surfedge

 [openedge,elemid]=surfedge(f)

 find the edge of an open surface or surface of a volume

 author: Qianqian Fang, <q.fang at neu.edu>
 date: 2007/11/21

 input:
      f: input, surface face element list, dimension (be,3)

 output:
      openedge: list of edges of the specified surface
      elemid (optional): the corresponding index of the 
                tetrahedron of an open-edge or triangle, 
                elemid has the same length as openedge.

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

0001 function [openedge,elemid]=surfedge(f,varargin)
0002 %
0003 % [openedge,elemid]=surfedge(f)
0004 %
0005 % find the edge of an open surface or surface of a volume
0006 %
0007 % author: Qianqian Fang, <q.fang at neu.edu>
0008 % date: 2007/11/21
0009 %
0010 % input:
0011 %      f: input, surface face element list, dimension (be,3)
0012 %
0013 % output:
0014 %      openedge: list of edges of the specified surface
0015 %      elemid (optional): the corresponding index of the
0016 %                tetrahedron of an open-edge or triangle,
0017 %                elemid has the same length as openedge.
0018 %
0019 % -- this function is part of iso2mesh toolbox (http://iso2mesh.sf.net)
0020 %
0021 
0022 if(isempty(f))
0023     openedge=[];
0024     return;
0025 end
0026 
0027 opt=varargin2struct(varargin{:});
0028 findjunc=jsonopt('Junction',0,opt);
0029 
0030 if(size(f,2)==3)
0031     edges=[f(:,[1,2]);
0032            f(:,[2,3]);
0033            f(:,[3,1])];             % create all the edges
0034 elseif(size(f,2)==4)
0035     edges=[f(:,[1,2,3]);
0036            f(:,[2,1,4]);
0037            f(:,[1,3,4]);
0038            f(:,[2,4,3])];             % create all the edges
0039 else
0040     error('surfedge only supports 2D and 3D elements');
0041 end
0042 % node4=[f(:,3);f(:,2);f(:,1)];   % node idx concatinated
0043 edgesort=sort(edges,2);
0044 [foo,ix,jx]=unique(edgesort,'rows');
0045 
0046 if(isoctavemesh)
0047         u=unique(jx);
0048         if(size(f,2)==3 && findjunc)
0049             qx=u(hist(jx,u)>2);
0050         else
0051         qx=u(hist(jx,u)==1);
0052         end
0053 else
0054     vec=histc(jx,1:max(jx));
0055         if(size(f,2)==3 && findjunc)
0056             qx=find(vec>2);
0057         else
0058         qx=find(vec==1);
0059         end
0060 end
0061 openedge=edges(ix(qx),:);
0062 if(nargout>=2)
0063     [elemid, iy]=ind2sub(size(f),ix(qx));
0064 end
0065 % node4=node4(ix(qx));