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% Ryan Steindl based on Robotics Toolbox for MATLAB (v6 and v9)
%
% Copyright (C) 1993-2011, by Peter I. Corke
%
% This file is part of The Robotics Toolbox for MATLAB (RTB).
%
% RTB is free software: you can redistribute it and/or modify
% it under the terms of the GNU Lesser General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% RTB 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 Leser General Public License
% along with RTB. If not, see <http://www.gnu.org/licenses/>.
%
% http://www.petercorke.com
function q = interp(Q1, Q2, r)
%Quaternion.interp Interpolate rotations expressed by quaternion objects
%
% QI = Q1.interp(Q2, R) is a unit-quaternion that interpolates between Q1 for R=0
% to Q2 for R=1. This is a spherical linear interpolation (slerp) that can be
% interpretted as interpolation along a great circle arc on a sphere.
%
% If R is a vector QI is a vector of quaternions, each element
% corresponding to sequential elements of R.
%
% Notes:
% - the value of r is clipped to the interval 0 to 1
%
% See also ctraj, Quaternion.scale.
q1 = double(Q1);
q2 = double(Q2);
theta = acos(q1*q2');
count = 1;
% clip values of r
r(r<0) = 0;
r(r>1) = 1;
if length(r) == 1
if theta == 0
q = Q1;
else
q = Quaternion( (sin((1-r)*theta) * q1 + sin(r*theta) * q2) / sin(theta) );
end
else
for R=r(:)'
if theta == 0
qq = Q1;
else
qq = Quaternion( (sin((1-R)*theta) * q1 + sin(R*theta) * q2) / sin(theta) );
end
q(count) = qq;
count = count + 1;
end
end
end