Re: [matplotlib-devel] Fixed contouring bugs.

[Eric F. <ef...@ha...>]

Ian Thomas wrote:
> Hello all,
> 
> I think I have fixed two bugs in the contouring code (src/cntr.c):
> 1) inconsistent behaviour in how contour and contourf handle saddle
> grid squares, and
> 2) incorrect handling of masked regions in filled contour plots.

Ian,

I have applied your patch and modified contourf_demo slightly to 
illustrate interior masking.  Thanks very much for the beautiful work! 
These contour bugs that you fixed were major mpl problems--general 
embarrassments, and specific impediments to my own applications, since 
the data sets I work with often have masked interior regions.  (And, I 
also use line contours on top of filled contours, so the saddle-point 
decision fix helps as well.)

It occurs to me that there might be a nice refinement: when following a 
masked boundary, how hard would it be to cross the single-cell gap 
diagonally instead of proceeding step-wise along the boundary?  In the 
case of the circular masked region that I added to the contourf_demo, 
this would simply smooth out the boundary of that region.

Eric

> 
> Attached is a gzipped tar file containing an explanation of the bugs
> and what I've done, as well as an svn diff against HEAD and small
> example scripts to demonstrate the bugs before and after the fixes.
> 
> I have tested the fixes for the cases I normally come up with, but
> this is by no means exhaustive.
> 
> Ideally it would be good if someone who is more familiar with cntr.c
> than I am could take a look at what I've done and see if it is OK.
> 
> Ian Thomas
> ian...@go...
> 
> 
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