NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Yet again still on LOPs
From: Bill Noyce
Date: 2002 May 3, 10:02 -0400
From: Bill Noyce
Date: 2002 May 3, 10:02 -0400
Peter Fogg writes: > While in nav. classes met a chap who encouraged me (and others) to meet > him at a place high on the cliffs above Bondi Beach. There, for years, > he has practised making observations.... Our > experience is that it is rare for our known position (it should be, we > lean up against a survey plinth!) to be outside our LOPs... This suggests that there is some systematic error that applies to all the sights. If the azimuths were ideally distributed (120 degrees apart), then a systematic error from mis-estimating height of eye or dip would lead to this result. (In fact, I think Bowditch points this out as a reason for preferring bodies 120 degrees apart rather than 60 degrees apart -- the latter leads to a nice triangle, but with the true position well outside it if there's a consistent error in dip.) But when you have less than 180 degrees of horizon, the consistent error would have to be that the readings on each side are too high, and the one in the center too low, or vice versa. It's hard for me to think of a mechanism for that, except possible abnormal refraction for the path that's over more land. If you reduce your sights using the known position as your AP (using formulas or computer, rather than the HO tables), do you find that the errors are all evenly distributed in Toward/Away, and uncorrelated?