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pythonmatlabmatplotlibshapely

Point in polygon using shapely?

I am running the following script which I believe should be returning TRUE for the point being in the polygon but it is returning FALSE.

from shapely import geometry

polygon = [(-1571236.8349707182, 8989180.222117377), (1599362.9654156454, 8924317.946336618), (-1653179.0745812152, 8922145.163675062), (-1626237.6614402141, 8986445.107619021)]

Point_X = -1627875.474
Point_Y = 8955472.968

line = geometry.LineString(polygon)
point = geometry.Point(Point_X, Point_Y)

print(line.contains(point))

When I plot the polygon and point in Matlab I get the following shape

enter image description here

from matplotlib import pylab as plt
poly = [[-1571236.8349707182, 8989180.222117377],
    [1599362.9654156454, 8924317.946336618],
    [-1653179.0745812152, 8922145.163675062],
    [-1626237.6614402141, 8986445.107619021]]

x = [point[0] for point in poly]
y = [point[1] for point in poly]

p1 = [-1627875.474, 8955472.968]
p2 = [-1627875.474, 8955472.968]
plt.plot(x,y,p1[0],p1[1],'*r',p2[0],p2[1],'*b')
plt.show()

Any idea why the shapely script is returning FALSE?

Solution

  • What you are testing is whether your point is on the object LineString.

    If you want to test that the point is in the polygon you must use the contains methods of class Polygon

    from shapely import geometry

polygon = [(-1571236.8349707182, 8989180.222117377), (1599362.9654156454, 8924317.946336618), (-1653179.0745812152, 8922145.163675062), (-1626237.6614402141, 8986445.107619021)]

Point_X = -1627875.474
Point_Y = 8955472.968

line = geometry.LineString(polygon)
point = geometry.Point(Point_X, Point_Y)
polygon = geometry.Polygon(line)

print(polygon.contains(point))

    ouput

    True

    see https://shapely.readthedocs.io/en/latest/manual.html