"The Invisible Shape of Things Past" by Dirk Lüsebrink and Joachim Sauter is an exploration of the representation of time and navigation through time in VR. Film sequences (time-based information) are transformed into interactive virtual objects.

Following a long interest in the representation of virtual space and navigation in virtual spaces, "The Invisible Shape of Things Past" is an exploration of the representation of time and navigation through time in VR. Our project enables users to transform film sequences (time-based information) into interactive virtual objects. This transformation is based on all the camera parameters of a particular film sequence (movement, perspective, focal length). The individual frames of the film are lined up along the path of the camera as it is transferred to virtual space.

The angle of the individual frames in relation to the virtual camera path depends on the perspective of the actual camera, the size of the individual frames depends on the focal length used. A virtual architecture of information emerges, which represents the underlying film sequence through its form. This object may be explored interactively, it is the spatial user interface (VRUI) to the information it contains. Activating the front side of the object, for example, "plays the movie" - a double click leads the user through the object along the virtual camera path.

Since there is not only a place but also a time for the occurrence of each film sequence, a virtual representation of the place of occurrence was modeled for the organization of the film objects, thus enabling the user to navigate through time. Using the example of Berlin, all the urban situations since the year 1900 were modeled, and the film objects were positioned according to the virtual location and the virtual time layer, where and when they were shot. Three concepts were developed for navigating through these time layers. The first and most obvious concept is based on the transformation from one temporal urban situation to the next (spatial morphing). With the help of a timeslider, the user can change the surroundings according to the year selected. The second concept is based on the spatial layering of the individual historical conditions. In this case, users navigate spatially through time. In the third and most VR-adequate concept, elements from different time layers may be individually configured, for example by placing the future building plan of Potsdamer Platz on a current aerial picture and adding the course of the Berlin Wall and all the film objects from 1940 to 1945.

In addition to a local interactive application, a networked VRML Web application has been developed, enabling Internet users to integrate their film sequences as objects in the virtual Berlin. In addition to the aspect of a spatial database of film material, another result is that through these film objects an urban architecture that was previously invisible is able to grow with the help of the Internet.

In a final step, a film object based on a sequence filmed in the Leipziger Strasse in 1941 is integrated into the exact same location as a simulation in the real space of today. This could be the starting point for designing a real architectonic or sculptural object.