[aprssig] Symbol set revisions

[Robert Bruninga]

> ... it's a large pain for me to fix aprs.fi to 
> support a new modified set. Lots of manual work.

Its great that APRS-FI is being actively supported and updated.
Thanks!

> ...I think it's not wise to modify it every year, 
> because that way the symbol sets in applications 
> will never be synchronized.

That is why over the decade up to now, none of the changes we
have made have involved removing or changing symbols, only
adding an occasional definition of some previously unused ones
and some overlay characters.  We would add these as requested,
since the requestor, could then start using it immediately, and
he could share with his evet participants what the new overlay
character meant for his event.

> If it is modified, it should be made as easy as 
> possible for everyone to update their applications. 

Up till now, most new definitions were simply defining the use
of certain overlays.  Such as suggesting an E overlay on a CAR
symbol would mean ELECTRIC, or an H overlay would mean a HYBRID.
In all cases, all software that can already do OVERLAYS would
display this definition as-is without any need for the
application to change anything.
And since UI-view and XASTIR and some others do support
overlays, this allows many people to begin using these new
definitions immediately.

This requires two technical things:
> 1) A machine-readable configuration file,

Unfortunately, this will be application specific, since all
existing applications did it differently.  But by making a good
effort -now- to better align the symbol database to take
advantage of overlays, then this allows orders of magnitude of
expansion in the future without needing new symbols, just
definitions of the overlays.  Future program writers will find
this data helpful.

> 2) A single standard source for the symbol images..

I think Stephen Smith WA8LMF has been doing that.  He may
clarify this statement a bit...

> I'm not sure which source should I trust to be *the* 
> definitive standard.... Is it Bob's symbolsX.txt, or?

Yes, that is the one approved in APRS addendum 1.1 that is
currently being maintained to the best of my ability.

> I'd like to implement [overlays] in the aprs.fi, 
> but... I have to pre-render [them] on top of the 
> symbol images, and on top of the pre-rendered 
> *rotated* symbol icons too (applicable only for 
> symbols which are rotatable). 

I am so glad to hear that you are considering displaying the
ROTATABLE symbols from the original APRS.  Those are the best
ones to use for public display, because it makes CARS, BOATS and
AIRPLANES actually -point- in the direction of travel.  Too many
APRS clones overlooked the value of these symbol attributes.

Glad to hear APRS-FI is keeping up.
Thanks
Bob, WB4APR