angle2dcm

[Siddharth Mahendran]

Hi, I have the MATLAB Total Academic Headcount license from my university and it doesn't have the aerospace toolbox as part of it. I wrote up a short script which I believe does what you want. I'd appreciate it if you can confirm it please.
Thanks !

function dcm = angle2dcm(r1, r2, r3, seq)
% my implementation of the angle2dcm code
% Usage in code: R = angle2dcm(euler(3), euler(2)-pi/2, -euler(1),'ZXZ'); 
seq = lower(seq);
angles = [r1 r2 r3];
dcm = eye(3);
for i = 1:length(seq)
	switch seq(i)
		case 'x'
			dcm = dcm * Rx(angles(i));
		case 'y'
			dcm = dcm * Ry(angles(i));
		case 'z'
			dcm = dcm * Rz(angles(i));
	end
end

function R = Rx(theta)
% rotation about x-axis by angle theta
R = [1 0 0; 0 cos(theta) -sin(theta); 0 sin(theta) cos(theta)];

function R = Ry(theta)
% rotation about y-axis by angle theta
R = [cos(theta) 0 sin(theta); 0 1 0; -sin(theta) 0 cos(theta)];

function R = Rz(theta)
% rotation about z-axis by angle theta
R = [cos(theta) -sin(theta) 0; sin(theta) cos(theta) 0; 0 0 1];

[Shubham Tulsiani]

I think the rotation this code returns is the transpose of the MATLAB implementation's result. This is because the rotations matrices Rx, Ry, Rz defined above are transposed compared to MATLAB convention and the matrices are multiplied as R1 X R2 X R3 (whereas in MATLAB it is R3 X R2 X R1).
See here for a reference implementation.

[Siddharth Mahendran]

Ahh... I was assuming the implicit 3D points are column-wise: 3 X N. But if the points are row-wise: N X 3.. with the rotation being applied as Y = X * R, you are correct. I'll make the change accordingly. Closing the issue now, thanks !