Plotting data contained in .mat file with python

Question

I have a file myfile.mat exported from octave, it contains three matrices X, Y, U all of them have same size and I want to plot surface U where X, Y are the x and y components of surface U. I can do it in octave with the following code:

surf(X,Y,U)

But I want to do it in python also. I am using pythonxy and for plotting the data in python first of all I import the data with spyder GUI interactively after I saw the matrices in variable explorer in spyder I implement the following codes

from mpl_toolkits.mplot3d import axes3d
import matplotlib.pyplot as plt
from matplotlib import cm

fig = plt.figure()
ax = fig.gca(projection='3d')

ax.plot_surface(X, Y, U, rstride=8, cstride=8, alpha=0.3)

But I see just a blank figure window. Here is the data myfile.mat

can you post the myfile.mat?

HYRY
– HYRY

2013-12-26 23:15:46 +00:00
Commented Dec 26, 2013 at 23:15 — HYRY
– HYRY, Commented Dec 26, 2013 at 23:15
I edit the post by adding the data.

user1772257
– user1772257

2013-12-27 11:45:29 +00:00
Commented Dec 27, 2013 at 11:45 — user1772257
– user1772257, Commented Dec 27, 2013 at 11:45

stachyra · Accepted Answer · 2013-12-27 15:44:11Z

2

I suspect that you are forgetting to include a call to plt.show() at the end. This function has no analog in MATLAB/Octave, but is absolutely required in matplotlib. Also, please be aware that plt.show() doesn't seem to work properly inside of loops in some Python environments, so if you are trying to generate multiple images at once (for example, generating 10 different figures inside of a "for" loop) that may be a hidden source of problems for you as well. Furthermore, you need to define a colormap using the cmap=cm.<whatever> option in the call to the ax.plot_surface() method. A list of all the colormaps that you may use can be found here. And finally, your strides are too large for the tiny little data file that you included. I've appended example code and the resulting image below. I left out setting alpha=0.3 because it is unnecessary for this data (there is nothing in front of or behind anything else) but you may put it back in if you like; the code will still work.

Example surface plot

import scipy.io
import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.mplot3d import Axes3D

data = scipy.io.loadmat('myfile.mat')
X = data['X']
Y = data['Y']
U = data['U']

fig = plt.figure()
ax = fig.gca(projection='3d')
surf = ax.plot_surface(X, Y, U, rstride=1, cstride=1, cmap=cm.jet)
fig.colorbar(surf)

plt.show()

answered Dec 27, 2013 at 15:44

stachyra

4,6134 gold badges25 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user1772257 Over a year ago

I had forgotten plt.show() code in the post but actually i was implementing it. Nevertheless the codes didn't work and i gave a small data for simplicity actually my data is bigger. Anyway I adopted your codes according to my data and they work fine. Thank you for your answer.

Collectives™ on Stack Overflow

Plotting data contained in .mat file with python

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related