[vtkusers] Creating a very large VTK array from a numpy array

[David Gobbi]

Hi Jim,

I've confirmed this error on my own machine and will start working on
a fix soon.  That second argument isn't the problem, the "error return
without exception" also occurs for SetImportVoidPointer(a).  When I
have a fix, I'll report back.

You can save memory by changing the code a bit:

# create uint8 array directly, rather than as double with conversion to uint8
a = numpy.zeros(2**32-1, numpy.uint8)
# directly use numpy array in VTK, avoid "tostring()"
im.SetImportVoidPointer(a)

 - David


On Mon, Sep 26, 2011 at 8:25 AM, Jim Geach <jimgeach at physics.mcgill.ca> wrote:
>
> Hi List,
>
> I'm rendering very large grids that require use of VTK's USE_64BIT_IDS. Following a previous post where I was having trouble with this, I upgraded to version 5.8 which fixed a bug that was not allowing ImageData to use the 64bit indexing (and this flag was set to "ON" in the CMake, and the machine is more than capable).
>
> Now I've got a new problem: I'm working from Python, and creating VTK arrays from numpy arrays, but I still run into problems when the number of elements gets too large. As an example of what I'm talking about:
>
> from numpy import zeros
> import vtk
>
> a = zeros(2**32 - 1).astype(uint8)              #to create a massive array
> im = vtk.vtkImageImport()                       #believe this is the standard method to convert to vtk
> im.CopyImportVoidPointer(a.tostring(),a.size)   #do conversion
>
> throws the following error:
>
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> SystemError: error return without exception set
>
> I'm guessing the type of the second argument of CopyImportVoidPointer is the key here, but trying a few different castings I can't get it to work.
>
> So, I guess my question boils down to: how do I convert extremely large numpy arrays into vtk arrays using the standard methods? (Note that in practice, my numpy arrays will consist of unsigned chars for volume rendering).
>
> Thanks, Jim
>
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