Different colours for arrows in quiver plot

Hi Everyone,

I want to plot arrows with different magnitude and directions in different colors.The code need to calculate the angle of the each vector and fit them in the colormap.

This is what I have wrote but is there anyone that can help me to find the example or any other command or function in matlab that can plot this for me?

for i=1:40
     structure(i,:,:)=rombohedral((i-1)*338+1:i*338,:);
   
     X=structure(i,:,4);
     Y=structure(i,:,5);
     Z=structure(i,:,6);
     U=structure(i,:,7);
     V=structure(i,:,8);
     W=structure(i,:,9);

     C=zeros(338,3);
     C(1:300,1)=1;
     C(300:end,2)=1;
     figure(i)

     figure(i)
     title('2D')
     t=num2str(i);
     xlabel([t,' ps'])
     hold on
    
    for j=1:338
        if (U(j)>0)
           quiver(X(j),Y(j),U(j),W(j),'color',[1 0 0])
        elseif (U(j)<0)
           quiver(X(j),Y(j),U(j),W(j),'color',[0 1 1])
        elseif (V(j)>0)
          quiver(X(j),Y(j),W(j),V(j),'color',[0 1 0])
        elseif (V(j)<0)
          quiver(X(j),Y(j),W(j),V(j),'color',[1 0 1])

        end
    end
   
 
end

[darova]

You don't want to use quiver? Or what do you want quiver do?

[Hamed Nobarani]

I want to use quiver which is corresponding to the magnitude and angle of the vectors and interpolate them in 360 degree colormap.

Answer 1

[Thorsten]

Create a circular colormap:

cmap = colormap(hsv(360));

In the loop: compute the angle and an index into the colormap from the angle

 alpha = atan2(W(j), U(j)); % or V(j), W(j) depending on your elseif clause

Convert angle to index

 idx = ceil(rad2deg(alpha));
 if alpha < 1 % negative indices and 0 are invalid 
     idx = idx + 360;
 end
 set(h, 'Color', cmap(idx,:)) % before, change each quiver command to h = quiver(...) 
 
 

[Hamed Nobarani]

Hi Thorsten,

Thanks for your answer.

My vectors are just U and V, I have added W to get the 3d quiver plot but I don't need that now.

So I need to calculate the orientation of vector of u and v with respect to the x axis (0-360 degree) and interpolate them with the colormap.

By using if and else if I was trying to define the color for each quadrant (so I had just 4 colors), which I don't need them anymore. Am I correct?

[Thorsten]

Yes.

[Hamed Nobarani]

Thanks,

I have modified my code but I'm getting this error:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in Colormap (line 39)

set(h, 'Color', cmap(idx,:)) % before, change each quiver command to h = quiver(...)

for i=1:40

structure(i,:,:)=rombohedral((i-1)*338+1:i*338,:);

X=structure(i,:,4);

Y=structure(i,:,5);

Z=structure(i,:,6);

U=structure(i,:,7);

V=structure(i,:,8);

W=structure(i,:,9);

C=zeros(338,3);

C(1:300,1)=1;

C(300:end,2)=1;

figure(i)

figure(i)

title('2D')

t=num2str(i);

xlabel([t,' ps'])

hold on

for j=1:338

cmap = colormap(hsv(360));

alpha = atan2(V(j), U(j));

idx = ceil(rad2deg(alpha));

if alpha < 1

idx = idx + 360;

end

h=quiver(X(j),Y(j),U(j),V(j));

set(h, 'Color', cmap(idx,:))

end

end

Answer 2

[Hamed Nobarani]

Hi

I have attached the example here:

clc

close all

clear all

deg=linspace(0,2*pi,720);

r=1;

hold on;

for i =1 :720

cmap = colormap(hsv(360));

u(i)=r*cos(deg(i));

v(i) = r*sin(deg(i));

alpha(i) = atan2(v(i), u(i));

idx = ceil(rad2deg(alpha(i)));

if idx < 1

idx = idx + 360;

end

x(i)=0;

y(i)=0;

quiver(x(i),y(i),u(i),v(i),'color',cmap(idx,:))

axis equal

end