def _pnpoly(x, y, coords):
    """
    the algorithm to judge whether the point is located in polygon
    reference: https://www.ecse.rpi.edu/~wrf/Research/Short_Notes/pnpoly.html#Explanation
    """
    vert = [[0, 0]]

    for coord in coords:
        for node in coord:
            vert.append(node)
        vert.append(coord[0])
        vert.append([0, 0])

    inside = False

    i = 0
    j = len(vert) - 1

    while i < len(vert):
        if ((vert[i][0] > y) != (vert[j][0] > y)) and (x < (vert[j][1] - vert[i][1])
                                                       * (y - vert[i][0]) / (vert[j][0] - vert[i][0]) + vert[i][1]):
            inside = not inside
        j = i
        i += 1

    return inside