Change marker size in legends of already plotted figures

Hi everyone,

I do not know why but whenever I save some plots in .fig format from Matlab, the size of the markers of the legend is always changed. That means that, if I open again the .fig file in Matlab, the size of the marker is just set to a default (tiny) size.

I know how to change the marker size in plotting phase, but I do not know how to access it again in already plotted figures.

I tried accessing the handle of the legend with

 hLegend = findobj(gcf, 'Type', 'Legend')

and then trying accessing the children of type 'line' to then change the 'Markersize' (as explained here https://stackoverflow.com/questions/28741747/change-the-symbols-size-in-matlab-legend)

 ch = findobj(get(hLegend,'children'), 'type', 'line');

but I fail in doing this as there is no this kind of 'Children'.

Any suggestion please?

Thanks and best regards

Answer 1

[Elizabeth Case]

I'm using Matlab 2021a. My case use is a bit different than most here but thinking this might prove useful to someone. I am plotting data in a loop, and want the size of the marker in the legend to match the markersize on the scatter plot. I only wanted certain entries to show up in the legend to avoid repetition (in this case, markersize is determined by year).

Note that this does throw warnings, but still seems to work.

Most relevant code for setting legend marker size is marked by %------> <------%

%create data structure -- 3 measurements at 3 locations over multiple years

x = linspace(1,10,12);

y = linspace(0,1,12);

z = linspace(-4,0,12);

names = ['a';'b';'c';'a';'b';'a';'b';'a';'b';'c';'a';'b']; %data

years = [1990,1990,1990,1992,1992,1995,1995,2000,2000,2000,2005,2005]; %data

for i = 1:length(x)

struct(i).x= x(i);

struct(i).y= y(i);

struct(i).z= z(i);

struct(i).name = names(i);

struct(i).year = years(i);

end

%create markersize structure based on year

uyrs = unique([struct.year]); %array of unique years

sz = linspace(10,35,length(uyrs)); %array of sizes, same length as year

for i=1:length(uyrs)

szplot(i).year = uyrs(i);

szplot(i).sz = sz(i);

end

%create color structure based on name

uname = unique({struct.name}); %array of unique names

cols = ['#8c510a';'#fc8d59';'#d8b365'];

for i=1:length(uname)

cplot(i).name = uname{i};

cplot(i).color = cols(i,:);

end

%%

n=1; %keeps track of number of years

figure; tiledlayout(1,2);

for ind=1:length(struct)

nexttile(1)

hold on;

if strcmp(struct(ind).name,'a') %conditional for x data I want to show in legend (1 per year)

cc = cplot(matches({cplot.name},struct(ind).name)).color; %finds correct color based on conditional

size = szplot(n).sz;

year = szplot(n).year;

p1(n) = scatter(struct(ind).x,struct(ind).y,size,'MarkerFaceColor',cc,'DisplayName',num2str(year)); %by giving it a handle (p1) & DisplayName, ensures desired labeled data shows up in legend

n=n+1; %keeps track of number of years

end

cc = cplot(matches({cplot.name},struct(ind).name)).color; %matches color to name

size = szplot([szplot.year]==struct(ind).year).sz; %matches size to year

scatter(struct(ind).x,struct(ind).y,size,'MarkerFaceColor',cc); %plot rest of x data

nexttile(2)

hold on;

scatter(struct(ind).z,struct(ind).y,size,'MarkerFaceColor',cc); %plot z data

drawnow;

%------> <------%

if ind==length(struct)

[lg1,obj]=legend(p1,'Orientation','Horizontal'); %creates obj to find marker size at end of plotting

end

%------> <------%

end

%------> <------%

objhl = findobj(obj, 'type', 'patch'); % finds objects in legend of type patch (e.g. marker)

for i = 1:length(objhl) %iterate through patches to set each size individually

set(objhl(i), 'Markersize', sqrt(szplot(i).sz)); % set marker size according to size structure

end

%------> <------%

lg1.Layout.Tile = 'North';

Answer 2

[per isakson]

Short answer: The behavior described in the stackoverflow thread is based on an undocumented feature.

I've reproduce your observations with the following script, which is based on the stackoverflow thread.

%%
plot(1:10, 'o-'); 
hold on
plot(5:12, 'r*--'); %// example plots
[ lgd, objh ] = legend({'one plot', 'another plot'}, 'location', 'NorthWest', 'Fontsize', 14);
%% // set font size as desired
objhl = findobj( objh, 'type', 'line' ); %// objects of legend of type line
set( objhl, 'Markersize', 18 ); %// set marker size as desired
%%
savefig('matte.fig');
delete( gcf )
%%
openfig('matte.fig')

I use R2018b. The syntax used to call legend with two output arguments, [ lgd, objh ] = legend(___), is not documented. Neither is it documented in R2019a.

Furthermore, I found these two lines in legend.m

% Legend no longer supports more than one output argument
% Warn the user and ignore additional output arguments.

objh used in the stackoverflow thread is not a legend object.

>> lgd
lgd = 
  Legend (one plot, another plot) with properties:

         String: {'one plot'  'another plot'}
       Location: 'northwest'
    Orientation: 'vertical'
       FontSize: 14
       Position: [0.1494 0.7758 0.2679 0.1250]
          Units: 'normalized'
  Show all properties
  
>> objh
objh = 
  6×1 graphics array:

  Text    (one plot)
  Text    (another plot)
  Line    (one plot)
  Line    (one plot)
  Line    (another plot)
  Line    (another plot)  

Maybe undocumentedmatlab has something to say on this. I found this comment

Tom Heine says: March 9, 2016 at 12:01 am

[...] For some reason, when I save the figure as a .fig, the legend title isn’t saved.

My guess:

• savefig doesn't save the legend
• openfig creates a default legend (How does it know it should do that?)

[MatteP]

Thanks for your reply.

So I guess there is no solution so far, except re-running the script to plot figures again, using the undocumented feature reported in stackoverflow.

What is even more bizzare is that once I open the figure .fig, I am able to retrieve (and edit) the entries of the legend, their fontsize, the marker shape but not marker size.

Best regards,

MatteP

[per isakson]

"even more bizzare" By design Matlab exposes a limited number of properties to the user. In this case fontsize, but not markersize.

Graphics Handles Are Now Objects, Not Doubles says:

[...] Starting in R2014b, graphics handles are object handles of various types, depending on the class of the graphics object. Graphics objects now behave like other MATLAB® objects.

See Save and Load Process for Objects although "behave like other" is not the same as "are".

"[...] guess there is no solution so far" There are two approaches, which might be worth trying

• Modify the Save and Load Process
• A Java-solution, see Undocumented Matlab and Undocumented Secrets of Matlab-Java Programming

Answer 3

[Mona Lacatusu]

For me it worked to change the marker size from a loaded image in the following way:

image1 = hgload('image_path/file_name.fig');
figure
h(1)=subplot(2,1,1);
copyobj(allchild(get(image1,'CurrentAxes')),h(1));
% Add legends
[~, objh]=legend(h(1),'Data1','Data2','Data3','Location','best')
objhl = findobj(objh, 'type', 'Line'); % objects of legend of type Line
set(objhl, 'Markersize', 40); % set marker size as desired

[Carl Witthoft]

Mona, what version of MATLAB are you using to get that success? Nobody I've found yet can get this to work with any 2019 version