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Re: spherical geometry

At 1:42 PM -0400 8/19/04, John Denker wrote:

Actually they changed long before that. If you know the
lat/lon of the origin and destination, you can write a
computer program that prints out the route, with waypoints
and headings at points every N miles along the route.

Well, when I last did any ship navigating was well before the days
when ships had computers of any kind, except the analog ones they
built for gunfire control. Same with long range over water flying.
I'm sure that ship's navigators have become pretty lazy fellows in
the past couple of decades or so, and its been at least that long
since airliners even carried a navigator. My days as an airplane
navigator ended when we routinely used bubble sextants and
occasionally hand-done loran, which was usually of pretty poor
quality in those days.

Actually on my last shipboard tour, in 1969, I was a member of the
air wing, so I didn't get to play navigator, but one of my buddies
was the asst. navigator and he showed me the hottest thing then,
which was getting line of position by measuring the Doppler roll-off
of the signal from a passing satellite. He could then go to a list of
known satellites and from the known time of closest point of approach
of the satellite, and the satellite's ephemerides, they calculated a
LOP. That was the latest Naval technology at the time.

For that matter, nobody wants to navigate a great-circle route
exactly anyway. You take that as a rough basis, and then
fudge it left or right to pick up more-favorable winds, avoid
nasty weather, et cetera.

Absolutely. But the deviations from a great circle route on a long
trip are usually minor, unless circimnavigating a typhoon or
hurricane or the like. Or seeking out favorable currents. Wind as a
factor for ships hasn't been a large factor for a century or so now.
:-) Airplanes, of course, are very different, and taking advantage
or avoiding a jet stream are often far more important than worrying
about a great circle route. But the last long over water flight on
which I was a member of the crew was in a DC-3 (1961), and we were
lucky to get above 10,000 feet in that, so we didn't pay much
attention to jet streams then.


Hugh Haskell

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