ABSTRACT
Chapter 14 discusses the more traditional development and applications of terrain models. Here, we look at some extensions of these models for specific problems.
15.1 DIGITAL TERRAIN MODELING WITH COMPLEX CONSTRUCTION
15.1.1 Manual Addition of Constructions on Terrain Surface For simplicity it is usually assumed that terrain models are monotonic in X and Y — there is only one possible Z for each XY location. This is often true in the real world, but not always — occasionally there are caves, tunnels, overhanging cliffs, bridges, and overpasses. In the work by Tse and Gold (2002), the standard TIN model is extended by merging some aspects of terrain modeling (TINs), computational geometry (the Quad-Edge data structure), and computer aided design or CAD (Euler operators, which guarantee to preserve the connectivity of the surface after they are applied). They found it easy to combine them to give the usual operations on a 2D triangulation — as well as add an operator that generates a hole between any two nonadjacent triangles (which is really the same thing as adding a bridge or handle to the surface). Figure 15.1, Figure 15.2, and Figure 15.3 give simple examples, and Figure 15.4 and Figure 15.5 show part of a Hong Kong city model.
