running mean of circular data (angles)

Hi there

Im trying to do a running mean of a quite large wind-direction data-set but I'm having trouble finding solutions that work. Does anyone know of a simple solution?

Thanks in advance

[Andrei Bobrov]

>> doc mean

Answer 1

[Mark Brandon]

You could look at the excellent "Circular Statistics Toolbox"

http://www.mathworks.com/matlabcentral/fileexchange/10676

[Ana Soph]

if i have the matlaba 2015, what can i do ?

[Walter Roberson]

You can still use that File Exchange contribution. Just download it and install it and add the directory to your MATLAB path.

[Ana Soph]

Thanks good man

[Ana Soph]

1. how can i use mean angle?
2. M = xlsread('Dic2019','Dic2019mat')
3. ten_minute_avarege = meanangle(reshape(M, 10, []), 'omitnan')
4. xlswrite('datosexcel1.xlsx', ten_minute_avarege, 'Hoja1', 'A1');

[Walter Roberson]

I am not aware of any meanangle() function that has 'omitnan' as an option.

Answer 2

[David Young]

Have a look at

 doc unwrap

Answer 3

[Jakob Sievers]

The Circular Statistics Toolbox doesnt appear to have a running mean function though. I have used its circ_mean function to make my own running mean but it takes hours to complete its calculation due to the size of the dataset (basically a long vector containing 10 million points).

Does anyone have any other suggestions?

[David Young]

Could you say more about what the problem is? What's actually going wrong, that can't be solved with unwrap? Do you know how to do a running mean on non-circular data?

[Jakob Sievers]

Well. I looked though the running mean function that I usually use, but it uses a trick looking like this: cumsum(angles)./wl where wl is the window length being meaned over, and im not sure how to transfer this fast method into a circular-data setting. So what I did was to do a "for" loop which continuously uses the circ_mean function from the above mentioned toolbox. Since I have this long dataset it takes around 5 hours to calculate it and im sure it can be done more easily. Im just not sure how.

What I did with your suggestion was:

angles2=unwrap(angles);

angles2_rm=runmean(angles2,100); %(where 100 is the window)

and then im thinking using the mod function to get back into circular mode:

mod(angles2_rm,360)

but it doesnt look right.

[David Young]

Note that unwrap assumes your angles are in radians. If you're using degrees (and from the 360 in your code I think you are), multiply your data by pi/180 before using unwrap. You can convert back afterwards if necessary by multiplying by 180/pi.

Also, perhaps there's a problem with runmean. Maybe you could explain a little more about what this function does, or if it's very short even copy it into your question. (Not into a comment or answer though.)

[Jakob Sievers]

Hi David

I just talked with a colleague who said that a 30min mean would be sufficient, meaning that I can make a simple running mean that runs in a 20 seconds or so myself using the circ_mean as described above. Thanks for the help though!