Regularization by CAD editing
This is a semi-automated supervised procedure, which operates only in planimetry. Therefore, it requires that the equal height condition is already observed during the point measurement phase. Then a grid of parallel construction lines is generated and overlaid to the measured lines. The measured lines are automatically adjusted to the direction of the grid. The grid's direction itself is derived from the average direction of the measured lines concerned. The selection of the concerned lines can be done automatically or manually. The overlay display is used for checking and manual editing if something went wrong.

The right angle, collinearity and the planar face constraints are automatically observed by that procedure. Since we use hard constraints here, the results are strict. An example is shown in Figure 5.

Figure 5. Line rectification (dotted line: before, solid line: after).
Topology adjustment
Inconsistencies in topology between adjacent buildings may arise because of measurement errors and because of mutually overlapping roofs.

Figure 6 shows a typical topology problem, which may exist even after the previous geometry regularization. For its solution, we provide both an automated and a semi-automated procedure.

Figure 6. CC-Edit: CCM user interface for editing with an example of topological inconsistency between adjacent buildings.
In the automated mode, the system selects a reference borderline which is kept fixed and onto which the points of the other lines are projected perpendicularly. As reference line, we select the longest line (which is supposed to be the most stable). In the semi-automated mode, this reference line is selected manually.

The functioning of the automated and semi-automated procedures described above can be monitored by an operator within an editing window as shown in Figure 6. This has of course a certain similarity with a CAD interface. It actually contains many typical CAD functions, but also others which are unique to our system and application-related. An example of automatic topology correction is shown in Figure 7.

Figure 7. CC-Edit: Result of editing with example of false (left) and automatically corrected topology (right).
Building facade integration
The aim is a higher level of detail in building modeling. Since facades are in general not visible in aerial images we use digital cadastral maps, which show the outer walls of buildings as part of the legal definition of real estate property. By integrating this infomation into the rooflandscape we are able to model the roof overhangs. What sounds like a simple problem at first sight turns out to be a formidable task to automate. In terms of structural detail, the rooflandscape looks very different from the facade landscape. Sometimes the maps are outdated and the roofs do not match the map content at all. Maps may also be inaccurate to an extent that the facade appears shifted and rotated with respect to the roof by a substantial amount. Facades can show a lot of additional, peripheral details, as for instance stairs and other add-ons (Fig. 8).

Figure 8. Plan view of roof landscape (dark) and the related facade representation from a map (light).