Peter FERSCHIN / Monika DI ANGELO / Stefan NIEDERMAIR
(University of Technology, Vienna, Austria)

Abstract: Aside of the architectural heritage that is readily visible to the public like well-known tourist sites, there are many objects which only exist in restricted excavation sites or in museums to where they have been moved. Some of them exist in literature only.
Archaeologists put a lot of effort into the reconstruction of architectural heritage, nowadays in digital form. Still, most of this work is hardly ever shown to the public in its original size.
We advocate the projection of architectural heritage in its reconstructed form. To make the reconstruction ever more convincing we suggest a projection in situ, showing the virtual reconstruction in its original place.
In this paper we address the challenge to project over existing architecture that now looks different to the past. As a methodology of our approach we apply 3 steps: firstly, a 3D reconstruction of architectural heritage (site) that is to be shown is called for. Then a 3D model of the original location at present must be prepared. Finally, the projection of the reconstruction onto its original place at present has to be developed. The challenge here is to take the uneven and textured surface of the existing architecture into account. This will be achieved through a projection mapping technique, correcting the geometric distortion as well as the texture variation of the natural projection environment.
As a result of this work we aim at a virtual reconstruction of past times as a nightly projection for the public to enjoy. With this approach a virtual time travel through different epochs is possible and made visible. The innovative technique of this approach lies in its mixed reality visualisation of architectural heritage: the (virtual) past is projected over the present in its original location.

Keywords: architectural heritage, 3D reconstruction, projection mapping