Integration of Terrain Models and Built-up Structures Using Cad- Type Euler Operators

Until recently terrain models were developed in a GIS, and built-up structures were modelled using a CAD system. Extending the current “2.5D” TIN model by incorporating CAD functions is a necessary development, while preserving topological integrity. A solid-modelling CAD system may be excessive for our “extended 2D” mapping needs, but the CAD “boundary representation” (brep) design, based on manifold models, addresses these problems well. TIN models of the terrain surface are well known in GIS, but are unable to represent cliffs, caves or holes, which are required to represent complex buildings. However, translating simple TIN operations into formal Euler Operators on a b-rep structure allow us to add simple CAD functionality by extending the number of Euler Operators, while guaranteeing the connectivity required for terrain modelling. Thus we may start with a TIN model and extrude buildings, bridges, etc. with operators that modify a specified number of faces, edges, vertices and holes, allowing the construction of a seamless representation of the single exterior surface of all land and building features.