Effect of control points distribution on the orthorectification accuracy of an Ikonos II image through rational polynomial functions

Effect of control points distribution on the orthorectification accuracy of an Ikonos II image through rational polynomial functions
Marcela do Valle Machado, Mauro Homem Antunes and Paula Debiasi

Federal Rural University of Rio de Janeiro, B4 465, km 7 – 23890-000 - Seropédica - RJ, Brazil (marcelamachado046@hotmail.com, mauroantunes@ufrrj.br, paula@ufrrj.br)

Abstract:  This paper evaluated the orthorectification of a high resolution image for distribution of points between a flat and a rugged area, using the rational polynomial functions. An Ikonos II image was orthorectified using a DEM from contour maps and points obtained in an orthophoto. Fifty-seven points were collected over the entire image, from which 13 and 8 control points were randomly selected from the flat and rugged areas. Thirty points from the entire area and 15 points randomly selected from these were also used in the orthorectification process for comparison purposes. The remaining points were used as check points. The vector errors using 30 or 15 points had the same standard deviation and errors increased with altitude. From the flat area 8 or 13 points yielded the same results and vector errors increased with terrain height. When points were only from the rugged area the average vector errors were smaller as compared with the points only from the flat area. A high correlation between height and vector errors was found when 30 points all over the area were used. It is concluded that the orthorectification using the rational polynomial functions is sensible to ground height and the point distribution.

Keywords: orthorectification, rational polynomial functions, Ikonos II.

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