The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
1141 
Scene 
Number accepted 
points (Mio.) 
Height difference to 
ICC DTM 
Mean (m) a (m) 
Cat 
21.5 
-0.80 
3.41 
115/207 
23.9 
-1.74 
4.14 
115/208 
24.1 
-2.14 
4.64 
116/207 
27.9 
-3.02 
4.84 
116/208 
26.3 
-2.82 
5.40 
116/209 
15.8 
-3.70 
5.43 
117/207 
18.0 
-3.26 
4.98 
117/208 
21.2 
-3.31 
5.59 
117/209 
7.5 
-4.83 
6.42 
Table 3: Accepted object points statistics 
3.4 DSM and Orthoimage creation 
After the outlier removal step, a DSM on a 10 meter grid is 
interpolated for all scenes. Figure 4 shows the difference 
between the ICC DTM and the generated DSM for the CAT 
scene. The consistency of the produced Aft/Fore orthoimages is 
assessed by image matching. Highly accurate tie points 
between each ortho pair have been established using LSM. The 
mean shift varies between 0.28 and 0.30 pixels, the 
corresponding standard deviation between 0.15 and 0.18 pixels. 
Figure 3 shows that the remaining subpixel shift between the 
Aft and Fore orthoimages is slightly regular. 
x (pixel) 
Figure 3: Shifts (averaged on a 150x150 pixel grid) between 
orthorectified Aft and Fore image of scene 116/208 
3.5 Mosaicing 
After each scene has been processed independently, DSM and 
Aft orthoimages of scenes (115-117)/(207-209) are combined 
into orthoimage and DSM mosaics. No further radiometric or 
geometric adjustment has been applied. To assess the 
consistency of the resulting mosaic, shifts between the 
neighbouring orthoimages are computed by LSM matching and 
shown in Table 4. This is a good result, considering that no 
bundle block adjustment was used, and all scenes were 
processed independently. The Ortho and DSM mosaics are 
shown in 
Figure 4: Height difference (meter) obtained by subtracting 
the CARTOSAT-1 DSM from the ICC DTM. 
Path/Row 
Lateral shift (m) 
mean a 
(115,116) / 207 
1.66 
1.46 
(116,117)/207 
0.92 
0.71 
(115,116)/208 
1.12 
0.64 
(115,116)/209 
3.12 
1.31 
Table 4: Lateral shift in overlapping areas of neighbouring 
orthoimages. Except for the overlap between scene 
115/209 and 116/209, subpixel shifts are found. 
4. CONCLUSIONS 
A highly automated DSM processor for CARTOSAT-1 scenes 
is presented. Key features include the automatic collection of 
reference data from Landsat ETM+ Geocover mosaic and the 
SRTM DSM, a novel affine RPC correction estimation 
approach which leads to ortho and DSM products with much 
higher lateral accuracy than the ETM+ Geocover mosaic. 
Comparison with reference data in Catalonia indicates a 
location accuracy of 3-4 meter, and a height accuracy of 3-4 m 
in terrain with good pattern matching characteristics. In 
mountainous terrain and with rather low sun elevations the 
normal problems of too steep slopes and large shadow areas 
without enough matching targets lead to coarse reconstruction 
and local artefacts in the DSM. 
The ability to produce quality DSM and ortho products without 
manually measured, highly accurate ground control points is 
especially valuable for emergency applications, mapping of 
remote areas and large scale DSM production. Seamless 
mosaics can be formed, even if all scenes were processed 
independently. Further work includes development of 
comfortable manual quality inspection and editing tools, as well 
as improved computational efficiency and better handling of 
occluded and shadowed areas in the stereo matching module. 
ACKNOWLEDGEMENTS 
EUROMAP provided most of the CARTOSAT-1 scenes used 
for this analysis, with the exception of the Cat scene, which was 
provided by ISRO/SAC as part of the CARTOSAT-1 Scientific 
Figure 5.