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[aprssig] The best resolution of position from APRS

Curt Mills archer at eskimo.com
Wed Jan 4 07:15:19 UTC 2006


On Tue, 3 Jan 2006, Scott Miller wrote:

> I still disagree with that move.  I say make the datum part of the spec -
> fix it at WGS84.  Much easier to have the GPS receiver take care of that,
> since it knows the math already.  If that had been part of the spec from the
> start, do you think Kenwood would have found space in their firmware for
> datum conversion?  I really doubt it.

I believe it has been in the spec from the first ratified spec.  It
is probably not as prominent as it should be, but it's in there.

Unfortunately people that ran mobile with laptops and commercial
mapping programs found that their position was off on those maps, so
they set their GPS to whatever the commercial map program told them
too, often NAD27.  That then threw off their APRS positions, but
their car was closer to the road on their local map.

Way back when some GPS's kept their NMEA stream in WGS84 datum and
only changed the display datum based on the user's whims.  Later on
many manufacturers made both of them change based on the display
datum, and that's when the problems began with APRS and datums
(other than WGS84).

-- 
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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