A GTP-based Entity Model for Underground Real 3D Integral Representation

Based on the amended and extended GTP model,the underground entity is extracted in levels of geosciences,geometry and topology,and eight geometric primitives including node,edge,arc,triangle,supper-surface,GTP,tetrahedron and super-body are abstracted.The arc refers to an unclosed curve comprised of two or more end-to-end edges,the supper-surface refers to a spatial surface represented by a group of triangles in order,and the supper-body is a spatial region enclosed by a few supper-surfaces or formed by a group of adjacent GTP elements.The geo-entity is 0-3D classified into point entity,line entity,face entity and body entity,and the body entity could be furthermore sorted as simple body entity,compound body entity and complex body entity.A GTP-based entity model(GTP-EM) is presented for underground real 3D integral representation and modeling.With object-oriented method,the topological relations are defined by geometrical elements.With the 3D integral geo-entity representation and modeling for the subway and its surrounding strata located underground,the central business district(CBD) in Beijing city is taken as an example.