How can I extract orientation of arrows from quiver function?

In quiver function where is the information about the arrow orientation?

Answer 1

[Sean de Wolski]

You'll need to use atan2 to get the orientation from u, v

q = quiver(1,1,1,0.5)
r = atan2(q.VData,q.UData)

r*180/pi to get it into degrees

Answer 2

[Michael Haderlein]

quiver actually plots the information.

quiver(x,y,u,v)

means arrows are drawn pointing in (u/v) direction and positioned at (x/y). So, if you have x=0, y=0, u=1, v=1, you get one arrow pointing top right. For multiple arrows, x, y, u and v have multiple values.

[annalisa08]

Thank you!

[annalisa08]

If I would like to report the vector in a compass plot mantaining the same orientation of the vector from quiver function how can I do? Compass plot draws vector starting from the origin and point to u,v coordinates on cartesian axes. Doing this the orientation of the vectors are different, is there a way to transform these coordinates?

[Michael Haderlein]

What do you mean, the orientation is different? It should be the same. You can prove it:

>> x=zeros(10,1);y=zeros(10,1);u=rand(10,1);v=rand(10,1);
>> compass(u,v)
>> axes
>> quiver(x,y,u,v,1,'color','r')
>> set(gca,'color','none')

Then select the arrow in the figure toolbar and match the origin of both axes and the scales as well (so (1/0) matches with r=1, angle=0 and (0/1) matches with r=1, angle=90°). You'll see that the arrows match perfectly. If you do not consider the scaling (that's the 1 in the quiver command), the length of the arrows differ. The orientation remains the same.

[annalisa08]

In this way is correct, but my vectors from quiver function start from different origins: x = [-15 0 15;-15 0 15;-15 0 15]; y = [8 8 8; 13 13 13; 18 18 18];u = rand(3,3); v = rand(3,3)

is it possible aligning the vectors in quiver on compass plot?

Thank you very much for the help!

[Michael Haderlein]

I don't get it... The origin is lost in the compass plot, but that's an inherent property of the compass plot and has nothing to do with the orientation. Set all x,y to zero and the arrows will align. Set x,y to their correct values (~=0) and they will shift to their correct position but remain their orientation.