SL Scripter/Builder: How to rotate an object to a target direction, when the object has STATUS_PHYSICS

If you're going to be a scripter in SL , soon or later you will crash into a bunch of problems, when trying to rotate objects/prims.
A good start for every scripters in the jungle of rotations, quaternions and vectors and other 3D space related manupulations are the following resources:
http://wiki.secondlife.com/wiki/Rotation
http://www.cprogramming.com/tutorial/3d/quaternions.html
http://www.euclideanspace.com/maths/index.htm


I had a problem like this lately. I'm working on a new product called Star Glider - a kind of stylish flying vehicle and needed to implement a feature called auto-landing.
During the auto-land sequence the vehicle needed to rotate its self(around the Y axis) and become parallel to the ground. The idea behind this is to avoid landing on the vehicle nose or tail, when the pilot approaches the ground.



So, here comes the problem - How to rotate an object to a target direction.
In the problem given up, I will consider (for simplicity) that the ground rotation is equal to zero. Looking up the image:

• V1 represents a ZERO vector <0,0,0> - a vector with ZERO angle relative to the Y axis. It is our target vector (note the image is not exact from a mathematical point of view)
• V2 represents the current direction of the object in the Y-Z plane

What we need is to calculate the angle between the two vectors , generate a rotation quaternion based on the angle and apply the quaternion over the object.
The following script may be used:

//getting current rotation of the object(global rotation of the root prim)
rotation currentRot = llGetRot();
//getting vector V2 - the direction in the Y-Z plane
vector v1 = llRot2Left(currentRot);
vector v2 =<0,0,0>;
//generate rotation based on the angle between two vectors
rotation targetRot = llRotBetween(v1,v2);
//apply rotation
llRotLookAt(targetRot,1,1);

If you have a situation like in the image, the object will rotate untill becomes parallel with the ground - e.g. untiul the angle become ZERO;

NOTE:
Instead of llRotLookAt one may try to use llSetRot. However llSetRot does not work over physical prims (STATUS_PHYSICS).

Links:
http://wiki.secondlife.com/wiki/Rotation
http://www.cprogramming.com/tutorial/3d/quaternions.html
http://www.euclideanspace.com/maths/index.htm