EuroSDR Projects - Host Ireland

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Preparation
Building Polygons, Triangle Net, Assignment Points to Building
Figure 3-20: Work flow used by C+B Technik in building extraction.
The results for each building have the following logical structure: the ground polygon, the outer walls,
the inner walls and the roof surfaces. The results can be output as ASCII- or DXF-data.
3.1.2.10 Delft University of Technology
Automatic Computation Step
Loop over all building polygons
Geometric Building Model Building Information
Interactive Step (Check, Editing)
Computation-Database for Complete Re-Computation
Check, Visualization Computation Parameters
Line- and Point Editing
Delft used their own software and methods to extract buildings using laser data and ground plans
based on studies by Vosselman and Dijkman (2001) and Vosselman and Süveg (2001). All work was
carried out by an experienced person. If building outlines were not available, they were manually
drawn in a display of the laser points with colour-coded heights. In the Hermanni test site, only
buildings with given ground plan were modelled.
If the point cloud within a building polygon can be represented by a simple roof shape (flat, shed,
gable, hip, gambrel, spherical, or cylindrical roof) the model of this roof is fitted to the points with a
robust Least Squares estimation. Often building models can be decomposed interactively such that all
parts correspond to the above mentioned shape primitives. If the point cloud is such that all roof
planes can be detected automatically, an automatic reconstruction is attempted based on the
intersection of detected neighbouring roof faces and the detection of height jump edges between roof
faces.
If the two situations above do not apply, the building polygon is split into two or more parts until each
part fulfils one of the two above conditions. Optionally, point clouds can be edited to remove outlier
points that would disable an automatic roof reconstruction.