Spikes in small wedges of a pie chart

[bronger]

The following applies to Python3 + matplotlib 1.5.1.

http://wilson.bronger.org/software.svg exhibits ugly spikes in the small wedges of this pie chart. After importing the SVG into Inkscape, the problem is even worse but can be fixed by changing the style of line vertices to "rounded".

The code is:

from matplotlib import pyplot
import matplotlib

figure = pyplot.figure()
axes = figure.gca()
axes.pie([23, 22, 2, 42, 1, 34, 17, 21, 15, 290, 897],
         labels=["Fedora", "CKAN", "dLibra" + 8 * " ", "DSpace",
                 "eSciDoc", "DataVerse", "EPrints", "MySQL", "Nesstar",
                 "sonstige", "unbekannt"],
         explode=[0, 0, 0, 0, 0, 0, 0, 0, 0, 0.1, 0.15],
         wedgeprops={"clip_on": True, "capstyle": "round"},
         shadow=True, startangle=150)
axes.set_aspect("equal")
figure.savefig("software.svg", bbox_inches="tight", transparent=True)

[tacaswell]

I am not sure that this is a bug in mpl. PNG output looks correctly and you report that this is svg render dependent.

Maybe the default capstyle in pie plots should be changed to rounded?

[bronger]

Is the PNG generated via SVG as an intermediate step?

[bronger]

Maybe the default capstyle in pie plots should be changed to rounded?

+1

[tacaswell]

No, the png is directly rasterized using Agg.

@bronger would you be willing to take a crack at changing that default?

[bronger]

No, I'm sorry. Although I acknowledge that this is a low-hanging fruit, I would have to dive into matplotlib's source code just for this (never hacked on it).

Besides, I found PDF export as a workaround, which is imported by Inkscape loss-less.

[tacaswell]

@bronger I think these changes would be limited to the def pie(self, ...) method in axes/_axes.py. It would be a very shallow dive.

[LindyBalboa]

I checked this out on mpl 1.5.1 and python 3.5. Setting wedgeprops={'capstyle': 'round'} had no effect in IE, Firefox, and Chrome. I also tested 'projecting' and that did not help as either. @tacaswell I think you were right that this might not be an mpl issue.

Edit to add: .eps is slightly distorted at the tip, .ps is badly distored, but .pdf is totally fine.

[bronger]

Had wedgeprops={'capstyle': 'round'} effect for PDFs?

[LindyBalboa]

@bronger Nope, wedgeprops={'capstyle': 'round'} didn't seem to have an effect on any of the formats as far as my standard Anaconda install goes.