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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
5. GEOMETRIC IMPROVEMENTS 
Some C-SAP investigators reported problems in generating 
DEM from the rational polynomial coefficients provided. Upon 
analysis, it was found that the denominators were crossing zero 
while using RPC coefficients. And wherever the zero crossovers 
were there, the coordinates were going out of bound. To solve 
this issue, the problem was analysed in detail. It was found that 
possible reasons for the zero-crossovers could include irregular 
image boundaries or absence of orbit-attitude values or jumps in 
attitude values, among others. To solve this issue, the problem 
was reformulated with common denominator coefficients for 
both line and sample directions. Also, wild point removal in 
attitude values and smoothing them were carried out. Further 
more orbit-attitude samples in top and bottom of the scene were 
considered for modelling. After this, a number of products were 
generated and verified. Earlier observations were not seen and 
consistent results achieved for all the C-SAP products. 
Also, rational polynomial coefficients were regenerated to take 
care of longitude convention from -180 to 180 degrees for 
investigators of C-SAP datasets as the ephemeris and attitude 
data available to data products is given in 0 to 360 degrees 
longitude convention. 
6. CONCLUSIONS 
In this Paper, the radiometric improvements incorporated to 
Cartosat-1 stereo orthokit products by way of MTF 
enhancements using laboratory measured sensor point spread 
functions for the Fore and Aft sensors including necessary pre 
and post-facto artifacts and noise removals and geometric 
improvements to re-compute the rational polynomial 
coefficients to take care of the denominator zero cross-overs are 
described. 
ACKNOWLEDGEMENTS 
Authors acknowledge the support provided by Mr. Satya Soma 
Sekhar and Dr. Arvind Kumar Singh from SIPA, SAC during 
this work. Authors acknowledge all the investigators of C-SAP 
Phase-I evaluations who presented their findings at Goa and 
Hannover which resulted in the improvements reported in this 
Paper. Authors thank Dr. RR Navalgund, Director, SAC and Dr. 
G. Madhavan Nair, Chairman, ISRO respectively for permitting 
this work to be presented at the ISPRS Congress and permitting 
the participation at Beijing, China during July 3-11, 2008. 
Suggestions for improving an earlier version of this Paper by 
Shri DRM Samudraiah, SEDA, SAC and Dr. JS Parihar, RES A, 
SAC are acknowledged. 
Figure 1: DEM derived from MTF Enhanced Cartosat-1 Stereo 
Orthokit over Hobart Test Site 
(Full Scene area covering 27.5 km x 27.5 km) 
Figure 2: DEM derived from MTF Enhanced Cartosat-1 Stereo 
Orthokit over Castel Gandolfo Test Site (Reference Area about 
4 km x 8 km) 
REFERENCES 
Nandakumar, R., PK Srivastava, David Holland & Alain 
Baudoin, THE C-SAP INITIATIVE BY ISPRS AND ISRO: A 
Scientific Assessment Programme for the high resolution 
panchromatic stereo sensors onboard CARTOSAT-1, ISPRS 
Commission IV Symposium on Geospatial Databases for 
Sustainable Development, Goa, 27-30 September, 2006. 
Srivastava, P.K.., Gopala Krishna, B., Srinivasan, T.P., Sunanda 
Trivedi, Amitabh and Nandakumar, R. (2006), Cartosat-1 Data 
Products for Topographic Mapping, ISPRS Commission IV 
Symposium on Geospatial Databases for Sustainable 
Development, Goa, 27-30 September, 2006.