poly_is_point_in_polygon checks if a given point is inside or outside a closed polygon.
bInside is TRUE (1) if the given point is inside the polygon and otherwise FALSE (0).
x is the x coordinate of the point.
y is the y coordinate of the point.
xpoly is a vector with x coordinates of the closed hull.
ypoly is a vector with y coordinates of the closed hull.
If a point is “exactly” on an edge (bounary) of a polygon it is possible that the function returns TRUE (inside) or FALSE (outside).