advancefront

 [elist,nextfront]=advancefront(edges,loop,elen)

 advance an edge-front on an oriented surface to the next separated by
 one-element width

 author: Qianqian Fang, <q.fang at neu.edu>
 date: 2012/02/09

 input:
      edges: edge list of an oriented surface mesh, must be in CCW order
      loop: a 2-column array, specifying a closed loop in CCW order
      elen: node number inside each element, if ignored, elen is set to 3

 output:
      elist: list of triangles that is enclosed between the two
             edge-fronts
      nextfront: a new edge loop list representing the next edge-front

 -- this function is part of iso2mesh toolbox (http://iso2mesh.sf.net)

0001 function [elist,nextfront]=advancefront(edges,loop,elen)
0002 %
0003 % [elist,nextfront]=advancefront(edges,loop,elen)
0004 %
0005 % advance an edge-front on an oriented surface to the next separated by
0006 % one-element width
0007 %
0008 % author: Qianqian Fang, <q.fang at neu.edu>
0009 % date: 2012/02/09
0010 %
0011 % input:
0012 %      edges: edge list of an oriented surface mesh, must be in CCW order
0013 %      loop: a 2-column array, specifying a closed loop in CCW order
0014 %      elen: node number inside each element, if ignored, elen is set to 3
0015 %
0016 % output:
0017 %      elist: list of triangles that is enclosed between the two
0018 %             edge-fronts
0019 %      nextfront: a new edge loop list representing the next edge-front
0020 %
0021 % -- this function is part of iso2mesh toolbox (http://iso2mesh.sf.net)
0022 %
0023 
0024 elist=[];
0025 nextfront=[];
0026 
0027 if(nargin<3) elen=3; end
0028 
0029 [hasedge, loc]=ismember(loop,edges,'rows');
0030 
0031 if(~all(hasedge))
0032    error('loop edge is not defined in the mesh');
0033 end
0034 
0035 nodenum=size(edges,1)/elen;
0036 
0037 elist=unique(mod(loc-1,nodenum))+1;
0038 nextfront=edges(elist,:);
0039 for i=1:elen-1
0040     nextfront=[nextfront;edges(elist+nodenum*i,:)];
0041 end
0042 nextfront=setdiff(nextfront,loop,'rows');
0043 
0044 % remove reversed edge pairs
0045 [flag,loc]=ismember(nextfront,nextfront(:,[2 1]),'rows');
0046 id=find(flag);
0047 if(~isempty(id))
0048     delmark=flag;
0049     delmark(loc(find(loc>0)))=1;
0050     nextfront(find(delmark),:)=[];
0051 end
0052 nextfront=nextfront(:,[2 1]); % reverse this loop, as it is reversed to the input loop