Assign a specific Value to Marker Size in relation with axes

im trying to plot circles horizontally with specific spacing ,adjusting the radius of marker size doesnt work because i want it in relation with axes unit, in micro meter to be specific

here is the code:

w = 10; %e-6 Beam radius in µm
frep = 100e3; % kHz Pulse repetition frequency.
T = 1/frep; %1/s Timelapse between 2 Pulses
vscan = 1000e-3; %m/s Scan velocity
dP = vscan*T;%m Spacing between two Circles
slx = 0.0001; %m Scan length in x-axis.
NxL = int16(slx/dP); % Number of Circles in x-axis
xL = double((0:NxL))*dP; %m
dL = 100e-6; %m Linienabstand
NyL=10;
yL = (0:NyL)*dL; %m
hold on
for ix = 1:NxL %Scan in x-Richtung
    plot(xL(ix),yL(NyL/2),'ro','Markersize',w)
  
end
hold off

[Simon Chan]

Do you want something like the following?

If yes, you can assign the marker size for each plot.

for ix = 1:NxL %Scan in x-Richtung
    plot(xL(ix),yL(NyL/2),'ro','Markersize',100000*xL(ix)+1);
    hold on
end

[Hussam Saddour]

actually not ,i want to adjust the marker size radius in Meters,so that all circles on the same scale as of the axis (not in pixels) which is default to matlab

Answer 1

[Voss]

MarkerSize is in points (not pixels).

You can do a conversion from axes data units (meters in this case) to the width of the axes in points, in order to set the MarkerSize appropriately. This will make the markers have a diameter of 10 microns:

w = 10; %e-6 Beam radius in µm
frep = 100e3; % kHz Pulse repetition frequency.
T = 1/frep; %1/s Timelapse between 2 Pulses
vscan = 1000e-3; %m/s Scan velocity
dP = vscan*T;%m Spacing between two Circles
slx = 0.0001; %m Scan length in x-axis.
NxL = int16(slx/dP); % Number of Circles in x-axis
xL = double((0:NxL))*dP; %m
dL = 100e-6; %m Linienabstand
NyL=10;
yL = (0:NyL)*dL; %m
hold on

ax = gca();
ax_units = get(ax,'Units');
set(ax,'Units','points');
ax_pos = get(ax,'Position')

ax_pos = 1×4

54.5527 34.6400 325.2182 256.6509

set(ax,'Units',ax_units);

h = zeros(1,NxL);
for ix = 1:NxL %Scan in x-Richtung
    h(ix) = plot(xL(ix),yL(NyL/2),'ro');%,'Markersize',w)
end

xl = get(ax,'XLim');
w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3)

w_pts = 32.5218

set(h,'MarkerSize',w_pts);

hold off

Of course whenever the width of the axes or the XLim change, you'd have to update the MarkerSize accordingly.

[Hussam Saddour]

that did it ! thank you ,there ist still a problem whenever i maximize the plot window the scale extends according to my monitor but the circles stay the same size, that makes them seem smaller according to the new scaling ,why is that?

w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3);

that looks like adjusting the scale of circles according to the axes, so you divided m/m and multiplied by points which ax_pos(3) i guess..... can you explain what is ax_pos(3)?

[Voss]

Positions of certain graphics objects in MATLAB are 4-element vectors of the form [left bottom width height], so ax_pos(3) refers to the width of the axes.

Regarding the MarkerSize not updating when the window is maximized, this is a limitation I stated in my answer: "Of course whenever the width of the axes or the XLim change, you'd have to update the MarkerSize accordingly."

In order to have the MarkerSize always stay accurate, it will be convenient to put the relevant code from my answer into a function:

function update_marker_size(ax,h,w)

% inputs: ax: handle of axes containing h
%         h: handle of line(s) to update
%         w: width (in microns) of marker

ax = gca();
ax_units = get(ax,'Units');
set(ax,'Units','points');
ax_pos = get(ax,'Position');
set(ax,'Units',ax_units);

xl = get(ax,'XLim');
w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3);
set(h,'MarkerSize',w_pts);

end

Then call that function when the figure's size changes (e.g., from within its SizeChangedFcn) or when the axes XLimits change (you might set the PostActionCallback of the zoom() and pan() objects in the figure for this, or add a listener to the XLimits property of the axes).

