Hi Ian
Thanks for your reply and help. I see your point. I guess it is only the
BoundaryNorm where it would make sense to have contourf use the boundary
levels from the norm. In my real problem described by the above example I
have long forgotten the levs variable when I arrive at the contourf point.
I will therefore instead just use levels=norm.boundaries.
Best regards,
Jesper
2014-03-28 15:17 GMT+01:00 Ian Thomas ianthoma...@gmail.com:
On 28 March 2014 12:56, Jesper Larsen jesper.webm...@gmail.com wrote:
I believe the normalization behaviour is wrong for contourf at least when
using a BoundaryNorm. In the script below I am using the same norm to plot
the same data using contourf and pcolormesh. The color should change around
an x value of 0.15 but it is shifted somewhat for contourf. I do realize
that the pcolormesh is in principle shifted a little - but with a grid
spacing of 0.001 that should not matter. Please see the example script
below.
Best regards,
Jesper
Test inconsistent normalization behaviour for matplotlib
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import from_levels_and_colors
# Make custom colormap and norm
levs = [0.0, 0.1, 0.2]
cols = [[0.00392156862745098, 0.23137254901960785, 0.07450980392156863],
[0.00392156862745098, 0.49019607843137253, 0.15294117647058825]]
extend = 'neither'
cmap, norm = from_levels_and_colors(levs, cols, extend)
# Setup testdata
a = np.arange(0.05, 0.15, 0.001, dtype=np.float_)
a, b = np.meshgrid(a, a)0
plt.contourf(a, b, a, norm=norm, cmap=cmap, antialiased=False)
plt.savefig('contourf.png')
plt.clf()
plt.pcolormesh(a, b, a, norm=norm, cmap=cmap, antialiased=False)
plt.savefig('pcolormesh.png')
Jesper,
Regardless of whether you specify a colormap and norm, if you want
contourf to calculate contours at particular levels
then you need to specify those levels. If you don't then contourf will
choose the levels for you, and in your case these are chosen to be
[0.045 0.06 0.075 0.09 0.105 0.12 0.135 0.15 ]
which is why you see the color transition at x=0.105.
To fix this, change your contourf line from
plt.contourf(a, b, a, norm=norm, cmap=cmap, antialiased=False)
to
plt.contourf(a, b, a, norm=norm, cmap=cmap, antialiased=False, levels=levs)
and you will get exactly what you want.
Ian
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