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GUI with moving marker

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Thomas
Thomas on 10 Oct 2012
Hello
I have programmed an GUI with two sliders. According to the slider movement, a marker should move along a given graph. I have realised this with following code:
% --- Executes on slider movement.
function slider1_Callback(hObject, eventdata, handles)
% hObject handle to slider1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'Value') returns position of slider
% get(hObject,'Min') and get(hObject,'Max') to determine range of slider
x=get(hObject,'value')
x_round=round(x)
set(hObject,'value',x_round)
y=(DataVector(x_round,1))
line(x_round,y,'linestyle','none','marker','o','markeredgecolor','r');
My problem is, that the marker does not vanish while it gets new coordinates from the slider. Thus I get multiple markers along the graph. My first idea was to delete the line-element:
delete(h);
x=get(hObject,'value')
x_round=round(x)
set(hObject,'value',x_round)
y=(DataVektor(x_round,1))
h=line(x_round,y,'linestyle','none','marker','o','markeredgecolor','r');
But it doesn´t work, with this i do not get an marker anymore. I have no idea to solve this problem, please help.
  2 Comments
Thomas
Thomas on 11 Oct 2012
Yes, you are right. I want to create a point moving along a graph.
The problem with set(...) is, that the commands (set and line) are executed while the usage of the slider. That´s the reason why the marker will be drawn again and not will be updated. Do you have an idea how I can avoid this problem?

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Accepted Answer

Dan K
Dan K on 11 Oct 2012
A couple of different options: Perhaps the simplest (although not very speed efficient) is to apply a tag to the marker when you first create it, then use findobj to locate it in the callback.
Do this when you're first creating the figure
hMarker=line(x_round,y,'linestyle','none','marker','o','markeredgecolor','r','Tag','MyMarker');
Then in your callback hMarker_local = findobj(gcf,'Tag','MyMarker'); set(hMarker_local,'Xdata',newX,'YData',newY);
Alternatively you can add extra parameters to your slider callback, one of which is the original hMarker.
A third choice is to nest your callback inside of the function where you're making your plot, in which case the callback has access to variables defined in the parent function, including hMarker.
Hope this helps. Dan

More Answers (3)

Sachin Ganjare
Sachin Ganjare on 10 Oct 2012
You can try 'cla' function.
Hope it helps!!!
  1 Comment
Thomas
Thomas on 11 Oct 2012
Thank you for your reply!
It works, but not in a way it should.
Because it deletes not only the marker(line-element), it also deletes the drawn graph. This is no huge problem, because the graph can be drawn new each time the slider moves.
The bigger problem is, that the marker related to the second slider is also erased while moving slider number one...

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Robert Cumming
Robert Cumming on 10 Oct 2012
you need to store the handle to the marker, e.g.
d = dialog ( 'windowstyle', 'normal' );
ax = axes ( 'parent', d, 'nextplot', 'add' );
x = [-pi:0.1:pi];
y = sin(x);
plot ( ax, x, y );
for i=1:length(x)
h = plot ( ax, x(i), y(i), 'rs' );
pause ( 0.1 );
delete ( h );
end
  1 Comment
Thomas
Thomas on 11 Oct 2012
Thank you for your reply I tried to realize your advice, but I am an absolutely MATLAB novice and so it doesn´t work. Do I have to program the command lines in the callback-function of the slider, like I did?
Please take a look at my code.
% --- Executes on slider movement.
function [hS1]=slider1_Callback(hObject, eventdata, handles)
% hObject handle to slider1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'Value') returns position of slider
% get(hObject,'Min') and get(hObject,'Max') to determine range of slider
load Data.mat
x=get(hObject,'value');
x_round=round(x)
set(hObject,'value',x_round);
y=(L_KnieAngle3D_orig(x_round,1));
line(x_round,y,'linestyle','none','marker','o','markeredgecolor','r');
h=line(x_round,y,'linestyle','none','marker','o','markeredgecolor','r');
delete(h);

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Image Analyst
Image Analyst on 11 Oct 2012
Edited: Image Analyst on 11 Oct 2012
Call this function right before you draw the "current" line to erase all previous lines on your axes:
%=====================================================================
% Erases all lines from the current axes.
% The current axes should be set first using the axes()
% command before this function is called,
% as it works from the current axes, gca.
function ClearLinesFromAxes()
axesHandlesToChildObjects = findobj(gca, 'Type', 'line');
if ~isempty(axesHandlesToChildObjects)
delete(axesHandlesToChildObjects);
end
return; % from ClearLinesFromAxes
  2 Comments
Image Analyst
Image Analyst on 11 Oct 2012
It doesn't do that for me, and I can't see anything in the code that would get rid of the whole graph. For me, it leaves the graph/plot area and just removes the lines. Of course if you plotted a line with plot() it will blow away that also. In that case, you'll have to keep track of which handle is the handle of the curve you plotted and don't delete that one.
handleToKeep = plot(......)

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