Fri 04 January 2008

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Recently Prabhu and I have been ironing the library aspect of Mayavi2 (library as opposed to application). One of the usecases we are interested in, is interative use, via for instance ipython, a la pylab.

Most people think of Mayavi as a big and powerful application, maybe a bit clunky to script and to get to interact with other bits of code. With the recent additions you can use mayavi just as you would use matplotlib, to complete matplotlib’s 3D plotting.

3D plotting from ipython

As Mayavi relies on wxPython (technical details, yes I know you don’t care), to use it with ipython, you have to start ipython with iptyhon -wthread. Using ipython from svn you can start ipython with both the -pylab and the -wthread options to use both pylab and mayavi for 2D and 3D plotting (beware of namespace mangling, don’t use from module import *).

The matlab/pylab-like interface to Mayavi is found in enthought.mayavi.tools.mlab(this will most probably change to enthought.mayavi.mlab, or to something else shorter), import this module to have familiar functions. Documentation is a bit missing for now, (you can grab some kind of a embryo at https://svn.enthought.com/enthought/attachment/wiki/MayaVi/mlab.pdf?format=raw ), so I’ll just show an example:

```from enthought.mayavi.toosl import mlab as M
from numpy import *

f = lambda x, y: sin(x + y) + sin(2*x - y ) + cos(3*x + 4*y)
x, y = mgrid[-7:7.05:0.1, -5:5.05:0.05]
M.surf(x, y, f)
M.axes()
M.title('Demoing mlab.surf')
```

Apart from the surf command, the different commands used have equivalents in pylab. surf is inspired from matlab: let us continue pylab’s work here. OK, the keyword arguments are not exactly the same, and not all pylab features are available through the mayavi/mlab interface. But the good news is that the objects created are VTK objects, even though it is a bit hidden by this simplified interface. This means that there is the power of VTK, and that you can always modify the resulting objects to fine tune properties that you cannot (yet) tweak with keyword arguments.

Modifying the plot from the GUI

OK, as you see, we can control Mayavi without all the fuss of the user interface. We get a really simple window that does not get in our way. But is this still Mayavi? This clunky UI was convenient to interact with the visualization. I can pop the pipeline up using M.show_engine(). Once I have the pipeline I can easily double click on any of the items I want to modify, and I get the usual Mayavi dialogs that are so convenient when trying to tweak a scene, for instance to modify the colormap:

This is still work in progress, but mlab is completely useable for real work (I use it whenever I want to make a figure in 3D). Beware that the API is not cast into stone (that’s a good moment to make remarks) and that it might change. Documentation is also lacking. Don’t worry it will come pretty soon, but I also have a thesis to defend :->.

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