[aprssig] APRS resolution

[Curt Mills]

On Sun, 16 Apr 2006, Andrew Rich wrote:

> What is the 'best' resolution aprs can return ?

About 60 feet if you use Mic-E or standard APRS posits.

About 2 feet if you use Base-91 compression (from the "Compressed"
chapter of the APRS spec).

GPGGA or GPRMC will give you whatever your GPS is putting out, but
the packets are LOOONNNNGGGG.  Mic-E or Base-91 are the shortest.


> I got about 50 cm's difference just walking around with the GPS

GPS will give a lot more variance than that just by sitting still!
Your position should be within something like 10 meters of your true
position if your HDOP is reasonable.

For the U.S. military if they have an HDOP figure higher than 1.6
they won't use the GPS position.  I've seen HDOP's as low as 0.8 on
a non-WAAS GPS.  WAAS or other types of corrections can give you
better positions.

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
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