MATLAB: Does quatrotate() produce negative rotations

Aerospace Toolboxquatrotate

Code
% YPR angles to rotate
yaw   = pi/4;
pitch = 0;
roll  = 0;
% Point to rotate
A = [ 1 0 0]
% Rotate (Negative)
Q = angle2quat(yaw, pitch, roll);
B = quatrotate(Q, A)
% Rotate (Expected result)
Q = angle2quat(-yaw, -pitch, -roll);
C = quatrotate(Q, A)
Results:
A =
     1     0     0
B =
    0.7071   -0.7071         0
C =
    0.7071    0.7071         0

Best Answer

Hello Dereck, there is a difference between a) rotating a reference frame (e.g. relative to a "fixed" vector) and b) rotating a vector relative to a reference frame. Check out this answer for reference.
angle2quat converts rotation angles [to quaternions]. Rotation angles in turn are used to rotate reference frames a), not vectors b). To illustrate, if you do not convert to quaternions but keep working with rotation angles and matrices you could do the same by computing the direction cosine matrix, DCM:
 DCM = angle2dcm(yaw,pitch,roll)
 DCM =
   0.707106781186548   0.707106781186547                   0
  -0.707106781186547   0.707106781186548                   0
                   0                   0   1.000000000000000
 rotate_Frame = DCM*A'
 ans =
   0.707106781186548
  -0.707106781186547
                   0
which, as pointed out above, rotates the reference frame relative to the vector.
If you need to rotate the vector instead, use rotx and equivalent:
 rotate_Vector = rotz(yaw*180/pi)*roty(pitch*180/pi)*rotx(roll*180/pi)*A'
 ans =
   0.707106781186547
   0.707106781186547
                   0
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