A mathematical model is designed to provide an accurate method of transforming PAN imagery from image space to object space and vice verse, using a minimum of one ground control point (GCP) to determine the exterior orientation of the images. The model, initially developed for SPOT images, uses collinearity condition equations to model the satellite path, while variations of the satellite attitude with time are modelled using higher order polynomials. Initial orbit information is obtained from the given ephemeris data and refinement is carried out using an iterative least squares solution. This model is tested for three different cases: (1) single image, (2) strip (acquired from one detector during a single orbit pass), and (3) stereopair. For the cases (1) and (2), an average error of 9.1 m in latitude and 7.6 m in longitude could be achieved using a single surveyed GCP for modelling. Using one ground control point identified from a 1 :50,000 scale map, accuracies in the order of 38.3 m in latitude, 42.6 m in longitude and 23.8 m in height were obtained for a stereopair. The results verify the model and give some idea of the extent to which IRS-1C PAN will be contributing to future evolutions in photogrammetry and cartography. The software for orbit attitude modelling described in this paper is a part of SOFTSPACE, a Softcopy Photogrammetric Workstation to handle stereo data of IRS-1C PAN and SPOT images, which is an integrated package of preprocessing, restitution, DTM and feature capture modules. (C) 1998 Elsevier Science B.V. All rights reserved.
