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[aprssig] Ambiguity due to GPS

Scott Miller scott at opentrac.org
Thu Jan 5 21:48:27 UTC 2006


> A very good point.  What would be even nicer would be to use the
> HDOP number to decide how much ambiguity to give the station on the
> map.  That would work fine for your local station on your own map,
> but we don't send HDOP in any of the APRS sentences except for NMEA,
> and those sentences are way too long.

Well, the OpenTracker does, but it wasn't intended to be a consistent,
machine-readable format, though it wouldn't be hard to parse.  And it's
several bytes, when one byte would be plenty for an exponential ambiguity
scale.  I *really* don't like the APRS convention of dropping the
least-significant digits.

The OpenTracker will also output HDOP in telemetry mode, but again that's
not going to help for this.  Also, I don't think there's a simple
relationship between HDOP and circular error probability.  Maybe Gerry could
answer that...

Scott
N1VG







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