Slerp

 Slerp

Slerp is shorthand for spherical linear interpolation, introduced by Ken Shoemake in the context of quaternion interpolation for the purpose of animating 3D rotation. It refers to constant speed motion along a unit radius great circle arc, given the ends and an interpolation parameter between 0 and 1.

rotation slerp( rotation a, rotation b, float f ) {
    float angleBetween = llAngleBetween(a, b);
    if ( angleBetween > PI )
        angleBetween = angleBetween - TWO_PI;
    return a*llAxisAngle2Rot(llRot2Axis(b/a)*a, angleBetween*f);
}//Written by Francis Chung, Taken from http://forums.secondlife.com/showthread.php?p=536622