph  406  in the local-navigation display  204  using the approach described above in  FIG. 5 . This may provide a smoother transition for long distances while allowing the user to retain a visual relationship between the two photographs and their position in the overall 3-D scene. 
     Referring now to  FIGS. 6 and 7 , additional details will be provided regarding the embodiments presented herein. It should be appreciated that the logical operations described with respect to  FIGS. 6 and 7  are implemented (1) as a sequence of computer implemented acts or program modules running on a computing system and/or (2) as interconnected machine logic circuits or circuit modules within the computing system. The implementation is a matter of choice dependent on the performance and other requirements of the computing system. Accordingly, the logical operations described herein are referred to variously as operations, structural devices, acts, or modules. These operations, structural devices, acts, and modules may be implemented in software, in firmware, in special purpose digital logic, and any combination thereof. It should also be appreciated that more or fewer operations may be performed than shown in the figures and described herein. The operations may also be performed in a different order than described. 
       FIG. 6  illustrates a routine  600  for performing the transition from the local-navigation display  204  to the top-down map display  302 , in the manner described above in regard to  FIG. 4 . According to embodiments, the routine  600  may be performed by the visualization client  116  described above in regard to  FIG. 1 . It will be appreciated that the routine  600  may also be performed by other modules or components executing on the server computer  102  and/or user computer  118 , or by any combination of modules and components. 
     The routine  600  begins at operation  602 , where the visualization client  116  transitions the camera view from the position and orientation of the starting camera view  402  of the currently-viewed photograph  206  in the local-navigation display  204  to high above the 3-D scene looking down at the top-down map display  302 . This may be performed by animating the view in the window  202  over a period of time while interpolating between the camera parameters for position and pitch, as described above in regard to stage  1  of  FIG. 4 . The interpolation of the parameters may be performed using a linear interpolation function, a sigmoid-based interpolation function, or any combination of these and other functions known in the art for interpolating parameters between camera views. 
     From operation  602 , the routine  600  proceeds to operation  604 , where the visualization client  116  then adjusts the field-of-view of the camera view  402  to produce the near-orthographic projection of the top-down map display  302 , as described above in regard to stage  2  of  FIG. 4 . This may also be performed by animating the view in the window  202  over a period of time while interpolating the field-of-view parameter between the initial field-of-view and the field-of-view of the ending camera view  404 . The visual effect of transitioning between these two fields-of-views is that walls and vertical structures visualized in the top-down map display  302  will appear to bend inward until they become lines. From operation  604 , the routine  600  ends. 
       FIG. 7  illustrates a routine  700  for performing the transition from the top-down map display  302  display to the local-navigation display  204 , in the manner described above in regard to  FIG. 5 . According to embodiments, the routine  700  may be performed by the visualization client  116  described above in regard to  FIG. 1 . It will be appreciated that the routine  700  may also be performed by other modules or components executing on the server computer  102  and/or user computer  118 , or by any combination of modules and components. 
     The routine  700  begins at operation  702 , where the visualization client  116  rotates the starting camera view  402  of the top-down map display  302  to a camera-up orientation in respect to the target photograph  406 , as described above in regard to stage  1  of  FIG. 5 . This may be performed by animating the view in the window  202  over a period of time while interpolating the roll parameter of the camera view for the top-down map display  302 . The roll parameter may be interpolated using a linear interpolation function, a sigmoid-based interpolation function, or any combination of these and other functions known in the art for interpolating parameters between camera views. 
     From operation  702 , the routine  700  proceeds to operation  704 , where the visualization client  116  adjusts the field-of-view from that of the top-down map display  302  to that of the target photograph  406 , as described above in regard to stage  2  of  FIG. 5 . The routine  700  then proceeds to operation  706 , where the visualization client  116  transitions the camera view from the starting camera view  402  high above the 3-D scene to an interim camera position  408  approximately at ground level with the orientation of the target-photograph  406 , as described above in regard to stage  3  of  FIG. 4 . This may be performed by animating the view in the window  202  over a period of time while interpolating between the camera parameters for position, pitch, and roll. The animation provides the effect of the camera flying down to ground level at a position slightly behind the ending camera view  404  of the target photograph  406 . 
     From operation  706 , the routine  700  proceeds to operation  708 , where the visualization client  116  animates the camera view to approach the ending camera view  404  of the target photograph  406  within the local-navigation display  204 , as described above in regard to stage  4  of  FIG. 5 . This may be performed by animating the view in the window  202  over a period of time while interpolating the camera position parameters using a linear interpolation function, a sigmoid-based interpolation function, or some other function or combination of functions known in the art. As the transition approaches the target photograph  406 , the visualization client  116  may further fade-in neighboring photographs in the local-navigation display  204 . From operation  708 , the routine  700  ends. 
       FIG. 8  shows an example computer architecture for a computer  10  capable of executing the software components described herein for transitioning between a top-down map display of a reconstructed structure within a 3-D scene and an associated local-navigation display, in the manner presented above. The computer architecture shown in  FIG. 8  illustrates a conventional computing device, PDA, digital cellular phone, communication device, desktop computer, laptop, or server computer, and may be utilized to execute any aspects of the software components presented herein described as executing on the user computer  118 , server computer  102 , or other computing platform. 
