Siting Observers

Programs viewshed and vix may be used to find a set of observers that jointly can see every point as follows.

1. Use vix to list all the points by visibility index, and hence, to find the most visible point. Place the first observer, O₁, there.
2. Use viewshed to find the points that O₁ cannot see.
3. Filter the sorted list of points to delete points that O₁ can see.
4. Find the most visible point that O₁ cannot see; that is the second observer, O₂.
5. Repeat until the set of observers can see every point.