James Boyle wrote:
> As far as I can tell, you cannot specify the color that contourf uses
> for masked values.
> The examples enclosed with matplotlib ( 0.98.3) specifically comment
> that this is the case.
> It appears that contourf just does not plot anything where the masked
> values occur and the background ( usually white ) is what is seen.
> This is very useful but ....
>
> I would like to have a bit more choice in how the areas of masked
> data are represented.
> I came up with the following hack which seems to work, but being far
> from expert I wanted to know if anyone wished to help or give advice.
> Is this reasonable or what ?
Jim,
It strikes me as the right way to do what you want; it is not a kludge
or a hack at all. Contourf generates patches for unmasked regions, not
for the masked region, so it is indeed up to you to set the background
as you have done.
I see that there is also an Axes.set_axis_bgcolor method, which I would
expect to be preferred; but it is strangely named. Should it not be
just Axes.set_bg or Axes.set_bgcolor? It corresponds to the axisbg
kwarg in the Axes initializer, perhaps another unfortunate choice of
names.
(Contourf has a longstanding bug in handling internal masked regions; I
hope you don't run into it. Both Mike D and I have tried to figure out
how to fix that bug, but so far without success.)
>
> In the code below data is a masked array with some areas masked.
> The result is that the missing areas are now black rather than white
> ( the default background, I guess)
>
> fig = pylab.figure()
> ax = fig.add_subplot(111)
> ax.axesPatch.set_facecolor('k')
> cs = ax.contourf(data)
> pylab.savefig('example')
>
> I am aware that pcolor , pcolormesh and using cm.set_bad will work
> but I also wanted the option for contourf - it produces nice looking
> plots.
I have not checked just now, but as I recall, pcolor acts like contourf
with respect to masked regions--it plots nothing there, leaving the
background showing through.
Eric
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