[vtkusers] vtk_to_numpy: how to get a vtk_array?

[Mathias Franzius]

Thanks for the quick reply!
I must be doing something wrong, though - probably something silly...
I try to access the scalars like this:

mapper = actor.GetMapper()
polyd = mapper.GetInput()
pointd = polyd.GetPointData()
scalars = pointd.GetScalars()
ar = vtk.vtk_to_numpy(scalars)

But pointd.GetScalars() returns None...
Any idea?

Thanks!
Mathias

-----Ursprüngliche Nachricht-----
Von: "Paul" <massivemonkeymayhem at gmail.com>
Gesendet: 23.03.09 16:27:33
An: Mathias Franzius <Mathias.Franzius at web.de>
CC: vtkusers at vtk.org
Betreff: Re: [vtkusers] vtk_to_numpy: how to get a vtk_array?

Looks like this:

import numpy
from vtk.util import numpy_support

# Reorder the data and flatten it so that it comes out in the order 
that VTK expects
# NOTE that we need to keep this numpy array stored so that python 
doesn't do garbage cleanup on it
# and thereby trash the VTK array as well unexpectedly (causes 
segfaults)

# Create a bunch of data into a numpy array. Here I use the ordering 
Data[x,y,z]
Data = numpy.array([[[1,2,3],[4,5,6],[7,8,9]],[[11,12,13],[14,15,16],[
17,18,19]]],'f')

# Need to transpose x and z coordinate because VTK's data ordering is 
different
flat_data_array = Data.transpose(2,1,0).flatten();

vtk_data_array = numpy_support.numpy_to_vtk(self.data_array)

points = image.GetPointData()
points.SetScalars(vtk_data_array)

image = vtk.vtkImageData() 
image.SetDimensions(Data.shape)
image.Update()

Make sure you keep flat_data_array alive in your namespace somewhere, 
because it actually shares memory with the corresponding VTK Array. 
If Python does garbage cleanup on flat_data_array then you'll lose 
the VTK array, and possibly your mind.

Back the other way:

vtk_data = image.GetPointData().GetScalars()
numpy_data = numpy_support.vtk_to_numpy(vtk_data)

dims = image.GetDimensions()

numpy_data = numpy_data.reshape(dims[2], dims[1], dims[0])
numpy_data = numpy_data.transpose(2,1,0)

numpy_data[x,y,z]...

Paul

On Mon, Mar 23, 2009 at 12:36 PM, Mathias Franzius <Mathias.Franzius@
web.de> wrote:
Dear ng,

I want to render offscreen into a numpy array. So far it works with 
writing to disk with a vtkWindowToImageFilter and an ImageWriter and 
then reloading it with PIL and converting via scipy.misc.fromimage.
However, the vtk.util.vtk_to_numpy seems much more straight-forward 
and efficient.
My problem is: how do I get the rendered image in vtk_data format? 
Now I use the renderWindow like this:
fil = vtk.vtkWindowToImageFilter()
fil.SetInput(renderWindow);

Thanks!
 Mathias
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