[aprssig] APRS LAT/LONG standards

scott at opentrac.org scott at opentrac.org
Fri May 27 00:42:41 EDT 2005

> Do you also not support the ARRL's use of a standard Phonetic 
> alphabet?  There are reasons that people involved in 
> comunicatinos like to have standards, it is to eliminate just 
> exactly the problem we have in HAM radio where not everyone 
> is using the DD MM.mmm... standard...

Speaking of coordinates and phonetics, I got to thinking about that the
other day.  A selection of 256 different two-syllable words could encode 8
bits per word.  Six words would be enough to encode a position anywhere in
the world to within a few meters.  You could do it in fewer words if you had
a larger selection, but it would get more difficult to find unambiguous
words.  You could also add an internal check digit to make sure the position
phrase was valid.

Anyway, the idea was that your GPS would give you the phrase, and you'd read
it out over the air and someone could enter it into a computer to get your
position.  That's usually what we're doing in the field, but it's more
tedious and error-prone with plain numbers.

It might sound a bit weird, though...  "My position is
'monkey-bogus-walnut-rooftop-widget-badger'."  Just a thought...


And in case anyone's curious about the calculations:

Circumference of the Earth = 40,075,160 meters
24 bits each for latitude and longitude

40,075,160 / 2^24 =~ 2.388 meters

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