Code covered by the BSD License

# geom3d

### David Legland (view profile)

19 Jun 2009 (Updated )

Library to handle 3D geometric primitives: create, intersect, display, and make basic computations

### Editor's Notes:

This file was selected as MATLAB Central Pick of the Week

meshEdgeFaces(vertices, edges, faces)
```function edgeFaces = meshEdgeFaces(vertices, edges, faces) %#ok<INUSL>
%MESHEDGEFACES Compute index of faces adjacent to each edge of a mesh
%
%   EF = meshEdgeFaces(V, E, F)
%   Compute index array of faces adjacent to each edge of a mesh.
%   V, E and F define the mesh: V is vertex array, E contains vertex
%   indices of edge extremities, and F contains vertex indices of each
%   face, either as a numerical array or as a cell array.
%   The result EF has as many rows as the number of edges, and two column.
%   The first column contains index of faces located on the left of the
%   corresponding edge, whereas the second column contains index of the
%   face located on the right. Some indices may be 0 if the mesh is not
%   'closed'.
%
%   Example
%   meshEdgeFaces
%
%
% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2010-10-04,    using Matlab 7.9.0.529 (R2009b)
% Copyright 2010 INRA - Cepia Software Platform.

Ne = size(edges, 1);

% indices of faces adjacent to each edge
edgeFaces = zeros(Ne, 2);

% different method for extracting current face depending if faces are
% stored as index 2D array or as cell array of 1D arrays.
if isnumeric(faces)
Nf = size(faces, 1);
for i = 1:Nf
face = faces(i, :);
processFace(face, i)
end
elseif iscell(faces)
Nf = length(faces);
for i = 1:Nf
face = faces{i};
processFace(face, i)
end
end

function processFace(face, indFace)
% iterate on face edges
for j = 1:length(face)
% build edge: array of vertices
j2 = mod(j, length(face)) + 1;

% do not process edges with same vertices
if face(j) == face(j2)
continue;
end

% vertex indices of current edge
currentEdge = [face(j) face(j2)];

% find index of current edge, assuming face is left-located
b1 = ismember(edges, currentEdge, 'rows');
indEdge = find(b1);
if ~isempty(indEdge)
if edgeFaces(indEdge, 1) ~= 0
error('meshes3d:IllegalTopology', ...
'Two faces were found on left side of edge %d ', indEdge);
end

edgeFaces(indEdge, 1) = indFace;
continue;
end

% otherwise, assume the face is right-located
b2 = ismember(edges, currentEdge([2 1]), 'rows');
indEdge = find(b2);
if ~isempty(indEdge)
if edgeFaces(indEdge, 2) ~= 0
error('meshes3d:IllegalTopology', ...
'Two faces were found on left side of edge %d ', indEdge);
end

edgeFaces(indEdge, 2) = indFace;
continue;
end

% If face was neither left nor right, error
warning('meshes3d:IllegalTopology', ...
'Edge %d of face %d was not found in edge array', ...
j, indFace);
continue;
end
end

end```