[vtkusers] vtk and python for large amout of data

[David Gobbi]

Hi Berk,

I thought that you had to convert the Numeric array to a string first, ie
  fa.SetVoidArray(a.tostring(),5,1)

 - David

-- 
  David Gobbi, MSc                dgobbi at imaging.robarts.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario

On 5 Dec 2002, Berk Geveci wrote:

> >
> > Now I would like to move the data as complete blocks of array, for example
> > something like:
> >
> > from vtk import *
> > import Numeric
> >
> >     list1=[3,2,3,4,3,5,2,8,3,9,1,5]
> >     enumber=3
> >     earray=Numeric.array(list1)
> >     list2=[5,5,5]
> >     ctarray=Numeric.array(list2,'int')
> >
> >     grid=vtkUnstructuredGrid()
> >     IdTArray=vtkIdTypeArray()
> >     IdTArray.SetVoidArray(earray,enumber,1)
> >     vtkCArray=vtkCellArray()
> >     vtkCArray.SetCells(enumber,IdTArray)
> >     grid.SetCells(ctarray,vtkCArray)
> >
> > Of course this doesn't work because SetVoidArray and SetCells are expecting
> > pointers
> > which I can't give them (in Python).
>
> Why not ? The python wrappers are smart enough to figure it out (I have
> to admit I am very impressed, I think python wrappers are the only ones
> which allow this, kudos to whoever added the feature) . The following
> works for me:
>
> import Numeric
>
> # Create an array (float)
> a=Numeric.zeros((5,), Numeric.Float32)
> for i in range(5):
>     a[i] = i
>
> from vtk import *
> # Create the corresponding vtk array
> fa=vtkFloatArray()
> # Assign the pointer. NOTE: DO NOT destroy the original
> # array object, it is responsible of keeping the actual
> # memory block around and will delete it if destroyed, i.e:
> # If you do
> # a = None
> # then
> # fa.GetTuple1(0)
> # will access invalid (freed) memory
> fa.SetVoidArray(a, 5, 1)
> print fa.GetTuple1(2)
>
> >>>> prints 2
>
> # To show that the two arrays point to the same memory.
> a[3]=11
> print fa.GetTuple1(3)
>
> >>>> prints 11
>
> # Now let's do another type
> a=Numeric.zeros((5,),Numeric.Int32)
> a[0]=5
> ar=vtkIdTypeArray()
> ar.SetVoidArray(a, 5, 1)
> print ar.GetValue(0)
>
> >>>> prints 5
>
> # Cell array
> ca=vtkCellArray()
> ca.SetCells(1, ar)
>
> Unfortunately, to create an unstructured grid, you have to use the
> following method:
>
> void vtkUnstructuredGrid::SetCells(vtkUnsignedCharArray *cellTypes,
>                                    vtkIntArray *cellLocations,
>                                    vtkCellArray *cells);
>
> This means that you have to compute cellTypes, cellLocations and cells.
> This is because the following is not wrapped:
>
> void  vtkUnstructuredGrid::SetCells(int *types, vtkCellArray *cells);
>
> (since it takes a pointer to a variable length in array).
>
> -Berk
>
>
>
>
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