Subdivision of polygon
Test to find out the visibility of a single surface are made through comparing surfaces that as polygons P along regarding a specified screen area A. There are four types of possibilities as:
i. Surrounding polygon: Polygon which completely comprises the area as in the figure (a).
ii. Intersecting or overlapping polygon: Polygon which intersects the area as in the figure (b).
iii. Contained polygon: polygon which is completely comprised inside the area as in the figure(c).
iv. Disjoint polygon: Polygon which is totally outside the area as in the figure (d).
The classification of the polygons inside a picture is the major computational expense of the algorithm and that is analogous to the clipping algorithms also. Along with the utilization of any one of the clipping algorithms there a polygon in category two as intersecting polygon that can be clipped into a comprised polygon and a disjoint polygon as in the figure 10. Thus, we could proceed as whether category 2 was removed.