Matplotlib contour map colorbar

Question

I am plotting my data into a contour map. The computations work on the translated values, so I need to put it back to its original value. On the fourth line of the code, is the re-translation process. However, when I plotted it the colorbar shows the relative values, and just a note of the shift value at the top of the color bar. It is just weird that I checked the matrix values, and it contains the original values.

How can I show the colorbar, with the original values displayed?

fig=plt.figure()
v=np.linspace(-180,180,25)
x,y = np.meshgrid(v,v)
z = np.add(z,-shift)
z = z.reshape(25,25).T 
plt.contourf(x,y,z,25)
fig.suptitle(AA(prefix)+' Input Data Contour Map')
plt.xlabel('$\phi$ (deg)')
plt.ylabel('$\psi$ (deg)')
plt.xticks(np.arange(-180, 181, 30))
plt.yticks(np.arange(-180, 181, 30))                                
plt.colorbar()

UPDATE: I used set_ticklabels() for a temporary fix, where labels is a list of custom labels.

But I am still looking for a better way to solve this problem.

plt.colorbar().set_ticklabels(labels)

updated contour map

Solution

Matplotlib doesn't know about your shift variable. It is choosing to plot it that way because the changes you are trying to visualize are 10^(-6) of the background value.

You can force the colorbar to have tick marks at specific locations as they do in this pylab example using:

cbar = fig.colorbar(cax, ticks=[-1, 0, 1])
cbar.ax.set_yticklabels(['< -1', '0', '> 1'])  # vertically oriented colorbar

However, doing so will make the scale very difficult to read.

Comments

[jjv]

just wondering, before the plotting command, I checked the values in the z variable and it contains the original values, so it is more of a plotting problem in matplotlib.