How are polygon surfaces represented in 3D

Polygon tables-Basic concept

Polygon table

data is placed into the polygon table for    processing

Polygon data table can be organised into two groups

  geometric table

  attribute table              

Storing geometric data

To store geometric data three lists are created

Vertex table – contains coordinate values for each vertex

Edge table – contains pointers back into the vertex table

Polygon table – contains pointers back into the edge table

Advantages of three table

 efficient display of objects

For faster info. Extraction

     expand edge table to include forward pointers to the polygon table

Plane Equation

                     Ax + By + Cz + D = 0

eqn. is solved by Cramer’s rule

Identification of points

    if Ax + By + Cz + D < 0 ,the points (x,y,z) is inside the surface

     if Ax + By + Cz + D > 0 ,the points (x,y,z) is outside the surface