[aprssig] APRS resolution

Scott Miller scott at opentrac.org
Mon Oct 1 11:02:51 CDT 2007

The OpenTRAC spec already gives you something like 2 cm resolution using 
a total of 8 bytes for lat/lon.  It's nothing revolutionary, though - 
it's probably the most obvious efficient binary coding scheme for a 
geographic position, and Garmin uses the same thing.  I think ArcGIS can 
use it, too.

I was playing around with another idea some time ago that might have 
interesting applications - it's actually rather like the Maidenhead 
format, but in binary, with lat and lon interleaved at a bit level.  The 
more bits you send, the more accurately you represent the position, but 
you can stop sending at any point.

The advantage of this format is that you could encode blocks of bits 
into phonetics.  Choose 256 different easily distinguished 2-syllable 
words and you can encode 8 bits per word.  The first word gets you 
within 2500 km, the second 156 km, the third 9.7 km, fourth 610 m, fifth 
38 m, and sixth 2.3 m.

If you're working in a limited area (like a particular county) you could 
eliminate a word or two.  If you used a different set of words for each 
group then ordering wouldn't be critical and you could (more) easily 
memorize an exact location.

Done right, it'd beat reading out numeric coordinates over the air...


Arno Verhoeven (PE1ICQ) wrote:
> Andrew Rich wrote the following on 2007-09-30 13:22:
>> I just did some tests, I worked out that APRS uncompressed gives you 
>> about 15 meters resolution.
>> I also made a tracker output data that gave me 30 cm resolution.
>> As for accuracy ....well
> What's your point? Are you proposing a change to the APRS spec?

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