[Insight-users] 4-Connectivity of itkMesh (load a PTX file)?

[Luis Ibanez]

Hi David,


A) The method for getting all the neighbors of a node in the QuadEdgeMesh
is:

    for( unsigned int pointId = 0; pointId < numberOfPoints; pointId++ )
      {
      const OutputPixelType & centralPixelValue = pointData->GetElement(
pointId );

      const EdgeType * edgeToFirstNeighborPoint = outputMesh->FindEdge(
pointId );
      const EdgeType * edgeToNeighborPoint = edgeToFirstNeighborPoint;


      do
        {
        const OutputPointIdentifier neighborPointId =
edgeToNeighborPoint->GetDestination();
        const OutputPixelType & neighborPixelValue = pointData->GetElement(
neighborPointId );

        edgeToNeighborPoint = edgeToNeighborPoint->GetOnext();

        //   Do your processing here...
        }
      while( edgeToNeighborPoint != edgeToFirstNeighborPoint );

      }



B)  Notice that the itkQuadEdgeMesh is designed to represent
      a 2D manifold embedded in a 3D space.  I presume that
      this is suitable for LiDAR data.... but just in case, it is good
      to point it out.



   Regards,


             Luis


---------------------------------------------------------------------------------
On Thu, Aug 13, 2009 at 3:50 PM, David Doria
<daviddoria+itk at gmail.com<daviddoria%2Bitk at gmail.com>
> wrote:

>
> On Sun, Aug 9, 2009 at 3:28 PM, Luis Ibanez <luis.ibanez at kitware.com>wrote:
>
>> Hi David,
>>
>>
>> Thanks for the list of algorithms.
>>
>>
>> Please find some comments below.
>>
>>
>> 1) This one is a challenging one. I agree with you that Octrees
>>      or a KdTree will be helpful here.
>>
>>
>> 2) We do search for closest points in the code
>>     recently posted to the Insight Journal:
>> http://www.insight-journal.org/browse/publication/645
>> http://hdl.handle.net/10380/3063
>>
>> This is done in the source code of the MeshInterpolator.
>>
>> You will also find the code at:
>>
>> http://svn.na-mic.org/NAMICSandBox/trunk/QuadEdgeMeshRigidRegistration/Source/
>>
>> You will see that the code uses a KdTree internally.
>>
>>
>> 3) Agree
>>
>> 4) Agree
>>
>> 5) It wouldn't be too hard to extend Region Growing algorithms
>>     to work on Meshes. They will have to be independent classes
>>     but will be easily build once we port a Mesh version of the
>>     FloodFill iterator.
>>
>>
>> Coming up with a hybrid data structure sounds like a good
>> idea. In this way the different needs could be balanced
>> without having to force the functionality of an existing data
>> structure.
>>
>> Have you had a chance to study the VTK classes ?:
>>
>>               vtkStructureGrid
>>               vtkUnstructureGrid
>>
>>
>> They will be a good reference.
>>
>>
>>          Luis
>>
>
> 1) The itk::Octree doesn't seem to have any line intersection functions.
> However, even better than an octree seems to be a modified BSP tree - there
> was just one added to vtk and it sped up my mesh/ray intersections almost
> 50x !! Should we port it to ITK? I never know where the overlap between ITK
> and VTK should stop... can anyone explain a bit more about that?
>
> 2) Great, got the kd-tree working, thanks.
>
> 5) There seems to be a decision here as to use a "grid mesh" (i.e. a mesh
> generated by uniform spherical sampling (like from a LiDAR scanner) has the
> same 4 (or 8) connectivity as an image would, just that the "pixels" live on
> a 2d surface embedded in 3d instead of on a flat "image plane") , versus
> using a general mesh.  It may be nice to have a flood fill operator on a
> general mesh though, and then the "grid mesh" would be handled
> automatically.
>
> Is there a way to get all the neighboring points of a point in an
> itk::Mesh? It looks like itkQuadEdgeMesh may have just about replaced
> itk::Mesh (all of the existing features + many more). In the quad edge mesh
> paper the claim you can access neighboring vertices of a vertex, but on the
> class documentation page I only see GetCellNeighbors<http://www.itk.org/Doxygen/html/classitk_1_1Mesh.html#5a80aa40a37e21266f23e65f83f7e942>.  Am I missing the GetVertexNeighbors?? There doesn't seem to be any
> examples of the QuadEdge (particularly traversal over neighboring vertices)
> in src/Examples - has anyone done this? Maybe someone can add examples like
> this to the /Examples directory? The mesh flood fill would just be doing
> this but "tagging" vertices along the way - just like the image flood fill
> but replacing "visit my 4 neighbors and recurse" with "visit all of my mesh
> neighboring vertices and recurse".
>
> Thanks,
>
> David
>
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