Check if geo-point is inside or outside of polygon
Here is a possible solution to my problem.
- Geographical coordinates must be stored properly. Example
np.array([[Lon_A, Lat_A], [Lon_B, Lat_B], [Lon_C, Lat_C]])
- Create the polygon
- Create the point to be tested
- Use
polygon.contains(point)
to test if point is inside (True
) or outside (False
) the polygon.
Here is the missing part of the code:
from shapely.geometry import Pointfrom shapely.geometry.polygon import Polygonlons_lats_vect = np.column_stack((lons_vect, lats_vect)) # Reshape coordinatespolygon = Polygon(lons_lats_vect) # create polygonpoint = Point(y,x) # create pointprint(polygon.contains(point)) # check if polygon contains pointprint(point.within(polygon)) # check if a point is in the polygon
Note: the polygon does not take into account great circles, therefore it is necessary to split the edges into many segments thus increasing the number of vertices.
Special case: If point lies on borders of Polygon
E.g. print(Polygon([(0, 0), (1, 0), (1, 1)]).contains(Point(0, 0)))
will fail
So one can use
print(polygon.touches(point)) # check if point lies on border of polygon
There is also an emerging python library turfpy. which is used for geospatial analysis.
Example:
from turfpy.measurement import boolean_point_in_polygonfrom geojson import Point, Polygon, Featurepoint = Feature(geometry=Point((-46.6318, -23.5523)))polygon = Polygon( [ [ (-46.653, -23.543), (-46.634, -23.5346), (-46.613, -23.543), (-46.614, -23.559), (-46.631, -23.567), (-46.653, -23.560), (-46.653, -23.543), ] ])boolean_point_in_polygon(point, polygon)
Another way to do it is by using the even-odd algorithm explained in this link https://wrf.ecse.rpi.edu//Research/Short_Notes/pnpoly.html The python code is given in wikipedia https://en.wikipedia.org/wiki/Even–odd_rule
Folks, just remember that the ORDER OF POINTS that make the polygon MATTER! I mean, different order results in different polygons.