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splitFV - split a mesh

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splitFV - split a mesh

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19 May 2010 (Updated )

Splits a 2D or 3D mesh defined by faces and vertices into separately connected mesh pieces.

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Description

  FVOUT = SPLITFV(F,V) separates disconnected pieces inside a patch defined by faces (F) and
  vertices (V). FVOUT is a structure array with fields "faces" and "vertices". Each element of
  this array indicates a separately connected patch.
  FVOUT = SPLITFV(FV) takes in FV as a structure with fields "faces" and "vertices"

  For example:
    fullpatch.vertices = [2 4; 2 8; 8 4; 8 0; 0 4; 2 6; 2 2; 4 2; 4 0; 5 2; 5 0];
    fullpatch.faces = [1 2 3; 1 3 4; 5 6 1; 7 8 9; 11 10 4];
    figure, subplot(2,1,1), patch(fullpatch,'facecolor','r'), title('Unsplit mesh');
    splitpatch = splitFV(fullpatch);
    colours = lines(length(splitpatch));
    subplot(2,1,2), hold on, title('Split mesh');
    for i=1:length(splitpatch)
        patch(splitpatch(i),'facecolor',colours(i,:));
    end

  Note: faces and vertices should be defined such that faces sharing a coincident vertex reference
  the same vertex number, rather than having a separate vertice defined for each face (yet at the
  same vertex location). In other words, running the following command: size(unique(v,'rows') ==
  size(v) should return TRUE. An explicit test for this has not been included in this function so
  as to allow for the deliberate splitting of a mesh at a given location by simply duplicating
  those vertices.

  See also PATCH

MATLAB release MATLAB 7.10 (R2010a)
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Comments and Ratings (7)
23 Jun 2014 Sven

Christopher, good spot and I agree completely - the xyzSub variable in the previous was not doing as intended. It would work in most cases simply because meshes are usually over-connected so the bug wouldn't come up. I've updated as per your change which should now be correct and a little faster.

23 Jun 2014 Christopher

This implementation is slightly flawed. It does not work on the face matrix
5 9 10
5 4 9
4 8 9
4 3 8
3 7 8
3 2 7
2 6 7
2 1 6

It erroneously splits this mesh into two pieces.

It seems that the lines
[availFaceSub, xyzSub] = find(ismember(f(availFaceInds,:), openVertices));
fSets(availFaceInds(availFaceSub)) = currentSet;
openVertices = f(availFaceInds(availFaceSub),xyzSub);

should be replaced by
[availFaceSub, ~] = find(ismember(f(availFaceInds,:), openVertices));
fSets(availFaceInds(availFaceSub)) = currentSet;
openVertices = f(availFaceInds(availFaceSub),:);

xyzSub is unneeded and f(availFaceInds(availFaceSub),xyzSub) is probably not working as the author intended (I'm not sure what the author intended here)---xyzSub is basically replicating particular columns of f(availFaceInds(availFaceSub),:). Thus, if xyzSub doesn't contain 1, 2, or 3, there may be some vertices missing from the openVertices list.

29 Apr 2013 Peter  
21 Jan 2013 Sharif  
24 May 2012 Anton Semechko  
06 Feb 2012 Sven

Thanks for the images Tom :)

22 Dec 2011 Thomas Clark

This did exactly what I wanted, straight out of the box, without editing a single line of code.

That's my kind of FEX submission!

NB For users wondering about this, it works in 3D too.

Sven, would you like some JPEGs of it decomposing different vortices in a fluid flow?

Updates
03 Feb 2012

Updated icon (thanks Tom Clark!)

24 Jun 2014

Implemented Christopher's amendment to fix bug in following connectivity matrix.

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