How to draw an arrow using non normalized coordinates?

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Mr M.
Mr M. 2017-6-26
编辑： Bill Tubbs 2023-3-22
I use: annotation('arrow',X,Y), and I tried to change units, but it is always normalized. How to use data units?
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Mr M.
Mr M. 2017-6-28
yes, but I cannot figure out how to use non-normalized units with annotation('arrow')

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回答（9 个）

KarlHoff
KarlHoff 2020-6-26
编辑：KarlHoff 2020-8-7
For me, using MATLAB R2018b,
the following works to produce an arrow at a location specified in data coordinates:
anArrow = annotation('arrow') ;
anArrow.Parent = gca; % or any other existing axes or figure
%EDIT thanks to @Moshe:
%anArrow.Position = [x_start, y_start, x_end, y_end] ;
anArrow.Position = [x_start, y_start, delta_x, delta_y] ;
The big advantage is that the arrow remains where it is with respect to other plot elements, even if the limits of the plot change afterwards.
This is not the case with all the approaches that convert data coordinates into other Units (Pixels, Inches, Normalized)
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Jean-Michel
Jean-Michel 2020-9-2
Thanks for that , I have been fighting quiver and annotation to get similare result! it would be a nice addition to the docuementation

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MICHAEL MUTWIRI
MICHAEL MUTWIRI 2021-8-21
Ran in:
Create the 'annotation' object for each subplot and edit their properties using dot notation.
For the X and Y properties you use similar values as your graph cordinates. The x-end and y_end are the tip of the arrow.
Below is a tested sample code
%Create sample data
x = linspace(0,2*pi,1e3);
y = sin(x); % Plotted of first subplot
z = cos(x); % Plotted of second subplot
fg1=figure(1);
% Specify different textarrows for different subplots
%%%**************** SUBPLOT 1 ********************
subplot(2,1,1);
plot(x,y,'k')
xlabel('x')
ylabel('Amplitude')
title('Sin(x)')
ylim([-1.1 1.1])
% Define X-Beginning and ending x-coordinates
x_start =pi-1;x_end = pi;
%Y- Beginning and ending y-coordinates
y_start =sin(x_end);y_end = sin(x_end);
anArrow = annotation('textarrow');
anArrow.Parent = gca;
anArrow.X = [x_start,x_end]; % set the x-property
anArrow.Y = [y_start ,y_end];
anArrow.String = 'sin(\pi)';
anArrow.Color = 'red';
%%%**************** SUBPLOT 2 ********************
subplot(2,1,2);
plot(x,z,'k')
xlabel('x')
ylabel('Amplitude ')
ylim([-1.1 1.1])
% Define X-Beginning and ending x-coordinates
x_start =1.5*pi-1;x_end = 1.5*pi;
%Y- Beginning and ending y-coordinates
y_start =cos(x_end);y_end = cos(x_end);
anArrow = annotation('textarrow');
anArrow.Parent = gca;
anArrow.X = [x_start,x_end]; % set the x-property
anArrow.Y = [y_start ,y_end];
anArrow.String = 'cos(3\pi/2)';
anArrow.Color = 'green';
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Bill Tubbs
Bill Tubbs 2023-3-22
编辑：Bill Tubbs 2023-3-22
Thanks. This works. Strange that you can't use axes co-ordinate system with the annotate command. It has a 'Units' argument but I can't find an appropriate value for this argument other than the default which is 'normalized' (where is the documentation?).

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Walter Roberson
Walter Roberson 2017-6-27
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Timon Rayis
Timon Rayis 2019-11-11
Any developments with R2019b? annotations with non normalized coordinates like text ?

