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[aprssig] Mic-E Issues

Robert Bruninga bruninga at usna.edu
Wed Jul 16 14:11:29 UTC 2008


> ... Mic-E in my section of the U.S. gives a 
> precision of about 40' by 60'.  Base-91 gives 
> something like 2' x 3'....
> Of course this begs the questions:  What datum 
> are these people using... and what is the accuracy 
> of their current GPS position?  Without 
> transmitting HDOP and datum and decoding that in
> the display software, this improved precision 
> capability of Base-91 is partially unused.

For what it is worth, that is why we came up with the !DAO!
Format which adds precision down to about a foot while also
providing a byte for identifying the Datum between the sender
and the receiver.  See:
http://www.ew.usna.edu/~bruninga/aprs/datum.txt

A benefit of the !DAO! Format is that it is backwards compatible
with all existing applications.  Existing applications will
display the existing precision to the nearest 60 feet, but those
that decode the additional !DAO! Can use the additional
precision and dataum infromation.

Though in my mind, for something like APRS, if you are within 60
feet of an APRS station or object you are basically there!

Bob, WB4APR





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