[aprssig] Degrees Minutes and APRS parser
Stephen H. Smith
wa8lmf2 at aol.com
Sun Dec 25 17:24:40 CST 2005
vk4tec at tech-software.net wrote:
> Working on a PERL to MySQL perl script for an Australian Experimantal
> Data Store
> I have got most of it working, in that I have callsigns and positions.
> I am getting the impression different systems use different
> co-ordinate formats.
> I am assuming from what I have seen that the degrees always stays the
> It is the bit after the decimal point that changes.
> I seem to have ended up with positions from the APRS stream in the
> format of deg minutes and seconds ???
> Wondering if there is some perl code floating around that converts deg
> min seconds to dec degrees ?
> My main use for this is google earth. Which seems to want decimal degrees.
The default APRS format is the native format for NMEA GPS data --
Degrees, Minutes and decimal fractions of minutes (not degrees, minutes
and seconds and not degrees and decimal degrees). If DD-MM-SS data is
appearing on the APRS Internet system, someone has incorrectly
configured a program or hardware device.
Note that DD MM.mm allows a slightly higher resolution than the classic
degs-mins-secs format for the same number of ASCII digits. (Two digits
used for seconds resolves 1/60ths of a minute while two digits used for
decimal minutes resolves 1/100ths of a minute.)
The position relative to the equator and prime meridian should be
delimited by E/W and N/S rather than +/- degrees. Thus a normal
APRS/NMEA posit would normally be transmitted or displayed as:
39 09.84 N
118 07.02 W (My QTH in Pasadena, California)
Some programs, notably UIview, have the user input this into the program
setup somewhat confusingly as:
with TWO periods in the string but it is still DD MM.mm format
-- NOT DD.dddddd all-decimal format or DD MM SS degs-minutes-seconds
I am also painfully aware of the nuisance of converting DD MM.mm to
all-decimal DD.dddddd format for several mapping applications I use
(notably MapPoint and MapInfo) but the math is trivial. Divide the
MM.mm part by 60, and add the results (which will always be a decimal
value less than 1.00) to the degrees part.
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com
"APRS 101" Explanation of APRS Path Selection & Digipeating
Updated APRS Symbol Chart
New/Updated "Rev G" APRS http://webs.lanset.com/wa8lmf/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:
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