Assessment of a Developed Combined Point/line–based Projective Equations

This paper presents the results of the assessment of the developed techniques for line-based and combined point/line-based eight parameters projective equations. The developed equations were implemented in a general least squares adjustment technique where both lines and/or points can be used for the rectification of both aerial and satellite images. Several experiments were performed using the developed line-based and combined point/line-based techniques to rectify the various types of satellite images and also aerial photographs. The experiments always started first with rectification of aerial photographs before applying to satellite imagery, since the developed projective equations were derived based on frame geometry assumptions. Then, the experiments were performed using several types of satellite imagery, such as Landsat7, SPOT4, IRS-1D, and IKONOS. In all experiments, comparisons were performed between line-based and the commonly used point-based projective equations. It was found that mostly similar results were obtained from both techniques. However, with points, usually a large number of control points are needed to achieve accurate results (around 1-2 pixel resolution). Approximately, around 30 control points are needed for most cases of satellite images. On the contrary, with lines, only 5 control lines are needed to achieve the same accuracy figures of 1-2 pixels. This can be justified since control lines can be considered as sequence of control points, and thus a line will provide much more control information than a point. The above conclusion presented a great reduction in the number of control features required for satellite image rectification. It provides a great save in the field collection process and, thus, a more economic technique for mapping from satellite imagery. In addition, the combined point/line-based developed technique will provide the flexibility, and thus speed, needed for the satellite images rectification process through the use of any available control features. Finally, conclusions and recommendations for future research were summarized.