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Geometry Processing

The basic input data that we have consist of architectural drawings provided by the city administration. These data were gathered some years ago when a 1:400 scale wooden model of the center of Tübingen was built. For almost every house we have floor plans for each layer (horizontal views) as well as drawings of the front and back of the house (vertical views). An example can be seen on the left. These drawings were the only data we had which meant that roofs, dormers and oriels were often only partially specified, forcing us to examine the real house and re-model those structures. An important point in this context is that the houses in Tübingen are quite irregular; e.g. it is very common for the upper floors to stick out a little relative to the lower floors.

The construction of the geometry consists of two steps: First we collected the appropriate drawings and used a drawing tablet to indicate relevant points (corners) on each of these. The selection of relevant points was a manual process that included some minor simplifications of the geometry. The vertical views were used to indicate the height of each floor and the roof. The basic assumption that we made was that all walls are vertical and flat. In the large majority of cases this is quite reasonable and simplifies the construction process considerably. Of course, individual adjustments have been made afterwards to make the geometry more realistic. After digitization of the drawings in a second step we used a custom-made software tool which generated a polygonal 3D-model of the house from the specified fiducial points. An additional problem that became apparent at this stage was that the drawings did not have alignment markers on them. This meant that the digitized drawings had to be aligned (shifting and rotating) manually using some assumptions about the actual spatial relationships between the different layers. The model was then converted to a format, which could be loaded into our 3D modeling program. We used this modeler to improve the geometry a little (filling gaps and taking care of some things the first program could not take care of, such as building the roof).

At this stage we have a triangulated wireframe model of the building (see the example on the left).















VRML-model of a wired building


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