In our research, a 3D terrain model is automatically generated from key contour polygons by straight skeleton computation. Based on key contours given elevation, the faces connecting key contours are automatically formed, and thus 3D terrain models are automatically created. The proposed system performs physical simulations, using a more realistic environment, such as an automatically generated 3D town model placed on a 3D terrain model, and mass granular flow based on Newtonian mechanics.

A 3-D city model as shown in Figure 1 is important in several fields, such as urban planning and gaming industries. However, enormous time and labour has to be consumed to create these 3-D models, using 3-D modeling softwares such as 3ds Max or SketchUp. For example, when manually modeling a house with roofs by Constructive Solid Geometry (CSG), one must use the following laborious steps:

Automatic generation of 3-D building models as shown in Figure 1 is important in several fields, such as urban planning and the gaming industries. We propose a GIS and CG integrated system that automatically generates 3-D building models, based on building contours (building polygons) on digital maps [1]. This integrated system partitions orthogonal building polygons into a set of rectangles and generates 3-D building models by placing rectangular roofs and box-shaped building bodies on these rectangles. In this paper, we propose a new method for automatic generation of 3-D building models with various shapes of roofs.

When a real urban world is projected into 3-D virtual space, buildings are major objects in this space. To realize the 3-D urban model by computer graphics (CG), it is important to generate building models efficiently. 3-D urban models are the important information infrastructures that can be utilized in several fields, such as landscape evaluation, city planning, civil engineering, architecture, disaster prevention simulation, etc. In this paper, we propose a system to generate 3-D building models semi-automatically by the integration of CG and GIS. Usually, urban planners design the future layout of a town by drawing a map. So, it is convenient for the urban planner who draws the future map to realize an alternative plan if the map can immediately be converted into a 3-D urban model. The system automatically generates a 3-D urban model so quickly that the system meets the urgent demand to realize another alternative plan.