DSM and Orthoimages from QuickBird and Ikonos Data using Rational Polynomial Functions

Kurzfassung

The rigorous approach for the derivation of digital surface models (DSM) and orthoimages from satellite and airborne scanner imagery via full modelling of the imaging process requires the knowledge of exterior and interior orientation of the camera. For IKONOS and QuickBird this basic data is not (fully) available to the user. Instead, rational polynomial functions (RPF) in standard form are provided as a substitute for describing the relationship between image and object space. To be able to derive DSM and orthoimages for this type of data even in the absence of appropriate ground control, software based on RPF has been developed. The software allows a lot of datums and projections for input and output data. This is important for worldwide application e.g. in case of catastrophes. The paper shows that a RPF is very near to linear in the object space variables longitude, latitude and height. This explains a large convergence radius and a rapid convergence in case of forward intersection. Residuals in image space from forward intersection are small and nearly constant in case of the GEO IKONOS-2 images tested. Large (also nearly constant) residuals in case of the QuickBird stereo pair can be used for a relative correction of the RPF either using residuals from verticality constraints with manually measured top/foot tie point pairs of large buildings or from forward intersection of a set of excellent tie points from matching. These corrected RPF can then be used to create a self-consistent set of DSM and orthoimages. The DSM derived from the high resolution data via RPF processing have been compared to best DSM available which was in most cases a C-Band SRTM model. Estimated mapping accuracy was found to correspond with the promises of the image provider in the case of available ground control.