Comparison of Different Methods to Rectify IKONOS Imagery without Use of Sensor Viewing Geometry.

Abstract

Satellite images can be rectified and adapted to map representation also without information about viewing geometry of the sensor. Polynomial Functions (PFs) or Rational Polynomial Functions (RPFs) can be applied for this purpose, both requiring Ground Control Points (GCPs), of which the positions in the image as well as in the real world must be known. Typically for PFs only planimetric (X, Y) positions of GCPs are used while for RPFs 3D coordinates (X, Y, Z) of them as well as a DEM (Digital Elevation Model) of the entire scene are required. Check Points (CPs) with the same characteristics of GCPs (but not coincident with them) are used to better verify the accuracy of the product. Not only topographic survey, but also maps or ortho-photos with adequate resolution supply the coordinates of GCPs as well as CPs. This paper is aimed to compare methods to rectify IKONOS images based on PFs or RPFs applications, considering the positional accuracy of the results as index for performance evaluation. Tests were executed on IKONOS panchromatic image of an area of the Cilento and Vallo di Diano National Park, in Campania Region (Italy): ortho-photos (scale 1:10,000) were used for GCPs and CPs planimetric position in the real world while for RPFs applications also DEM (cell size 20 m) was considered as source of 3D information. To compare the selected methods, differences (residuals) between the X, Y coordinates of GCPs (but also of the CPs) on the ortho-photos and corresponding values in the rectified image were calculated and evaluated. The positional accuracy of the resulting products in relation to the method as well as to the number of GCPs was analyzed; also the implications of the calculation of Rational Polynomial Coefficients (RPCs) in alternative to the use of the values supplied for them by the image provider were investigated.