[vtkusers] How to get access to polygons?

[David Gobbi]

Hi Wenlong,

My favorite way of getting polygons out of a vtkCellArray is with
a loop like this:

  vtkIdType numCells = cellArray->GetNumberOfCells();
  vtkIdType cellLocation = 0; // the index into the cell array

  for (vtkIdType i = 0; i < numCells; i++)
    {
    vtkIdType numIds; // to hold the size of the cell
    vtkIdType *pointIds; // to hold the ids in the cell

    cellArray->GetCell(cellLocation, numIds, pointIds);
    cellLocation += 1 + numIds;

    ...
  }

 - David


On Fri, Jan 4, 2013 at 2:44 PM, Wenlong Wang <scc.wwl at gmail.com> wrote:
> Hi, all
>
> I am looking into a 3D shape model. It has 5,000+ points, and 9,000+ cells.
> Thus in the .vtk file, I have the polygon data in the format such as follows
>
> POLYGONS 9637 38548
> 3 0 1 2
> 3 1 3 4
> 3 2 1 4
> 3 3 5 6
> 3 4 3 6
> 3 5 7 8
> .......
>
> The first number of each line indicates how many points are included in the
> cell, and the next 3 numbers indicate the point ids. In my case, the polygon
> is combined by triangles.
>
> I use vtkGenericDataObjectReader to open the .vtk file, and then use
> vtkPolyData::GetPolys to get the polygons of the shape model, whose type is
> vtkCellArray pointer.
>
> Here is my code clip:
>     vtkSmartPointer<vtkGenericDataObjectReader> reader =
> vtkSmartPointer<vtkGenericDataObjectReader>::New();
>     reader->SetFileName("C:\\meanshape.vtk");
>     reader->OpenVTKFile();
>     reader->Update();
>
>     vtkSmartPointer<vtkPolyData> shape =
> vtkSmartPointer<vtkPolyData>::New();
>     shape = reader->GetPolyDataOutput();
>
>     vtkSmartPointer<vtkCellArray> polys =
> vtkSmartPointer<vtkCellArray>::New();
>     polys = shape->GetPolys();
>
> My problem is: After I have polygon data in a vtkCellArray instance, how can
> I get access to the point ids in each triangle cell? For example, I want to
> read "0 1 2" in the first line, "1 3 4" in the second line, etc.
>
> Can you help me out of this? Many thanks in advance for your kind help.
>
> All bests
> Wenlong