Davis WeaterLink software possible data error

[FlixtonWX]

Hi Guys,
I keep my data backed up on both Weatherlink and Cumulus whilst also sending it to various sites. While talking to a fellow enthusiast (Ray, Cheadle Hulme weather) It became apparent that although we live only 12 miles apart his dominant wind direction was form a SW direction whilst mine was from the NW. On thinking back my memory tended to agree with Ray over the direction.
On checking this data in WeatherLink a NW dominant direction over the year was returned, but when checking both Cumulus & Weatherunderground a SW dominant direction was returned.
So I am asking if anyone on the forum also uses two or more programs one of which is WeatherLink and if so could they compare like for like and see if this is indeed a fault within WeatherLink or just an error at my end. If it is then I will let Davis know.
Cheers Alan… FlixtonWX

[mcrossley]

You don't have a direction offset defined in Cumulus do you? The console shows the same direction as Cumulus?

[FlixtonWX]

Hi Mark,
Just checked and no offset is applied, also the data set is sent to Met office WOW and Wunderground via Meteohub and to Cumulus and WL via a different system i.e respective software on PC. the two systems having separate Receivers and loggers but both being configured the same.
Alan

[RayProudfoot]

Hi Alan,

I wonder how you're determining the dominant wind direction with WeatherLink. The only way I could find was to view NOAA Year reports. WL reported S for every full year since 2010.

Viewing NOAA reports generated via Cumulus shows it varies from SW to S. Seems to me like two slightly different procedures are calculating that direction. I did find the direction odd for one year as according to the WL monthly dominant direction 6 of them showed WNW but the yearly direction was still south.

I have a 90 offset for my anemometer in the Davis console as I share a chimney with my neighbours and didn't want the ane arm encroaching on their side of the divide. As it's on the console it is corrected before either WL or Cumulus reads it.

If you do contact Davis their response will be interesting.

[steve]

Cumulus takes the wind speed into account when calculating the average wind direction. Perhaps Weatherlink does not?

[FlixtonWX]

Hi Steve,
Tnx for reply How Davis works this out is not known. I will be contacting them as if we go by majority vote then WL is wrong, but I would have thought that the NOAA reports would use basic raw data regardless of the software being employed thus giving consistent results no mater ware submitted from leaving individual software to use its own formula for its own displayed results.
It has been suggested that WL may just use a sort of "hit" count to determine dominate direction i.e NW got more hits than SW although most of the day/month a more constant direction was SW, who knows at this stage.
On reflection Steve with regard to the data for the NOAA report do you use raw data or apply the speed and direction calculations first?
Alan

[FlixtonWX]

Hi Ray,
Yes the NOAA reports, as these are common to both Cumulus & WeatherLink (not sure about WU). I have had some interesting replies and theories and it appears not to be as straight forward is I first believed, various ways of calculating the dominant direction. and how this employed within software. My plan of attack is to contact Davis and try to contact NOAA themselves as to how the like to determine the dominant direction.
Cheers Ray... And yes Thursday works for me

[steve]

On reflection Steve with regard to the data for the NOAA report do you use raw data or apply the speed and direction calculations first?

Sorry, I don't understand the question. The data for the NOAA reports comes mainly from dayfile.txt. If you're asking about the dominant wind direction specifically, that's calculated by taking all of the relevant entries in the monthly logs files, creating a vector based on the wind speed and direction in each entry, and summing the vectors.

[FlixtonWX]

Steve
Sorry, basically is the formula that you use specified by NOAA i.e the use of a vector based calculation on the wind ect as you say Cumulus employs or is this "your take" on what formula to employ to generate this NOAA report.
The only reason I ask this is two sets of software proposing to generate the same report from the same data give two different results. ergo one must be incorrect. I tend to agree with the results of Cumulus as this ties in with my physical observations and results from my data sent to WU.
What I would like to establish is why one is wrong (I think WL) and to point this out so we are all on the same page when comparing data. Plus I was curious to see if anyone else had noticed this.
Alan

[steve]

I think the method Cumulus uses just came from discussions in the forum (and other places on the web discuss the same method). I don't think there's a standard, it just depends on what you're trying to measure. The method Cumulus uses makes sense to me, but I can also see that other methods which don't take speed into account, and just use the most commonly occurring direction are equally valid.

Note that these reports are "NOAA-style" reports, i.e. they are reports in the same format as a NOAA report (well, apparently - I can't find a definition of them anywhere; I just copied the Weatherlink format). There is no implication that the data within in them is determined using NOAA standard definitions, where one exists.