# How to draw an arrow using non normalized coordinates?

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##### 4 Comments

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)

### Answers (9)

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
on 2 Sep 2020

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
on 22 Mar 2023

Edited: Bill Tubbs
on 22 Mar 2023

Walter Roberson
on 27 Jun 2017

##### 8 Comments

Timon Rayis
on 11 Nov 2019

Any developments with R2019b? annotations with non normalized coordinates like text ?

Adam Danz
on 11 Nov 2019

Check out release notes for any updates on any release.

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
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)))

##### 0 Comments

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

##### 0 Comments

Marc Compere
on 14 Aug 2021

##### 1 Comment

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.

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

Vitaly Fedoseev
on 1 Jun 2021

Where should the line

delete(gca)

be inserted in the code above?

Walter Roberson
on 1 Jun 2021

Bruce Jackson
on 26 Oct 2022

##### 2 Comments

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
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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