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[aprssig] case sensitivity of NSWE in posit reports

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Dec 29 12:41:53 UTC 2010

VK6 UFO wrote:
> Couple of questions of the nit-picking variety.

As a software developer, one of my mantras is "all nits need to be picked!".

> Is it fair to say that an APRS uncompressed position report should (or 
> must?) use N,S,W and E (capitals) to comply with APRS specs, but APRS 
> applications should be prepared to expect n,s,w and e from APRS 
> stations anyway? Is it possible that future revisions of the APRS 
> specification will use the case for some purpose in the same way as it 
> was originally proposed for the 'operator present' bit?

See http://www.aprs.org/aprs12/operator-bit.txt  Apparently lower case 
has been proposed for some things, but UI-View breaks.  I can only speak 
authoritatively for my own APRSISCE/32 and it explicitly upcases the 
NSWE before checking it for validity.  I call that defensive coding 
until some spec comes out that puts meaning onto the case of those 2 
characters (NS or EW).

> Is it valid for a station reporting weather to use a symbol that is 
> not normally recognised as a weather station (eg is it OK to use a 
> digipeater symbol with a wx report?) Will some APRS applications break 
> if this happens? Should the wx be decoded and used anyway or should it 
> slip through as a comment?

Give the vast amount of variability in user-specified comments, my own 
client only parses weather data if it is explicitly weather by data-type 
(#, *, ., and _)  or uses a weather station symbol (_).  I 've been 
looser in my comment string interpretation in other areas (like the 
/A=), but ended up tightening up my parser as it had strange results 
when parsing through the world feed of packet variability.

So, since the spec says "weather must use a weather symbol", that's the 
only place I try to interpret weather from.

As always, YMMV, and I'm only relating my implementation choices and 
reasoning, not attempting to establish a standard here.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

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