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[aprssig] APRS radios

Robert Bruninga bruninga at usna.edu
Tue May 27 20:40:57 UTC 2008


>> Third party and Objects is where I think the spec 
>> overly complicated APRS.  It was so simple.  An object 
>> is NOT a special packet with its own formats.  It is 
>> simply a position report of an object name that is 
>> not a callsign.  So the name has to be in the packet, 
>> and not in the AX.25 header where the callsign is.
>> 
>> On receipt, all one was supposed to do was chop off 
>> the header, and then use what remained (which now 
>> contains a NAME instead of a call) as if it had been 
>> received on RF directly.  Just rearrange the name 
>>into a pseudo packet and then continue parsing like 
>> any other packet.
> 
> Ok... what if the object has the '_' symbol?  Do you 
> interpret the 000/000 extension as wind direction and 
> speed, as you would for a non-object packet?  

Yes, it would be parsed exactly like any other packet with that
field.  SO  a WX packet can be transmitetd from a TNC with its
own station call in th eheader, or a weather report can be
transmitted as an object, with its name included in the data
field.  But everything after the LAT/LONG should be parsed
identically, and handled the same.  Though a reference to the
transmitting station needs to be retained so we can trace
ownership.

> Or would it be course/speed, per the object report 
> format on page 68?  According to that, wind isn't 
> one of the allowable extensions.

Yep, this is a spec error.  An object once the NAME has been
extracted is supposed to be parsed like any other position
report.

> This is exactly the sort of inconsistency I'm talking about.  
> A formal grammar would specify exactly what can and can't go
where.

Yep, instead of taking my original design which was verbally
presented as I have presented it above (an OBJECT should be
parsed identically to any other position format).  The Techincal
author attempted then to do as you suggest, and that is
re-specifiy every possible field in an Object.  Which in my mind
was not a good idea, as it could lead to omissions and confusion
as noted above. 

Bob, WB4APR





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