www.gusucode.com > 机器人工具箱 - robot源码程序 > robot\@quaternion\subsref.m
%SUBSREF Reference methods on a QUATERNION object % % QUATERNION.d return a 4-vector of quaternion elements % QUATERNION.s return the scalar component % QUATERNION.v return the vector component % QUATERNION.t return a 4x4 homogeneous transform % QUATERNION.r return a 3x3 orthonormal rotation matrix % Copyright (C) 1999-2008, 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/>. function v = subsref(q, s) if s(1).type == '.' % NOTE WELL: the following code can't use getfield() since % getfield() uses this, and Matlab will crash!! el = char(s(1).subs); switch el, case 'd', v = double(q); case 's', v = q.s; case 'v', v = q.v; case 't', v = q2tr(q); case 'r', v = q2tr(q); v = v(1:3,1:3); end else error('only .field supported') end %Q2TR Convert unit-quaternion to homogeneous transform % % T = q2tr(Q) % % Return the rotational homogeneous transform corresponding to the unit % quaternion Q. % % See also: TR2Q % Copyright (C) 1993 Peter Corke function t = q2tr(q) q = double(q); s = q(1); x = q(2); y = q(3); z = q(4); r = [ 1-2*(y^2+z^2) 2*(x*y-s*z) 2*(x*z+s*y) 2*(x*y+s*z) 1-2*(x^2+z^2) 2*(y*z-s*x) 2*(x*z-s*y) 2*(y*z+s*x) 1-2*(x^2+y^2) ]; t = eye(4,4); t(1:3,1:3) = r; t(4,4) = 1;