Check if functionality of contour and contour_map can be combined

[hoyer-a]

Check if functionality of contour and contour_map could be condensed into one function.

Right now sp.plot.contour_map uses matplotlib's contour / contourf while sp.plot.contour uses tricontour / tricontourf. Maybe both plot-function can use contour / contourf.

The projection parameter could be used to get both mappings into one function.

[hoyer-a]

So this should generally be possible

Key differences

• Triangulation: tricontour takes care of triangulation itself while contour expects data on a regular grid. Therefore a manual interpolation and triangulation is implemented, which produces slightly different results

Left: Contour (rectilinear)    |    Right: Tricontour

• Rad / Degree: sph.plot.contour_map currently plots the data in radians, contour uses degree. Geographic projections only work correctly with radians.

Discussion

• Refactor interpolation / triangulation used in sph.plot.contour_map: as discussed in Contour map plot fails #91, we should refactor the interpolation method to something that solves the missing data problem in geographic plots (at the poles) as well as in other projections
• Handle rad / degree: both functions take coordinate objects, but geographic projections need radians ((-pi, pi), (-pi/2, pi/2)) to work correctly, rectangular projections also make sense with degrees. We could add checks that automatically use rad when a projection is geographic (not sure how to avoid matching strings) or add a parameter with "rad" and "degree" as options.

[ahms5]

@hoyer-a is this still open?

[hoyer-a]

Yes, i would say. Now that contour and contour_map both use _combined_contour (matplotlib.tricontour) for the plot, it could be easy to combine.

[mberz]

@ahms5, @hoyer-a Is there an open PR for this? If not, please move to ready for pickup

[hoyer-a]

Is this still relevant for 1.0.0? If so, i could pick it up.

[mberz]

I don't think it's high priority and can be worked on after the release of 1.0.0, since it will not require any changes to the public API