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%QINTERP Interpolate rotations expressed by quaternion objects
%
% QI = qinterp(Q1, Q2, R)
%
% Return a unit-quaternion that interpolates between Q1 and Q2 as R moves
% from 0 to 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 cell array of quaternions.
%
% See also TR2Q
% 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
% MOD HISTORY
% 2/99 convert to use of objects
% Copright (C) Peter Corke 1999
function q = qinterp(Q1, Q2, r)
q1 = double(Q1);
q2 = double(Q2);
if (r<0) | (r>1),
error('R out of range');
end
theta = acos(q1*q2');
q = {};
count = 1;
if length(r) == 1,
q = quaternion( (sin((1-r)*theta) * q1 + sin(r*theta) * q2) / sin(theta) );
else
for R=r(:)',
qq = quaternion( (sin((1-R)*theta) * q1 + sin(R*theta) * q2) / sin(theta) );
q{count} = qq;
count = count + 1;
end
end