[Insight-users] Can a Vertex find its Lines?

[Paul Dennis]

First of all, I apologize in advance if this is a stupid question that gets
asked every month. I'm relatively new to programming and even more new to
ITK, so I am unsure if this is a reasonable query or not.

Here's the problem: using the "Mesh" structure of ITK (an itk::Mesh), is it
possible for a VertexCell to have information about the higher-dimension
cells that it's associated with? In other words, is there an equivalent to:

pointerToMyVertexCell->GetLinesAssociatedWithMe(dimension);

My initial findings seem to indicate that no, there is no built in way to do
this in ITK. I am using a K-complex from the
itk::AutomaticTopologyMeshSource template. I have quite a few triangles,
each of which has 3 lines and 3 points attached to it. I'm using the
following code segment to iterate through all the cells and print out
information (sorry this is dense and without commenting):


void printCells(MeshType::Pointer pMesh)
    {
        CellIterator cellIterator    = pMesh->GetCells()->Begin();
        CellIterator cellEnd        = pMesh->GetCells()->End();

        CellType::CellAutoPointer tempCellPointer;

        while( cellIterator != cellEnd )
        {
            CellType * pCell = cellIterator.Value();
            cout << pCell->GetNameOfClass() << endl;

            int type = pCell->GetType();
            int a = pCell->GetNumberOfBoundaryFeatures(VERTEX_DIMENSION);
            int b = pCell->GetNumberOfBoundaryFeatures(LINE_DIMENSION);

            switch (type)
            {
                case CellType::VERTEX_CELL:
                    cout << "\tpointId = " <<
((VertexType*)pCell)->GetPointId() << endl;
                    cout << "numBoundfeats = " <<
((VertexType*)pCell)->GetNumberOfBoundaryFeatures(LINE_DIMENSION) << endl;
                    break;

                case CellType::LINE_CELL:
                    for (int i = 0; i < a; i++)
                    {
                        pCell->GetBoundaryFeature(VERTEX_DIMENSION, i,
tempCellPointer);
                        cout << "\t" << tempCellPointer->GetNameOfClass() <<
endl;
                        VertexType * pVertex = dynamic_cast< VertexType* >(
tempCellPointer.GetPointer ());
                        assert (pVertex != NULL);
                        cout << "\t\tpointId = " << pVertex->GetPointId() <<
endl;
                    }
                    break;

                case CellType::TRIANGLE_CELL:
                    for (int i = 0; i < b; i++)
                    {
                        pCell->GetBoundaryFeature(LINE_DIMENSION, i,
tempCellPointer);
                        cout << "\t" << tempCellPointer->GetNameOfClass() <<
endl;
                        int c =
tempCellPointer->GetNumberOfBoundaryFeatures(VERTEX_DIMENSION);
                        VertexType::CellAutoPointer tempVertexPointer;
                        for (int j = 0; j < c; j++)
                        {

tempCellPointer->GetBoundaryFeature(VERTEX_DIMENSION, j, tempVertexPointer);

                            cout << "\t\t" <<
tempVertexPointer->GetNameOfClass() << endl;
                            VertexType * pVertex = dynamic_cast< VertexType*
>(tempVertexPointer.GetPointer ());
                            assert (pVertex != NULL);
                            cout << "\t\t\t pointId = " <<
pVertex->GetPointId() << endl;
                        }
                    }
                    break;

                default:
                    cout << "Unrecognized format." << endl;
                    break;
            }
            ++cellIterator;
        }
    }

Which generates output like this:

TriangleCell
    LineCell
        VertexCell
           pointId = 4223
        VertexCell
           pointId = 3958
etc etc...

However, so far I have only been able to iterate downwards in the dimension
tree (i.e. Triangle->Line->Vertex) and not up.

Alternatively, if it's not possible to find higher-dimension cells from
lower-dimension ones, is there a good way to find the neighboring
VertexCells of a given VertexCell? One approach would be to go through
allof the cells and call their euclideanDistanceTo(Point) methods, but
this
would be a)time-consuming and b) unreliable.

At the moment, I'm thinking of creating a separate array and filling it when
I call the addTriangle(Point, Point, Point) method so that I have
independent information about which triangles a given point is a member of.
Is there a better way?

Thanks,
Paul Dennis

-- 
-Deal in puns!
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