# Deciding if a Point is Inside a Polygon - Pure Python

This is not a particularly tricky problem, but there wasn't a Python solution on the net when I went looking. I've simply adapted some C code I found at this excellent page.

# determine if a point is inside a given polygon or not # Polygon is a list of (x,y) pairs. def point_inside_polygon(x,y,poly): n = len(poly) inside =False p1x,p1y = poly[0] for i in range(n+1): p2x,p2y = poly[i % n] if y > min(p1y,p2y): if y <= max(p1y,p2y): if x <= max(p1x,p2x): if p1y != p2y: xinters = (y-p1y)*(p2x-p1x)/(p2y-p1y)+p1x if p1x == p2x or x <= xinters: inside = not inside p1x,p1y = p2x,p2y return inside