facilitating 
Iterest, the 
easily ob- 
untered in 
aforemen- 
(periments 
. gaps, low 
veness of 
  
d road 
led least 
esents at 
s method. 
the white 
/hite dots 
> tracking 
(position 
a corner, 
atching to 
  
results 
on of this 
segments 
raction or 
failure due to its localized character. 
À comparison of least squares template matching to 
active contour models has also been performed and 
Fig. 10 shows some examples of these experiments. 
As expected, least squares template matching of- 
fered a large amount of highly precise edge points 
and can be very effective when the edges to be ex- 
tracted are rather smooth. On the other hand, active 
contour models may not be as precise but their global 
nature enables them to avoid distractions due to radi- 
ometric or even semantic noise. 
  
Fig. 10: Edge detection with active contour models 
(left) and least squares template matching (right) 
Globally enforced least squares template matching, 
presented in section 6 and currently under develop- 
ment, is expected by design to fuse the advantages 
of both techniques and overcome their inefficiencies. 
8. CONCLUDING REMARKS 
The semi-automatic object extraction strategies pre- 
Sented in this paper can be ideally used for monoplot- 
ting on a digital photogrammetric station. They all 
have their share of merits and shortcomings which 
make each of them appropriate for a more or less ex- 
tensive variety of object types and/or applications. By 
applying them to orthophotos tied to corresponding 
DTMS, survey coordinate information can also be as- 
Signed to the extracted objects. Thus, a powerful and 
highly automated digital photogrammetric GIS data 
capture scheme is emerging, which can substantially 
improve the performance of this currently cumber- 
Some and relatively costly procedure. 
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