[aprssig] APRS symbol codes clarified

Robert Bruninga bruninga at usna.edu
Thu Aug 28 12:30:47 EDT 2014

The file: http://aprs.org/symbols/symbolsX.txt

Has just been updated.  No new symbols were actually added, but the dozen
or so symbols made available for expansion back in 2007 are now more easily
identified as AVAIL and there is an indicator to where those WX symbols
were moved.  This makes the annotation consistent between the above symbols
file and the new 2007 proposals in http://aprs.org/symbols/symbols-new.txt

For example:  Alternate symbol D used to be Drizzle with 36 potential
varieties of overlays made no sense.  So in 2007, Drizzle was simply moved
to be a D overlay on the general Precipitation symbol.  Thus making the
alternate basic symbol “D” and its 36 possible overlays available for a new
family of 36 possible symbols (overlays).


In 2007, we proposed moving several WX symbols to overlays to free up
hundreds of ICON space in the APRS spec.  For example, it did not make
sense to use up 11 of the possible 200 original APRS symbols just for
different types of precipitation when instead we could have a single FAMILY
called precipitation “P” and then have up to 36 possible varieties
represented simply as overlays.  And then let authors draw any matching
symbols for the varieties within this family.

These basic ALTERNATE characters then are now possibly available for new

Bb{*:DFeGJp as well as the final three that were held in reserve: ZQ and
possibly ] and }.

Although this opens up hundreds of possibilities, it must be noted that
backwards compatibility demands that all future possibilities be
constrained though, into only these 13 or so familiies.  And that is it.
So we must be very cautious and all-knowing and all-seeing with how we use
up these last available families.  And we will not use up any of these if a
possible existing FAMILY can be used with a new overlay to represent some
new request.

Again, this announcement simply cleans up the basic symbol list and
new-symbol files to better show the openings.

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