Determining if a point lies on the interior of a polygon

link: http://paulbourke.net/geometry/insidepoly/

 

here is the python code snippet:

 

def point_inside_polygon(cls, lon,lat, coors):
        n = len(coors)
        inside = False
        p1x,p1y = coors[0]
        for i in xrange(n+1):
            p2x,p2y = coors[i % n]
            if lat > min(p1y,p2y):
                if lat <= max(p1y,p2y):
                    if lon <= max(p1x,p2x):
                        if p1y != p2y:
                            xinters = (lat-p1y)*(p2x-p1x)/(p2y-p1y)+p1x
                        if p1x == p2x or lon <= xinters:
                            inside = not inside
            p1x,p1y = p2x,p2y
        return inside

 

the following is a cython version:

 

cpdef point_inside_polygon(double x,double y,list poly):
    cdef int n = len(poly)
    inside = False
    cdef int i
    cdef double p1x,p1y,p2x,p2y,xinters
    p1x,p1y = poly[0]
    for i in xrange(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

 

the cython version is 10x faster that the first.