How do I set limits on ticks, colors, and labels for colorbar contourf

Question

I've a spatial field of values that I'm outputting on a regular interval over the course of a day. I'm plotting with contourf and I would like to do the following over the course of the day's data:

limit the colors on the colobar to values that represent the min and max of the day's data
hold the color bar static over 24 hourly plots at the max and min of the days data
hold the labels static over the course of those 24 hours

For example:

data = np.random.uniform(0, 5, size=(24,30,30))
data[3,:,:]=np.random.uniform(1,3,size=(30,30))  # example of bad plot
fgsize=(12,4)
numrecs = np.size(data,axis=0)
cbar_min = np.min(data)
cbar_max = np.max(data)
cbarlabels = np.linspace(np.floor(cbar_min), np.ceil(cbar_max), num=5, endpoint=True)


for tt in range(0, numrecs):
    plt.figure(figsize=fgsize, dpi=80)
    plt.title('this is a title')
    plt.contourf(data[tt, :, :], 35, vmin=cbar_min, vmax=cbar_max, cmap='coolwarm')
    cbar =plt.colorbar()
    cbar.set_ticks(cbarlabels)
    cbar.set_ticklabels(cbarlabels)
    cbar.set_label('my data has units')
    plt.show()
    plt.close()

Here is and example of a bad plot. The colors seem limited, but the color bar changes its color/label limits. How do I fix this?

Here is an example of a good plot.

score 4 · Accepted Answer · edited May 23 '17 at 12:23

It turns out that contourf is a bit tricky in setting the levels for the colormap, see this answer. You can get the proper limits and colours by normalising the contours, as follows:

import numpy as np
import matplotlib.pyplot as plt

data = np.random.uniform(0, 5, size=(24,30,30))
data[3,:,:]=np.random.uniform(1,3,size=(30,30))  # example of bad plot
fgsize=(12,4)
numrecs = np.size(data,axis=0)
cbar_min = np.min(data)
cbar_max = np.max(data)
cbarlabels = np.linspace(np.floor(cbar_min), np.ceil(cbar_max), num=5, endpoint=True)

# Set the normalisation for 35 levels (as in your example)
import matplotlib.colors as mc
levels = np.linspace(np.floor(cbar_min), np.ceil(cbar_max), 35) # to draw 35 levels
norm = mc.BoundaryNorm(levels, 256)

for tt in range(0, numrecs):
    print cbar_min, cbar_max
    plt.figure(figsize=fgsize, dpi=80)
    plt.title('this is a title')

    # Draw those levels, with proper normalisation, here:
    plt.contourf(data[tt, :, :], levels, vmin=cbar_min, vmax=cbar_max, cmap='coolwarm', levels=levels, norm=norm)

    cbar = plt.colorbar()
    cbar.set_ticks(cbarlabels)
    cbar.set_ticklabels(cbarlabels)
    cbar.set_label('my data has units')
    plt.show()

thanks lab, i got it fixed with your help. It was making weird numeral limits to the plot without having the cbar_min cbar_max rounded down/up accordingly. but it's fixed! many thansk — SBFRF, Jan 27 '16 at 21:52
@SBFRF glad I could help! If you like the answer, would you mind accepting it? — lab, Jan 27 '16 at 21:56

How do I set limits on ticks, colors, and labels for colorbar contourf

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