Asked by MathWorks Support Team
on 10 Jul 2013

I have a few MATLAB figures, but no MATLAB code associated with it. I want to extract the data from the curves in the figures.

Answer by MathWorks Support Team
on 8 Aug 2019 at 4:00

Accepted Answer

This example shows how to extract data from a MATLAB figure.

If the figure is stored in a file, such as 'example.fig', then open the figure file using 'openfig'. Assign the Figure object to the variable 'fig'.

fig = openfig('example.fig');

If the figure is already open, then use 'gcf' to access the Figure object and assign it to the variable 'fig'.

fig = gcf;

There are several ways to access the data for the plotted graphics objects. You can use the Children property or you can use 'findobj'.

Use Children Property

Access the plotted graphics objects through the Children properties. The Axes objects are children of the figure. The plotted graphics objects are typically children of the Axes object.

axObjs = fig.Children

dataObjs = axObjs.Children

The 'dataObjs' array that appears in the Command Window indicates the types of graphics objects in the axes. Different graphics objects store data differently. For example, Line objects store the data in the 'XData', 'YData', and 'ZData' properties. If the first element in 'dataObjs' is a Line object, then access its data using this code.

x = dataObjs(1).XData

y = dataObjs(1).YData

z = dataObjs(1).ZData

If the figure contains other types of graphics objects, then use the appropriate properties to access the data. For a list of graphics objects and their properties, see:

Use findobj Function

Alternatively, you can find all the graphics objects in a figure with a certain data property. For example, find all graphics objects that have a 'YData' property. Then access the 'YData' values for the first object.

dataObjs = findobj(fig,'-property','YData')

y1 = dataObjs(1).YData

Answer by Felipe Bittencourt de Souza
on 15 Dec 2017

I was having the same error message mentioned before: "Error using get Conversion to double from cell is not possible."

I solved this issue with Walter Roberson's answer, using the following code:

open('example.fig');

a = get(gca,'Children');

xdata = get(a, 'XData');

ydata = get(a, 'YData');

zdata = get(a, 'ZData');

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Answer by Michael
on 13 Jun 2014

Edited by Michael
on 13 Jun 2014

I tried to follow these steps, but when I got to objTypes = get(dataObjs, 'Type') I got this error:

Error using get Conversion to double from cell is not possible.

I don't know Matlab's figure format and I'm not familiar with Matlab's API for accessing figure data. I'm not sure what this error means.

If anyone else happens upon this: Matlab figures are just ".mat" files. The scipy.io library in Pylab can read Matfiles into numpy structures using the 'loadmat' command. One can then browse the figure data in Python and locate the data.

Edit: one can also step through the figure data in Matlab, by loading the figure using the command "s=load('Figure.fig','-mat')". The solutions using "get" never really worked for me. I think this is because every figure is structured slightly differently, and people are posting solutions that work for a particular figure, but don't generalize well. If you just grab the figure data structure, you can step through it and find what you need.

Cameron
on 30 Jun 2014

I managed to get a similar error when running the line:

dataObjs = get(axesObjs, 'Children');

I'm not entirely sure why it's unable to access the handles using the 'get' method, but changing the code to

dataObjs = axesObjs.Children;

seems to have done the trick. Hope this helps.

Julia Mödl
on 26 Jun 2015

i tried all answers and always get an error. i got the converting to double error too and with the last answer i got this error: No appropriate method, property, or field 'Children' for class 'matlab.graphics.Graphics'.

Error in daten_auslesen (line 5) dataObjs = axesObjs.Children; I dont know how to fix this code, so id be happy to get some help.

Walter Roberson
on 12 Nov 2016

Julia Mödl : you would have that problem if the axes you were looking at was a placeholder rather than an axes object.

all_axesObjs = findobj(h, 'type', 'axes');

now only examine the items in all_axesObjs.

