How do I plot wind direction timeseries with arrows

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giacomo labbri
giacomo labbri on 12 Jun 2020
Edited: David on 21 Jan 2022
Hi,
I would like to plot a timeseries of wind direction. I would like represent the direction at each point in time with an arrow. The direction of the wind is expressed in degrees. I have saw that quivers might do what I want with some tricks but I was wondering if there was a more specific function.
Thanks in advance,
Giacomo
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Accepted Answer

Adam Danz
Adam Danz on 12 Jun 2020
Edited: Adam Danz on 21 Jan 2022
The quiver() function is what you want to use. It's desiged exactly for this purpose.
Since your vectors are in degrees and the quiver function requires the x,y component vectors, use pol2cart() to convert your polar vectors to cartesian vectors. You'll also need to convert deg-->rad for the pol2cart inputs.
% WindDirection is the direction of wind (deg)
% WindSpeed is the magnitude of the wind vector
[xWind, yWind] = pol2cart((pi/180).*WindDirection, WindSpeed);
quiver(x, y, xWind, yWind)
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More Answers (1)

David
David on 20 Jan 2022
Edited: David on 21 Jan 2022
A problem with quiver for this is that the horizontal axis is shared by both time and the x component of windspeed, so you have to make choices about how you scale things if you want northeast winds to go on the 45° angle and the y axis to measure speed
If you leave the aspect ratio free, the date axis is correct, but the 45° winds won't be proper.
x = datenum(t); y=x*0;
quiver(x,x*0, xWind, yWind,0,'.');
datetick;
If you make the aspect ratio equal (`axes equal`) then the 45° will be proper, but you may need to scale the time data to see your data, and then that screws up the automatic date tick labelling. Then getting the time tickmarks right is tricky. You can capture the automatically generated tickmarks, find the corresponding times, and then replace the labels with the corresponding times. See https://www.mathworks.com/matlabcentral/answers/391904-datetick-at-feather-plot#answer_312939
If you don't need the dateticks, this works well for maintaing angles through resizing and zooming:
sfact = 1000; % or whatever looks nice
x = datenum(t); y=x*0;
quiver(x*sfact,x*0, xWind, yWind,0,'.');
axis equal;
set(gca,'XTickLabel',[],'YTickLabel',[])
% ... tickmark replacement magic
Or if you keep the time axis, and the yWind, you could scale the xWind by a factor to match the aspect ratio between time and yWind, but then you can't resize/reshape your plot without decalibrating the angles.
I like this one best if you want to label the time axis:
x = datenum(t);
y= x*0;
quiver(x, y, xWind, yWind,0,'.')
x = datenum(t); y=x*0;
sfact = 1;
rg=1000:3200;
quiver(x(rg),x(rg)*0, xWind(rg)*sfact, yWind(rg),0,'.');
ylim([-10,10]);
xlim([min(x(rg)),max(x(rg))])
% asjust plot to desired size/shape/aspect
datetick;
% capture the aspect ratio between time and yWind
dd=daspect;ax=gca; sfact = 1/(dd(2)/dd(1)/ax.PlotBoxAspectRatio(2));
[dd(2)/dd(1) ax.PlotBoxAspectRatio dd(2)/dd(1)/ax.PlotBoxAspectRatio(2) sfact]
quiver(x(rg),x(rg)*0, xWind(rg)*sfact, yWind(rg),0,'.'); %replot scaling xWind to match time
ylim([-10,10]);xlim([min(x(rg)),max(x(rg))])
datetick; % add dateticks

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