4. Transform the scene into an absolute coordinate system. This step has to be handled explicitly, because the epipolar geometry allows the 3D reconstruction only in an arbitrary coordinate frame. To compute the transformation, at least three 3D world points and its 2D projections have to be known. In archaeology, such points are already determined during the documentation procedure by photogrammetric techniques. Hence, we call them photogrammetric points . For
each photogrammetric point a corresponding 3D point in the model’s coordinate system can be computed by triangulating [5] from its 2D projections. We use the method described in [6] to compute the transformation. Transforming the scene
into the absolute coordinate system not only allows to measure in the virtual model, but also to geo-reference it.