Re: Mercator vs. Great Circle Charts
Subject: Re: Mercator vs. Great Circle Charts
From: nigel_gardner (Nigel_Gardner@XXX.XXX)
Date: Wed Aug 29 2001 - 17:15:29 EDT
In spite of the rather unfortunate initial exchanges, an interesting point
is raised about what is meant by 'great circle charts'. Probably the most
commonly used is Lambert's conformal, although not strictly a GC chart
because of distortion away from the standard parallels is near enough for
practical purposes, gnomonic projections (although correct) suffer from
scale exaggeration away from the centre; esoteric ones such as the Mecca
azimuthal or the Rugby diagram are precise but only from or to the one
point. Interestingly when I was scratching a living navigating aircraft,
for crossings between UK and Canada we calculated the latidude intercept
for every 5deg of long. plotted these on a mercator and flew each leg as a
rhumb line, any HF radio bearings that we got were plotted using the
conversion angle. Other oceanic crossings tended to be at lowish latitudes
so a mercator was good enough.
A friend of mine was a master on super-tankers and required the mate of the
watch to take a sun sight each day from the deck watch, arguing that GPS
might get switched off or the nav equipment might suffer a major failure.
NG
