Mayavi Contour 3D

Question

If I plot a 3d data using contour3d option of mayavi, there are 3 default contours but how they spaced. I understand the number of contours can be changed, but can they be at user specified values (I would surely guess that is possible). I would like to know how are the default 3 contours drawn. Depending on maximum value of scalar and how is it distributed.

Answer 1

As it happens I just had the same problem and found a solution. Here is some sample code:

import numpy as np
from mayavi import mlab
from mayavi.api import Engine

def fun(x, y, z):
    return np.cos(x) * np.cos(y) * np.cos(z)

# create engine and assign figure to it
engine = Engine()
engine.start()
fig = mlab.figure(figure=None, engine=engine)
contour3d = mlab.contour3d(x, y, z, fun, figure=fig)
scene = engine.scenes[0]

# get a handle for the plot
iso_surface = scene.children[0].children[0].children[0]

# the following line will print you everything that you can modify on that object
iso_surface.contour.print_traits()

# now let's modify the number of contours and the min/max
# you can also do these steps manually in the mayavi pipeline editor
iso_surface.compute_normals = False  # without this only 1 contour will be displayed
iso_surface.contour.number_of_contours = 2
iso_surface.contour.minimum_contour = -1.3
iso_surface.contour.maximum_contour = 1.3

Now about the meaning of the contours. Well, the number obviously says how many contours are created. Then the values for min/max will define a linear space over which the contours will be spread. The value should basically influence the shrinkage/expansion along the surface normals.

Edit: Here's a tip. When you got your plot window, click on the mayavi pipeline icon in the top left. There you can modify your object (usually lowest in the tree). When you press the red record button and start modifying things it will give you the corresponding lines of code.