This is actually revealing a secondary bug. It is a bug that filled
objects are being simplified at all. For various reasons, the
simplification algorithm is not safe for use with filled regions (mainly
because it doesn't ensure the end points match up). The Agg backend
turns simplification off for filled objects, but the PDF, PS and SVG
backends were not doing this. I've committed a fix to the branch and
trunk, so in the future, this "path.simplify: False" workaround for
contours should not be necessary.
Mike
Eric Firing wrote:
> Jouni K. Seppänen wrote:
>> Jordan Dawe <jd...@eos.ubc.ca> writes:
>>
>>> Contourf plots that I output in vector format files have little
>>> triangular glitches at the contour boundaries if the contoured array
>>> is larger than about 200x200. The same files in png format are
>>> perfect, even at very high dpi values.
>>
>> The current svn trunk doesn't have the really jarring little triangles
>> (at least in the pdf output), but there are still several very obtuse
>> white triangles between the regions. Rasterization at a high dpi makes
>> the output somewhat better at the cost of larger output files:
>>
>> c=contourf(X, Y, Z, 10)
>> axis((-3, 3, -3, 3))
>> savefig('unrasterized.pdf')
>> for d in c.collections:
>> d.set_rasterized(True)
>> savefig('rasterized.pdf',dpi=200)
>
>
> At least in the trunk--and maybe in 0.99.0--the problem is caused by
> path simplification. In the trunk, for the eps file, it goes away
> completely if I use a matplotlibrc with
>
> path.simplify : False
>
> In the trunk, what seems to be happening is that when a contour
> boundary is almost straight, but has an inflection point, the curves
> for the adjacent patch boundaries are simplified slightly
> differently. This is not surprising; if nothing else, the path will
> be traveled in a different direction when it is an outer boundary than
> when it is an inner boundary (for a set of concentric boundaries).
>
> Jordan, try using a local matplotlibrc with the above. Unless you are
> already customizing via a local matplotlibrc, that line is all you need.
>
> One reason the trunk behavior differs from 0.99.0 is that contour
> patch boundaries are now being turned into compound boundaries instead
> of using a branch cut to connect the outside path to the inside path.
> I suspect simplification is causing the artifacts in both cases, though.
>
> Eric
--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA
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