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[aprssig] APRS resolution

scott at opentrac.org scott at opentrac.org
Sun Apr 16 01:52:54 UTC 2006


Not necessarily - your GPS might be capable of more resolution that it puts
out in NMEA.  Garmin GPS receivers will output their position in
double-precision floating point, which the T2 will convert to Base92 for a
max resolution of a couple of feet.  Some PC-based clients can probably do
the same thing.

Scott
N1VG

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Andrew Rich
> Sent: Saturday, April 15, 2006 3:00 PM
> To: Curt Mills; TAPR APRS Mailing List
> Cc: ozaprs
> Subject: RE: [aprssig] APRS resolution
> 
> 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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