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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
smooth. However, it is probable the geometry of vector data
may get worse if higher weed tolerance is given (Eker, 2006).
3. TEST STUDIES
Test studies were carried out with the program developed in
two groups in order to determine the usefulness and
effectiveness of this new approach exposed.
In the first group test study a 1:16000 scale black/white digital
aerial photograph was used. Thus it was investigated whether
the software would be used or not to extract some features in
large scaled mapping.
In the second group study Another application with 1:5000
scaled two ortho images which have 0.50m resolution. These
ortho images are generated from 1:16000 scaled color aerial
photographs. In this test area, an accuracy test is also carried
out to find the accuracy of the developed method.
3.1 Test 1
In the first test work that a 1:16000 scaled white/black aerial
photo which was scanned at 20 microns was used. This image
includes a village center. Roads were selected as the features
that were extracted semi-automatically from the image. It is
shown in the Figure 1 that vector data which were obtained
from the result of feature extraction studies. Roads were
vectorized from their edge lines. The roads’ surfaces are not
homogeneous. Because of this in this image the extraction of
the roads were a hard work. In this image, if we selected a big
tolerance value the extraction extended out of the roads. On the
other hand if we selected small tolerance values we saw that we
had to make small propogations and select a lot of starting
points. This increased the time of the extraction.
(a) • (b)
(c)
Figure 1. (a) The original image (b) Mask image of the
extracted roads (c) Extracted vectors.
3.2 Test 2
It is thought that this software can be used in producing maps
and in collecting the vector data for GIS. Another application
with 1:5000 scaled two ortho images which had 0.5m
resolution of Ayazaga Campus of istanbul Technical
University. These ortho images were generated from 1:16000
scaled color aerial photographs. In this test area, an accuracy
test was also carried out to find out the accuracy of the
developed method. In this accuracy test, vector data of the roads
and buildings were collected semi-automatically with the
developed sofware (Figure 2) and also manually with an
experienced operator (Figure 3). The data collected by the
operator were assumed as the correct ones and they were
compared with the others collected by the software. The
accuracy test was carried out in two groups. In the first group,
roads were used and on 422 road check points were measured,
In the second group, buildings were used and 281 check points
were measured. The results are shown in Table 1.
é **» !<-*» V, *«.
Figure 2. Semi-automatically extracted features.
Figure 3. Manually extracted features by the operator.