Actually, it seems I have partially answered my own question. Since I am
calling axis('off'), I do not notice the effect of clipping the other
artists since I made a call to axis('off'). Without it the spines and axes
rectangle are still removed but the ticks are still visible. I suppose this
is fine for my own purposes of contouring within one country on a map since
I would want to use something like axis('off') anyway, but then it would
not work if I wanted to use the axes background. Another approach I have
tried is to use the clip_path keyword in the plotting functions themselves,
which works for imshow and pcolor, but not contourf. Any other ideas?
Alex
On Mon, Sep 2, 2013 at 12:18 PM, Alex Goodman <alex.good...@colostate.edu>wrote:
> 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
>
--
Alex Goodman
Graduate Research Assistant
Department of Atmospheric Science
Colorado State University
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