For example, to get the marker to update when the figure's size changes, you can do this:

frep = 100e3; % kHz Pulse repetition frequency.
T = 1/frep; %1/s Timelapse between 2 Pulses
vscan = 1000e-3; %m/s Scan velocity
dP = vscan*T;%m Spacing between two Circles
slx = 0.0001; %m Scan length in x-axis.
NxL = int16(slx/dP); % Number of Circles in x-axis
xL = double((0:NxL))*dP; %m
dL = 100e-6; %m Linienabstand
NyL=10;
yL = (0:NyL)*dL; %m

f = figure();
hold on
h = zeros(1,NxL);
for ix = 1:NxL %Scan in x-Richtung
    h(ix) = plot(xL(ix),yL(NyL/2),'ro');%,'Markersize',w)
end

set(f,'SizeChangedFcn',@scf);
scf(f);


function scf(fig,~)
    ax = get(fig,'CurrentAxes');
    lines = findobj(ax,'Type','line');
    w = 10; %e-6 Beam radius in µm
    update_marker_size(ax,lines,w);
end


function update_marker_size(ax,h,w)

% inputs: ax: handle of axes containing h
%         h: handle of line(s) to update
%         w: width (in microns) of marker

ax = gca();
ax_units = get(ax,'Units');
set(ax,'Units','points');
ax_pos = get(ax,'Position');
set(ax,'Units',ax_units);

xl = get(ax,'XLim');
w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3);
set(h,'MarkerSize',w_pts);

end

[Hussam Saddour]

You are a beast, thats exactly what i was looking for

[Voss]

Excellent!

[Hussam Saddour]

i'm having now another similar issue ,i'm trying to plot the circles in both x,y axis ,but it seems like the y axis needs also the same axis manipulation, i got confused actually, can you please look that up?

% w = 20; %e-6 Strahlradius in µm
% frep = 100e3; % kHz Pulsfolgefreq.
% T = 1/frep; %1/s zeitl. Abstabd zw. 2 Pulsen
% vscan = 1000e-3; %m/s
prompt=  {'Strahlradius eingeben in \mum:', ...
    'Pulsfolgefrequenz eingeben in kHz:', ...
    'Scangeschwindigkeit eingeben in mm/s:', ...
    'Scanlänge eingeben in \mum' ...
    'Linienabstand in\mum','Zahl der Linien'};
title = 'Parametereingabe';
dimension=[1 60];
default = {'5','10','100','100','10','5'};
opts.Interpreter = 'tex';
answer = inputdlg(prompt,title,dimension,default,opts);
w=str2num(answer{1})*2;
frep=str2num(answer{2});
vscan=str2num(answer{3})/1000;
slx = str2num(answer{4})/(10^6);
dL = str2num(answer{5})/(10^6);
NyL=str2num(answer{6});

T=1/frep/1000; % 1/kHz
dP = vscan*T;%m
%slx = 0.0001; %m Scanlänge in x-Rtg.
NxL = int16(slx/dP); %Zahl der Punkte in x-Rtg
xL = double((0:NxL))*dP; %m 

%dL = 10e-6; %m Linienabstand
%NyL = 5; %Zahl der Linien in y-Richtung

yL = (0:NyL)*dL; %m 
hold on

ax = gca();
ax_units = get(ax,'Units'); %Verwendete achsen einheit aufrufen
set(ax,'Units','points'); %Achsen Einheit auf Points umwandeln
ax_pos = get(ax,'Position'); %Achsen position aufrufen
set(ax,'Units',ax_units); 
h=zeros(NyL,NxL); %Plot funktion definieren
for ix = 1:NxL %Scan in x-Richtung
    for iy= 1:NyL %Scan in y-Richtung
        
        h(ix,iy)=plot(xL(ix),yL(iy),'ro');%,'Markersize',w)
    end
    
end
xl = get(ax,'XLim');
w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3); %(m/m) *Points d.h. w_pts=w*faktor
set(h,'MarkerSize',w_pts);
hold off

[Voss]

