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Questions about wind readings

Discussion of Mark Crossley's HTML5/Javascript gauges

Moderator: mcrossley

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lloydh
Posts: 8
Joined: Sat Oct 29, 2016 8:55 pm
Weather Station: Home made
Operating System: Centos 7
Location: Brisbane, Australia

Questions about wind readings

Postby lloydh » Thu Nov 09, 2017 5:50 am

I have my Davis 6410 temporarily installed at the front of the house (not a good position) just while I am testing and I think I am very close, it will soon be installed on the peak of a gable on the roof which should be in reasonably clear air.

On the Arduino I am reading the wind speed and wind direction from the Davis every 10 seconds. I save the readings and keep the last 5 readings, I then take the average of the 5 readings and that goes to the station as wlatest and bearing, I also send the maximum speed reading and its bearing of the 5 readings as windgust and windgustbearing. For the average I use the formula from http://www.webmet.com/met_monitoring/622.html with a lot of help from http://www.scadacore.com/2014/12/19/ave ... ind-speed/. If there is no wind for the 5 readings I set both wlatest and bearing to zero.

On the station I do the 10 minute averages for wind and wind gust using the same formula as above and also save the maximum wind gust.

For the dominant wind direction I started by saving avgbearing (and wspeed) every 10 minutes but only if there was wind. I then did a circular average on the number of saved values only and then convert it to a cardinal reading.

The wind rose, I guestimated that the 16 values were 16 cardinal points going clockwise from N so every 10 minutes I cleared the wind rose data and then added the saved wspeed values to their correct cardinal point and this seems to work.

For wind run I add all the saved wspeed readings and divide by the number of 10 minute periods since midnight to give me the true average km/h and then I divide by the number of hours since midnight (to 2 decimal places) to give me the wind run in klm.

Since finishing that I have changed the saving of avgbearing and wspeed from every 10 minutes to every 5 minutes giving me a maximum of 288 readings each day but I didn't notice any real change of what I saw on the gauges after I did this.

All I am asking is am I going in the right direction or have I made mistakes, the attached graphic is what the gauges look like. I've done all of this on a second Raspberry and I will transfer it to the main station when I am happy with it.
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mcrossley
Posts: 5006
Joined: Thu Jan 07, 2010 9:44 pm
Weather Station: Davis VP2
Operating System: Jessie Lite rPi
Location: Wilmslow, Cheshire, UK
Contact:

Re: Questions about wind readings

Postby mcrossley » Thu Nov 09, 2017 12:11 pm

It sounds reasonable to me. The only significant differences to how I think Cumulus handles things are:

Cumulus just passes the last reading for 'wlatest' and 'bearing' rather than a rolling 50 second average.

Cumulus uses the 10 minute high gust value for 'wgust'.

Does 'windgustbearing' exist? I don't think the gauges use it, though it would be a nice addition to CMX. The problem is that it may not be available if it is read from either the logger or Davis records values (ignoring other station types).

User avatar
lloydh
Posts: 8
Joined: Sat Oct 29, 2016 8:55 pm
Weather Station: Home made
Operating System: Centos 7
Location: Brisbane, Australia

Re: Questions about wind readings

Postby lloydh » Sat Nov 11, 2017 7:27 am

Mark, thanks for your comments and it looks like I am there.

I have a lot of extra variables and lists in the background for calculations and sometimes for graphs. I try to keep to the names on your Wiki but there are probably some that are not being used anymore and I have been doing some housekeeping in the past few days to try and tidy things up.

I made a decision in the early days to do a small amount of averaging on the sensors because I am only taking readings every minute.

I may look at things like BearingRangeFrom etc at a later date maybe but I have already had one comment from a friend saying it looks too complicated already.

User avatar
mcrossley
Posts: 5006
Joined: Thu Jan 07, 2010 9:44 pm
Weather Station: Davis VP2
Operating System: Jessie Lite rPi
Location: Wilmslow, Cheshire, UK
Contact:

Re: Questions about wind readings

Postby mcrossley » Sat Nov 11, 2017 11:07 am

lloydh wrote:I may look at things like BearingRangeFrom etc at a later date maybe but I have already had one comment from a friend saying it looks too complicated already.

I always take the view that my web page is mainly for me - given the numbers of visitors it isn't a competitor for BBC/weather! - so I put up what I want to see and if others find it useful or conversely over technical so be it :lol:


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