On 07/14/2010 12:52 PM, Steve McFarlin wrote:
Hello,
I am trying to create a color map that maps 18 colors across 50 levels. As an
example let say I have three colors [r,g,b] and want everything between 1 an 2
to be r, 3 through 10 to be g, and 11 through 50 to be b. From what I can tell
it does not seem to be possible. Currently this is what I have, but it does not
seem to work as I assumed.
colorList =
[[0.,0.,102./255.],[0,42./255.,217./255.],[0,110./255.,217./255.],[0,178./255.,217./255.],
[0,212./255.,212./255.],[0,217./255.,166./255.],[0,217./255.,0],[149./255.,217./255.,0],
[217./255.,217./255.,0],[217./255.,174./255.,0],[217./255.,131./255.,0],[217./255.,87./255.,0],
[217./255.,0,0],[174./255.,0,0],[140./255.,0,0],[135./255.,0,0],
[105./255.,0,0],[65./255.,0,0]]
levels = [1,2,3,4,5,6,7,8,9,10,12,15,20,25,30,35,40,50]
cmap = matplotlib.colors.ListedColormap(colorList, name = 'theColorMap', N =
len(colorList))
...
m.contourf(x,y,z,cmap=cmap, levels=levels, extend='both')
If the levels array is continuous then it works as expected. With the above
settings I get unexpected results, which includes 'ghost contour lines'. The
data I am rendering is from a GRIB file from NOAA.
I think there is some confusion of terminology here, and the "ghost
contour lines" are the least of your problems.
The contourf "levels" are giving boundaries of regions, so with 18
levels, you have 17 regions.
I suspect that what you want is illustrated by the attached extremely
simple example. (You may or may not want to use the spacing kwarg to
colorbar.)
Eric
Is this possible?
Thanks,
Steve
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import numpy as np
import matplotlib.pyplot as plt
import matplotlib.colors as mcolors
x = np.arange(15)
y = np.arange(10)
X, Y = np.meshgrid(x, y)
Z = X**2 + Y**2
boundaries = [0, 80, 160, 280] # 4 boundaries
cmap = mcolors.ListedColormap(['r', 'g', 'b']) # 3 colors
norm = mcolors.BoundaryNorm(boundaries, 3)
plt.contourf(X, Y, Z, levels=boundaries, cmap=cmap, norm=norm)
plt.colorbar(spacing='proportional')
plt.show()
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