OpenGLChapter8.ppt

Computer Graphicswith OpenGL 3e Chapter8 Representation and modeling of 3D objects PREFACE Graphics scenes contain many different kinds of objects and material surfaces: trees, flowers, clouds, rocks, water, bricks, wood paneling, rubber, paper, steel, glass, plastic, cloth…… There is no single method to describe objects. Polygon and quadric surfaces :provide precise descriptions for simple objects; spline surfaces and constructive solid-geometry : useful for designing aircraft wings ……; procedural methods, such as fractal constructions and particle systems:used to model terrain features, clouds……; physically based modeling methods :used to describe the nonrigid behavior of cloth or jello(凝胶物); octree encodings:used to represent internal features of objects( medical CT images). Two representation of solid objects: Boundary representations: describe a three-dimensional object as a set of surfaces that separate the object interior from the environment(polygon facets and spline patches ). Space-partitioning representations: used to describe interior properties(as octree) outline 8-1 Polyhedra(多面体) 8-12 B-Spline Curves 8-3 Curved Surfaces 8-18 OpenGL Approximation-Spline 8-4 Quadric Surfaces Functions 8-5 Superquadrics 8-19 Sweep Representations(扫描表示) 8-6 OpenGL Quadric-Surface 8-20 Constructive Solid-Geometry and Cubic-Surface Functions Methods 8-7 Blobby(柔性) Objects 8-21 Octrees 8-8 Spline Representations 8-22 BSP Trees Methods 8-9 Cubic-Spline Interpolation 8-23 Fractal-Geometry Methods 8-24 Other Procedural Methods 8-10 Bezier Spline Curves 8-25 Particle Systems 8-11 Bezier Surfaces 8-1 Polyhedra The most commonly Boundary representations is a set of surface polygons that enclose objects interior To describe a set of polygon surfaces, we use a list of vertex coordinates for each polygon over the object surface outline 8-1 Polyhedra(多面体) 8-12 B-Spline Curves 8-3 Curved Surfaces