3D Object representations

                                                3D Object representations

Graphical scenes can contain many different kinds of objects like trees, flowers, rocks, waters...etc. There is no one method that we can use to describe objects that will include all features of those different materials. To produce realistic display of scenes, we need to use representations that accurately model object characteristics.

·         Simple Euclidean objects like polyhedrons and ellipsoids can be represented by polygon and quadric surfaces.

·         Spline surface are useful for designing aircraft wings, gears and other engineering objects.

·          Procedural methods and particle systems allow us to give accurate representation of clouds, clumps of grass, and other natural objects.

·         Octree encodings are used to represent internal features of objects. Such as medical CT images.

Representation schemes for solid objects are often divided into two broad categories:

1.      Boundary representations: describes a 3D object as a set of polygonal surfaces, separate the object interior from environment.

2.      Space-partitioning representation: used to describe interior properties, by partitioning the spatial region, containing an object into a set of small, non overlapping, contiguous solids. e.g. 3D object as Octree representation. 

Boundary Representation: Each 3D object is supposed to be formed its surface by collection of polygon facets and spline patches. Some of the boundary representation methods for 3D surface are:

1. Polygon Surfaces: It is he most common representation for 3D graphics object. In this representations, a 3D object is represented by a set of surfaces that enclose the object interior. Many graphics system use this method. Set of polygons are stored for object description. This simplifies and speeds up the surface rendering and display of object since all surfaces can be described with linear equations.

 

The polygon surface are common in design and solid-modeling applications, since wire frame display can be done quickly to give general indication of surface structure. Then realistic scenes are produced by interpolating shading patterns across polygon surface to illuminate.