3D Object Representations graphics scenes contain solid geometric objects trees, flowers, clouds, rocks, water representations surface ↔interior models procedural models physically based models boundary representations (B-reps) space-partitioning representations
Polygon Surfaces (1) set of surface polygons enclose object interior = Boundary Representation (“B- rep”) wireframe representation of a cylinder with back (hidden) lines removed
polygon tables (B-rep lists) geometric and attribute tables vertex, edge, polygon tables consistency, completeness checks
Polygon Surfaces: Data Structure
Polygon Surfaces: Plane Equation Ax+ By+ Cz+ D = 0 Cartesian coefficients A,B,C,D normal (A,B,C) distance to origin D
Polygon Meshes efficient data structures for tiled surfaces triangle strip n-2 triangles for n vertices
quadrilateral mesh (n-1)x(m-1) quadrilaterals
Curved Lines and Surfaces defined by mathematical functions (implicit, explicit, parametrically) set of data points (surface fitting) tesselation to get polygon mesh aproximation triangles quadrilaterals... (planar?!)
Quadric Surfaces defined by second degree equations (quadrics) – sphere – ellipsoid – torus – paraboloid – hyperboloid
Quadric Surfaces: Sphere implicit parametric φ φ θ π θ π φ θ π φ π sin cos sin, - cos cos, - /2 /2 z r y r x r = = ≤ ≤ x2 + y2 + z2 = r2