%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) 1993-2002, by Peter I. Corke% MOD.HISTORY% 1/95	take mean of both values in the skew-symmetric matrix% 2/95	add two argument version as part of ikine() revamp% $Log: tr2diff.m,v $% Revision 1.3  2002/04/14 11:01:23  pic% Updated see also line.%% Revision 1.2  2002/04/01 11:47:18  pic% General cleanup of code: help comments, see also, copyright, remnant dh/dyn% references, clarification of functions.%% $Revision: 1.3 $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