[aprssig] APRS SPEC: Wind Speed confusion

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Fri Oct 14 15:16:05 CDT 2016

On 10/14/2016 12:11 PM, Greg Trasuk wrote:
> I meant “if it’s going to change, then standardize on KTS”.  I’m not sure if internal consistency is a good enough reason to break backwards compatibility in the on-air formats.

Amen.  IMHO, backward compatibility must rule in this case.

> So, if I were writing a new APRS presentation layer, I’d probably want to give users the option to view the data in KTS, MPH, or “as per spec”.  But there’s no real reason for the transmission format to change.  If one of the message formats is in mph, and another one is in KTS, the program can cover that over so the user gets a consistent representation.

Yes, that's the logical approach.

> Which is another interesting question - do people really consider the data formats to be “human-readable” at this time?  I know that at some point, we were probably looking at the reports on a serial terminal or on the D700 screen, but I’d guess that today, most people are seeing the data through a graphical client like Xastir, APRSIS32 or YAAC if they’re looking at over-the-air data.  Or one of the Internet clients, if they’re seeing web data.

I certainly don't consider anything in APRS to be humanly readable. 
That's why we have friendly clients, to interpret the packets and 
present them in a much more useful fashion.  Just look at the new 
weather data display on the Kenwood D74 and compare it to the original 
raw display on the D700.

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

> Cheers,
> Greg Trasuk
>> On Oct 14, 2016, at 11:46 AM, Kenneth Finnegan <kennethfinnegan2007 at gmail.com> wrote:
>> On Fri, Oct 14, 2016 at 8:33 AM, Greg Trasuk <trasukg at trasuk.com> wrote:
>> Unless there’s a compelling reason otherwise, I’d standardize on knots,
>> I'd say the compelling reason is that the weather data packet format on page 64 of APRS 1.0.1 says mph, so it's likely that the majority of implementations working off the spec already use mph.
>> Knots is currently used for the Wind Direction and Wind Speed data extension and the storm data report. I think the distinction of where we use MPH vs Knots is pretty clear, but accepting Bob's premise:
>> * We can't change the Wind Direction/Speed extension to mph since it's indistinguishable from the Course and Speed extension. Where is this extension even used? I'd vote for deprecating it.
>> * I'd be ok changing the Storm Data report to MPH, but I live in California so my indifference is high on this one.
>> --
>> Kenneth Finnegan
>> http://blog.thelifeofkenneth.com/
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