
124 Computing in Geographic Information Systems
FIGURE 7.1
Polygonal curves
Let us denote the interior of the polygon, as int(P), as an open set which
does not contain the boundary. When discussing a polygon P, sometimes it
is the interior region of the polygon, that is of interest. Therefore unless ex-
plicitely mentioned a polygon means unambiguously the int(P).
O’Rourke makes the rather standard convention that when dealing with
polygons, the edges are directed in counter clockwise order about the bound-
ary. Thus the interior of the polygon int(P) is locally to the left of the directed
boundary. Such a listing of the edges is called a boundary trav ...