Middle scale mapping of cultural sites based on high resolution satellite images

The availability and variety of high resolution satellite images (Eros, QuickBird, Ikonos, Spot5 supermode) have led us to consider the possibility of updating middle scale cartography. This paper presents a methodology to produce accurate orthocorrected images which can be used to generate updated maps at a scale of 1:10000. Even though commercial software already allow such operations to be made, we have implemented an alghorithm that is based on the RFM (Rational Function Model) in order to control the positioning errors and the influence of the ground control point distribuition on the results. Such an approach also permits us to investigate whether any of the 78 RPCs (Rational Polynomial Coefficients) are negligible. We assume that a DEM (Digital Elevation Model) of the investigated area is available (e.g. from SAR interferometry, SPOT5 mission,...). In order to define the maximum obtainable map scale (which depends on the geometric resolution of satellite images and on the adopted sensor model) accuracy tests have been carried out using a reasonable number of check points: the results are presented in this paper. The spectral information from multispectral data (XS, with a lower geometric resolution than the panchromatic band, PAN) can be used to produce thematic maps which can be considered as an added value of the process, especially in sites of cultural value. A PanSharpening algorithm has been implemented paying particular attention to the file size management (through a partitional approach) and the corrispondences between PAN and XS spectral ranges. An example of a land cover map that was produced through a neural classification of such orthocorrected images is presented. 1. IMAGE ORTHOPROJECTION Cultural site investigations require updated middle scale cartography to refer to. High resolution satellite images could be succesfully used to face such needs, but orthoprojection has to be taken into consideration. In literature remotely sensed satellite images have been orthocorrected using both rigorous sensor models and general non parametric models.