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
1. Gopala Krishna, B., Manfred Lehner, 1994.
Mathematical Formulation and Design for
Photogrammetric Bundle Adjustment Software for
Optical Stereos, IB Nr. 552-5/94, DLR-OP, June
1994.
2. IRS-1C Stereo Data Products Team, 1993. IRS-1C
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Products Software, Report IRS-1C/SAC/DP/TN-
01/June 1993, Image Processing and Data Products
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996