It may be sufficient to force the axes x- and y-limits to be on the same scale using axis equal:

% % w = 20; %e-6 Strahlradius in µm
% % frep = 100e3; % kHz Pulsfolgefreq.
% % T = 1/frep; %1/s zeitl. Abstabd zw. 2 Pulsen
% % vscan = 1000e-3; %m/s
% prompt=  {'Strahlradius eingeben in \mum:', ...
%     'Pulsfolgefrequenz eingeben in kHz:', ...
%     'Scangeschwindigkeit eingeben in mm/s:', ...
%     'Scanlänge eingeben in \mum' ...
%     'Linienabstand in\mum','Zahl der Linien'};
% title = 'Parametereingabe';
% dimension=[1 60];
default = {'5','10','100','100','10','5'};
% opts.Interpreter = 'tex';
% answer = inputdlg(prompt,title,dimension,default,opts);
answer = default;
w=str2num(answer{1})*2;
frep=str2num(answer{2});
vscan=str2num(answer{3})/1000;
slx = str2num(answer{4})/(10^6);
dL = str2num(answer{5})/(10^6);
NyL=str2num(answer{6});

T=1/frep/1000; % 1/kHz
dP = vscan*T;%m
%slx = 0.0001; %m Scanlänge in x-Rtg.
NxL = int16(slx/dP); %Zahl der Punkte in x-Rtg
xL = double((0:NxL))*dP; %m 

%dL = 10e-6; %m Linienabstand
%NyL = 5; %Zahl der Linien in y-Richtung

yL = (0:NyL)*dL; %m 
hold on

ax = gca();
ax_units = get(ax,'Units'); %Verwendete achsen einheit aufrufen
set(ax,'Units','points'); %Achsen Einheit auf Points umwandeln
ax_pos = get(ax,'Position'); %Achsen position aufrufen
set(ax,'Units',ax_units); 

h=zeros(NyL,NxL); %Plot funktion definieren
for ix = 1:NxL %Scan in x-Richtung
    for iy = 1:NyL %Scan in y-Richtung
%         h(ix,iy)=plot(xL(ix),yL(iy),'ro');%,'Markersize',w)
        h(iy,ix) = plot(xL(ix),yL(iy),'ro');%,'Markersize',w)
    end
end

axis equal
xl = get(ax,'XLim');
w_pts = w*1e-6/(xl(2)-xl(1))*ax_pos(3); %(m/m) *Points d.h. w_pts=w*faktor
set(h,'MarkerSize',w_pts);
hold off

Or you may need to allow different x- and y-scales, in which case you can plot your own circles instead of using a marker:

figure();
hold on

t = linspace(0,2*pi,50);
x_circle = w/2*1e-6*cos(t);
y_circle = w/2*1e-6*sin(t);

h=zeros(NyL,NxL); %Plot funktion definieren
for ix = 1:NxL %Scan in x-Richtung
    for iy = 1:NyL %Scan in y-Richtung
        h(iy,ix) = plot(xL(ix)+x_circle,yL(iy)+y_circle,'r');
    end
end
hold off

Since the data are equally spaced with the same spacing in both x and y, then these are in fact circles (in data units) that look like ellipses if the x- and y-scale of the axes are different.

[Hussam Saddour]

i know that if i ask this it might be against community rules ,but what is the best way of learning all these commands, i'm actually a little bit lost where should i begin

[Voss]

I don't think it's against the rules to ask for help learning MATLAB - in fact, that's the purpose of MATLAB Answers.

I can only speak from my own experience learning MATLAB, but for me the best way to learn new MATLAB commands is to read the MATLAB documentation and try the commands out myself on the command line or in a simple script until they make sense to me. I might have to make several attempts, trying different things until I get it to do what I'm trying to do. It's all about experimentation and learning from what I've tried - seeing (and remembering) what works and what doesn't work.

In addition to experimentation/trial-and-error, there are structured courses you may be interested in:

https://matlabacademy.mathworks.com/

Remember (to paraphrase a quote attributed to Niels Bohr): "An expert is someone who has made all the mistakes that can be made, in a very narrow field." So try things yourself, post a question here if you get stuck, and someone who has made the same mistake before will help you out.