[vtkusers] Neighbours of a point in a mesh

[David Doria]

On Sat, Apr 24, 2010 at 8:31 AM, rashedk <rashed.vtk at googlemail.com> wrote:
>
> Hi all,
>
> A simple question: How do I get the neighbouring points of a point in a
> vtkpolydata polygonal (strictly triangular) mesh?
>
> Thanks,
>
> Rashed.


I just did this last week :)

I would highly recommend adding it to VTK.

//mesh is the input polydata, seed is the vertex you want to get the
neighbors of, and the list of neighbors is returned in
connectedVertices

void vtkPolyDataToGraph::GetConnectedVertices(vtkSmartPointer<vtkPolyData>
mesh, int seed, vtkSmartPointer<vtkIdList> connectedVertices)
{

  //get all cells that vertex 'seed' is a part of
  vtkSmartPointer<vtkIdList> cellIdList =
      vtkSmartPointer<vtkIdList>::New();
  mesh->GetPointCells(seed, cellIdList);

  //cout << "There are " << cellIdList->GetNumberOfIds() << " cells
that use point " << seed << endl;

  //loop through all the cells that use the seed point
  for(vtkIdType i = 0; i < cellIdList->GetNumberOfIds(); i++)
    {

    vtkCell* cell = mesh->GetCell(cellIdList->GetId(i));
    //cout << "The cell has " << cell->GetNumberOfEdges() << " edges." << endl;

    //if the cell doesn't have any edges, it is a line
    if(cell->GetNumberOfEdges() <= 0)
      {
      continue;
      }

    for(vtkIdType e = 0; e < cell->GetNumberOfEdges(); e++)
      {
      vtkCell* edge = cell->GetEdge(e);

      vtkIdList* pointIdList = edge->GetPointIds();
      //cout << "This cell uses " << pointIdList->GetNumberOfIds() <<
" points" << endl;
      /*
      for(vtkIdType p = 0; p < pointIdList->GetNumberOfIds(); p++)
        {
        cout << "Edge " << i << " uses point " << pointIdList->GetId(p) << endl;
        }
        */
      if(pointIdList->GetId(0) == seed || pointIdList->GetId(1) == seed)
        {
        if(pointIdList->GetId(0) == seed)
          {
          connectedVertices->InsertNextId(pointIdList->GetId(1));
          }
        else
          {
          connectedVertices->InsertNextId(pointIdList->GetId(0));
          }
        }
      }


    }

    //cout << "There are " << connectedVertices->GetNumberOfIds() << "
points connected to point " << seed << endl;
}

Let me know if that does the trick.

Thanks,

David