meshBoundary

MESHBOUNDARY Boundary of a mesh as a collection of 3D line strings.

   CURVES = meshBoundary(V, F)

   Example
     % create centered icosahedron
     [v, f] = createIcosahedron;
     v(:,3) = v(:,3) - mean(v(:,3));
     % convert to simili-sphere
     [v2, f2] = subdivideMesh(v, f, 3);
     v3 = normalizeVector3d(v2);
     % clip with plane
     plane = createPlane([0 0 0], [-1 -2 3]);
     [vc, fc] = clipMeshVertices(v3, f2, plane, 'shape', 'plane');
     figure; drawMesh(vc, fc); axis equal; view(3);
     % draw mesh boundary
     curves = meshBoundary(vc, fc);
     hold on; drawPolygon3d(curves{1}, 'linewidth', 2, 'color', 'b');

   See also
     meshes3d, meshBoundaryEdgeIndices, meshBoundaryVertexIndices

0001 function polyList = meshBoundary(varargin)
0002 %MESHBOUNDARY Boundary of a mesh as a collection of 3D line strings.
0003 %
0004 %   CURVES = meshBoundary(V, F)
0005 %
0006 %   Example
0007 %     % create centered icosahedron
0008 %     [v, f] = createIcosahedron;
0009 %     v(:,3) = v(:,3) - mean(v(:,3));
0010 %     % convert to simili-sphere
0011 %     [v2, f2] = subdivideMesh(v, f, 3);
0012 %     v3 = normalizeVector3d(v2);
0013 %     % clip with plane
0014 %     plane = createPlane([0 0 0], [-1 -2 3]);
0015 %     [vc, fc] = clipMeshVertices(v3, f2, plane, 'shape', 'plane');
0016 %     figure; drawMesh(vc, fc); axis equal; view(3);
0017 %     % draw mesh boundary
0018 %     curves = meshBoundary(vc, fc);
0019 %     hold on; drawPolygon3d(curves{1}, 'linewidth', 2, 'color', 'b');
0020 %
0021 %   See also
0022 %     meshes3d, meshBoundaryEdgeIndices, meshBoundaryVertexIndices
0023 %
0024  
0025 % ------
0026 % Author: David Legland
0027 % e-mail: david.legland@inra.fr
0028 % Created: 2019-05-01,    using Matlab 8.6.0.267246 (R2015b)
0029 % Copyright 2019 INRA - Cepia Software Platform.
0030 
0031 [vertices, edges, faces] = parseMeshData(varargin{:});
0032 
0033 % Compute edge-vertex map if not specified
0034 if isempty(edges)
0035     edges = meshEdges(vertices, faces);
0036 end
0037 
0038 bndEdgeInds = meshBoundaryEdgeIndices(vertices, edges, faces);
0039 bndEdges = edges(bndEdgeInds, :);
0040 
0041 if isempty(bndEdgeInds)
0042     polyList = {};
0043     return;
0044 end
0045 
0046 % allocate empty array
0047 polyList = {};
0048 
0049 nPolys = 0;
0050 while ~isempty(bndEdges)
0051     nPolys = nPolys + 1;
0052     
0053     % current edge
0054     edge = bndEdges(1, :);
0055 
0056     % initialize new polyline at first vertex
0057     ind0 = edge(1);
0058     vertexInds = ind0;
0059     
0060     % current vertex
0061     index = edge(2);
0062     bndEdges(1, :) = [];
0063     
0064     % iterate over edges until current vertex becomes ind0
0065     while index ~= ind0
0066         % append current vertex to list of indices for current polygon
0067         vertexInds = [vertexInds ; index]; %#ok<AGROW>
0068         
0069         % index of the next edge containing current vertex
0070         edgeInd = find(sum(bndEdges == index, 2) > 0);
0071         
0072         % check validity
0073         if isempty(edgeInd)
0074             error('could not find next edge for vertex index %d', index);
0075         end
0076         if length(edgeInd) > 1
0077             error('two many edges contains vertex index %d', index);
0078         end
0079         
0080         % remove current edge from the list of edges to process
0081         edge = bndEdges(edgeInd, :);
0082         bndEdges(edgeInd, :) = [];
0083         
0084 %         % check if current edge closes current polygon
0085 %         if index == ind0
0086 %             break;
0087 %         end
0088         
0089         % identify the next index
0090         index = edge(edge ~= index);
0091     end
0092     
0093     % create the 3D polyline
0094     polyList{nPolys} = vertices(vertexInds, :); %#ok<AGROW>
0095 end