ORBIT ATTITUDE MODELING AND DERIVATION OF GROUND COORDINATES FROM SPOT STEREOPAIRS

A method for modelling the orbit attitude parameters of SPOT images has been developed. Using these updated orbits, the three-dimensional co-ordinates of the points of interest are derived from a stereopair. The basic equations arc the collinearity conditions. Description of the approach, mathematical formulations and the experimental details are reported. In this model, a rigorous geometric reconstruction of spatial relations between image and ground scene combining the principles of photogrammetric bundle formulations modified in a time-dependent mode are derived from known orbital relations. With this approach, the orbit attitude modelling of a stereopair has been done with a single GCP and terrain co-ordinates are derived up to an accuracy of 28 m in latitude, 40 m in longitude and 27 m in height (average of RMS errors in two different experiments) when the GCP used for modelling was collected from 1:50,000 maps. These figures are inclusive of the measurements errors (map accuracies, map reading accuracies, manual pixel pointing etc.) as well as the modelling error. The software for modelling and ground co-ordinates derivation have been developed in C language on SUN 4.1.1 workstation under a UNIX operating system using Motiff windows, and is presently being used for DTM, geocoded image and orthoimage generation.