pinned down the problem. Was a minor sign error in the offsets. Why is it that simple sign errors are ALWAYS the hardest things to track down? Now, open question: should x,y scaling be free parameters or not? What I mean is, when I measure the positions of bolometers on the array using the planet map, should I allow the X and Y stretch (the bolometer spacing) to change? Should it be a uniform stretch in X and Y or should it be allowed to 'distort' too? My opinion is, none of the above: I'm measuring their actual positions (in terms of a fixed spacing) and therefore stretching or distorting to match the nominal positions is not necessary.