stanbul 2004
und
Independent
n height and
topographic
yn horizontal
Without lost
higher than
re are plenty
the sampling
is high. And
een adjacent
there has an
on.
, we propose
(l)
t’s height (H).
and on the
de surveying
| points into
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
[Yi 70 )= x Zul (2)
[0 J
And then calculate the quantity of projected points of each grid;
regard the number value as the DoPP of that grid. So the DoPP
can be presented discretely. According to the definition above,
we can calculate the value of DoPP of each grid if we select
reasonable grid size, for example, form grids according to the
sampling interval designed by scanning system. And the value
of DoPP has feature as follows (see Fig. 5):
|
A2 I em 3
Pi TERN Bl 4)
| l
1 ü 0 1 1
1 1
1 1
Figure 5: DoPP on a horizontal mesh grid with a
building and other objects
® DoPP has a smaller value and is evenly distributed on the
surface of the ground;
® DoPP obviously has a higher value along the boundary of the
building (the gray band in Fig.5) than in other regions, and
form continuous band;
® The DoPP in the inside region of the building is equal to zero
if without the effect of noise points;
® The DoPP of an independent object such as lamp pole is
greater than that of surroundings objects.
With use of the above knowledge, select reasonable thresholds
T), T, object segmentation can be carried out according to
formula 3:
| >7 building
DoPP À cT. ground (3)
else else objects
Thresholds T1, T2 are determined by formula 2 according to
practical condition and the purpose of data processing. After
segmentation, we can get the range images of ground, of
buildings and of other objects. The data processing, feature
extraction and modeling. visualization for theme image are much
easier than for original range image. Especially segmented
buildings, feature extraction of building's surface outline based on
the segmented image can be realized, and the vertical feature of
building through further combination with the value of Z can be
reconstructed.
4. Experimental Study
Two experimental studies were carried out to demonstrate the
feasibility of the above-proposed method of segmenting
different objects and of extracting urban building objects. The
operational workflow for processing range image data is as
follows: 1) Form a grid mesh with grid size of 0.1m X 0.1m to
the surveying region; 2) Project all the points in the range
image onto the grid and calculate the DoPP for each grid; 3)
Select reasonable DoPP threshold to segment the original range
image and get the special topic range image.
4.1 Case 1
Fig. 6b is the special range image formed by getting rid of
ground points from the original range image (Fig. 6a), which
preserves the targets with certain height. Building can be
extracted and rebuilt by using the height value information of
points.
pole
wall
(a)
(b)
Fig. 6 a) Image for testing building; b) Range image as DoPP>10
937