GCPs selection from multi-source data over mountainous topography

GCP selection in mountainous relief is a difficult process. This paper shows methods using topographic, SAR and visible image data to define ridge points as GCPs. The SAR layover and shadow boundaries method is the best method but it depends of the back and fore slopes versus the look angle. Using SPOT ortho-images the results depend mainly on the visibility of the feature between the SAR and visible images. Simulated SAR is not a good solution since the DEM induces too large planimetric errors.