Abstract:
A method for providing panoramic videos and images to a user using a server-client architecture while minimizing the wait time necessary before still images are available for viewing or videos begin playing. A series of location-referenced panoramic images are separated into one-dimensional tracks. Intuitive user controls are provided which allow the user to start and stop video playback, step through the panoramas in a track one at a time, and change the viewing orientation within the panorama. A video will start playing as soon as the video files for the preferred projected cube faces have been downloaded. This delay is reduced by storing the videos as keyframe distance files for opposing directions for each cube face and further reduced by encoding videos with different starting points so that they are staggered by a portion of the keyframe distance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/909,211, entitled “Process for Displaying and Navigating Panoramic Video and Method and User Interface for Streaming Panoramic Video and Images Between a Server and a Browser-Based Client Application” by Joakim Arfvidsson, Hendrik Dahlkamp, Andrew Lookingbill and Sebastian Thrun, filed Mar. 30, 2007, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to providing panoramic video, and more particularly to providing it between a server and a user over a network. 
     2. Description of the Related Art 
     For the purpose of allowing a user to explore a dataset consisting of many location-referenced image panoramas in an immersive manner, a responsive, intuitive user interface and a client-server architecture that minimizes user wait time are critical. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for providing panoramic videos and images to a user using a server-client architecture while minimizing the wait time necessary before still images are available for viewing or videos begin playing. A series of location-referenced panoramic images are assumed to be available. These panoramas are separated, based on their real-world locations, into tracks. These tracks are one-dimensional, and might include all the panoramas corresponding to moving down a city block, for example. 
     While viewing a panorama within a track, a user may move to the panorama on any side of the current panorama, or initiate playback of a video sequence that contains imagery from every panoramic node on the track. These tracks meet at intersections, where users may select from the available tracks and begin traversal of another track. 
     A set of intuitive user controls are provided which allow the user to start and stop video playback, step through the panoramas in a track one at a time, and change the viewing orientation within the panorama. 
     A method is provided for reducing the amount of time a user must wait for video playback to start once playback has been initiated. The video will start playing as soon as the video files for the preferred cube faces have been downloaded up to the frame that contains the desired imagery. This delay is reduced by storing the videos as keyframe distance length files for opposing directions for each cube face and further reduced by encoding videos with different starting points so that they are staggered by a portion of a keyframe distance. Although server-side storage requirements are increased due to the added redundancy of the data, user wait time is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a block diagram of the components for viewing video according to the present invention. 
         FIGS. 2-7  are screenshots illustrating aspects of the user interface according to the present invention. 
         FIG. 8  is a representation of the panorama and related video segments according to the present invention. 
         FIG. 9  is a representation of the encoding scheme of the video segments of  FIG. 8 . 
         FIG. 10  is a flowchart of system operation according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates exemplary components used in various embodiments. A user computer  102  executing a web browser is connected to a network  104 , such as the Internet, to connect in turn to a web server  106 . The web server  106  is connected to a streaming video server  108  which processes stored still images and video present on the video storage  110  to provide the desired panoramic images as described below. The streaming video server  108  contains the necessary programs to stream the desired video, to provide desired still images and to provide and interact with a user interface displayed on the user computer  102  in the web browser. In an alternative, a web server  112  contains both the Internet connectivity software of the web server  106  and contains the still image and video software of the streaming video server  108 . The web server  112  has its associated video storage  114 . This is a simplified illustration and numerous other arrangements of servers and networks can readily be utilized. 
     Referring now to  FIGS. 2-7 , the user interface includes two logical parts, a panorama viewer and a panorama display control. 
     The panorama viewer executes on the streaming video server  108 . When the user is at rest, this component receives six rectangular 2D still images and applies them as textures to the faces of a cube to create a full panorama. The user can pan around to look in any direction by using the panorama display control, which provides commands to the panorama viewer. To reduce bandwidth requirements, and decrease the wait time for imagery, the panorama viewer only loads the cube faces currently visible to the user to the browser window  200 . As the user pans in the image, other cube faces are loaded as necessary. To further reduce the wait time, three levels of still images exist for each cube face, each with a successively higher jpeg compression quality. The images with the smallest file size are loaded first, and replaced as the larger, higher-resolution images are downloaded. The panorama viewer provides the streaming video to the user browser when the user is not at rest in the panorama. Details on this operation are provided below. 
     The control for changing the panorama currently displayed is responsive to user actions. The user actions and corresponding changes in the displayed panorama  200  are: 
     A single-step button  202  for each nearby panorama. A click of the single-step button  202  changes the displayed panorama to the corresponding adjacent one. 
     A play button  204  for each nearby sequence of panoramas. Clicking this play button  204  begins a video which starts from the current panorama, and displays the imagery from each successive panorama until a stopping point such as an intersection is reached, or the user presses a stop button  206 . 
