Hello folks,

I am new to this gamedev.net forum that I searched for and found. I searched for angular velocity and quaternion on Google but they did not help so much. I implemented quaternion and angular velocity control (by using keyboard). When I pitch to 90 degrees down, I tried to yaw right but it rolls right instead. At zero Z-axis angle, it normally yaw right or left. I want to rotate at current local axes, not origin axes. My code implementation is:

dr = (angularVelocity * 0.5) * orientation;

orientation += (dr * dt);

orientation.normalize();

Where dt = delta time, dr = delta rotation

Does anyone have different angular velocity/quaternion formula to yaw, pitch, and roll at current local axes?

Thanks,

Sword7

If q_t is the current orientation of the object (the rotation accumulated so far), d the local rotation and x the point you want to transform, then you want to compute qdxd*q* (where quaternion multiplication is denoted by juxtaposition and q* and d* are the conjugate of q and d). You are currently computing instead dqxq*d*. You have to store the current orientation somewhere and multiply the two rotations in the correct order.

http://www.euclideanspace.com/physics/kinematics/angularvelocity/QuaternionDifferentiation2.pdf

Ok, I changed that lines to:

dr = orientation * (angularVelocity * 0.5) * orientation.conjugate();

orientation += (dr * dt);

I resolved a problem but I got another new problem. For example, When I roll right to 90 degress, tried to yaw right but rotate 45 degrees between pitch and yaw axis. Also, I continued to play controls, controls became locked out. I can't yaw, pitch, or roll anymore after a few minutes when w in orentation became zero [ 0 (x, y, z)].

I tried that 'dr = orientation * angularVelocity * orientation.conjugate()' but it resulted the same.

Quaternion<double> conjugate()

{

return Quaternion<double>(w, -x, -y, -z);

}

Right?

Thanks!

Sword7

Hello folks,

Good news!!! I now found a problem and corrected formula. It finally works!!!

Quaternion w(0, angularVelocity);

dr = 0.5 * (orientation * w);

orientation += (dr * dt);

orentation.normalize();

It now rotates in local axes!!

If w * orientation, it rotates in world axes.

if orientation * w, it rotates in local axes.

I googled and found article that explains about world axes and local axes in quaternions.

http://stackoverflow.com/questions/9715776/using-quaternions-for-opengl-rotations

http://www.arcsynthesis.org/gltut/Positioning/Tut08%20Quaternions.html

This is actually very easy to prove:

dq/dt = 0.5 * w * q // The quaternion time derivative

w = q * w' * conjugate( q ) // Here w' is the local angular velocity and we transform it to world space. Now we simply plug this into the equation above

dq/dt = 0.5 * ( q * w' * conjugate( q ) ) * q = 0.5 * q * w'