Michael,
You have found a big bug that I introduced recently. Here is a patch,
which I committed to svn: (watch out for line-breaking by the mailer)
--- lib/matplotlib/contour.py (revision 2899)
+++ lib/matplotlib/contour.py (working copy)
@@ -680,7 +680,12 @@
if self.extend in ('both', 'max', 'min'):
self.norm.clip = False
self.set_array(self.layers)
- # self.tcolors will be set by the "changed" method
+ # self.tcolors are set by the "changed" method,
+ # but need to be set here also
+ # until some refactoring is done.
+ tcolors = [ (tuple(rgba),) for rgba in
+ self.to_rgba(self.cvalues,
alpha=self.alpha)]
+ self.tcolors = tcolors
def _process_linewidths(self):
linewidths = self.linewidths
As the comments indicate, I think I will want to make more extensive
changes, but this removes the immediate problem.
To get the result you want, however, I think that your approach using
the norm will not work; maybe it should, but right now it doesn't.
Instead, simply specify the contour levels that you want, like this:
contourf(x, y, z, linspace(minVal, maxVal, 20), cmap=matplotlib.cm.RdBu_r)
The option you were using, specifying only the number of contours, is
designed for quick-and-dirty automatic contouring, not for fine control.
Eric
Michael Galloy wrote:
> Hello,
>
> I'm having trouble scaling the z-values for a filled contour plot. I
> would like to produce a series of plots like:
>
> plot.contourf(x, y, z, 20, cmap=matplotlib.cm.RdBu_r)
>
> but I would like there to be an absolute correspondence between a given
> z-value and a given color in the colormap no matter what the range of
> z-values for a particular plot. I thought the way to do this would be to
> use the norm keyword like:
>
> normFunction = matplotlib.colors.normalize(vmin=minValue, maxValue)
> plot.contourf(x, y, z, 20, norm=normFunction, cmap=matplotlib.cm.RdBu_r)
>
> but this gives the error:
>
> File
> "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/matplotlib/axes.py",
>
> line 4054, in contourf
> return ContourSet(self, *args, **kwargs)
> File
> "/Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/site-packages/matplotlib/contour.py",
>
> line 456, in __init__
> for level, level_upper, color in zip(lowers, uppers, self.tcolors):
> AttributeError: ContourSet instance has no attribute 'tcolors'
>
> Any suggestions?
>
> Thanks,
> Mike
>
>
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