Optimized patch backprojection in orthorectification for high resolution satellite images

The objective of this investigation is to build up a fast orthorectification procedure for high resolution satellite images. The proposed scheme comprises two major components: (1) orbit modeling, and (2) image orthorectification. In the orbit modeling, we provide a collocation procedure to determine the precision orbits. In the image orthorectification, the area of interest is sequentially subdivided into four quadrate tiles until a threshold is met. The threshold of maximum terrain variation in a tile will be optimized according to the computation efficiency and accuracy requirements. Once the ground tiles are determined, we perform adaptive patch backprojection to correspond to the image pixels. Selecting the highest elevation in the tile, the four corners of the tile are projected on the image to form a set of anchor points. Another set of anchor points with the lowest elevation are generated in the same manner. Assuming that the relief displacement in a moderate tile is linear, a groundel within the tile is projected into the image space according to the groundel elevation and the two associated anchor point sets. Tests of images include SPOT 5 supermode and QuickBird panchromatic satellites. Experimental results indicate that the computation time is significantly reduced without losing accuracy.