     The computer architecture shown in  FIG. 8  includes one or more central processing units (“CPUs”)  12 . The CPUs  12  may be standard central processors that perform the arithmetic and logical operations necessary for the operation of the computer  10 . The CPUs  12  perform the necessary operations by transitioning from one discrete, physical state to the next through the manipulation of switching elements that differentiate between and change these states. Switching elements may generally include electronic circuits that maintain one of two binary states, such as flip-flops, and electronic circuits that provide an output state based on the logical combination of the states of one or more other switching elements, such as logic gates. These basic switching elements may be combined to create more complex logic circuits, including registers, adders-subtractors, arithmetic logic units, floating-point units, and other logic elements. 
     The computer architecture further includes a system memory  18 , including a random access memory (“RAM”)  24  and a read-only memory  26  (“ROM”), and a system bus  14  that couples the memory to the CPUs  12 . A basic input/output system containing the basic routines that help to transfer information between elements within the computer  10 , such as during startup, is stored in the ROM  26 . The computer  10  also includes a mass storage device  20  for storing an operating system  28 , application programs, and other program modules, which are described in greater detail herein. 
     The mass storage device  20  is connected to the CPUs  12  through a mass storage controller (not shown) connected to the bus  14 . The mass storage device  20  provides non-volatile storage for the computer  10 . The computer  10  may store information on the mass storage device  20  by transforming the physical state of the device to reflect the information being stored. The specific transformation of physical state may depend on various factors, in different implementations of this description. Examples of such factors may include, but are not limited to, the technology used to implement the mass storage device, whether the mass storage device is characterized as primary or secondary storage, and the like. 
     For example, the computer  10  may store information to the mass storage device  20  by issuing instructions to the mass storage controller to alter the magnetic characteristics of a particular location within a magnetic disk drive, the reflective or refractive characteristics of a particular location in an optical storage device, or the electrical characteristics of a particular capacitor, transistor, or other discrete component in a solid-state storage device. Other transformations of physical media are possible without departing from the scope and spirit of the present description. The computer  10  may further read information from the mass storage device  20  by detecting the physical states or characteristics of one or more particular locations within the mass storage device. 
     As mentioned briefly above, a number of program modules and data files may be stored in the mass storage device  20  and RAM  24  of the computer  10 , including an operating system  28  suitable for controlling the operation of a computer. The mass storage device  20  and RAM  24  may also store one or more program modules. In particular, the mass storage device  20  and the RAM  24  may store the visualization service  110  and visualization client  116 , both of which were described in detail above in regard to  FIG. 1 . The mass storage device  20  and the RAM  24  may also store other types of program modules or data. 
     In addition to the mass storage device  20  described above, the computer  10  may have access to other computer-readable media to store and retrieve information, such as program modules, data structures, or other data. By way of example, and not limitation, computer-readable media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. For example, computer-readable media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, digital versatile disks (DVD), HD-DVD, BLU-RAY, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by the computer  10 . 
     The computer-readable storage medium may be encoded with computer-executable instructions that, when loaded into the computer  10 , may transform the computer system from a general-purpose computing system into a special-purpose computer capable of implementing the embodiments described herein. The computer-executable instructions may be encoded on the computer-readable storage medium by altering the electrical, optical, magnetic, or other physical characteristics of particular locations within the media. These computer-executable instructions transform the computer  10  by specifying how the CPUs  12  transition between states, as described above. According to one embodiment, the computer  10  may have access to computer-readable storage media storing computer-executable instructions that, when executed by the computer, perform the routines  600  and  700  for transitioning between the top-down map display  302  display and the local-navigation display  204 , described above in regard to  FIGS. 6 and 7 . 
     According to various embodiments, the computer  10  may operate in a networked environment using logical connections to remote computing devices and computer systems through a network  114 . The computer  10  may connect to the network  114  through a network interface unit  16  connected to the bus  14 . It should be appreciated that the network interface unit  16  may also be utilized to connect to other types of networks and remote computer systems. 
     The computer  10  may also include an input/output controller  22  for receiving and processing input from a number of input devices, including a keyboard  30 , a mouse  32 , a touchpad, a touch screen, an electronic stylus, or other type of input device. Similarly, the input/output controller  22  may provide output to a display device  120 , such as a computer monitor, a flat-panel display, a digital projector, a printer, a plotter, or other type of output device. It will be appreciated that the computer  10  may not include all of the components shown in  FIG. 8 , may include other components that are not explicitly shown in  FIG. 8 , or may utilize an architecture completely different than that shown in  FIG. 8 . 
     Based on the foregoing, it should be appreciated that technologies for transitioning between a top-down map display of a reconstructed structure within a 3-D scene and an associated local-navigation display are provided herein. Although the subject matter presented herein has been described in language specific to computer structural features, methodological acts, and computer-readable media, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features, acts, or media described herein. Rather, the specific features, acts, and mediums are disclosed as example forms of implementing the claims. 
     The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.