Digital Elevation Model

This chapter presents the mathematical techniques, required to model and determine the digital elevation model (DEM) or the three-dimensional coordinates of points on earth’s surface (and hence the elevation above a reference ellipsoid). A generic statistical photogrammetric adjustment approach where all parameters, viz. camera model, platform position and orientation, image point pairs, and ground control points, are assigned appropriate weights and adjusted simultaneously is described. Details of coordinate transformations in case of satellite photogrammetry are presented. The Scale invariant feature transform (SIFT) is introduced as a support algorithm for generating DEM from digital frame images with very large overlap acquired by Unmanned Aerial Vehicles. Brief description of image matching algorithms used for finding homologous points in digital imagery is given. The image processing techniques developed in Computer Science are finding more and more inroads in getting precise and dense DEM for the planet Earth. On the other hand, the techniques for determination of position and orientation of imaging camera, well developed in the discipline of Photogrammetry, are being used in simultaneous localization and mapping (SLAM) of autonomous devices.