In CCM, the image interpretation and the measurement task is done by the operator. The software does the structuring. For visualization, simulation, animation and analysis we largely resort to other parties, mostly commercial software.

Figure 1 describes the work- and dataflow of CCM. The operator measures on an Analytical Plotter or on a Digital Station in the stereomodel individual points that fully describe the visible part of an object, i.e. the roof of a building.

Figure 1. Work- and dataflow of CCM
CCM presents a new method for fitting planar faces to the resulting 3-D point cloud. This face fitting is defined as a consistent labeling problem, which is solved by a special version of probabilistic relaxation. In theory there are various labeling methods available, but only one solution is desired, which meets the inherent topological constraints of the object. From a geometrical point of view, the inherent topological constraints can be summarized as:

1. a 3-D object is a closed multiple-plane object;
2. planes are not supposed to pierce each other;
3. every two adjacent boundary points are always part of a face.

As an automatic topology generator, CCM is generic in the sense that any object, which is bounded by a polyhedral surface, can be structured. With this technique, hundreds of objects may be measured in a day. The computation of the structure is much faster than the measurements of the operator, such that the procedure can be implemented in on-line mode. If overlay capabilities are available on the stereo device the quality control and the editing by the operator becomes very intuitive and efficient.

The DTM, if not given a priori, can also be measured and integrated.

Texture from aerial images is mapped automatically on the terrain and on the roofs, since the geometrical relationship between object faces and image planes has been established. Facade texture is produced semi-automatically via projective transformation from terrestrial images, usually taken by camcorders or still video cameras. If it is necessary to map more than one image for one facade, the images are mapped together by CCM.

The system produces its own internal 3-D data structure, including texture. Interfaces to major public data formats are available.

The system and software are fully operational. In the order of 100’000 buildings at high resolution have been generated already with this approach. Figure 2 shows one of the models, the Congress Center RAI, Amsterdam, location of the XIX th ISPRS Congress 2000.

Figure 2. 3-D model of the Congress Center RAI, Amsterdam, produced with CCM (vector data, overlaid with natural texture).