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[aprssig] APRS Parser posted

Robert Bruninga bruninga at usna.edu
Fri May 30 19:09:17 UTC 2008


OK, I was wrong when I implied APRS was only 4 simple
packets....  

Parsing APRS is quite tedious if you want to pick up everything
going on in packet radio including DX clusters, DX spots, BBS
MAIL beacons, NET Rom beacons, The MAIL directory on the ISS
BBS, Meteor scatter packets, Grid squares, NTS traffic, and all
the other stuff that was in the original APRS.
(Remember, it was designed to capture EVERYTHING on the air
going on in your area and try to figure out where it all was and
to present it in a useful display so you could get the big
picture of all activities in your area.)

Just for grins, last night, I took the main APRSdos parser and
converted it all from tedious Qbasic code to a more concise
english summary.  Even I found a few things in there that I can
finally get rid of...  Anyway, if you want to take a look, there
is a link on the 8th line down on my APRS page:

http://www.ew.usna.edu/~bruninga/aprs.html

Called "Commented parser".  The file has some other routines
that I also converted, but there are some near the end that I
still have not converted to English.  Maybe Ill get back to them
someday.

Basically, the parser first looks for raw data formats from GPS
or WX or DF units (which might be sharing the same serial
port)... Then it looks for own station digipeated packets, then
other special strings, then it looks for positions, Then it
looks for STATUS, QUERIES and MESSAGES.  Anything that doesn't
meet any of the previous  criterial are placed in STATUS if
empty until a real STATUS overwrites it. 

The result is that EVERY packet gets captured somehwere and even
without a position, the station is given a vicinity plot near
its first digi until replaced with better info.  This way, we
could even get a sense of the connectivity and location of BBS
networks too.

Bob, WB4APR





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