[vtkusers] Strange return of grid objects from a Python function

[Guðni Karl Rosenkjær]

Hi all,

After a good nights sleep, I figured out the problem. Since the numpy
array's that store the node coordinates aren't return from the function,
the returned object has a broken reference to the data. By deep-coping the
numpy data into the object, the problem is fixed.

The code that I had to change is:
       nodCvtk = npsup.numpy_to_vtk(nodC,deep=1)

I hope this helps someone else.
Thanks,
Gudni




On Tue, Aug 27, 2013 at 11:33 AM, Guðni Karl Rosenkjær
<grosenkj at eos.ubc.ca>wrote:

> Hi all,
>
> I have written a python function to setup a curvilinear structured grid
> and returns the grid object at the end. In the returned grid object, I
> don't have the points as assigned rather very small values (order of e-50
> to e-300) that is effectively 0.
>
> The code is as follows:
>     import vtk, numpy as np
>     # The test function
>     def testGrid():
>         ''' Small test setting up a cuivilinear grid vts'''
>         x = np.arange(-1,0.6,0.5)
>         y = np.arange(-2,0.1,1.0)
>         z = np.arange(2,-1.1,-0.5)
>         gx,gy,gz = np.meshgrid(x,y,z)
>         nodC =
> np.hstack((gx.T.reshape((np.prod(gx.shape),1)),gy.T.reshape((np.prod(gy.shape),1)),gz.T.reshape((np.prod(gz.shape),1))))
>         nodCvtk = npsup.numpy_to_vtk(nodC)
>         points = vtk.vtkPoints()
>         points.SetData(nodCvtk)
>
>         color = np.arange(np.prod(gx.shape-np.array([1,1,1])))
>         cellColors = npsup.numpy_to_vtk(colorReSh)
>         cellColors.SetName('Colors')
>         sgrid = vtk.vtkStructuredGrid()
>         sgrid.SetDimensions(gx.shape)
>         sgrid.SetPoints(points)
>         sgrid.GetCellData().AddArray(cellColors)
>         def writeVTSFile(fileName,vtsObj):
>             vtsWriter = vtk.vtkXMLStructuredGridWriter()
>             vtsWriter.SetFileName(fileName)
>             vtsWriter.SetInput(vtsObj)
>             vtsWriter.Update()
>         writeVTSFile('vts3DFile.vts',sgrid)
>         return sgrid
>
>     # Read the file
>     vtsReader = vtk.vtkXMLStructuredGridReader()
>     vtsReader.SetFileName('vts3DFile.vts')
>     vtsReader.Update()
>     sgridReader = vtsReader.GetOutput()
>     # Excute the function
>     sgridFunc = testGrid()
>
>     # Print out the first point
>     print sgridFunc.GetPoint(0)
>     print sgridReader.GetPoint(0)
>
>
> The results from the print function are:
> (-1.6934276617628493e-54, 3.4178058e-316, -1.1548972446486807e-82)
> (-1.0, -2.0, 2.0)
>
> However, if I write the object to a file and read it everything is working
> order. Are there some special tricks to return a grid object from a python
> function?
>
> I am running on a Linux 64-bit Fedora 17, with self-compiled version of
> vtk 5.10.1 and python 2.7.
>
> Thanks,
> Gudni
>
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