How to create a quiver plot with logarithmic scaled arrows

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Yoav Romach
Yoav Romach 2016-3-7
评论： Yoav Romach 2019-3-16
Hey, I have a vector field with a large dynamic range; therefore the only way to properly see it in a quiver plot is if the length of the vectors will scale logarithmic instead of linearly.
As far as I know, there is no built in way to do it. Manually take the log before calling quiver will not work as it will change the angles, and therefore the quiver plot will be wrong.
I tried searching online but couldn't a way to do it, anyone knows one?
Another option is starting with the matlab built in quiver plot code and manually making another function that fixes it, is there anyway to get it?
  2 个评论
Chad Greene
Chad Greene 2016-3-7
Interesting problem. The code for quiver is viewable. Type
open quiver
and it should be relatively painless to manually hack the length scaling.
Yoav Romach
Yoav Romach 2016-3-7
Thanks! Didn't know it was that simple to open the code for matlab functions :)
Unfortunately, it did not help me; taking a look at the code, the important lines are just these two:
h = matlab.graphics.chart.primitive.Quiver;
set(h,'Parent',parax,'Color_I',c,'LineStyle_I',ls,pvpairs{:});
pvpairs is simply the x,y,u,v data, so it seems that the behavior is hard-coded into a primitive "Quiver" chart type :\
Any other ideas?

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采纳的回答

Star Strider
Star Strider 2016-3-7
I’m not certain what you’re plotting, so I’m guessing here.
This is one approach:
t = linspace(1E-3, 6*pi);
x = t .* cos(t) + 2;
y = t.* sin(t) + 2;
dx = gradient(x);
dy = gradient(y);
figure(1)
quiver(x, y, dx, dy) % Retain Scaling
grid
axis equal
log_dx = log(hypot(dx,dy)) .* (dx);
log_dy = log(hypot(dx,dy)) .* (dy);
figure(2)
quiver(x, y, log_dx, log_dy, 0) % Log Arrows, No Scaling
grid
axis equal
  6 个评论
显示 4更早的评论
Arthur Ku
Arthur Ku 2018-9-22
编辑：Arthur Ku 2018-9-22
Very nice, Yoav!
I tested this out with a few point charges and it looks great when superimposed on a contour plot. Thank you both for your solutions. As Star Strider said, this would be great on File Exchange.
Yoav Romach
Yoav Romach 2018-10-15
编辑：Star Strider 2018-10-15
Thanks Arthur.
About two years later, I added it to file exchange with some additional commenting (but no significant code changes). If people will report bugs, I'll try to fix them.
Hopefully it'll help people :)
The file can be found at: https://www.mathworks.com/matlabcentral/fileexchange/69109-quiverinlogscale

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更多回答（1 个）

Angelo Hafner
Angelo Hafner 2019-3-15
编辑：Angelo Hafner 2019-3-15
Just enter the u,v,w components in the function log_cv... The function returns the log components of the vector [u,v,w]...
function [log_ax,log_ay,log_az] = log_cv(u,v,w)
r = sqrt(u.^2 + v.^2 + w.^2);
rho = sqrt(u.^2 + v.^2);
t = atan2(rho,w);
f = atan2(v,u);
log_ax = log10(r) .* sin(t) .* cos(f);
log_ay = log10(r) .* sin(t) .* sin(f);
log_az = log10(r) .* cos(t);
end
  1 个评论
Yoav Romach
Yoav Romach 2019-3-16
Hey Angelo,
This was answered two years ago, and I created a function to solve it, see above.
Your function would not work properly if r will be smaller than 1 (I mean it will work, but will mess up the quiver).

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