EuroSDR Projects - Host Ireland

Detailed Description (Letters refer to steps in the block diagram (Table 3-2))
Common steps for both methods:
A: Polygon splitting is done interactively. Based on the outline of the building, preferred directions of
lines for splitting the polygon are generated. These lines can be moved interactively over the polygon.
At the optimal position, the polygon can be split by clicking a mouse button.
Shape primitive fitting method (left side of diagram):
E: After selection of the optimal model by the operator, the approximate values of the parameters of
this model are derived from the height histogram of the points within the polygon.
F: The height of a point is expressed as a function of the model parameters and linearised. In a robust
estimation (ignoring points more than 0.5 m away from the roof surface) the roof shape parameters are
obtained.
Automatic roof reconstruction (right side of diagram)
K: Splitting of polygon into concave segments by extending the building outlines at the concave
corners of the outline. See (Vosselman and Süveg, 2001) for details.
L: Detection of planar faces in the segments using a 3D Hough transformation. After detection the
planar faces are grown and merged over the borders of the ground plan segments. See (Vosselman and
Dijkman, 2001) for details. Planes that are nearly parallel or nearly horizontal are constrained to be
exactly parallel or horizontal.
M: Detection of intersection lines between roof faces by intersecting all pairs of detected planes and
checking if both planes of a pair have points near (the same segment) the intersection line. Also
detection of height jump edges between neighbouring roof faces.
N: The segments are further split at the positions of the detected intersection lines and height jump
edges until the points in each segment can be represented by one plane.
O: All adjacent segments that can be represented by the same plane are grouped to one segment.
T: Sometimes, a small part of the building (e.g. a dormer) may be missed by the automatic
reconstruction procedure, whereas the rest of the building is modelled correctly. In this case, the
model is accepted. The missing feature is extracted from the point cloud and fit to the model of a
shape primitive.
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