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qua2euler.m
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qua2euler.m
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function euler = qua2euler(qin)
% qua2euler: transforms quaternion to Euler angles.
%
% INPUT:
% qin, 4x1 quaternion.
%
% OUTPUT:
% euler, 3x1 updated Euler angles (rad).
%
% Copyright (C) 2014, Rodrigo Gonzalez, all rights reserved.
%
% This file is part of NaveGo, an open-source MATLAB toolbox for
% simulation of integrated navigation systems.
%
% NaveGo is free software: you can redistribute it and/or modify
% it under the terms of the GNU Lesser General Public License (LGPL)
% version 3 as published by the Free Software Foundation.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU Lesser General Public License for more details.
%
% You should have received a copy of the GNU Lesser General Public
% License along with this program. If not, see
% <http://www.gnu.org/licenses/>.
%
% Reference:
%
% Version: 003
% Date: 2016/11/26
% Author: Rodrigo Gonzalez <rodralez@frm.utn.edu.ar>
% URL: https://github.com/rodralez/navego
% Quaternion format used in Crassidis' quaternion equations.
qua(1) = qin(4);
qua(2) = qin(1);
qua(3) = qin(2);
qua(4) = qin(3);
% ZYX rotation sequence
c1 = 2.*(qua(2).*qua(3) + qua(1).*qua(4));
c2 = qua(1).^2 + qua(2).^2 - qua(3).^2 - qua(4).^2;
c3 = -2.*(qua(2).*qua(4) - qua(1).*qua(3));
c4 = 2.*(qua(3).*qua(4) + qua(1).*qua(2));
c5 = qua(1).^2 - qua(2).^2 - qua(3).^2 + qua(4).^2;
psi = atan2( c1, c2 ); % yaw
theta = asin( c3 ); % pitch
phi = atan2( c4, c5 ); % roll
euler = [phi theta psi];
end