Re: [Matplotlib-users] jagged edges on masked contour plots

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

John,

You are correct about the way contour handles masked data, and I agree 
that it is ugly; unfortunately, it is inherent in the routine we are 
using.  You could reduce but not eliminate the problem by interpolating 
to a finer grid.

The routine we are using, which came from the gist package, has the 
virtues of an acceptable license, production of regular and filled 
contours, and handling of missing data (but with the problem you note, 
plus one bug that I have not been able to fix yet.)  I think it is also 
very efficient, although I have not done any benchmarking. If a better 
routine with the essential virtues could be found, we would probably use 
it; but I don't know of any.  In particular, open source routines that 
handle filled contours and masking seem to be very rare.

Eric

John Pye wrote:
> Hi all
> 
> I have an application requiring that I do contour plots for masked data.
> At the edge of my contour plots, I'm getting fragmented contours due to
> missing points on the corner of a cell in my grid.
> 
> Is there any way that the contour drawing code can be set up so that it
> plots contours even if a cell in the grid only has data on two sides?
> 
> I suspect that the rule for contour plots is that no contours are shown
> if *any* of the point on the four corners are missing.
> 
> There is an example with the jagged edge shown in the attached image.
> 
> Cheers
> JP
> 
> 
> 
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