overlay_all_ratios plot missing centerlines when exported to PDF

[NanoExplorer]

Hello again!
I recently exported my PDR model to PDF, and the PDF is missing the center-lines of each ratio in parameter space. It is unclear to me why this might be the case, as I have not yet had time to debug, and the .png export works fine. I'll attach the two files...

pdrmodel_alllines.pdf

[mpound]

I can reproduce this issue in my own sandbox. I suspect a matplotlib bug.

[mpound]

It may have to do with PDF not preserving zorder of shading versus contours. A workaround is to add an extra call to ax.contour in _plot_no_wcs. At line 686 in modeplot.py:

if kwargs_opts['shading'] != 0:
    cset = self._axis[axidx].contourf(x.value,y.value,k.data,levels=m.levels, colors=colors,alpha=kwargs_opts['shading'])
    # Add extra call to plot contour because savefig("file.pdf") gets zorder of shading vs. contour wrong and contour lines don't show up. Only a bug when output is pdf. Harumph.
    # See https://github.com/mpound/pdrtpy/issues/23
    cset2 = self._axis[axidx].contour(x.value,y.value,k.data,levels=[m.levels[1]], colors=colors, alpha=kwargs_opts['shading'])
else:
    cset = self._axis[axidx].contour(x.value,y.value,k.data,levels=m.levels,
                                         linestyles=lstyles, colors=colors)