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[aprssig] Using Overlays creatively

Robert Bruninga bruninga at usna.edu
Tue Apr 10 18:23:12 UTC 2007


> I sure wish all APRS programs supported OVERLAYS on ALL
SYMBOLS!
>
> The APRS symbol spec found at your website seems to imply 
> that only around 10 symbols have support for overlay by 
> showing a GPSxyz with a "#" in the "z column".  Is that in 
> error or am I just misreading the document?  MJ

You are correct, but it's 15.  Again, the original APRS concept
was overlays on all symbols.  But as we moved from the original
APRSdos into a published SPEC we could not get agreement on all
symbols and so only a subset was included in the spec.  It kinda
made sense, since the base symbol had to be big enough and have
a clear area in its center for the overlay character to be
visible....

But those 15 existing overlayable symbols do offer as many as
540 different combinations to be used.  Too bad some programs
don't display them.  I answered your email on the APRSSIG in
case others have this same question.

Kenwood solved the overlay problem by displaying it in the upper
corner of a SYMBOL field so that it can apply to any symbol.

When we first came up with overlays, the classic example was to
have all of these Numbered and Lettered CAR and TRUCK symbols so
that CALLSIGNS could be turned off on maps with dozens of
vehicles all
Closely clustered at a special event.  The OVERLAY made it easy
to distinguish every mobile uniquely without all the map clutter
of all those callsigns.

Bob





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