5. RESULTS AND CONCLUSIONS 
At Space Applications Centre (ISRO) the above 
facilities are being developed in following phases: 
1. Development of models and software for DEM, 
orthoimage etc, 
2. Development of GIS and IP functionalities 
3. Integration with a standard mapping package for 
integrated testing 
4. Development of texture mapping based integrated 
software system for topographic map updation. 
The first phase has been completed and is available 
on Silicon Graphics Indigo-2 R-4000 workstation with 
stereo viewing capability. The model is checked on 
three data sets of 23x23 km area of IRS-1C stereo 
data having tarrain undulations of about 2 km. Overall 
DEM accuracies of 10-35m (rms value) in planimetry 
and 13-30m in height are obtained using four control 
points per scene. Accuracies quoted above are 
obtained on check points. It is to be noted the control 
and check points are collected from the existing 
1:25000 and 1:50000 scale maps, hence the point 
accuracy itself may vary between 10-20m in 
planimetry and 10-20m in height (depending on the 
contour interval). In addition to this one has to count 
for identification error of the point in the image (order 
of one pixel). Hence the accuracy of DEM can be 
further improved by using a better control. 
Three orthoimages are generated one from each set, 
corresponding to an area of 1:25000 scale map. The 
rms accuracies on check points obtained are 15-35m 
depending on the control accuracy (derived either 
from 1:25000 scale map or from 1:50000 scale map). 
As a qualitative evaluation the map features are 
traced and overlaid on to the orthoimage generated to 
the same scale. The features are matching within a 
mm. The above results show, that the accuracies 
obtained from IRS-1C stereo data are in conjunction 
with the required onces, for updating maps of 
1:50000 scale [Srivastava, PK etal, 1996a. 
,Srivastava PK etal, 1996b.]. 
The second and third phases are currently in progress 
Once these are ready, a digital overlay of map 
features with the orthoimage is possible for direct 
verification. The third phase is in design stage and it 
is expected to be completed by the end of 1996, for 
testing and usage of very high resolution imagery 
from spaceborne line scanner sensors likely to be 
available by then. The proposed system specifications 
are shown in figure 1. 
Acknowledgements 
Authors wish to acknowledge with gratitude, the 
guidance and encouragement provided by Dr. George 
Joseph, Director, Space Applications Centre (SAC), 
Shri. AKS Gopalan, Deputy Director, Remote Sensing 
Area, SAC, Shri. AR Dasgupta, Group Director, Image 
Processing and Data Products Group, SAC and Dr. KL 
484 
Majumder, Head, Image Processing and Products 
Division, SAC. 
References 
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Mathematical Formulation and Design for 
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