The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
Contours-Based Visual Analysis 
To complement the Cartosat-1 DEM’s accuracy assessment, 
a contours-based visual analysis was also undertaken. Both 
the Cartosat- and NED-derived DEMs were first subjected to 
a low-pass filter to remove noise and/or striping artifacts. 
Contours were generated at 50-meter intervals in a particular 
area of significant relief for both DEMs and draped atop the 
respective DEMs as depicted in Figure 9. This work was 
accomplished using the ArcGIS software system. 
These studies further provide evidence that the software used 
to generate the DEMs is an important factor in determining 
their accuracy. 
References 
Bailey G.B., Evans G., Ramachandran B., and Cheng P., 
2006. Assessing the Accuracy of Digital Elevation Models 
Generated from Cartosat-1 Stereo Image Data. Unpublished 
study presented at the 2006 ISPRS Symposium in Goa, India. 
Figure 9: NED and Cartosat-1 DEM-derived contours 
Both the NED- and Cartosat-derived contours were 
superimposed over the Cartosat November forward-looking 
image (Figure 10). Both sources of contours align well with 
each other and the topography. Overall, the contours 
complement the quantitative analysis. 
Publicly available sources of ground truth data: 
NED: 
http://ned.usgs.gov/ (U.S. coverage) 
http ://seamless .usgs.gov/ 
SRTM: 
http://edcsnsl7.cr.usgs.gov/srtmbil2/ (1 arc second) (U.S. 
coverage) 
http://edcsnsl7.cr.usgs.gov/srtmbil/ (3 arc second) (Global 
coverage) 
DOQQ: 
http://www.usgsquads.com/prod_doqq.htm (U.S. coverage) 
NED_DEM_50m_Contours 
Cartosat_DEM_50m_Contours 
Figure 10: NED DEM- and Cartosat DEM-derived contours 
superimposed atop the Cartosat image 
6. Conclusions 
Cartosat-1 absolute DEMs are shown to have vertical 
accuracies that are virtually the same as those derived from 
SRTM 30-meter data. The Cartosat-1 DEMs are also 
somewhat more accurate than ASTER DEMs, although these 
comparisons were made with ASTER DEMs generated 
without GCPs.