Data Cursor Position Issue

2011 6 20
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I have a number of bar charts in a figure window and each has the datacursormode enabled. When I click on a bar with a negative value, a y position of 0 is returned. It seems to work fine for bars of positive values so I'm somewhat perplexed.

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Richard
Richard 2011-6-20
A simple example ( bar(-5:5) ) works OK for me. Do you have some code that reproduces the problem? Also, which version are you using?
Conor
Conor 2011-6-28
Im using 7.4.0
main program goes through a complex set of calculations to determine values to plot and calls the function below.
function BarPlots(Radii, RDI,...)
global H; %H is a global variable containing handles to multiple uicontrols and plots in a gui
...
H.hRDI=subplot('position',[3/6 b+h/2.5 w h/1.575]);% b w h]);
bar(Radii,RDI)
% After main progam has run, using the Data Cursor tool and clicking on a
% plot triggers this callback function
function CT = DataCursorClick(empty,eventdata)
global H;
set(H.hContourPlot,'fill','on')
P = get(eventdata,'Position');
T = get(eventdata,'Target');
G = get(T,'Parent');
if % structure to determine which axes has been clicked on
...
elseif G == H.hRDI
CT = {['Radius: ',num2str(P(1))],['RDI: ',num2str(P(2))]};
elseif
...
end
The problem seems to be coming from
P = get(eventdata,'Position');
When the y value, P(2) is negative on the bar plot, 0 is returned for P(2).
Thanks for the help!!

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Richard
Richard 2011-8-3

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Conor, sorry for the delay, I didn't notice your comment until today.
This is a bug in older versions of MATLAB. I can see the issue in v7.4 for a simple bar chart with a standard data cursor:
bar(-5:5)
For all of the bars, the data cursor is being placed at the maximum Y value instead of at the maximum absolute Y value, and for negative bars this is always 0 instead of being -5, -4, -3 etc. This incorrect value is also passed into your custom datatip function. There is no easy way to directly get the correct Y (RDI) value, however you could look up the X (Radii) value in the target's XData and then use the corresponding YData value:
xd = get(T, 'XData');
[~,idx] = min(abs(xd-P(1)));
yd = get(T, 'YData');
ThisRDI = yd(idx);
This bug has been fixed in a more recent version of MATLAB - I believe from R2008b onwards, so upgrading is another option.

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Conor
Conor 2011-8-4
Thanks Richard
I did end up using the XData and YData of the plots to display the correct value. Only issue with that is the actual data cursor remians at the 0 location for negative bars. I haven't played with it in a few weeks now, but I'll try changing the data cursors position in the callback next.
Thanks again!

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