[vtkusers] Dependencies between vtkPolyData::BuildCells and ::BuildLinks

[Hentschel, Bernd]

Hi all,

I'm currently doing some mesh editing with vtkPolyData. Since this
involves some "topologically complex queries", I make use of
vtkPolyData::BuildCells and ::BuildLinks. The following snippet is meant
to illustrate the problem: 

vtkPolyData *pTarget = pReader->GetOutput();
std::set<vtkIdType> setIds;
pTarget->BuildLinks();
ComputeVertexNeighbors(0, pTarget , setIds);

Where ComputeVertex is (...well, if anyone came up with a more efficient
way of computing the 1-ring neighborhood, I would surely appreciate
that):

void ComputeVertexNeighbors(vtkIdType iVertexId, vtkPolyData* pMesh,
set<vtkIdType>& setNeighbors)
{
    vtkIdType* pIncidentCells;
    unsigned short iNumCells;
    
    pMesh->GetPointCells(iVertexId, iNumCells, pIncidentCells);
    
    int i=0;
    int j;
    vtkIdType* pIncidentPoints;
    vtkIdType iNumPoints;

    for(; i<iNumCells; ++iNumCells)
    {
        pMesh->GetCellPoints(pIncidentCells[i], iNumPoints,
pIncidentPoints);
        for(j=0; j<iNumPoints; ++j)
            if(j!=iVertexId)
                setNeighbors.insert(j);
    }
}

Later in my code I want to use vtkPolyData::GetCellPoints which needs
::BuildCells to be called beforehand. So I did the call and ended up
with ::GetPointCells(...) crashing in subsequent calls. Inserting
::BuildCells just before ComputeVertexNeighbors in the above snippet
will just do the same. So it seems to me, that ::BuildCells interferes
with ::BuildLinks, since mixing the two always ends with a crash at some
point in my final program. Moreover, as the ::Build* routines are rather
expensive, I want to call them as little as possible. So, could anyone
explain me the key dependencies and how to use this stuff "correctly"?
Thanx in advance!

Cheers,
	Bernd