Add arrows to surface plot to represent wind direction

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mashtine
mashtine 2015-9-23
评论： mashtine 2015-9-24
Hi there,
I am seeing a lot of information about the quiverm function but I only have my wind direction data in degrees and not in the u and v components. Is there a simple way to project a matrix of wind direction values (360 degrees) onto a sufacem plot? Perhaps there is a way to add and arrow and align it based on the wind direction value? I do not want to add magnitude as well, just direction.
Many thanks,
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mashtine
mashtine 2015-9-23
Hi Kirby,
I believe the NCL website is giving the correct data as it will produce the correct wind direction for the negative quadrants. I am also getting the expect wind direction (easterly winds). For instance,
atan2(sind(181),cosd(181))*r2d
ans =
-179
where I should not be getting a negative direction but degrees in 0 to 360. I believe it is accounting for matlab use of the atan2 function as this differs in some software
Kirby Fears
Kirby Fears 2015-9-23
-179 is the correct answer.
-179+360=181
The NCL website adds 180 to this, which would be
-179+180=1, which is incorrect.

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Kirby Fears
Kirby Fears 2015-9-23
编辑：Kirby Fears 2015-9-23
I'm posting an example as described in my earlier comment.
Code below creates a 10x10 grid of arrows that are all pointing at 120 degrees.
x=repmat(1:10,10,1);
y=x';
deg=120; % all points have same direction
% if you have a degree array the same size as x,
% you can use cosd and sind on "deg" without
% using repmat after
u=repmat(cosd(deg),size(x));
v=repmat(sind(deg),size(x));
% you can multiply u and v by magnitude of required
quiver(x,y,u,v);
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mashtine
mashtine 2015-9-24
Thanks a lot Thorsten! As the I would like the arrows to point to where the wind is going to, I will use
cosd(270 - deg)
sind(270 - deg)
That seems to be working well for all degrees.

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