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[aprssig] The best resolution of position from APRS

Robert Bruninga bruninga at usna.edu
Tue Jan 3 22:19:50 UTC 2006


>>> scott at opentrac.org 01/03/06 3:55 PM >>>
	
>> Would it not make sense that THE best accuracy would be 
>> obtained by sending the RAW GPRMC string in its entirity ?
>
>Depends on your input format.  Garmins ... protocol)
>send their position as double-precision... in radians.
>the OpenTRAC position format) is 32 bits and works 
>out to around 2 cm resolution.
>
>The newer NMEA format supports extra precision 
>- though I understand that caused some trouble with 
>the Kenwoods when it started appearing. 

That is not exactly correct as stated. All of the older
NMEA formats also allowed floating point precision
and supported positions down to 6 inches and all of
the kenwoods (except the very first D7's all of which
were recalled) all will decode that.  So all radios on the
air can receive raw $GPRMC and $GPGGA sentences
on the air independed of precision.

What you are aluding to is the most recent NMEA183
version 3 (I think) that snuck in an additional digit
somewhere else in the protocol (not in the position)
which caused problems.

Just trying to clarify, though I might not have it 
exactly right above either.

Bob





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