[aprssig] APRS resolution
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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