[vtkusers] vtkCellArray - efficient use

[Burlen Loring]

Here is an example using vertex cells.


  vtkIdTypeArray *va=vtkIdTypeArray::New();
  va->SetNumberOfTuples(2*nCells);
  vtkIdType *verts=va->GetPointer(0);
  vtkPoints *pts=vtkPoints::New();
  pts->SetData(xyzArray);
  for (int i=0; i<nCells; ++i)
    {
    verts[0]=1;
    verts[1]=i;
    verts+=2;
    }
  polydataset->SetPoints(pts);
  pts->Delete();
  vtkCellArray *cells=vtkCellArray::New();
  cells->SetCells(static_cast<vtkIdType>(nCells),va);
  polydataset->SetVerts(cells);
  cells->Delete();
  va->Delete();


Paul Harris wrote:
> Hi,
>
> I have the following code:
>
> vtkCellArray * p_cells = vtkCellArray::New();
>
> p_cells->Allocate( ids.size() );
>
> for ( vector<vtkIdType>::const_iterator id = ids.begin(), id_end = 
> ids.end(); id != id_end; ++id )
>    p_cells->InsertNextCell(1,&*c);
>
>
> But, I am not sure that my Allocate() call is correct.  Should it be:
> Allocate(ids.size()*2);
>
> ... the reason I ask is that I wanted to try and use 
> p_cells->WritePointer() to do the copying with a memcpy, but it looks 
> like the format of a CellArray is something like:
>
> [cellid, pointid, cellid, pointid, cellid, pointid]
>
> if i had 2 points per cell it would be
> [cellid, point1, point2, cellid, point1, point2, etc]
>
> if this is so, then in order to create a cellarray of 20 points, each 
> in their own cells, i'd need to alloc room for 40.
>
>
> Am I reading the code correctly?
> Does anyone do efficient copies, or does everyone use InsertNextEtc() 
> methods?
>
> thanks,
> Paul
>
>
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-- 
Burlen Loring
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x137