[time-nuts] FW: IIMorrow GPS units non-functional since Sunday
Arnold Tibus
Arnold.Tibus at gmx.de
Wed Aug 20 12:51:18 UTC 2008
On Wed, 20 Aug 2008 16:24:31 +1000, Jim Palfreyman wrote:
>Wow.
>Don't tell me people still use miles? Nautical or otherwise?
>What's wrong with the good old kilometre?
>Jim
Jim,
it is quite easy to give an answer to your question:
Even using GPS geographic coordinates are still (and will be
in future) in use, because the earth is a globe (even a bit
deformed like a potato but is not a flat surface like a disk ;-) ! )
with a circumference of roughly 40000 km divided in
360° or 21600 (arc)min = 21600 nautical miles (NM or nmi).
Nautical charts are divided in degrees and minutes by a grid
of intersecting lines thus allowing very easy and quick to
measure distances positions and passages just applying a
nautical divider (attn.: to me adjusted o n l y on the right or left
side of the chart, the meridians N or S value!)
To avoid nm (nanometers) with nautical miles:
The preferred abbreviation of the IEEE is nmi
For aviation use, the preferred abbreviation of the ICAO is NM
A nmi = 0.9998834 mean meridian arc minutes
= mean historical nautical miles (approx.)
In 1929 when the International Extraordinary Hydrographic
Conference held in Monaco was adopted a definition of
one (1) international nautical mile as being equal to 1,852 m
exactly.
more eg.:
http://en.wikipedia.org/wiki/Nautical_mile
http://encyclopedia.farlex.com/nautical+mile
http://citadelnavy.files.wordpress.com/2008/02/02-terrestrial-coord-sys-charts.ppt
I think even in 'modern' times the use of nmi will therefore
not disappear!
regards
Arnold
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