13-09-2013, 11:54 AM
3D Object Representations
3D Object Representations.pptx (Size: 3.53 MB / Downloads: 30)
Introduction
Line and circle and polygon algorithms-
represented simple and smooth object .
Some Natural object are neither perfectly flat nor smoothly curved but often----
rough ,Jagged .
These object have different characteristic and different material
So there is no one method to described such object
Different Method
Polygon and Quadric surfaces: For simple objects
such as polyhedrons and ellipsoids
Spline surfaces and construction: For curved surfaces for eg. Aircraft wings ,gear and other engg. Structure
Procedural methods: Fractals, Particle systems
for eg. Mountains ,clouds, clumps of grass etc..
Space-partitioning representations
IT describes interior properties by partitioning the spatial region containing an object into a set of small ,nonoverlapping ,contiguous solids.
Eg. Octree Representation
Polygon Surfaces
The most commonly used boundary representation object is a set of polygon surfaces that enclose the object interior .
It describe polygon surfaces with linear equation
This method simplifies and speeds up the surface rendering and display of objects.
1) Geometric table
It contain the vertex co-ordinates and parameter to identify the spatial orientation of the polygon surface.
Geometric data table: vertices, edges, and
polygon surfaces
2) attribute table
It contain an object includes parameters specification the degree of transparency of the object and the surface reflectivity and texture characteristics.
Polygon meshes
A polygon mesh is collection of edges ,vertices and polygon connected such that each edge is shared by at most two polygons.
A polygon mesh can be represented in several ways
Explicitly
Pointers to a vertex list,
Pointers to an edge list.
Pointer to a vertex list:
store all vertices once into a numbered list, and represent each polygon by its vertices. It saves space (vertex only listed once) but still has no explicit representation of shared edges and vertices