How to implement panning by moving SCNCamera

Question

I have looked at this post and rickster's answer and lorenzo's sample code

Lorenzo's code works well. I am trying to extend it and add a conventional pan where you can move the scene left, right, up and down.

Here is what I have tried:

-(void) handlePan2F :(UIPanGestureRecognizer*)recognizer {

CGPoint translation = [recognizer translationInView:recognizer.view];

CGFloat xVal =  translation.x * 0.025 ; // apply some damping
CGFloat yVal =  translation.y * 0.025 ;  

if (recognizer.state == UIGestureRecognizerStateChanged) {
    self.cameraOrbit.position  = SCNVector3Make(-xVal, yVal ,0.0);   // what should the value be for z?
   }
}

The issues I am running into are:

1. The pan works kind of - but not well.

2. If I add a SCNLookAtConstraint to point an area in the scene then the pan2F gesture rotates the scene. Why is that?

3. The behavior I am trying to implement is to just to pan left/right/up down over the scene without any scene rotation. How to fix this code?

I am willing to give up SCNLookAtConstraint as long as I can zoom to a specific area within the scene.