Integration of off-nadir VHR imagery with elevation data for advanced information extraction

Integration or registration of optical images with elevation data is important for many applications such as building detection. Despite the fact that VHR (very high resolution) satellite images are acquired mostly off-nadir, the use of such images in the previous research works is less common than the nadir ones. This is due to the high relief distortion of above-ground objects, such as buildings, in these off-nadir images. For the applications of information extraction, which prefer the integration of the optical images and elevation data, this relief distortion makes the integration between the perspective off-nadir VHR optical images and orthographic digital surface models (DSMs) almost impossible unless a true orthorectification process is implemented. However, true orthoimages are expensive, time consuming and mostly difficult to achieve. This paper proposes an integration method of the DSMs elevations with off-nadir VHR optical imagery by projecting the ground elevations back to the image space using the relevant sensor model. Elevation data is derived using off-nadir VHR stereo images which one of them is then used for the integration. The proposed method is found to be efficient in terms of sub-pixel accuracy and ease of implementation. Additionally, it preserves the original image information which is essential for some applications such as image classification.