dcm2angvec

 DCM2ANGVEC facilitates the use of the function dcm2angle.

 DCM2ANGVEC facilitates the use of the function dcm2angle.
 The function outputs the Euler angles of the rotation matrix phi.
 
 CONVENTION:
     Let Ri be the rotation matrix that rotates the 'axes' about axis i.
     Then phi=Rz*Ry*Rx. See angvec2dcm for further details.
 
 
 USAGE:
     rot=dcm2angvec(phi);
 INPUTS:
     phi: 3x3 rotation matrix.
 
 OUTPUTS:
     rot: 3x1 Euler angles vector

 Abdallah Kassir 1/3/2010

0001 function rot=dcm2angvec(phi)
0002 % DCM2ANGVEC facilitates the use of the function dcm2angle.
0003 %
0004 % DCM2ANGVEC facilitates the use of the function dcm2angle.
0005 % The function outputs the Euler angles of the rotation matrix phi.
0006 %
0007 % CONVENTION:
0008 %     Let Ri be the rotation matrix that rotates the 'axes' about axis i.
0009 %     Then phi=Rz*Ry*Rx. See angvec2dcm for further details.
0010 %
0011 %
0012 % USAGE:
0013 %     rot=dcm2angvec(phi);
0014 % INPUTS:
0015 %     phi: 3x3 rotation matrix.
0016 %
0017 % OUTPUTS:
0018 %     rot: 3x1 Euler angles vector
0019 %
0020 % Abdallah Kassir 1/3/2010
0021 
0022 % [rx,ry,rz]=dcm2angle(phi,'xyz'); % requires aerospace toolbox
0023 % rot=[rx;ry;rz];
0024 
0025 if phi(3,1)~=1 && phi(3,1)~=-1
0026     ry=asin(phi(3,1));
0027     rz=atan2(-phi(2,1)/cos(ry),phi(1,1)/cos(ry));
0028     rx=atan2(-phi(3,2)/cos(ry),phi(3,3)/cos(ry));
0029 else
0030     rz=0;
0031     ry=asin(phi(3,1));
0032     if phi(3,1)==1
0033         rx=atan2(phi(1,2)/phi(3,1),-phi(1,3)/phi(3,1));
0034     elseif phi(3,1)==-1
0035         rx=-atan2(phi(1,2)/phi(3,1),-phi(1,3)/phi(3,1));
0036     end
0037 end
0038 rot=[rx;ry;rz];
0039 end
0040