[WIP] Plot poloidal plane with contourf

[TomNicholas]

Adds accessor methods to plot poloidal slices using the old griddata approach. Should be general enough to work for any tokamak geometry.

Adds da.bout.contourf(), which gives:

Optionally plots both separatrices, and optionally marks the positions of the limiters with hatched lines to indicate solid surfaces.

Also adds da.bout.regions(), which I created for debugging purposes, but it helps understand how the griddata-style plotting approach works:

To get this to work for any geometry I had to extend the old griddata and fix a few bugs with it, but the result is that it can now handle both X-points, both separatrices, and knows how big the limiters should be, as you can see in this s-alpha plot:

It would be good if someone could try it with (or just send me) a single-null grid file to test against, as I've only tried it with these two examples.

One problem I'm still having is getting the aspect ratio of the plot correct automatically. If I force it with plt.set_aspect() then I end up with loads of whitespace which I can't seem to get rid of.

(@ZedThree This PR should be based off of the grids PR, branch feature/grids on my forked version of xBOUT, but I couldn't quite work out how to do that.)

[pep8speaks]

Hello @TomNicholas! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file examples/plot_grid.py:

Line 6:90: E501 line too long (94 > 89 characters)
Line 7:90: E501 line too long (99 > 89 characters)
Line 14:1: E265 block comment should start with '# '
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Line 21:1: E265 block comment should start with '# '

• In the file xbout/boutdataarray.py:

Line 106:90: E501 line too long (112 > 89 characters)

• In the file xbout/plotting/plotfuncs.py:

Line 8:1: E302 expected 2 blank lines, found 1
Line 45:1: E303 too many blank lines (3)

• In the file xbout/plotting/utils.py:

Line 162:38: E221 multiple spaces before operator
Line 163:21: E128 continuation line under-indented for visual indent
Line 163:38: E221 multiple spaces before operator
Line 164:21: E128 continuation line under-indented for visual indent
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Line 165:34: E221 multiple spaces before operator
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Line 167:38: E221 multiple spaces before operator
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Line 169:21: E128 continuation line under-indented for visual indent
Line 169:34: E221 multiple spaces before operator
Line 187:20: E128 continuation line under-indented for visual indent
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Line 369:53: W292 no newline at end of file

Comment last updated at 2019-08-19 15:22:39 UTC

[codecov-io]

Codecov Report

Merging #34 into master will decrease coverage by 14.84%.
The diff coverage is 7.48%.

@@             Coverage Diff             @@
##           master      #34       +/-   ##
===========================================
- Coverage   48.76%   33.91%   -14.85%     
===========================================
  Files           8        9        +1     
  Lines         404      628      +224     
  Branches       79      108       +29     
===========================================
+ Hits          197      213       +16     
- Misses        185      393      +208     
  Partials       22       22

Impacted Files	Coverage Δ
xbout/plotting/animate.py	13.51% <ø> (-1.49%)	⬇️
xbout/plotting/plotfuncs.py	13.33% <13.33%> (ø)
xbout/plotting/utils.py	5.34% <4.51%> (-14.66%)	⬇️
xbout/boutdataarray.py	30% <60%> (+4.28%)	⬆️

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