polylinesimplify.m

function [newnodes, len]=polylinesimplify(nodes, minangle)
%
% [newnodes, len]=polylinesimplify(nodes, minangle)
%
% Calculate a simplified polyline by removing nodes where two adjacent
% segment have an angle less than a specified limit
%
% author: Qianqian Fang (q.fang at neu.edu)
%
% input:
%    node: an N x 3 array defining each vertex of the polyline in
%          sequential order
%    minangle:(optional) minimum segment angle in radian, if not given, use
%          0.75*pi
%
% output:
%    newnodes: the updated node list; start/end will not be removed
%    len: the length of each segment between the start and the end points
%
%
% -- this function is part of brain2mesh toolbox (http://mcx.space/brain2mesh)
%    License: GPL v3 or later, see LICENSE.txt for details
%

if(nargin<2)
    minangle=0.75*pi;
end

v=segvec(nodes(1:end-1,:), nodes(2:end,:));
ang=acos(max(min(sum(-v(1:end-1,:).*(v(2:end,:)),2),1),-1));

newnodes=nodes;
newv=v;
newang=ang;

idx=find(newang<minangle);

while(~isempty(idx))
    newnodes(idx+1,:)=[];
    newv(idx+1,:)=[];
    newang(idx)=[];
    idx=unique(idx-(0:(length(idx)-1))');
    idx1=idx(idx<size(newnodes,1));
    newv(idx1,:)  =segvec(newnodes(idx1,:),newnodes(idx1+1,:));
    idx1=idx(idx<size(newv,1));
    newang(idx1)  =acos(sum(-newv(idx1,:).*(newv(idx1+1,:)),2));
    idx0=idx(idx>1);
    newang(idx0-1)=acos(sum(-newv(idx0-1,:).*(newv(idx0,:)),2));
    idx=find(newang<minangle);
end

if(nargout>1)
    len=newnodes(1:end-1,:) - newnodes(2:end,:);
    len=sqrt(sum(len.*len,2));
end

function v=segvec(n1, n2)

v=n2-n1;
normals=sqrt(sum(v.*v,2));
v=v./repmat(normals,1,size(v,2));