[aprssig] USN(G) and APRS

[Robert Bruninga]

> USNG and/or MGRS and/or UTM
> coordinate systems with APRStt:
> 
> 1)  Your major hurdle is going to be the proper 
> entry and decoding of the grid zone and 100km2 
> square info which are only partially numeric.

But not within simplex range of an APRStt gateway.  I think
within that short range, only the least significant numeric
digits are needed.  The alphanumeric characters are needed to
get you in he region...

> 2) In many ways, grid is much easier to manage than lat/long.
No
> worries about N/S/E/W precursors for coords, and no
> confusion/difficulties with DD.DDD vs. DD MM.MMM vs. DD MM SS
> interpretation.  

Only in Greenwich England will there be a change between W and E
within local simplex range.  But otherwise simplex range is
assumed to reside within a given hemisphere...  And the use of
"seconds" shouldn't have been a problem if everyone stuck with
the APRS and WG84 and NMEA standard of degrees and decimal
minutes.

But again, APRStt can use any grid, or system as needed for the
local application.  We are making it general so that it can be
configured any way needed.