     If there is currently a video playing, clicking the stop button  206  interrupts that video and triggers the loading of higher-quality still images for the current panorama. 
     A double-click on any part of the currently displayed panorama sets the currently displayed panorama to whatever panorama has the best view of the indicated object. 
     A click-and-drag interface allows the user to click on any portion of the visible panorama imagery and drag the mouse to a new position within the visible area. The viewing orientation of the panorama smoothly changes to accommodate this user input, so that at any point in time the pixel that the user clicked on remains under the mouse pointer. 
     The user is allowed to zoom into or out of the imagery currently displayed. In the preferred embodiment, the user signals this with either the mouse wheel or a combination of keyboard inputs, such as CTRL for zooming out and SHIFT for zooming in. To maintain the illusion of a full 3D panorama, minimum and maximum zoom levels are enforced. 
     Part of the screen is occupied by an integrated map  208 , which displays the current viewpoint in the context of its surroundings. When the user interacts with the panoramic component, this viewpoint in the map  208  is updated in real-time and vice versa. The streets for which panoramic imagery is available are indicated in the map by a coloring schema. 
     Entry of a street address into a text-box  210  looks up the address in a geocoding database. The system then changes viewpoint of the currently displayed panorama to the geographical coordinates in the image database that is closest to the address given. 
       FIGS. 5 ,  6  and  7  are three views taken at the same location, taken at roughly 45° increments. If the user places the cursor over the map  208 , its size increases to ease operations on the map  208 . In addition to movement options, such as the double click described above, if the cursor is placed over the map  208  at a location near the indicated user position  212  and in the view field  214 , clicking and dragging allows the view field  214  to be easily rotated around the user position  212 . In this manner the resultant displayed still panoramas change in 45° increments in  FIGS. 5 ,  6  and  7 . 
     Referring to  FIG. 8 , to implement the video functionality discussed above, the panorama viewer applies 2D video images to the faces of a cube  800 , with the cube faces being  802 ,  804 ,  806 ,  808 ,  810  and  812 . After the video images are applied to the cube faces, the resultant 2D video image based on the particular view of the user onto the cube faces is provided to the user for display in the browser. In the preferred embodiment there are six videos, one for each cube face  802 - 812 , for each track. To reduce seek time when changing between adjacent frames, there should be separate sets of videos for going forward and backward along the same track so that there are videos  802   f ,  802   D ,  804   f ,  804   b , etc. Finally, the videos  802   f - 812   b  should be encoded at different resolutions and bitrates, so that the video that provides the best trade-off between download wait time and viewing quality can be provided to each user based on connection bandwidth. 
     In addition, a preferred video encoding schema minimizes bandwidth and latency for the end-user. Since the user is allowed to jump to a random point on the map  208 , the system needs to be able to resume video playback from any such point. The system allows for this functionality by splitting any server video stream into separate video segments instead of one, continuous stream. Referring to  FIG. 9 , this results in video segments  802   f   1x ,  802   f   2x , and  803   f   3x . The video segment lengths correspond to the keyframe distance of the underlying video codec, thus requiring almost no additional bandwidth compared to a single video stream as every keyframe starts in a new video file. As the keyframe distance is relatively short, the size of the video segment is relatively small, allowing faster download, thus further making the system feel more responsive to the user. Furthermore, every location is covered by three separate streams for every direction, whose starting points are spaced apart by ⅓ of the keyframe distance. This results in video segments  802   f   x1 ,  802   f   x2 , and  803   f   x3 . This division ensures that for a random user entry point, the nearest video starting point is always less than ⅙th of the keyframe distance away, resulting in a rapid video playback start when requested by the user. Thus the complete forward direction video segment list for the cube face  802  at a single resolution is  802   f   11 ,  802   f   21 ,  802   f   31 ,  802   f   12 ,  802   f   22 ,  802   f   32 ,  802   f   23  and  802   f   33 . It is noted that similar sets of video segments are present for each desired resolution, direction and cube face. While this results in a large number of stored video segments, the relatively low cost of storage and the resulting improvement in system response times is considered worth the extra storage costs. 
     Proceeding to  FIG. 10 , operation begins at step  1000  where the starting location is determined. In step  1002  the still images for this location are retrieved, projected on the 3D proxy, the desired 2D image is obtained and transmitted to the user. In step  1004  the user&#39;s desired movement indication is received. In step  1006  the closest video segments are retrieved as discussed above. In step  1008  the retrieved video segments are projected onto the 3D proxy and the 2D view of the desired view is obtained. In step  1010  the video is compressed and transmitted to the user. 
