Orthorectification of Spot Images with the Same-pass Constraints

SPOT images are one of the most widely used satellite images in middle scale mapping applications for its stereo capability, wide coverage area and well-known satellite model which is supported nearly in all photogrammetric software. Stereoscopic imaging capability of SPOT allows generating digital elevation models (DEM) from a pair of overlapping images. DEMs based on satellite images are essential for many applications when you need up-to-date and cost-effective information about terrain relief. Topographic mapping contouring and orthoimage generation are the two widely used application areas. The accuracy of orthoimages is a function of many variables, one of which is the accuracy of the ground control information used in a simultaneous adjustment and updating the satellite model parameters. Both the number and distribution of the ground control points are of great importance. Some techniques can reduce the needed number of ground control points in the modelling of SPOT images. This is important when the control points are acquired by expensive differential GPS measurements. GCPs are used to calculate the position and orientation (i.e. roll, tilt, and yaw) of the imaging system at the moment of image taken. This calculation is accomplished using standard photogrammetric algorithms, such as a space resection or bundle adjustment. In these algorithms, same constraints may reduce the number of the ground control point needed. For SPOT system, when the images are taken in the same-pass, some additional constraints can be added to the adjustment process which will reduce the number of unknowns resulting reduction of the number of GCPs. By this way, the production cost and time will be also reduced. In this study, a block with two columns each of which consists of three SPOT frames from the same pass was used. Finally, the accuracies were investigated.