[vtkusers] Filling vtkPoints and vtkCellArray fast

[Matt]

Thanks so much! That was really helpful.
I am able to access my C array directly for vtkPoints.  That is awesome.
You explanation and advice really helped my understanding.

I am now trying to figure out this vtkCellArray which I understand takes a
vtkIdTypeArray which contains vtkIdType.
Again, I would like to be able to access my c array directly (if possible).
Or, use the least overhead possible.
My c array is of type int and takes the form:  N, p1, p2, p3, N, p2,  p3,
p4, p5, N, .... The number of points per cell varies.
I guess I can't access this c array directly because it is not the right
type.  Seems a shame.  The data seems to be represented exactly as the
vtkCellArray is organized or at least in my limited understanding it does.

So, what's the best plan of action?  Fill an array of vtkIdType with the
contents of my int c array. And, then pass that into a vtkIdTypeArray, which
I then pass onto the vtkCellArray.

Any advice, code snippets would be much appreciated.  I am a bit stuck.

Matt



On Fri, Jan 15, 2010 at 11:03 AM, David Gobbi <david.gobbi at gmail.com> wrote:

> 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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