[Insight-users] Region growing on a mesh

[Dan Mueller]

Hi David,

You might want to investigate Review/QuadEdgeMeshFrontIterator class.

It was first proposed in the following Insight Journal paper (I think
there is even some example code):
    http://www.insight-journal.org/download/viewpdf/122/4

Hope this helps.

Cheers, Dan

2009/9/2 David Doria <daviddoria+itk at gmail.com>:
> I am trying write some classes to allow region growing on a mesh - that is,
> specify a seed node, then, based on some criteria, find which nodes in the
> mesh are "connected" to the seed. A simple example is to find all nodes that
> can be reached by traveling less than a distance threshold from a neighbor
> already in the region. Here is an example:
>
> If '0' represents a node and '.' represents a unit of distance, if the seed
> on this simple mesh was the left most '0', and the distance threshold was
> set to 5, the five nodes on the left would be "connected" and the node on
> the far right would not be connected to that group:
>
>       0..0
>       .
>       .
>       .
> 0...0...0.....................0
>
> I have a few questions as I get started:
>
> 1) itkMesh vs itkQuadEdgeMesh
> Should this be based on itkMesh or itkQuadEdgeMesh? itkQuadEdgeMesh seems to
> have better functions for traversal - however it is not currently part of
> ITK. (if my code is useful and QEMesh doesn't end up getting added to ITK,
> then my code becomes not as easily usable for people - how is this typically
> handled?)
>
> 2) Ways to store the result:
> a) An in-place filter where somehow a boolean is attached to each node (this
> could be very difficult as the user could have overridden DefaultMeshTraits
> to store other data in the nodes already...)
> b) Return a separate sub-mesh. The problem with this is that the user would
> have a hard time iterating over the original mesh and asking "is this node
> part of the segmented region?"
> c) Return a separate sub-mesh as well as a boolean version of the original
> mesh. That is - create a new mesh the same size and with the same
> coordinates as the input mesh, but store as PointData a boolean that
> indicates whether each node belongs to the region that was grown. I was
> leaning toward this method.
>
> 3) How to iterate over the mesh?
> I was going to do something like this:
> - Create a queue of NodeIds that are part of the region (initialized to be
> the seed node).
> - Check all of the seed node's neighbors and see if the pass the "connected
> criteria" test
> - Add each node that passes the test to a list of nodes that belong to the
> region. Add the node to the process queue if it is not already on the list
> of nodes that belong to the region
> - do until the queue is empty
>
> Does that sound reasonable?
>
> 4) There would not need to be such a complex class hierarchy as with region
> growing on an itkImage. The only thing that would need to be provided is a
> class that has a Compare() function that takes two nodes that are known to
> be connected.
>
> Does anyone have any comments on any of these issues?
>
> Thanks,
>
> David
>
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