[vtkusers] Filling vtkPoints and vtkCellArray fast

[David Gobbi]

The vtkPoints() class has a SetData() method as you have already seen,
and the vtkCellArray class has a method called SetCells(int ncells,
vtkIdTypeArray *cells) that takes a vtkDataArray that contains the
connectivity array.

For vtkPoints::SetData(), the vtkDataArray must be either a
vtkFloatArray or a vtkDoubleArray.  For vtkCellArray::SetCells(), only
a vtkIdTypeArray containing "vtkIdType" values is allowed... vtkIdType
is a typedef for either "int" or "long long" depending on whether
VTK_USE_64BIT_IDS was set by cmake.

You can efficiently set up a vtkDataArray by using the SetTuple()
method, since it is an inline method.  In fact, so is the
vtkPoints::SetPoint() method.

If you have a huge data set and don't want to copy your data, you can
have VTK use your C arrays directly.  The VTK arrays have a method
called "SetArray()" that can be used like this:

vtkFloatArray *array = vtkFloatArray::New();
array->SetNumberOfComponents(3);
array->SetArray(c_array, number_of_points*3, 1);

The "1" on the end tells VTK not call "delete []" or "free()" on
c_array when the vtkDataArray is freed.  You don't have to call
SetNumberOfTuples() because VTK will automatically set the size of the
array from the size of the c_array you give it.

Note that VTK always uses vtkIdType for its cells, you can't choose
whether to use 32-bit or 64-bit ids at run time.

   David


On Fri, Jan 15, 2010 at 9:21 AM, Matt <pspmatt at gmail.com> wrote:
> Hello,
>
> I have recently started using VTK.  First, let me say thanks! It is amazing.
> I am working on an application in ITTVIS IDL that will communicate with a
> DLL (C++) that contains VTK code.
> I have the DLL and the communication working fine and am able to pass data
> between the programs.
> I want to make a bunch of polygons and pass them through the generate tube
> filter before passing it back to IDL.
>
> I am passing two arrays from IDL:
>
> 1) Array of points in floats. 1D.    Form:    X0 Y0 Z0 X1 Y1 Z1 X2 Y2 Z2
>
> 2) Array of connectivity in int. 1D    Form:        N P0 P1 P2 N P1 P3 N P2
> P3
>
>
> ** I think the data is in the form that it is represented in memory in VTK.
> (As in pg. 126 4th edition, OO approach to 3D graphics)
>
> The usual approach would be to create a vtkPolyData array (for the
> polygons), vtkPoints, and a vtkCellArray for connectivity).
> And, then to fill them using vtkPoints->InsertPoint,
> vtkCellArray->InsertNextCell, and then vtkPolyData->setPoints.
>
> However, I need this to be very effcient as I may be calling these routines
> repeatedly.  Given, that the data is almost in the form that VTK expects.
> I want to be able to stuff the data in whole vs point by point, cell by
> cell.
>
> I can't seem to find a good explanation on how I would go about doing this.
>
> There seems to be a ->setData method in vtkPoints class but it takes a
> vtkDataArray and I currently just have a plain old array of floats.
> I think the same goes for setCells in the vtkCellArray class.
>
> Could someone give me a quick example of the few lines of code it would take
> to impelement this.  Or,, point me to a resource that shows an example of
> this
>
> Thanks
>
> Matt
>
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