Geoscience Reference
In-Depth Information
Fig. 1
Two
different
segmentations
on
the
same
geometry
with
different
quality
values
(Thiemann and Sester
2004
)
Thiemann and Sester (
2004
) presented a research on segmentation of 3D
building for generalization that utilized an adaptation of algorithm by Ribelles
et al. (
2001
). Ribelles proposed a segmentation process that will detect holes,
bumps and notches on a 3D building model by segmenting the model with one or
more planes of its boundary.
The same polyhedron can be segmented with different operations and combi-
nation of planes which resulted in many different features. Ribelles et al. (
2001
)
determine the best feature by dividing the new area of the splitting face with the
old area, where the smaller value indicate a better feature. Figure
1
shows two
different segmentation on the same body where a protrusion (left) is detected with
the quality value, v, of 3 while a complex hole (right) is detected with better
quality value, v, of 3/7.
However, Thiemann and Sester (
2004
) considered the algorithm by Ribelles
et al. (
2001
) employed a ''brute force'' method as it tries all split with all com-
binations of planes increases the complexity of the algorithm and running it with
four or more splitting planes makes it extremely time consuming.
To counter the problems, Thiemann and Sester (
2004
) introduced an extension
from the original algorithm based on the theory that reducing the number of
Boolean operation will reduce the complexity of the algorithm and its processing
time. They suggested that only one split-plane is used and only if it yields no
result, then two or more split-planes will be used. In order to balance out the
separation of bad protrusion features before the good complex hole, they also
introduced a heuristics where only parts with value smaller than 1 are considered
as valid. Figure
2
shows the segmentation on a building with 34 different split-
planes.
