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

[Alexandre GOUAILLARD]

Hi paul,

At the cell level, the cell interface API (boundaryfeatures functions) gives
you only informations about their boundaries i.e. All the cells of
(topological) dimension equal or inferior to itself¹s.

At the itk::Mesh level, you have an interface to get what you want, even
though it has not been directly exported into a nice GetPointCells function.
The structure is there though. You need to call BuildLinks first and then to
access directly the CellLinksContainer. You can take a look at the
implementation of getCellNeighbors to see how it works.
Indeed a lot of filter implementations recode a local array to stock this
information (simplex mesh, spherical wavelet, ...). Alas.

If you use the cvs version of ITK, compiled with the advanced USE_REVIEW
option on, and if you mesh is a surface mesh, you can use an
itk::QuadEdgeMesh which will give you a direct iterator to the 1-ring of a
point (Point->GetEdge( )->BeginGeomOnext( )). This iterator is consistant
with the orientation and allows you to access the points (GetDestination( ))
as well of the faces (GetLeft( )) of the one ring.

Alex.

On 7/26/07 3:16 PM, "Paul Dennis" <aaeamdar at gmail.com> wrote:

> 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 all  of 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


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