*75*

# Area Subdivision Algorithm

It was invented by John Warnock and also called a Warnock Algorithm. It is based on a divide & conquer method. It uses fundamental of area coherence. It is used to resolve the visibility of algorithms. It classifies polygons in two cases i.e. trivial and non-trivial.

Trivial cases are easily handled. Non trivial cases are divided into four equal subwindows. The windows are again further subdivided using recursion until all polygons classified trivial and non trivial.

## Classification of Scheme

It divides or classifies polygons in four categories:

- Inside surface
- Outside surface
- Overlapping surface
- Surrounding surface

**1. Inside surface:** It is surface which is completely inside the surrounding window or specified boundary as shown in fig (c)

**2. Outside surface:** The polygon surface completely outside the surrounding window as shown in fig (a)

**3. Overlapping surface:** It is polygon surface which completely encloses the surrounding window as shown in fig (b)

**4. Overlapping surface:** It is surface partially inside or partially outside the surface area as shown in fig (c)