How to get scale and coordinates from quiver function?

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Yuvarajendra Anjaneya Reddy 2023-1-8

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编辑： Adam Danz 2024-4-26

Let's say I create a quiver plot with X, Y, U and V. If we think in the sense of particles, consider 'n' number of particles that particles have location [X,Y] and corresponding velocities [U, V]. The result from using 'quiver' function is, I get a vector plot that has vectors indicating direction and magnitude of particle displacement. This means that the particles have new locations [X1, Y1]. Is there a way to get this new location data?

I have checked the "get(hQ, 'Xdata')", function that gets me the original data that I have provided to the 'quiver' function, but I could not find the updated location data as inferred from the quiver plots.

I also, understand that scaling the arrows can have an impact on the new locations [X1, Y1]. But, that can not be a concern as of now. Any help is appreciated. Thanks in advance.

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Answer 1

Adam Danz 2023-1-8

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https://ww2.mathworks.cn/matlabcentral/answers/1890377-how-to-get-scale-and-coordinates-from-quiver-function#answer_1144172

编辑：Adam Danz 2024-4-26

在 MATLAB Online 中打开

> the particles have new locations [X1, Y1]. Is there a way to get this new location data?

If you already have the X, Y, U and V values, then the new location is

xnew = x+u;

ynew = y+v;

However, unless scaling is turned off, the head of the quiver arrows will likely not be at [xnew, ynew] because quiver internally scales the magnitude of the arrows so they all fit nicely in the axes. Here are two solutions.

Example: turn off scaling

x = rand(1,20)*20 - 10;

y = rand(1,20)*10 + 40;

u = rand(1,20)*6 - 3;

v = rand(1,20)*10 - 5;

quiver(x,y,u,v,'off')

x1 = x + u;

y1 = y + v;

hold on

plot(x, y, 'bo') % mark arrow tail

plot(x1, y1, 'rs') % mark arrow head

Example: Use the ScaleFactor property (R024a)

Starting in R2024a, the quiver object returned by quiver contains a read-only ScaleFactor property that can be used to compute the magnitudes of the quiver arrows whether auto scaling is turned on or off. Multiply U and V by the scale factor to get the horizontal and vertical distance between the arrow tails and arrow heads.

figure()

h = quiver(x,y,u,v);

h.ScaleFactor

ans = 0.8243

x1 = x + h.ScaleFactor*u;

y1 = y + h.ScaleFactor*v;

hold on

plot(x, y, 'bo') % mark arrow tail

plot(x1, y1, 'rs')

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Yuvarajendra Anjaneya Reddy 2023-1-10

@Adam Danz Thank you.. It is much clear now..

Adam Danz 2024-4-26

I've updated my answer to include a new solution available in R2024a using the ScaleFactor property.

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Answer 2

MJFcoNaN 2023-1-8

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Hello,

The vector field is instantaneous, therefore, you have to provide the increment of time for getting a new proximate location. Or you can calculate it from a time series of vector fields.

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Yuvarajendra Anjaneya Reddy 2023-1-8

@MJFcoNaN Thank you for your answer. Involving time variable can get tricky and complex in the code I'm using, anyways I appreciate the valid comment.

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