Tatsuya Nemoto

Construction and Visualization of a Three Dimensional Geologic Model Using GRASS GIS

Recently, the need of the geologic information has been rising in many fields such as environmental geology, disaster mitigation, and urban geological applications. For these fields, it is effective to provide geologic information as a three dimensional(3-D) model that can be generated and visualized in general purpose GIS software. The present work aims at introducing a basic theory, implementing methodology and algorithms for 3-D modeling and visualization of geologic model using the Open Source GRASS GIS environment. 3-D geologic model is constructed from the boundary surfaces of geologic units and the logical model of geologic structure. The algorithms for construction and visualization of the proposed model are based on the geologic function g. The geologic function g assigns a unique geologic unit to every point in the objective 3-D space. The boundary surface that divides the objective space into two subspaces, were estimated using data from field survey. The logical model showing the hierarchical relationship between these boundaries surfaces and geologic units can be automatically generated based on the stratigraphic sequence and knowledge of geologic structures. Based on these algorithms, 3-D geologic model can be constructed virtually on GRASS GIS. Applying this model, various geologic surface and section models can be visualized in GRASS GIS environment. Further, “Nviz” was used for dynamic visualization of geologic crosssections and generation of animated image sequences.