Average Wind Dir in toservice

[Freman]

Is there any way to get the average wind direction (over the past hour) in the toService live view?

[Jim Easterbrook]

On 21/03/12 03:52, Freman wrote:
> Is there any way to get the average wind direction (over the past hour)
> in the toService live view?

Not without writing a function to compute it in toservice.py, a bit like
'rain_hour' but rather more complicated.

To get any useful answer you need to take account of the wind speed as
well as direction. If most of the last hour had no wind but the vane
rested in one position, the average wind might still be from a
completely different direction. Have a look at Process.py where I do a
vector sum to get an average direction.
--
Jim Easterbrook <http://www.jim-easterbrook.me.uk/>

[Freman]

It is all good. I decided to do the averaging in my daemon - it's done over the last 30 entries which equates to less than 30 minutes but it's enough for my purposes.

I do take into account the wind direction and speed.

here's the code in javascript (nodejs) but I can port it to any language you would like to try it in.

function avg(array) {

        var sum = 0;

        for (i in array) {

                sum += parseFloat(array[i]);

        }

        return sum / array.length;

}

function calc_average_wind_dir(data) {

// Store a number of U's and V's

        u_comp.push(-1 * (data.windspeedms * Math.sin(data.winddir * Math.PI/180)));

        v_comp.push(-1 * (data.windspeedms * Math.cos(data.winddir * Math.PI/180)));

// Store a number of wind speeds (for future use, not used atm)

        ws.push(data.windspeedms);

// Dispose of any entries older than 30

        while (u_comp.length > 30) {

                u_comp.shift();

                v_comp.shift();

                ws.shift();

        }

// Calculate the average u and v

        var u_avg = avg(u_comp);

        var v_avg = avg(v_comp);

// Calculate the average wind direction

        var avg_wd;

        if (u_avg > 0) {

                avg_wd = 90 - 180 / Math.PI * Math.atan(v_avg / u_avg) + 180;

        }

        else if (u_avg < 0) {

                avg_wd = 90 - 180 / Math.PI * Math.atan(v_avg / u_avg);

        }

        else {

                if (v_avg < 0) {

                        avg_wd = 360;

                }

                else if (v_avg > 0) {

                        avg_wd = 180;

                }

                else {

                        avg_wd = 0;

                }

        }

        return avg_wd

}

(I admit it's based on pseudo code I found via google, no idea where now though)