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Subject: Re: Yet again still on LOPs
From: Noyce, Bill (William.Noyce@XXX.XXX)
Date: Fri May 03 2002 - 10:02:57 EDT
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?
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