Re: [Matplotlib-users] logairthmic contour plot

[Eric F. <ef...@ha...>]

On 06/13/2012 07:31 AM, jonasr wrote:
>
> Hi,
>
> im actually trying to make a countour plot Z=f(X,Y) from two variables X,Y .
> My Problem is that i have to use a logarithmic scale for the Z values.
> If i plot the data with the logarithmic scale it gets pretty ugly, because i
> have a lot of values which are zero,
> which means on the log scale the value goes to -inf.
> Here is an example what i mean
>
> http://www.imagebanana.com/view/qh1khpxp/example.png
>
> I acutally have no idea how to make the plot look better,
> maybe somebody has an idea ?

Use np.ma.masked_less to mask out values below some threshold before 
taking the log.

e.g.,

import matplotlib.pyplot as plt
import numpy as np
x = np.arange(0, 1, 0.01)
y = np.arange(0, 8, 0.05)
X, Y = np.meshgrid(x, y)
Z = 10 ** (-5 + 11 * X * np.sin(Y))
Z = np.ma.masked_less(Z, 1e-4)
Zlog = np.ma.log10(Z)
CS = plt.contourf(X, Y, Zlog, levels=np.arange(-3, 5.01, 1.0), 
extend='both')
plt.colorbar()



Eric

>
> thank you