3d-object-representation.pdf
- 1. 3 D Object Representations RIDHIMA DUTTA POONAM DHAND
- 2. Solid Object Representation -: • Representation for solid objects can be divided into two categories. BOUNDARY REPRESENTATION SPACE PARTITIONING REPRESENTATION
- 3. Boundary representation describe a 3-D object as a set of surfaces that separate the object interior from the environment. Eg:Polygon Facets,Spline Patches Space Partitioning Representations are used to describe interior properties, by partining the Spatial region containing the object into non overlapping ,contiguous solids. Eg:Octree Representation.
- 4. 1.Polygon surfaces: • Many graphics system stores all the object description as a set of surface polygons. • Speeds up surface rendering and display of objects, since all surfaces are described with linear equations.
- 5. Polygon tables • We can specify a polygon surface with a set of vertex coordinates and associated attribute parameters Geometric tables Polygon Table Attribute tables
- 6. Geometric tables consists of: • VERTEX TABLE • EDGE TABLE • POLYGON SURFACE TABLE VERTEX TABLE V1 X1,Y1,Z1 V2 X2,Y2,Z2 V3 X3,Y3,Z3 V4 X4,Y4,Z4 V5 X5,Y5,Z5 EDGE TABLE E1 V1,V2 E2 V2,V3 E3 V3,V1 E4 V3,V4 E5 V4,V5 E6 V5,V1 POLYGON-SURFACE TABLE S1:E1,E2,E3 S2:E3,E4,E5,E6
- 7. SOME OF THE TEST THAT GRAPHIC PACKEGES SHOULD PERFORM ARE: • THAT EVERY VERTEX LISTED AS END POINT OF AT LEAST TWO EDGES. • THAT EVERY EDGE IS PART OF ATLEAST ONE POLYGON • THAT EVERY POLYGON IS CLOSED • THAT EACH POLYGON HAS ATLEAST ONE SHARED EDGE
- 8. PLANE EQUATIONS • THE EQUATION FOR A PLANE SURFACE CAN BE EXPRESSED IN FORM Ax+By+Cz+D=0
- 10. • A polygon mesh is a collection of vertices, edges and faces that defines the shape of a object in 3D computer graphics and solid modeling. The faces usually consist of triangles, quadrilaterals or other simple convex polygons. • For a triangle mesh n-2 triangles may be needed
- 11. 2…Curved Lines and Surfaces • Displays of 3-D curved lines and surfaces can be generated from an input set of mathematical functions defining the object or from set of user specified data points. • When a set of co-ordinate points used to design a new object shape ,a function is obtained that fits best according to the constraint of application.eg spline curves