Stream: python-questions

Topic: Robinson plot of CAM ne120 : cartopy error?

view this post on Zulip Stephen Yeager (Aug 06 2021 at 23:27):

I am using matplotlib to plot CAM ne120 data. This CAM grid is unstructured, so surface temperature (TS) and lat/lon all have dimensions (ncol: 777602). The tricontourf method works fine for cartopy's crs.PlateCaree() projection, but has a problem with crs.Robinson (see below). I don't know if it's a cyclic point issue, but add_cyclic_point from cartopy.util chokes on ne120 data. Any ideas how to fix this?

Screen-Shot-2021-08-06-at-5.24.14-PM.png Screen-Shot-2021-08-06-at-5.24.33-PM.png

view this post on Zulip Daniel Marsh (Aug 07 2021 at 14:05):

Is it an issue with the number of points or in general? I was able to get crs.Robinson to work with the tripcolor method on 48600 points. See last plot here: /glade/u/home/marsh/demo/se_plot.ipynb
It is slow - can't imagine how much slower it will get with 777K points.

view this post on Zulip Max Grover (Aug 09 2021 at 16:41):

@Stephen Yeager could you share the path to that notebook?

view this post on Zulip Stephen Yeager (Aug 09 2021 at 16:59):

@Max Grover Here's a short, simple notebook that illustrates the issue by comparing global contour maps for 3 different CAM grids:
/glade/u/home/yeager/analysis/python/Robinson.ipynb

@Daniel Marsh Thanks for the pointer to your notebook. Mine computes a Triangulation object via the tricontourf method and doesn't take long at all for NE120 (see above notebook). But the result is flawed...

view this post on Zulip Daniel Marsh (Aug 09 2021 at 17:31):

@Stephen Yeager If I understand your code, it's having to calculate a triangulation on each call to tricontourf(), whereas I do it once ahead of calling tripcolor(). So you'd think my code might be faster in the end.

view this post on Zulip Stephen Yeager (Aug 09 2021 at 17:58):

I added a cell to my notebook that uses tripcolor() instead of tricontourf(). It takes much longer (~11 minutes as opposed to ~8s), but it does generate a reasonable-looking Robinson plot.

Last updated: Jan 30 2022 at 12:01 UTC