Direct Method in Strict Digital Geometric Rectification for SPOT Imagery

The direct method has shown us its advantages in the procedure of strict digital geometric rectification, because of the central projection in each scan line of SPOT image and the time-sequeutial changes of exterior orientation elements for each line. This paper, therefore, proposes the principles and technologies for taking the direct method into use, and points out the key techniques and the approaches to assure the accuracy and reliability of anchor points. Since the direct method can correctly determine, without iteration, the exterior orientation elements of the line at which anchor point is located, the calculating speed is faster than indirect method and the experiment results are better in accuracy of anchor points, precision comparison for evoluating the interpolation within each grid cell when using anchor points as control points, and the cheek and the analysis for the geometric precision of rectified images, thus proving the resouableness and corrcctuess of the proposed principles and approaches.