[Xastir] Own Weather Reports

[Gerry Creager N5JXS]

I'll try to wander thru the code tonight, too, plus or minus a dtabase 
problem that's kicking my rear for Mesonet.

Curt Mills wrote:
> On Sat, 5 Feb 2005, Clay Jackson wrote:
> 
> 
>>I'm having some problems wWeather reports.  I've got a Davis WMII,
>>w/meteo capturing the data, and db2APRS sending the data from a
>>different system to Xastir.  I've hacked db2APRS a bit, to make it
>>conform to the APRS 1.1 spec for positionless weather data -  so, it's
>>sending packets that look like this:
>>
>>_0205101900c161s001g005t040r000p009P008h88b10225xDvs
> 
> 
> I should have thought about this from some of your earlier messages
> about it:  Positionless weather is considered to be an abomination
> by a lot of people.  I think it was added to the spec merely because
> one of the weather stations was able to put out that format
> directly.  Most people that have commented on this have suggested
> that some other weather format be used normally that includes the
> position of the weather station along with each packet.  That way
> you don't have to combine posits with WX packets in order to have a
> complete picture.

Positionless weather reports are EVIL.  Next question?

>>According to the spec r000 is rain in the last hour, p009 is rain in the
>>last 24 hours and P008 is rain since midnite.  HOWEVER, Xastir is
>>reporting total rain of 0.09 and 0.00 for the other rain values.  The
>>other data points (wind, temp, humidity) all look OK.
> 
> 
> Xastir calculates this stuff itself as I recall.  I've been into
> that code more than once, and rewrote part of it, but it's been long
> enough that I don't remember all the details anymore.  As I recall
> though Xastir ignores the values for 24-hours and since-midnight
> that are sent by the weather station and computes them itself.  If
> you haven't run Xastir connected to the WX station that long, the
> values won't match the values that the WX station might be telling
> you.

The spec had a lot of input from some real content experts.  This didn't 
stop 'em from codifying what the s/w authors of the day THOUGHT should 
be there.  That's why Xastir calculates it itself: to do it better than 
the spec thinks it should be.

>>Also, I'm not seeing anything in the Dew Point, High Wind, Wind
>>Chill/Heat Index and Hi and Low Temps - is Xastir expecting those from
>>the Weather Station, or calculating them?
> 
> 
> I'd have to go look at the code.  I think most things come from the
> weather station, but of course most things aren't put out by most
> weather stations, so they don't ever get filled in.


In general, humidity is easy to measure with an electronic instrument, 
while dew point is not (but a sling psychromoeter is not too hard for a 
human, who then calculates humidity usually using tables, and ignorant 
of the differential equations that go into the overall calculation... 
but that's not important right now).  FindU uses a table lookup to get 
the Td.  If the values for peak wind, gusts, etc are reported, it uses 
'em, as I recall.Heat Index and Wind Chill are trivial to calculate. 
Xastir, really, should be accounting for high/low temps, IMNSHO.

gerry
-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
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