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## Copyright (C) 2024 David Legland
## All rights reserved.
##
## Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions are met:
##
## 1 Redistributions of source code must retain the above copyright notice,
## this list of conditions and the following disclaimer.
## 2 Redistributions in binary form must reproduce the above copyright
## notice, this list of conditions and the following disclaimer in the
## documentation and/or other materials provided with the distribution.
##
## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ''AS IS''
## AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
## IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
## ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
## ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
## DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
## SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
## CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
## OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
##
## The views and conclusions contained in the software and documentation are
## those of the authors and should not be interpreted as representing official
## policies, either expressed or implied, of the copyright holders.
function varargout = meshVertexClustering(vertices, faces, spacing, varargin)
%MESHVERTEXCLUSTERING Simplifies a mesh using vertex clustering.
%
% [V2, F2] = meshVertexClustering(V, F, SPACING)
% [V2, F2] = meshVertexClustering(MESH, SPACING)
% MESH2 = meshVertexClustering(...)
%
% Simplifies a mesh using vertex clustering. Input mesh is specified
% either by a pair V, F containing the vertex coordinates and the faces
% informations, or by a structure with fields 'vertices' and 'faces'.
%
% The SPACING input defines the size of the grid. It can be either a
% scalar (uniform grid) or a 1-by-3 row vector.
%
% The output is specified either in two outputs, or in a structure with
% fields 'vertices' and 'faces'.
%
% Example
% [x, y, z] = meshgrid(1:100, 1:100, 1:100);
% img = hypot3(x-51.12, y-52.23, z-53.34);
% [faces, vertices] = isosurface(img, 45);
% [v2, f2] = meshVertexClustering(vertices, faces, 10);
% figure; axis equal; axis([0 100 0 100 0 100]);
% drawMesh(v2, f2);
%
% See also
% reducepatch, smoothMesh
% ------
% Author: David Legland
% E-mail: david.legland@inrae.fr
% Created: 2019-01-28, using Matlab 9.5.0.944444 (R2018b)
% Copyright 2019-2023 INRA - Cepia Software Platform
%% Initialisation
if isstruct(vertices)
if nargin > 2
varargin = [{spacing} varargin(:)];
end
spacing = faces;
mesh = vertices;
vertices = mesh.vertices;
faces = mesh.faces;
end
% ensure input mesh is a triangulation
faces = triangulateFaces(faces);
% ensure spacing is a 1-by-3 array
if isscalar(spacing)
spacing = [spacing spacing spacing];
end
% extract grid origin
origin = [0 0 0];
if ~isempty(varargin)
origin = varargin{1};
end
%% Apply grid simplification
% identify the vertices belonging to the same grid
[v2, I, J] = unique(round(bsxfun(@rdivide, bsxfun(@minus, vertices, origin), spacing)), 'rows');
%% compute reduced vertex coordinates
% compute coordinates of new vertices
for iVertex = 1:length(I)
gridVertices = vertices(J == iVertex, :);
v2(iVertex, :) = mean(gridVertices, 1);
end
%% Compute new faces
% create empty array
faces2 = zeros(0, 3);
% iterate over old faces, and keep only faces whose vertices belong to
% different cell grids
nFaces = size(faces, 1);
for iFace = 1:nFaces
% current face
face = faces(iFace, :);
% equivalent face with new vertices
face2 = J(face)';
% some vertices may belong to same cell, so we need to adjust
% processing
nInds = length(unique(face2));
if nInds == 3
% vertices belong to three different cells -> create a new face
% keep smaller vertex at first position
[tmp, indMin] = min(face2); %#ok<ASGLU>
face2 = circshift(face2, [1-indMin 0]);
% append the new face to the array
faces2 = [faces2 ; face2]; %#ok<AGROW>
end
end
% remove duplicate faces
faces2 = unique(faces2, 'rows');
if nargout == 1
varargout{1} = struct('vertices', v2, 'faces', faces2);
else
varargout = {v2, faces2};
end
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