1117 
UTILIZATION POTENTIAL OF HIGH RESOLUTION STEREO DATA FOR 
EXTRACTING DEM AND TERRAIN PARAMETERS 
P. Jayaprasad, Ritesh Agrawal, S. K. Pathan* 
Space Applications Centre, Indian Space Research Organisation (ISRO), Ahmedabad-380 015, 
India - (jayaprasadp, ritesh agrawal, subhan_kp)@sac.isro.gov.in 
*Secretary Commission IV 
KEY WORDS: CARTOSAT-1, Stereo data, RPCs, DGPS, DEM, Ortho Image, Accuracy Assessment, terrain parameter 
ABSTRACT: 
Cartosat-1 data provides along track stereo data continuously with its fore and aft cameras. 10 bit quantization and near real time 
imaging between the stereo pairs which improve the image matching accuracies. Stereo data along with Rational Polynomial 
Coefficients (RPCs), provides an opportunity for photogrammetric processing for DEM and ortho image generation. The present 
study focuses on the effect of the number of Ground Control Points (GCPs) and polynomial order for the refinement of RPCs for 
generating an accurate Digital Elevation Model (DEM). 10 GCPs were used in the refinement process and 9 Independent Check 
Points (ICPs) used for accuracy analysis. Both GCPs and ICPs were derived using Differential GPS survey (DGPS). Effect of DEM 
resolution while generating the Ortho Image is also studied. Terrain parameters such as slope, aspect and drainage network have been 
automatically extracted. The drainage network was extracted at different DEM resolution using similar area specific (5000 m 2 ) 
accumulation threshold and a comparative analysis of the order of the drainages has been carried out. The accuracy analysis shows 
that RMS errors of DEM and ortho images were within 5m both in elevation and planimetry respectively with 10 GCPs and 
polynomial order 2. 
1. INTRODUCTION 
Launch of CARTOSAT-I on 5 th May 2005 has opened a new 
era in civilian community for addressing newer applications at 
larger scale. With its capability to acquire stereo images with 
Fore (+26°) and Aft (-5°) cameras and a nominal B/H ratio of 
0.62, it gives a stereo data at 2.5 m spatial resolution. Less than 
a minute interval acquisition time between the stereo pair makes 
an ideal imaging condition. The repetitivity of the satellite is 
126 days with a revisit capability of 10 days and the scene size 
of 30 km * 30 km has shown tremendous potential in the field 
of satellite photogrammetry. Stereo pairs are formed either from 
across track geometry or from along track geometry. 
Advantageous and disadvantages of the along track and across 
track stereo viewing mainly depends on the slope and aspect of 
the terrain towards the viewing geometry and illumination 
conditions of the two imageries. The Fore and Aft cameras 
onboard provides a continuous strip of stereo data. The mono- 
scopic camera on board IRS 1C/ID, Ikonos, SPOT and 
QuickBird generates a stereo pair by steering the camera 
(along/across track depending on the capabilities) and provides 
a limited stereo coverage rather than a continuous one. For three 
cameras system, in addition to fore and aft imagery, nadir 
imagery also provides the satellite capable of taking triplet 
imagery (ALOS-PRISM). 
Satellite Photogrammetry techniques have been extensively 
used by the scientific community in deriving high resolution 
DEM, Ortho image and terrain parameters such as slope, aspect, 
contours, drainage etc. Digital Elevation Model (DEM) has 
become an inevitable component in most of the remote sensing 
applications viz. infrastructure development, watershed 
management and development, hydro-geomorphology, urban 
morphology, disaster management etc. Keeping these 
applications in view, the current study aimed at exploitation of 
Cartosat-1 stereo data for various applications. 
Rational functions models (RFMs) have gained popularity, with 
the recent advent of high resolution data supplying Rational 
Polynomial Coefficients (RPCs) along with stereo / mono data. 
Providing these coefficients along with stereo data, instead of 
delivering the interior and exterior orientation parameters and 
other properties related to physical Sensor, one can proceed to 
satellite photogrammetric processes which approximate the 
sensor model itself. 
A detailed study of the RFMs for photogrammetric processing 
has been carried out by Tao and Hu (2001). Di et. al. (2003) 
demonstrated different ways to improve the geo-positioning 
accuracy of Ikonos stereo imagery by either refining the vendor 
provided RF (Rational Function) coefficients, or refining the RF 
derived ground coordinates. Poon et al. (2007) focuses on 
Digital Surface Model (DSM) generation from high resolution 
satellite imagery (HRSI) using different commercial of the shelf 
(COTS) packages. They validated the stereo DEM with InSAR 
DEM for different land forms. Nadeem et. al (2007) validated 
DEM generated from Cartosat-1 stereo data. Crespi et. al. (2006) 
evaluated the DSM by comparing the heights of several 
buildings and points on the road axis derived from a large scale 
(1:2000) 3D map. Fracer and Hanley (2005) demonstrated the 
wide applicability of bias compensated RPCs for high accuracy 
geo-positioning from stereo HRSI for a mountainous terrain. 
Chen et. al. (2006) compared geometrical performance between 
rigorous sensor model (RSM) and RFM in the sensor modeling 
of FORMOSAT-2 satellite image. Dabrowski et. al. (2006) 
evaluated DEMs generated with different numbers of GCPs 
from Cartosat-1 stereo data at large number of evenly 
distributed check points. Similar attempts to evaluate the 
accuracy of the DEM using different number of GCPs have 
been made by Michalis and Dowman (2006) and Rao (2006). 
RFM based processing methods and mapping applications was 
developed for 3D feature extraction, ortho rectification and