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[aprssig] Compressed, Course/Speed, Weather question

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Nov 10 14:50:11 UTC 2010


I discovered this morning to my chagrin that I wasn't parsing the course 
and speed information out of compressed packets in my APRSISCE/32 
client.  I've rectified that situation, but am now faced with a question 
of the interaction between compressed packet's course/speed information 
versus a weather station.  Page 27 (PDF's 37) shows the CSE/SPD and 
DIR/SPD as the same format Data Extension where the latter is for 
Weather Reports.  Further, given the Complete Weather Report Format - 
with Compressed Lat/Long position on page 66 (PDF 76), it would 
definitely seem to be that the compressed course and speed are in fact 
wind direction and speed when transmitted by a weather station (_ symbol).

Is my reading of the spec correct?

Here's a sample compressed weather station packet captured from aprs.fi 
in it's Decoded form:

2010-11-10 14:35:49 UTC: *N9QGS 
<http://aprs.fi/?c=raw&limit=&call=N9QGS>*>APU25N,TCPIP*,qAC,CORE-2:@101435z/;0Q`9,?J_Z!bg001t045r000p000P000h84b10230/georgetownscottcountyweather.org {UIV32N}
   type: location
   srccallsign: N9QGS
   dstcallsign: APU25N
   latitude: 38.22749825425411 °
   longitude: -84.55066863380289 °
   course: 228 °
   speed: 0 km/h
   symboltable: /
   symbolcode: _
   messaging: 1
   posresolution: 0.291 m
   comment: /georgetownscottcountyweather.org {UIV32N}
   wx:
      pressure: 1023.0
      temp: 7.2
      wind_gust: 0.4
      rain_24h: 0.0
      humidity: 84
      rain_midnight: 0.0
      rain_1h: 0.0

Note the course and speed elements outside of the wx: section.  By way 
of comparison, here's aprs.fi's interpretation of a non-compressed 
weather packet.  Note the wind_direction/speed in the wx: section.

2010-11-10 14:31:40 UTC: *CW8596 
<http://aprs.fi/?c=raw&limit=&call=CW8596>*>APRS,TCPXX*,qAX,CWOP-1:@101431z2810.50N/08042.27W_324/001g004t066r000p000P000h79b10189.DsVP
   type: location
   srccallsign: CW8596
   dstcallsign: APRS
   latitude: 28.175 °
   longitude: -80.7045 °
   symboltable: /
   symbolcode: _
   messaging: 1
   posresolution: 18.52 m
   posambiguity: 0
   comment: .DsVP
   wx:
      wind_direction: 324
      pressure: 1018.9
      rain_1h: 0.0
      wind_gust: 1.8
      temp: 18.9
      rain_24h: 0.0
      wind_speed: 0.4
      rain_midnight: 0.0
      humidity: 79

Depending on the answer(s) to my assumption, I'll either be changing my 
interpretation that compressed course and speed for weather stations 
actually is the wind direction and speed, or I'll be contacting Hessu to 
fix up aprs.fi so that it begins treating compressed course and speed as 
wind direction and speed for weather which he currently doesn't seem to 
be doing.

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

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