Hi Phil,
Thanks, that is more or less what I was looking for. However, I still think
that generalizing this approach for other types of plotting functions that
don't return artists directly would be useful. Your solution gave me
another idea for doing this, which would be to iterate through all of the
child artists on the axes using the get_children() method and then calling
set_clip_path() on each artist. This would make the methodology very
general but I am not sure if there are any negative side effects to
resetting the clip path on the other artists besides the PatchCollections.
I modified my simple example script and it seems to work well for
contourf(), pcolor(), and imshow():
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import RegularPolygon
data = np.arange(100).reshape(10, 10)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.contourf(data)
poly = RegularPolygon([ 0.5, 0.5], 6, 0.4, fc='none',
ec='k', transform=ax.transAxes)
for artist in ax.get_children():
artist.set_clip_path(poly)
ax.add_patch(poly)
ax.set_aspect('equal')
ax.axis('off')
plt.show()
Also, I appreciated the cartopy example. I think it has the potential to be
a good basemap replacement thanks to the more robust shapefile support
(which you have very elegantly shown), and I hope the development goes well.
Thanks,
Alex
On Mon, Sep 2, 2013 at 2:33 AM, Phil Elson <pelson....@gmail.com> wrote:
> Great question. The contour set itself does not have a set_clip_path
> method but you can iterate over each of the contour collections and set
> their respective clip paths, i.e.:
>
> cs = plt.contourf(data)
> for collection in cs.collections:
> collection.set_clip_path(poly)
>
> Of course, you can use this approach in either Basemap or cartopy, but
> I've put together an example of doing it in cartopy to demonstrate the neat
> Shapely integration: http://nbviewer.ipython.org/6410510
>
> HTH,
>
> Phil
>
>
> On 2 September 2013 05:40, Alex Goodman <alex.good...@colostate.edu>wrote:
>
>> Hi all,
>>
>> I want to be able to plot data on maps (using basemap or cartopy) inside
>> specific regions, eg a single state, province or country. A similar
>> question was asked a long time ago on the mailing list and the suggested
>> solution back then was to read the bounding polygon from a shapefile and
>> then check if each individual point was inside that polygon. Currently I
>> have no problem doing this if I use matplotlib.path.Path.contains_points()
>> to mask the original data array, but the disadvantage to this solution is
>> that it is very slow. Another solution that I have discovered recently is
>> to use the set_clip_path() method for artists. In addition to being much
>> faster, this also makes the areas near the polygon boundary look much
>> smoother since the actual items being clipped are individual pixels and not
>> data points.
>>
>> Here is an example script that plots an image via imshow, but the only
>> part of the image that gets shown is inside the hexagon.
>>
>> import numpy as np
>> import matplotlib.pyplot as plt
>> from matplotlib.patches import RegularPolygon
>>
>> data = np.arange(100).reshape(10, 10)
>> fig = plt.figure()
>> ax = fig.add_subplot(111)
>> im = ax.imshow(data)
>> poly = RegularPolygon([ 0.5, 0.5], 6, 0.4, fc='none',
>> ec='k', transform=ax.transAxes)
>> im.set_clip_path(poly)
>> ax.add_patch(poly)
>> ax.axis('off')
>> plt.show()
>>
>> While this does seem like an ideal solution, it doesn't work for every
>> type of plot. The most notable example is contourf(). It returns a
>> QuadContourSet instance which does not inherit from Artist, so it does not
>> contain the set_clip_path() method. My main question is whether there is a
>> mechanism in matplotlib that can convert something like a QuadContourSet
>> into an image so I can make use of this solution for contourf() as well. Or
>> better yet, is there perhaps another artist within the axes that I can use
>> the set_clip_path() method for and still get what I want?
>>
>> Thanks,
>> Alex
>> --
>> Alex Goodman
>> Graduate Research Assistant
>> Department of Atmospheric Science
>> Colorado State University
>>
>>
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>
--
Alex Goodman
Graduate Research Assistant
Department of Atmospheric Science
Colorado State University
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