running mean of circular data (angles)

Jakob Sievers さんによって質問されました 2011 年 10 月 5 日

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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

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Andrei Bobrov 2011 年 10 月 5 日

>> doc mean

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回答者: Mark Brandon 2011 年 10 月 5 日

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You could look at the excellent "Circular Statistics Toolbox"

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

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回答者: David Young 2011 年 10 月 5 日

Have a look at

doc unwrap

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回答者: Jakob Sievers 2011 年 10 月 5 日

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?

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Jakob Sievers 2011 年 10 月 5 日

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 2011 年 10 月 5 日

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 2011 年 10 月 5 日

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!

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