RIGOROUS GENERATION OF DIGITAL ORTHOPHOTOS FROM SPOT IMAGES

An original method that rigorously generates digital orthophotos from SPOT images is presented. In place of the ray tracing method, we have developed an algorithm that determines the corresponding image coordin ates for a ground element, provided that the time dependent orientatio n parameters and a DTM are available. In this paper, a rigorous bundle adjustment program for pushbroom scanning images that models the dyna mic orientation for SPOT data is first developed. Incorporating the DT M, a non-linear equation is formulated that determines the image coord inates in the flight direction in terms of the sampling time for a gro und element. The Newton-Raphson method is then applied in order to sol ve the non-linear equation. The along-track and across-track image coo rdinates for the corresponding ground element can thus be calculated. After a bilinear interpolation, the pixel grey value for the ground el ement in the orthophoto is determined. Experimental results indicate t hat the generated orthoimages attain an accuracy better than two-third s of a pixel.