Re: [Matplotlib-users] removing paths inside polygon

[Phil E. <pel...@gm...>]

That's really weird. @mdboom, do you have any idea what the difference is
when drawing a Path which has a clip path? (I've looked at anti-aliasing &
snapping without success)





On 12 March 2013 17:17, Andrew Dawson <da...@at...> wrote:

> I tried this and although it sort-of works, it doesn't really do what I
> need. I tried using this:
>
> import matplotlib.pyplot as plt
> import matplotlib.path as mpath
> import numpy as np
> import copy
>
> # create figure and axes
> fig = plt.figure(figsize=(6, 6))
> ax = fig.add_axes([.1, .1, .8, .8])
> ax.set_xlim([-3, 3])
> ax.set_ylim([-3, 3])
>
> # a circle at the origin with radius 1
> circle = plt.Circle((0, 0), 1, transform=ax.transData,
>                     edgecolor='k', facecolor='none')
>
> # from Phil's example
> exterior = mpath.Path.unit_rectangle()
> interior = circle.get_path()
> exterior = mpath.Path(copy.deepcopy(exterior.vertices),
>                       copy.deepcopy(exterior.codes[:]))
> interior.vertices = interior.vertices[::-1]
> exterior.vertices *= 6
> exterior.vertices -= 3
> clip_path = mpath.Path(vertices=np.concatenate([exterior.vertices,
> interior.vertices]),
>                        codes=np.concatenate([exterior.codes,
> interior.codes]))
>
> # lines from the origin dividing the axes into 8 sectors
> end_coords = [(3, 0), (3, 3), (0, 3), (-3, 3),
>               (-3, 0), (-3, -3), (0, -3), (3, -3)]
> for x, y in end_coords:
>     line, = ax.plot((x, 0), (y, 0), color='k')
>     line.set_clip_path(clip_path, ax.transData)
>
> ax.add_artist(circle)
>
> plt.show()
>
> and the result is the attached image with_clipping.png. You should see
> that the circle is no longer circular, and also there are weird line width
> issues. What I want it basically exactly like the attached
> without_clipping.png but with paths inside the circle removed.
>
> Thanks
>
>
>
> On 12 March 2013 16:43, Phil Elson <pel...@gm...> wrote:
>
>> You could just use paths which have holes in them, making the exterior so
>> broad that you wouldn't notice the edge of the clipping. I've put together
>> an example of doing just that:
>>
>> import matplotlib.pyplot as plt
>> import matplotlib.path as mpath
>> import matplotlib.collections as mcol
>> import numpy as np
>> import copy
>>
>>
>> exterior = mpath.Path.unit_rectangle()
>> exterior = mpath.Path(copy.deepcopy(exterior.vertices),
>>                       copy.deepcopy(exterior.codes[:]))
>> exterior.vertices *= 4
>> exterior.vertices -= 2
>> interior = mpath.Path.unit_circle()
>> interior.vertices = interior.vertices[::-1]
>> clip_path = mpath.Path(vertices=np.concatenate([exterior.vertices,
>> interior.vertices]),
>>                        codes=np.concatenate([exterior.codes,
>> interior.codes]))
>>
>> star = mpath.Path.unit_regular_star(6)
>> star.vertices *= 2.6
>>
>>
>> ax = plt.subplot(321)
>> col = mcol.PathCollection([clip_path], facecolor='yellow')
>> ax.add_collection(col)
>> ax.set_title('Clip path')
>> ax.set_xlim([-3, 3])
>> ax.set_ylim([-3, 3])
>>
>>
>> ax = plt.subplot(322)
>> col = mcol.PathCollection([star], facecolor='red')
>> ax.add_collection(col)
>> ax.set_title('Target polygon')
>> ax.set_xlim([-3, 3])
>> ax.set_ylim([-3, 3])
>>
>>
>> ax = plt.subplot2grid((3, 2), (1, 0), colspan=2, rowspan=2)
>> col = mcol.PathCollection([star])
>> col.set_clip_path(clip_path, ax.transData)
>> ax.add_collection(col)
>>
>> ax.set_title('Target polygon clipped by clip_path')
>> ax.set_xlim([-3, 3])
>> ax.set_ylim([-3, 3])
>>
>> plt.tight_layout()
>>
>> plt.show()
>>
>> [image: Inline images 1]
>>
>>
>>
>> There are other options if this doesn't cut the mustard.
>>
>> HTH,
>>
>>
>>
>>
>>
>>
>>
>> On 12 March 2013 15:37, Andrew Dawson <da...@at...> wrote:
>>
>>> Hi
>>>
>>> I'd like to be able to clip a line so that the portion of it lying
>>> outside of a given polygon remains visible and the part that lies inside of
>>> the polygon is not visible. What I want is basically the opposite of:
>>>
>>>     line.set_clip_path(polygon)
>>>
>>> which leaves only the part of the line inside the polygon visible. Is
>>> this possible?
>>>
>>> I know I can just fill the polygon with the background color or
>>> something but this gets messy when there are other lines on the plot that
>>> don't need to be clipped.
>>>
>>> Thanks,
>>> Andrew
>>>
>>>
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>>
>
>
> --
> Dr Andrew Dawson
> Atmospheric, Oceanic & Planetary Physics
> Clarendon Laboratory
> Parks Road
> Oxford OX1 3PU, UK
> Tel: +44 (0)1865 282438
> Email: da...@at...
> Web Site: http://www2.physics.ox.ac.uk/contacts/people/dawson
>