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marcus yoder
marcus yoder 2018-8-23
编辑：marcus yoder 2018-8-23
I tested the code by Walter Robinson and had to make a few changes to get it to work.
function obj = dataArrow(Xdata,Ydata,ax)
%This function will draw an arrow on the plot for the specified data.
%The inputs are
oldunits = get(ax, 'Units');
set(ax, 'Units', 'Normalized');
axpos = ax.CurrentAxes.Position;
set(ax, 'Units', oldunits);
%get axes drawing area in data units
ax_xlim = ax.CurrentAxes.XLim;
ax_ylim = ax.CurrentAxes.YLim;
ax_per_xdata = axpos(3) ./ diff(ax_xlim);
ax_per_ydata = axpos(4) ./ diff(ax_ylim);
%these are figure-relative
Xpixels = (Xdata - ax_xlim(1)) .* ax_per_xdata + axpos(1);
Ypixels = (Ydata - ax_ylim(1)) .* ax_per_ydata + axpos(2);
obj = annotation('arrow', Xpixels, Ypixels, 'Units', 'pixels');
end
Robert
Robert 2019-9-7
I wanted to do something similar, here's an example that adds a double arrow between the x-values 1 and 5 with y-values 5 in a simple plot:
pos=[.1,.1,.85,.85];
figure;ax=axes('position',pos);plot(1:10)
x=[1,5];y=[5,5];
rx=xlim(ax);ry=ylim(ax);
cx=pos(3)/diff(rx);cy=pos(4)/diff(ry)
annotation('doublearrow',pos(1)+cx*(x-rx(1)),pos(2)+cy*(y-ry(1)))
MichailM
MichailM 2020-4-4
Maybe a function like the below could help. The x and y inputs are actual coordinates on the plot. Here I just need to draw an arrow but you can modify it
function myarrow(x,y)
ax = gca;
axpos = get(ax, 'Position');
X = get(gca,'XLim');
Y = get(gca,'YLim');
difX = X(2) - X(1);
difY = Y(2) - Y(1);
newx = x./difX;
newy = y./difY;
annotation('arrow',[newx(1)*axpos(3)+axpos(1) newx(2)*axpos(3)+axpos(1)],[newy(1)*axpos(4)+axpos(2) newy(2)*axpos(4)+axpos(2)])
end
Marc Compere
Marc Compere 2021-8-14
Scaling to achieve arrow annotations in axes units should be built into Matlab. The utility coord2norm() handles this easily.
This is a similar question with more discussions, but the short answer is: use coord2norm()
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Adam Danz
Adam Danz 2021-8-15
Thanks for pointing out that function, Marc, I'm sure it will be helpful in many cases.
Since it's a static, once-and-done, conversion, the annotation object may no longer be in the correct position if there are any changes to the figure size, axis size or position, axis limits, or aspect ratios. Calling the function after all plotting is complete would help to solve some of those issues. A more robust solution would be to assign listeners that update annotation objects when a resize or reposition event occurs but really what we need is for MathWorks to update the annotation function to support data units or offer users an alternative.

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Vitaly Fedoseev
Vitaly Fedoseev 2021-5-26
The following code (Matlab R2019a) draws an arrow in the plot coordinates from point P1 to point P2. Zoom in/out shifts position of the arrow:
P1=[10,-1]; %from point
P2=[70,2]; % to point
figure;
Xlim=[-1 110];
Ylim=[-2 3];
Pos = [0.10 0.55 0.85 0.4];
subplot('Position', Pos)
hold on
X_conv(1)=Pos(1)+(Pos(3))/(Xlim(2)-Xlim(1))*(P1(1)-Xlim(1));
X_conv(2)=Pos(1)+(Pos(3))/(Xlim(2)-Xlim(1))*(P2(1)-Xlim(1));
Y_conv(1)=Pos(2)+(Pos(4))/(Ylim(2)-Ylim(1))*(P1(2)-Ylim(1));
Y_conv(2)=Pos(2)+(Pos(4))/(Ylim(2)-Ylim(1))*(P2(2)-Ylim(1));
x=0:0.1:100;plot(x, sin(x));plot([-100 1000], P2(2)*[1 1]); plot(P2(1)*[1 1], [-100 100]);
plot(x, sin(x));plot([-100 1000], P1(2)*[1 1]); plot(P1(1)*[1 1], [-100 100])
xlim(Xlim)
ylim(Ylim)
annotation('arrow', X_conv, Y_conv)
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Walter Roberson
Walter Roberson 2021-6-1
It should not be added to the code. Adam is saying that if you wanted to illustrate that the arrow did not follow the axes, then you could delete the axes and observe that the arrow is still there.

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Bruce Jackson
Bruce Jackson 2022-10-26
It is absurd that we have to jump through hoops or download submitted code to plot an arrow in data units on a plot.
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Adam Danz
Adam Danz 2022-10-27
Ran in:
Depending on what you're looking for, you can already plot simple arrows in data units using text().
x = rand(1,5);
y = rand(1,5);
plot(x,y,'o')
text(x,y,repmat({char(8594)},size(x)), ...
'HorizontalAlignment', 'right', ...
'VerticalAlignment', 'middle', ...
'FontSize', 14)
https://unicode-table.com/en/sets/arrow-symbols/
Bruce Jackson
Bruce Jackson 2022-10-27
Thanks for the suggestion, but I would like to place and point arrows with a specified length and direction. The innovative use of UNICODE arrows unfortunately doesn't allow for more than four or maybe eight directions, I expect.
[The excellent coord2norm() function, written by user sco1, should be part of core MATLAB and not require me to download and install third-party code, which I'm attempting to avoid to have a marketable toolbox.]

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