matplotlib-users Mailing List for matplotlib

I'm trying to use path.Path.contains_point for point-in-polygon testing and
am running into a few different confusing situations. My specific
issues/questions are:
1. I'm seeing different behaviour dependent on path direction (clockwise or
counter-clockwise). Is there a "correct" direction to use?
2. What is the expected behaviour for Path.contains_point when the point is
on a boundary?
3. What is the radius parameter supposed to do? The docs say it "allows
the path to be made slightly larger or smaller", but I'm clearly not
understanding this properly (see the cw_path hit test failure with r=0.1
below).
Here is a short example showing some issues with a unit rectangle...
>>> from matplotlib.path import Path
>>> cw_path = Path([[0,0], [0,1], [1,1], [1,0]])
>>> ccw_path = Path([[0,0], [1,0], [1,1], [0,1]])
>>> #Point on x axis not detected for either path...
... cw_path.contains_point([0.5, 0])
0
>>> ccw_path.contains_point([0.5, 0])
0
>>> #Add a large radius and ccw_path works, but not cw_path (!!?)...
... r = 0.1
>>> cw_path.contains_point([0.5, 0], radius=r)
0
>>> ccw_path.contains_point([0.5, 0], radius=r)
1
The following ipython notebook has more detailed tests, but the main points
are in the sample above.
http://nbviewer.ipython.org/7e1b347b8b21b338bee1
I've found at least one reference [1] online indicating that "this function
is intended for use when mouse-clicking". Does that mean I should not use
it for generic point-in-polygon testing?
Thanks,
Russ
[1] http://goo.gl/GtVM6