Or use what I posted earlier,

lineObjs = findobj(dataObjs, 'type', 'line');

xdata = get(lineObjs, 'XData');

ydata = get(lineObjs, 'YData');

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Answer by Yair Altman
on 21 May 2018

Edited by Yair Altman
on 21 May 2018

Note that the official MathWorks answer above relies on opening and displaying the figure (using the open() function) before extracting its contents. This is both slow and potentially unwanted (we don't always want to display the figures), especially if we're looping over many FIG files.

Instead, users can directly read and analyze the *.fig file by loading it into Matlab memory using the load() function, since *.fig files are basically simple MAT files with a .fig (rather than .mat) file extension.

Fortunately, the internal format of these files has changed very little over the years - a few fields have changed their name, but the basic file data structure remained the same. So essentially the same code can be used to extract data from .fig files created a decade ago, as well as the latest Matlab release.

Note that the fact that FIG files are basically just MAT files is an undocumented feature of Matlab, and so it might change one day. But for now it is a very handy feature to use.

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Answer by Parrish.Ch
on 23 Jul 2015

Hi all,

I noticed people were having issues with getting the following error when attempting to run:

objsTypes = get(dataObjs,'Types')

Error using get Conversion to double from cell is not possible.

I think I have a solution to the issue. For surface plots, I noticed that the children of an axes object (so dataObjs in this case) may contain a subgroup that is a complex cell. You have to use cell2struct to break this cell into it's basic pieces so you can extract the data. Here is the code for my solution:

h = gcf;

axes = get(h,'Children');

dataObjs = get(axes,'Children');

Props = cell2struct(dataObjs,'SurfaceProps',2);

SurfaceData = Props.SurfaceProp;

XData = SurfaceData(3,1).XData;

YData = SurfaceData(3,1).YData;

ZData = SurfaceData(2,1).ZData;

**Before you just copy paste this code, there are a few important things to know.

My variable dataObjs is a 2x1 cell. The first index in the cell is empty but the second index is a 3x1 Group. I have to convert this cell group to a structure that can then be used to access my data. From there, I use cell2struct on the second index to accomplish this. The cell2struct generates a property that is named in the second argument of the cell2struct command ('SurfaceProp' for me). Props.SurfaceProp extracts the various "children" from the 3x1 Group in dataObjs. In my case, I have three objects in Props.SurfaceProp: two light objects and one surface object. The surface object contains the x, y, and z data. My surface object is the third index in the matrix generated by Props.SurfaceProp, so I use SurfaceData(3,1).XData to access the XData handle that is in the third index of the SurfaceData array.

I hope this helps!

Houghton
on 12 Nov 2016

I tried your code. But I got an error.

Undefined function 'cell2struct' for input arguments of type 'matlab.graphics.primitive.world.Group'.

- I typed

which cell2struct

- I got the answer

built-in (/Applications/MATLAB_R2014b.app/toolbox/matlab/datatypes/@cell/cell2struct) % cell method >>

what should I do?

Thanks

Walter Roberson
on 12 Nov 2016

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Answer by Daniel Ares
on 19 Jun 2017

Hi to everybody,

i can´t run it, i get this error, with this code.

open('Force vs Time.fig');

h = gcf; %current figure handle

axesObjs = get(h, 'Children'); %axes handles

dataObjs = get(axesObjs, 'Children'); %handles to low-level graphics objects in axes

lineObjs = get(dataObjs, 'type', 'line'); %type of low-level graphics object

xdata = get(lineObjs, 'XData'); %data from low-level grahics objects

ydata = get(dataObjs, 'YData');

zdata = get(dataObjs, 'ZData');

Thanks

Jan
on 19 Jun 2017

You forgot to mention the error you get. But please remove this message and post it as a new question, because this is the section for answers. Thanks.

You will get an answer like:

lineObjs = get(dataObjs, 'type', 'line')

get() does not accept 3 inputs. Do you mean:

lineObjs = findobj(dataObjs, 'type', 'line')

? Note: Please delete this message even if this solves your problem.

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Answer by Stephen Becker
on 25 Jun 2018

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