euler2qua.m

function qua = euler2qua(euler)
% Ali Mohammadi_INS/GNSS

% euler2qua: converts from Euler angles to quaternion.
% 
% INPUT
%   euler:3x1 Euler angles [roll pitch yaw] (rad, rad, rad).
%
% OUTPUT
%   qua: 4x1 quaternion.
%%

% Rearrange vector for ZYX rotation sequence
euler = [euler(3) euler(2) euler(1)];

c_eul = cos( euler./2 );
s_eul = sin( euler./2 );

% ZYX rotation sequence
q = [ c_eul(1).*c_eul(2).*c_eul(3) + s_eul(1).*s_eul(2).*s_eul(3), ...
      c_eul(1).*c_eul(2).*s_eul(3) - s_eul(1).*s_eul(2).*c_eul(3), ...
      c_eul(1).*s_eul(2).*c_eul(3) + s_eul(1).*c_eul(2).*s_eul(3), ...
      s_eul(1).*c_eul(2).*c_eul(3) - c_eul(1).*s_eul(2).*s_eul(3)];

% Quaternion format from Crassidis' book.
qua = [q(2) q(3) q(4) q(1)]';

end