[vtkusers] vtk_to_numpy: how to get a vtk_array?

[Mathias Franzius]

Hm, that doesn't help - I still get a None for scalars (in python).
I'd expect to possibly get an all-zero result without update, but the None return type usually signals some kind of error...?

Thanks,
   Mathias

-----Ursprüngliche Nachricht-----
Von: "David E DeMarle" <dave.demarle at kitware.com>
Gesendet: 24.03.09 16:52:42
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?

I think you need a call to mapper->Update() in there.

The VTK pipeline uses lazy evaluation, it doesn't do anything until
you tell it to, and thereafter only does as much as it has to to give
a correct answer.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109



On Tue, Mar 24, 2009 at 11:46 AM, Mathias Franzius
<Mathias.Franzius at web.de> wrote:
>
> 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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