Gabriel-p
1/15/2015 - 4:45 PM

## python convex polygon scaling

python convex polygon scaling

``````import itertools as IT
def scale_polygon(path,offset):
center = centroid_of_polygon(path)
for i in path:
if i[0] > center[0]:
i[0] += offset
else:
i[0] -= offset
if i[1] > center[1]:
i[1] += offset
else:
i[1] -= offset
return path

def area_of_polygon(x, y):
"""Calculates the signed area of an arbitrary polygon given its verticies
http://stackoverflow.com/a/4682656/190597 (Joe Kington)
http://softsurfer.com/Archive/algorithm_0101/algorithm_0101.htm#2D%20Polygons
"""
area = 0.0
for i in xrange(-1, len(x) - 1):
area += x[i] * (y[i + 1] - y[i - 1])
return area / 2.0

def centroid_of_polygon(points):
"""
http://stackoverflow.com/a/14115494/190597 (mgamba)
"""
area = area_of_polygon(*zip(*points))
result_x = 0
result_y = 0
N = len(points)
points = IT.cycle(points)
x1, y1 = next(points)
for i in range(N):
x0, y0 = x1, y1
x1, y1 = next(points)
cross = (x0 * y1) - (x1 * y0)
result_x += (x0 + x1) * cross
result_y += (y0 + y1) * cross
result_x /= (area * 6.0)
result_y /= (area * 6.0)
return (result_x, result_y)
``````