Quaternion.LookRotation() What does it do?

Hi I have an embarrassingly simple problem that I just can't solve.

I am using Unity3D as a client and I have a server that uses an External 3D Math Library that includes Quaternions but does not included the method "Quaternion.LookRotation()" or anything that I can find like it.

So what does Quaternion.LookRotation() do exactly?
The best I could come up with after searching around the interwebs was...

Vector3 dir = (Target.position - transform.position);
Vector3 axis = Vector3.Cross(Vector3.up, dir.normalized);
float angle = Vector3.Dot(Vector3.right, dir.normalized);

rotationToTarget = Quaternion.AngleAxis(angle, axis);
//rotationToTarget = Quaternion.LookRotation(dir);

//transform.rotation *= rotationToTarget
transform.rotation = Quaternion.Slerp(transform.rotation, rotationToTarget, Time.deltaTime);

But this just rotates to 'identity'?
I am missing something obvious and simple I know I am...

Not 'strictly' a Unity3D question exactly I know, but currently I have spent 3 days trying to work this out and it seems like it should be so simple.

 

I'm not sure what the code you posted is supposed to do, but it doesn't make any sense to me (and I think it's safe to say it's not what LookRotation() does).

LookRotation() basically does the same thing as a typical 'look-at' view transform function, except that there's no translation involved (since we're just dealing with a quaternion), and the transform is not inverted.

The code might look something like this (untested):

Code (csharp):

1. vector3 z = direction.normalize();
2. vector3 x = cross(up, z).normalize();
3. vector3 y = cross(z, x);
4. return quaternion_from_basis_vectors(x, y, z);

The 'quaternion from basis vectors' part is basically a matrix-to-quaternion conversion, which is a little less straightforward than converting the other way, but is nevertheless fairly well documented online and elsewhere.