Keeping 3D layers oriented upright

In this first example, both layers rotate in 3D space like normal.

 <http://photobucket.com>

This second example is using Dan's formula to keep the triangle facing the
camera

fromPoint = thisComp.layer("Camera 1").transform.pointOfInterest;
atPoint = thisComp.layer("Camera 1").transform.position;

lookAt(fromPoint, atPoint);

 <http://photobucket.com>

Looks great, but the triangle still has Z rotation. How to do I keep a layer
always upright as seen in the third example (which was hand keyframed)?

Hmmm.... Where did you get the expression? It doesn't look right for this
application. Can't imagine why the camera's POI would show up in there.

I'm not sure how you're moving your camera but if you want to take a look at
this <http://www.hottek.net/samples/ComplexCameraMove.aep> project you may
get a better idea about how to move the camera in complex paths.

As for your rotation problem I think you want to use this expression on the
triangle layer's orientation property

      angle = toWorld(anchorPoint) - thisComp.activeCamera.toWorld([0,0,0]);
      correction = radiansToDegrees(Math.atan2(angle[0],angle[2]));
       x = value[0];
       y = value [1] + correction;
       z = value[2];

      [x, y, z]