[vtkusers] Filling vtkPoints and vtkCellArray fast

[David Gobbi]

Hi Matt,

If your vtk is built with VTK_USE_64BIT_IDS=OFF, then vtkIdType is
just a typedef for "int" and vtkIdType will be interchangeable with
int.  If vtkIdType is a 64-bit int (or if you want your code to work
when vtkIdType is 64-bit) then yes, you will have to copy your int
data into the vtkIdTypeArray.

   David


On Fri, Jan 15, 2010 at 2:03 PM, Matt <pspmatt at gmail.com> wrote:
> 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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