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[aprssig] Degrees Minutes and APRS parser

Stephen H. Smith wa8lmf2 at aol.com
Sun Dec 25 23:24:40 UTC 2005


vk4tec at tech-software.net wrote:
> Gudday
>  
> 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 
> same.
>  
> 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:
   39.09.84N
  118.07.02W

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 
formats. 

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
  http://webs.lanset.com/wa8lmf/DigiPaths

Updated APRS Symbol Chart
  http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf   


New/Updated "Rev G" APRS     http://webs.lanset.com/wa8lmf/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:


 
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