[ODE] getting an entity to follow another

[Dan]

Hi,

My entities in my game have functions goLeft(), goRight() which apply
dBodyAddRelTorque to steer them, then I add forward force to move
them.

I want one entity to follow another, how do I do this? I only need it
in the horizontal plane.

I guess something can be done with the first entity's angle and the
target entity's position.

But I have no idea how to get the bearing to the target position or to
get the entities angle from its matrix or quaternion or how to compare
them if I could...

Any help appreciated!

Thanks,

Dan