1287 
PRECISE GEOREFERENCING OF CARTOSAT IMAGERY VIA DIFFERENT 
ORIENTATION MODELS 
J. Willneff, T. Weser, F. Rottensteiner, C. S. Fraser * 
Cooperative Research Centre for Spatial Information, Department of Geomatics, The University of Melbourne, 
VIC ЗОЮ, Australia-jwillneff@web.de, (tweser, franzr, c.fraser)@unimelb.edu.au 
Commission I, SS-11 
KEY WORDS: CARTOSAT, high-resolution, satellite, orientation, comparison 
ABSTRACT: 
The CARTOSAT 1 satellite, launched by the Indian Space Research Organisation (ISRO) in 2005, can provide panchromatic along- 
track stereo imagery with a ground resolution of 2.5 m. Along with the imagery, encrypted files with rational polynomial 
coefficients (RPCs) and meta-data are distributed by ISRO. The RPCs allow direct georeferencing within certain limits depending 
on the on-board systems for registering the orbit path and attitudes of the satellite. At the Cooperative Research Centre for Spatial 
Information at the University of Melbourne (Australia), the software package Barista for the processing of high-resolution satellite 
images is being developed. Barista offers three techniques for precise georeferencing of such image data, namely the 3D affine 
model, bias correction for RPCs, and a generic pushbroom sensor model. The 3D affine model can only be applied when ground 
control points (GCPs) are available. The RPC model can be improved beyond the limits of direct georeferencing by correcting for 
the biases contained in the original RPCs. This process requires at least one well-defined GCP per image. Whereas the meta-data for 
CARTOSAT 1 imagery do not contain all the information required for using the generic pushbroom sensor model for direct 
georeferencing, they provide initial values for such a sensor model to be determined if enough GCPs are available. In this paper, the 
authors compare the geopositioning accuracy achievable with CARTOSAT 1 imagery via the 3D affine, bias-corrected RPC and 
generic pushbroom sensor models. A stereo pair of images covering Hobart, Australia, was processed using Barista. In addition to 
the imagery, an object point array of altogether 69 3D GPS-surveyed points was utilised. They were distributed all over Hobart and 
covered about one quarter of the scene. In order to assess the georeferencing accuracy that can be achieved using CARTOSAT 1 
images, bundle adjustment was carried out using all three sensor models and nine well-distributed GCPs. The absolute accuracy was 
then assessed via the remaining 60 points, which served as independent checkpoints. The georeferencing results obtained for 
CARTOSAT 1 in the Hobart test field are very encouraging. Whereas direct georeferencing using the RPCs provided by ISRO 
yielded sub-optimal results, the provision of a small number of GCPs is enough to boost the positioning accuracy to subpixel level in 
planimetry and to make it slightly better than 1 pixel in height, independent from the sensor model used. 
1. INTRODUCTION 
The number of commercial high-resolution satellites has 
steadily increased over recent years. The available image 
products from the current operational satellites have a ground 
resolution from a few metres to half a metre and are used for the 
extraction of spatial information for a variety of mapping and 
GIS applications. For the extraction of metric information from 
images, suitable sensor orientation models describing the 
relationship between image space and object space are 
necessary. This paper describes the application of three 
different sensor models and the assessment of their accuracy 
from processing a data set acquired with the CARTOSAT 1 
satellite. Launched in 2005 by the Indian Space Research 
Organisation (ISRO), CARTOSAT 1 can provide panchromatic 
along-track stereo imagery with a ground resolution of 2.5 m. 
The radiometric resolution is 10 bit. One option for sensor 
orientation of CARTOSAT 1 images is a camera replacement 
model using rational polynomial coefficients (RPCs), 
comprehensively described in Grodecki and Dial (2001) and 
Tao and Hu (2002). Along with the imagery, encrypted files 
with RPCs and meta-data are distributed by ISRO. Certified 
software distributers will additionally be provided with 
decryption software for these RPCs so that they can be accessed 
and used for direct georeferencing of the imagery within certain 
limits. These limits depend on the accuracy of the on-board 
systems for registering the orbit path and attitudes of the 
satellite in order to generate the RPCs from a generic 
pushbroom scanner model. In the case of CARTOSAT 1, the 
RPCs provided by ISRO should allow direct georeferencing 
with an accuracy of about 30 pixels. As the provided metadata 
contain neither a precise camera calibration nor information 
about orbit path and attitude angles, direct georeferencing is not 
possible with a generic pushbroom sensor model. 
At the Cooperative Research Centre for Spatial Information 
(CRC-SI) at the University of Melbourne, Australia, the 
software package Barista for the processing of high-resolution 
satellite images is being developed to support various research 
initiatives dealing with the extraction of spatial information. 
Barista offers three techniques for precise georeferencing of 
satellite images and all require ground control points (GCPs). 
First, the 3D affine model has been shown in the past to deliver 
pixel-level results for high-resolution satellite imagery in scenes 
of limited extent. In this case, no additional information is 
required from the vendor of the satellite images. Second, bias 
corrections can be applied to the RPCs provided by ISRO if 
they can be accessed. These bias corrections can be modelled 
Corresponding author.