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How to draw an arrow using non normalized coordinates?

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Mr M.
Mr M. on 26 Jun 2017
Commented: Kaluri on 23 May 2024 at 1:01
I use: annotation('arrow',X,Y), and I tried to change units, but it is always normalized. How to use data units?
  4 Comments
Mr M.
Mr M. on 28 Jun 2017
yes, but I cannot figure out how to use non-normalized units with annotation('arrow')
Kaluri
Kaluri on 23 May 2024 at 1:01
Yes using normalised coordinated is a big problems. For cartesion frame work we have ds2nfu.m is available and works good but I struggled to solve this for polarplot(theta,rho) not polar(theta,rho). Aspect ratio is a problem. Please use this code below. I have modified the original code.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clc; clear all;
% Dr Kaluri V Ranga Rao life senior member IEEE princeton kaluri@ieee.org
close all;
theta = linspace(0,360,180);
max = 1;
r = linspace(max,0.2,180);
s = 60; e = 20;
ra = [r(s) r(e)];
th = [theta(s) theta(e)];
h = polarplot(theta*pi/180,r,'.-r',th*pi/180,ra,'ob');
for k=1:180
[xaf,yaf] = polarDS2nfu([theta(k) theta(k)]*pi/180,[r(k)*0.5 r(k)]);
hT = annotation('arrow',xaf,yaf);
pause(0.5);
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Michelle Hirsch
% mhirsch@mathworks.com
% Copyright 2006-2014 The MathWorks, Inc
% updated for polar kaluri@ieee.org
%I modified this and works well for polarplot
function varargout = polarDS2nfu(varargin)
% polarDS2NFU Convert data space polar units into normalized figure units.
%
% [Xf, Yf] = DS2NFU(X, Y) converts X,Y are theta,r polar coordinates from
% data space to normalized figure units, using the current axes. This is
% useful as input for ANNOTATION.
%
% POSf = DS2NFU(POS) converts 4-element position vector, POS from
% data space to normalized figure units, using the current axes. The
% position vector has the form [Xo Yo Width Height], as defined here:
%
% web(['jar:file:D:/Applications/MATLAB/R2006a/help/techdoc/' ...
% 'help.jar!/creating_plots/axes_pr4.html'], '-helpbrowser')
%
% [Xf, Yf] = DS2NFU(HAX, X, Y) converts X,Y coordinates from
% data space to normalized figure units, on specified axes HAX.
%
% POSf = DS2NFU(HAX, POS) converts 4-element position vector, POS from
% data space to normalized figure units, using the current axes.
%
% Ex.
% % Create some data
% t = 0:.1:4*pi;
% s = sin(t);
%
% % Add an annotation requiring (x,y) coordinate vectors
% plot(t,s);ylim([-1.2 1.2])
% xa = [1.6 2]*pi;
% ya = [0 0];
% [xaf,yaf] = ds2nfu(xa,ya);
% annotation('arrow',xaf,yaf)
%
% % Add an annotation requiring a position vector
% pose = [4*pi/2 .9 pi .2];
% posef = ds2nfu(pose);
% annotation('ellipse',posef)
%
% % Add annotations on a figure with multiple axes
% figure;
% hAx1 = subplot(211);
% plot(t,s);ylim([-1.2 1.2])
% hAx2 = subplot(212);
% plot(t,-s);ylim([-1.2 1.2])
% [xaf,yaf] = ds2nfu(hAx1,xa,ya);
% annotation('arrow',xaf,yaf)
% pose = [4*pi/2 -1.1 pi .2];
% posef = ds2nfu(hAx2,pose);
% annotation('ellipse',posef)
%% Process inputs
error(nargchk(1, 3, nargin))
aspectRatio = 1.15;
XaspectRatio = 0.69;
% Determine if axes handle is specified
if length(varargin{1})== 1 && ishandle(varargin{1}) && strcmp(get(varargin{1},'type'),'axes')
hAx = varargin{1};
varargin = varargin(2:end);
else
hAx = gca;
end;
errmsg = ['Invalid input. Coordinates must be specified as 1 four-element \n' ...
'position vector or 2 equal length (x,y) vectors.'];
% Proceed with remaining inputs
if length(varargin)==1 % Must be 4 elt POS vector
pos = varargin{1};
if length(pos) ~=4,
error(errmsg);
end;
else
[th,r] = deal(varargin{:});
[x y] = pol2cart([th(1) th(2)],[r(1) r(2)]*aspectRatio);
x = x*XaspectRatio;
if length(x) ~= length(y)
error(errmsg)
end
end
%% Get limits
axun = get(hAx,'Units');
set(hAx,'Units','normalized');
axpos = get(hAx,'Position');
ax = axis(hAx);
axlim =[-ax(4) ax(4) -ax(4)*aspectRatio ax(4)*aspectRatio];
axwidth = diff(axlim(1:2));
axheight = diff(axlim(3:4));
%% Transform data
if exist('x','var')
varargout{1} = (x-axlim(1))*axpos(3)/axwidth + axpos(1);
varargout{2} = (y-axlim(3))*axpos(4)/axheight + axpos(2);
else
pos(1) = (pos(1)-axlim(1))/axwidth*axpos(3) + axpos(1);
pos(2) = (pos(2)-axlim(3))/axheight*axpos(4) + axpos(2);
pos(3) = pos(3)*axpos(3)/axwidth;
pos(4) = pos(4)*axpos(4)/axheight;
varargout{1} = pos;
end
%% Restore axes units
set(hAx,'Units',axun)

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Answers (9)

KarlHoff
KarlHoff on 26 Jun 2020
Edited: KarlHoff on 7 Aug 2020
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)
  3 Comments
Jean-Michel
Jean-Michel on 2 Sep 2020
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 on 21 Aug 2021
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';
  1 Comment
Bill Tubbs
Bill Tubbs on 22 Mar 2023
Edited: Bill Tubbs on 22 Mar 2023
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 on 27 Jun 2017
  8 Comments
Timon Rayis
Timon Rayis on 11 Nov 2019
Any developments with R2019b? annotations with non normalized coordinates like text ?

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marcus yoder
marcus yoder on 23 Aug 2018
Edited: marcus yoder on 23 Aug 2018
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 on 7 Sep 2019
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 on 4 Apr 2020
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 on 14 Aug 2021
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()
  1 Comment
Adam Danz
Adam Danz on 15 Aug 2021
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 on 26 May 2021
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)
  3 Comments
Walter Roberson
Walter Roberson on 1 Jun 2021
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 on 26 Oct 2022
It is absurd that we have to jump through hoops or download submitted code to plot an arrow in data units on a plot.
  2 Comments
Adam Danz
Adam Danz on 27 Oct 2022
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)
Bruce Jackson
Bruce Jackson on 27 Oct 2022
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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