A first approach to obtain a virtual reality model for a whole site consists of taking a few overview photographs from the distance. Since our technique is independent of scale this yields an overview model of the whole site. The only difference with the modeling of smaller objects is the distance needed between two camera poses. For most active techniques it is impossible to cope with scenes of this size. The use of a stereo rig would also be very hard since a baseline of several tens of meters would be required. Therefore one of the promising applications of the proposed technique is large scale terrain modeling.
In Figure 9.18, 3 of the 9 images taken from a hillside near the excavation site are shown. These were used to generate the 3D surface model seen in Figure 9.19. In addition one can see from the right side of this figure that this model could be used to generate a Digital Terrain Map or an orthomap at low cost. In this case only 3 reference measurements -GPS and altitude- are necessary to localize and orient the model in the world reference frame.