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[aprssig] APRS resolution

Andrew Rich vk4tec at tech-software.net
Sat Apr 15 21:59:56 UTC 2006


So really GPRMC is the best you can send in APRS

You get no resolution being sacrificed for payload 

-----------------------------------------
Andrew Rich
Amateur radio callsign VK4TEC
email: vk4tec at tech-software.net <mailto:vk4tec at tech-software.net> 
web: http://www.tech-software.net
Brisbane AUSTRALIA 



-----Original Message-----
From: Curt Mills [mailto:archer at eskimo.com]
Sent: Sunday, 16 April 2006 7:58 AM
To: vk4tec at tech-software.net; TAPR APRS Mailing List
Cc: ozaprs
Subject: Re: [aprssig] APRS resolution


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
  Lotto:  A tax on people who are bad at math. - unknown
Windows:  Microsoft's tax on computer illiterates. - WE7U.
The world DOES revolve around me:  I picked the coordinate system!"






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