[aprssig] The best resolution of position from APRS
bruninga at usna.edu
Tue Jan 3 23:27:48 CST 2006
>> The !DAO! format in APRS1.2 is 100% backwards
>> compatible to everything including the kenwoods
>> provides resolution down to a foot. ALSO and of
>> equal importance it included the DATUM as well.
>> SInce in my opinion, sending that kind of precision
>> is useless if the datum is not included.
>>> scott at opentrac.org 01/03/06 11:09 PM >>>
>I still disagree with that move. I say make the datum
>part of the spec -fix it at WGS84.
It is. The APRS on-air DATUM is WGS84. But when SAR
people use very high precision maps, and want to plot and
display 1 foot resolution, then many of their maps are NOT
WGS84. So in the !DAO! format the precision is still
transmitted as WGS84, but the !DAO! tells you what
MAP datum the sender is using so that the recepient can
use the same if he wants to really SEE that precision the
same way as the sender.
>If DATUMS 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.
Exactly. That is why I established APRS with one and only
one on-air datum. WGS84. But equally, with the demand
for users to use other maps and datums, I responded with
the !QAO! construct that not only gave them the precision
they wanted, but also the ability to say what DATUM map
they were using to display such resolution. Yet, the
on-air positin still remains WGS84.
I think the !DAO! format is a nice solution. It gives the
precision AND it gives the DATUM for alternate maps
AND it is 100% compatible with every existing APRS system.
and Obsoletes no one.
That is why I oppose the use of compressed objects for
high precision which have none of these advantages and
in addition, obsolete 10,000 kenwood users.
de Wb4APR, Bob
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