Quiver. Make wind scale of 1m/s inside plot

I have had a really tough time thinking of a way to show a scale of the wind vectors that Im plotting.

Im using quiversc(lon,lat,u,v) but I dont know how to put a magnitude of reference (1 m/s for example) , as in the plot below.

Thanks!

Answer 1

[Chunru]

[x, y] = meshgrid(-2:.2:2);
z = x.*exp(-x.^2-y.^2);
[dx, dy] = gradient(z, 0.2);

sc = 'off';     % scale 
quiver(x,y,dx,dy, sc);
axis tight;
hold on
a = axis;
% posision of the ref arrow
xr = a(1)+0.1*(a(2)-a(1));
yr = a(4)-0.1*(a(4)-a(3));
quiver(xr, yr, 1, 0, sc)  % unit lenght

[Luis Jesús Olvera Lazcano]

Hi, thank you very much for your answer!

I think I didnt explain very well. My question is related to give the plot a vector magnitude reference. Specifically to indicate the size of an arrow that has 1 m/s as the magnitude. That way, the plot can help to see if other vectors are more or less faster

[Chunru]

See the edited above

[Luis Jesús Olvera Lazcano]

Thanks! So I deactivated the scaling, but now the arrows are very tiny so I cant see anyone, not even the reference (which i cant find). This is my code (its into a subplot for cycle so I will only put the important parts and a plot of reference)

quiver(LON, LAT, u, v, sc,'k')
hold on
a = axis;
xr = a(1)+0.1*(a(2)-a(1));
yr = a(4)-0.1*(a(4)-a(3));
quiver(xr, yr, 1, 0, sc,'r')  % unit lenght

[Chunru]

You can change ux(=1) to any suitable value to make it visible and label it with the appropriate magnitude and unit for reference.

You may also want to change to the following:

manual_sc = 100;  % adjust this val
quiver(LON, LAT, manual_sc*u, manual_sc*v, sc,'k')

Or you can post your data if you need further help.

[Luis Jesús Olvera Lazcano]

Hi thank you very much! Thanks to your code I manage to do some arrangements, even put the reference arrow to fit more in the plot.

However I have some doubts about it. My code is this one (I use quiversc instead of quiver to control the density of the arrows, but the scaling is the same, I corroborated that):

quiversc(LON,LAT,u*2.5,v*2.5,'off','k','density',60,'LineWidth',1) % off is for scaling
colormap(brewermap(10,'PuBuGn'))
caxis([0 5])
borders('countries','k','LineWidth',1)
borders('countries','k','LineWidth',1)
axis equal
ylim([-30 36])
xlim([30 178])
yticks(-30:30:30)
yticklabels({'30°S','EQ','30°N'})
xticks(40:40:160)
xticklabels({'40°E','80°E','120°E','160°E'})
hold on
a = axis;
xr = a(1)+0.1*(a(2)-a(1));
yr = a(4)-0.1*(a(4)-a(3));
hold on
b = rectangle('Position',[xr-15 yr-6 15 12],'FaceColor','white');
hold on
quiver(xr-13,yr,1*12.5,0,'k','LineWidth',1,'MaxHeadSize',2.5)

The resulting plot is:

So my question is this: I put the manual_sc = 2.5 for the u,v values. Then, to show the reference arrow, I multiply it per 12.5. I understand that, if the whole quiver plot is adjusted with 2.5 and the reference arrow is adjusted with 12.5, then the reference arrow has a magnitude of 4 m/s? I thought about it cause its 4 times bigger than the main quiver plot vectors.

[Luis Jesús Olvera Lazcano]

Hey I managed to realize that my question is resolved! I saw the measure of the reference arrow and its indeed the quantity I determined. Thank you so much for your answer, you helped me a lot to improve my plots and to give them a better style

I let my code available for the future if someone has a similar problem