|Ph.D Thesis||Department of Civil and Environmental Engineering|
|Supervisor:||Prof. Doytsher Yerach|
|Full Thesis text - in Hebrew|
DTMs describing the terrain relief constitute a central component of mapping and GIS applications in general and photogrammetric mapping in particular. DTMs are used in various applications - all requiring the DTM to be free of gaps and discontinuities. In practice however, the same area may be covered by several overlapping terrain databases collected from diverse sources, differing in their densities and/or accuracy. The goal is to merge all DTMs in order to achieve a complete and continuous representation of the terrain, with the continuity expressed both in terms of continuous heights and topological representations. Common algorithms currently used to merge overlapping DTMs offer a partial solution as they address only the issue of continuity representation of terrain’s height, but not its characteristics.
New algorithms for two alternative approaches are developed to solve the problem of conflating and merging adjacent DTMs. While each of these algorithms provides a solution to a different type of merging problem, they are aimed at achieving a continuous topological representation and "correct" morphological structures of the terrain. The first algorithm - “Spatial Rubber Sheeting” - deals with merging two adjacent DTMs of different accuracies and densities. Based on homologous 3D polylines in the overlapping zone of the adjacent DTMs, a seam line and two rubber bands are defined and a spatial 3D transformation for merging the rubber bands is applied. The second algorithm - “Piece-wise Spatial Fusion” - deals with merging two DTMs of similar accuracies and densities. Based on terrain’s characteristic analysis and homologous 3D point pairs, a piece-wise spatial transformation for merging the overlapping region is defined and applied. This transformation is performed by morphing two homologous TINs (triangular irregular network) from their original position into a target TIN that is calculated as a weighted linear combination of the original TINs.
In contrast with the current relatively inaccurate methods, the proposed algorithms facilitates an accurate spatial conflation and merging process of different DTMs into a unified DTM, providing solutions for achieving a continuous terrain representation with continuity expressed both in terms of continuous height and topological representations.
Additional developed algorithms of analysing and processing DTMs deal with, inter alia, registering two overlapping DTMs and locating homologous point pairs, applying 3D affine transformation to DTMs, calculating color shaded relief maps and a higher density shading than the original DTM’s density, fusing terrain break-lines with gridded DTMs.