     In step  1012 , a determination is made whether the user indicated a new location or direction. If so, operation returns to step  1006  to retrieve the video for the new location. As discussed above, due to the organization the stored video segments, the retrieved video segments will be close to the new location and the transmission can begin very quickly, providing a very responsive system to the user. 
     If the user has not indicated a new location or direction, in step  1014  it is determined if the particular track has ended or the user has indicated a desire to stop movement along the track. As discussed above, the video segments are for various tracks, with tracks starting and ending at selected locations, such as intersections. If the track has ended or movement is to be stopped, operation returns to step  1002  for delivery of the still image for the location. If not ended or stopping, operation proceeds to step  1016  where the next sequential video segments are retrieved and then to step  1008 . 
     The above disclosure generally describes the preferred embodiment only. Those familiar with the skill in the art recognize that there are many different embodiments of the invention. Hitherto we discuss some of the alternative embodiments. The discussion is provided for purposes of illustration only, and thus does not limit the present invention. 
     In the preferred embodiment, the video playback rate is constant once video play has commenced. Clearly, any adaptive frame rate that takes into account the number of frames remaining in the video buffer may be used to eliminate any pauses during video playback due to inadequate buffering. 
     In the preferred embodiment the videos are encoded using a version of the On2 encoder from On2 Technologies. Clearly other encoders could be utilized, such as H-264, MPEG4, MPEG2, WMV9 and the like. 
     In the preferred embodiment, the panorama viewer uses the proxy of a cube with six texture-mapped faces. Clearly other proxies, such as a sphere, may be used in the panorama viewer. Furthermore, other texture tilings are also possible using more or fewer than 6 tiles to cover the surface of the proxy. 
     In the preferred embodiment, a specific set of videos is described for reducing wait times when starting video play. The videos in the set vary by which cube face they describe and at what time they start. Clearly you can also have a larger set of videos that vary also by quality, length, frame rate, proxy, texture tiling on the proxy, and other parameters. 
     In the preferred embodiment, specific user interface elements are described. Clearly one can also use other means of instructing the software to perform its functions, such as pre-recorded user interface actions or using the output of any other software to direct changes. 
     In the preferred embodiment, a full panorama is intended to be available. Clearly the invention can be used with image data produced by any set of cameras or renderings. 
     In the preferred embodiment, a single resolution and frame rate are used for all the cube face videos. Clearly one could use different resolutions or frame rates for video faces with low information content (such as those describing the sky or the ground) or faces that are only partially visible in order to reduce bandwidth requirements while maintaining the perceived quality. This could include efforts to maximize the resolution of areas of the video that are the likely target of user foveation while allowing areas in the periphery to be downloaded at reduced bitrates. User foveation could either be determined using monitoring hardware or probabilistic methods based on video content. 
     In the preferred embodiment, 2D videos and images are downloaded from the server by the client. Clearly any data format could be used including, but not limited to, laser range information, full 3D models, or simplified geometric scene representations. 
     In the preferred embodiment, the imagery being used is outdoor panoramic imagery. Clearly, any images or data visualization could be used, including, but not limited to, medical imaging data volumes, model-based computer graphics, and microscopy image data sets. 
     In the preferred embodiment, the display is a 2D browser window on the client computer. Alternatively, any display could be used, including heads-up displays in vehicles, VR goggles, or mobile device screens. 
     In the preferred embodiment, a rectangular 2D subset of the full panoramic image is used as the visualization framework. Clearly, other visualizations could be used such as a spherical representation of the panoramic image sitting on a plane corresponding to the ground, a set of fixed, static views corresponding to a view of points of interest, such as building facades, or a 2.5 dimensional integration of the panoramic information and strictly 2D information such as maps or satellite imagery. 
     In the preferred embodiment, the client application is assumed to be a standalone browser window offering the user interface functionality discussed above. Clearly, however, the application could also be embedded within other applications such as a pop-up window triggered by user actions in a 2D map. Alternatively, the application itself could be used as a matrix or portal from which other information or applications with geographic significance could be accessed by the user. 
     The panoramic projection of 2D images onto a 3D proxy and then developing a 2D view of the projected image is considered known to those skilled in the art. An early example is in the paper by Boult, T. E., “Remote reality via omnidirectional imaging,” SIGGRAPH 1998 Technical Sketch, p. 253, which is hereby incorporated by reference. Similar systems were developed by Uyttendaele et al., U.S. Pat. No. 6,968,973 and Foote et al., U.S. Pat. No. 7,096,428, both of which are hereby incorporated by reference. A further improvement in these systems is provided in Arfvidsson et al. U.S. patent application Ser. No. 11/837,224 entitled “System and Process for Synthesizing Location-Referenced Panoramic Images and Video,” filed Aug. 10, 2007, which is hereby incorporated by reference. Other techniques and embodiments will be well known to those skilled in the art. 
     While the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.