3. Automobile tracking method
We examined two automobile tracking methods using TLS gray scale image.
3.1 brightness difference from a pair of images
Since moving objects on the road are only automobiles, it is possible to track automobile
objects using differential image from a pair of image covering the same area at the different times
(Fig.3). We calculate object's speed by dividing the ground distance of centroids of each object by
time difference. Fig.3 shows a result of tracking a white bus. But any automobiles whose color is
similar to road surface are not tracked. In addition, we can't apply this method to track standing
automobiles due to a traffic jam or an accident.
Fig.3: Differential image and a pair of image covered the same area at the different times
3.2 Template matching
In order to track stopping automobiles, I used template matching method using Hausdorff
distance. First operation in the processing is edge detection from TLS image. Secondary is
making a proper size rectangle template according to altitude of a platform or image resolution
since all automobiles in aerial images have rectangular shape. Last one is affine transformation of
TLS image and template matching. We narrowed down the operation image area to roads to
improve the accuracy of the matching.
The distance between the each pixel of the template and the nearest TLS edge point defines the
Hausdorff distance. We detected template position whose summation of each points Hausdorff
distance is under set threshold as automobile object.
Fig.4: Detected objects by template matching
4. Conclusions
This study show that it is possible to track automobiles using TLS gray scale image.
Differential image method depends on brightness of TLS image, so automobiles whose colors are
similar to those of road surfaces were not tracked. It is difficult to detect edge in template
matching method since the test image is experimental with no enough quality. Further studies are
required to improve the accuracy of tracking objects using color image and high resolution image
from the TLS.
References
- Shunji Murai, Yositaka Matsumoto, Li Xun, 1995, stereoscopic imagery with an air borne
three-line scanner (TLS), ISPRS commission V, Intercom mission Workshop, pp20-25
- Michihiro Murao, Yasuyuki Matsushita, Katsushi Ikeuchi, Masao Sakauchi, 2000, Visualization
of traffic Conditions for Drivers, UM3’2000 session D, p22
