Line-of-sight vector adjustment model for geopositioning of SPOT-5 stereo images

We formulate and present a new geopositioning method for SPOT-5 High-Resolution Geometric (HRG) stereo images, named the line-of-sight (LOS) vector adjustment model. It is applicable to satellites that move along a well-defined close-to-circular elliptical orbit with a predicted orbit close to true. SPOT-5 satisfies these requirements because it has the improved capability of providing accurate satellite attitude and a look angle for each detector. The method's core idea is that only the LOS vector was adjusted when correcting the geometric distortion of SPOT-5 imagery. One advantage of this method is that it achieves high geopositioning accuracy with a limited number of ground control points (GCPs). Although a minimum of three GCPs is needed for processing, a test result satisfied the accuracy requirement within one pixel of a SPOT-5 panchromatic image even with only three GCPs. The performance in terms of root mean square error (RMSE) improved as the number of GCPs increased. Five GCPs were found to be the optimal number in the practical application of the LOS vector adjustment model. Using five GCPs, the RMSEs were 0.48 m and 0.64 m in planimetry and height, respectively. The test results indicate that the proposed method is superior to the bundle adjustment method for the geopositioning of SPOT-5 HRG stereo images.