geospatialpython/pointinpoly.py at master · GeospatialPython/geospatialpython · GitHub

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# Determine if a point is inside a given polygon or not

# Polygon is a list of (x,y) pairs. This fuction

# returns True or False. The algorithm is called

# "Ray Casting Method".

def point_in_poly(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

## Test

polygon = [(0,10),(10,10),(10,0),(0,0)]

point_x = 5

point_y = 5

## Call the fuction with the points and the polygon

print point_in_poly(point_x,point_y,polygon)

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