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Fig. 11.6 The window scans
all regions while changing the
window size
method in the voting space of the Hough parameter. To show the filtering effect for
nonplanar and noisy surfaces, construct a nonplane environment that is filled with
crumpled chapter as shown in Fig.
11.5
a. Figure
11.5
b-e shows the Hough
parameter space, where (b, c) is the result of the conventional RHT method and
(d, e) is the result of the proposed RHT method, respectively. Although the range
data have no plane, RHT has voted on many parameters and count of maximum
peak is 158. In contrast, the proposed RHT's voting count is much smaller and the
maximum peak is 61. Obviously, the proposed method is less affected by the noise.
11.3.2 Speed Up via the Scan Window
The conventional RHT involves voting on many data points which are selected
randomly from the whole image region. It requires a lot of sampling to prove that
the peak from the interesting shape is more salient than those of the noises in
Hough parameter space.
In case of plane detection from 3D range data, we use the scan window for
accurate and rapid detection of the surface by using the local consistency for data of
planar surface. Plane data points have the locality property, because the data points
in local region have higher probability to be a plane than far distance data. The scan
window is a similar method to that of searching face in AdaBoost [
10
].
Window that shifts fixed number of pixels scans the whole area. The size of the
scan window is initially small and is increased to the image size (see Fig.
11.6
).
A certain number of data points in each window region are sampled and voted on.
The scan window of various sizes can reflect the locality and the overlapping
region of each window provides a more significant peak of the plane parameter
than the conventional searching method.
11.3.3 Look Up Table
We compare the normal vector from the initial three vertices with the vector from
the rotated three vertices, for planarity evaluation. Equation (
11.9
) is needed for
rotation of the three vertices.
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