Help with quats!

I want to provide a rotation around a specific single axis to look at (or near rather) a (potentially) moving point - think tracking the sun's rotation approximately by rotating around the world's Z axis for example.

llRotBetween would take a unit axis and the relevant rotation and rotate around all the axes (in general anyway, some might by chance give a single axis).

Any good tips or pointers? Or even a code snippet for a general axis solution?

Well. You could cheat by limiting two of the axes (as with llSetStatus(STATUS_ROTATE_X | STATUS_ROTATE_Y, FALSE);) and using llLookAt.

Failing that, there is a way to do it the long way... but it's messy. I'll dig it up if needed though.

I usually just set the Z of what I'm trying to look at to be the same as the Z of the looker.

e.g.

point_at_z(vector target)
{
   vector pos = llGetPos();
   target.z = pos.z;
   llSetRot(llRotBetween(<1.0, 0.0, 0.0>, llVecNorm(target - pos)));
}

I've found the snippet of code here very useful for pointing objects at things