%TR2DIFF Convert a transform difference to differential representation%%	D = TR2DIFF(T)%	D = TR2DIFF(T1, T2)%% First form converts a homogeneous transform representing an% infinitessimal motion to a 6-element differential representation.% Such a homogeneous transform has a rotational submatrix that is,% approximately, skew symmetric.%% Second form returns the 6-element differential motion required to move% from T1 to T2 in base coordinates.%% See also: DIFF2TR.% Copyright (C) 1993-2008, 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 d = tr2diff(t1, t2)	if nargin == 1,		d = [	t1(1:3,4);			0.5*[t1(3,2)-t1(2,3); t1(1,3)-t1(3,1); t1(2,1)-t1(1,2)]];	else		d = [	t2(1:3,4)-t1(1:3,4);			0.5*(	cross(t1(1:3,1), t2(1:3,1)) + ...				cross(t1(1:3,2), t2(1:3,2)) + ...				cross(t1(1:3,3), t2(1:3,3)) ...			)];	end