Visorama - Overview


A panorama is a sort of mural painting created on a circular space around a central platform where spectators can look around in all directions and see a scene as if they were in the middle of it. It was patented by Robert Baker in 1787 and at that time was a very popular way to represent landscapes and historical events. They were usually built in two or three storey buildings so spectators could walk through different scenes. The drawing in Figure 1 shows a section in a three storey panorama building in 1810.

Figure1:Section of a panorama building.

By the beginning of this century, several variations of panoramas had been created. One example is the Cinerama, in which cinematographic images were projected onto a circular surface covering 180 degrees. Although three different projections were used, the image appeared to be only one. Some of these variations used additional resources to enhance the user's sense of being immersed in the fictitious world created by the panorama. In the Hale's Tour, for example, which simulated a train ride, the spectators actually sat inside a train, and the images were displayed through the windows. In another variation, the Sensorama, effects such as stereo sound and odors were used to simulate a motorcycle ride through Brooklyn, New York City.

All of these variations share a number of common characteristics. The spectators are inside an environment and images are shown around them. These images display the views that would be seen by the spectators if they were in the middle of a real scene, always trying to achieve as much realism as possible to immerse the observer in this scene. The way panoramas interact with the spectator is accepted naturally, since it resembles the way we usually observe the world around us, as if we were in the center of it. Perhaps this is the psycological reason why panorams have always been so popular.

Virtual Panoramas

Recent advances in image-based rendering techiques have enabled the real-time simulation of panoramas on the computer, which we call virtual panoramas.

In a virtual panorama a digital image is "painted" onto a panorama surface using environment mapping techniques. A virtual camera is then used by the spectators to observe the panorama interactively by rotating the camera around its nodal point and changing its field-of-view, which provides a zooming effect. The image to be projected on the surface is called the panoramic image. This is ilustrated in Figure 2. A few systems have been developed which use virtual panoramas.

Figure2:A virtual camera observing a panorama

A virtual panorama system must provide authoring tools to generate the panorama image and project it onto the panorama surface. The panorama image is generated using photographs from different sources: the real world, in which case a real photographic camera is used, synthetic world, by using a virtual camera, or both by compositing two or more images.

When projected on the panorama surface the panorama image can be interactivelly obseved on the screen, as if the user were at the location where the pictures were taken.

The process described above involves two projections:

Projecting the panorama surface on the virtual camera screen is equivalent to reprojecting an environment map, which is a common operation in computer graphics. Systems may also provide means for playing sound files in the virtual panoramas and for compositing images, animations or 3D objects with the painted panorama image.