How to get the exact position of a plotted point?

Hi,

I've plotted a graph and additionally marked a specific point. A 'ButtonDownFcn' is assigned to the point, to enable user interaction.

By clicking onto the point I would like to receive its exact x and y coordinates.

My approach:

function getPlotPointCoord()
clc;
figure(1);

x = -2*pi:0.05:+2*pi;

subplot(1,2,1);
hold on;

plot(x, sin(x));

% plot point at (x=0, y=0)
plot(0, sin(0), 'bx', 'ButtonDownFcn', @getPoint);

      function getPoint(varargin)
          currentPoint = get(gca, 'CurrentPoint');
          fprintf('Hit Point! Coordinates: %f, %f \n', ... 
                   currentPoint(1), currentPoint(3));
      end

end

The call _get(gca, 'CurrentPoint') for instance returns the following values:

Hit Point! Coordinates: 0.000000, 0.002924 
Hit Point! Coordinates: 0.000000, 0.002924 
Hit Point! Coordinates: 0.000000, 0.002924 
Hit Point! Coordinates: -0.106952, -0.008772 
Hit Point! Coordinates: 0.106952, -0.014620

Is there a way to receive the true values (x=0, y=0) of the 'button' instead of the current (most likely) mouse-coordinates?

Thank you!

Answer 1

[Fangjun Jiang]

What do you mean? You want the x/y value of the data points? You can get that from menu Tools->Data Cursor and then click along the curve.

[BF83]

Thanks for your answer.

I don't want to use the data cursor in this special case. I wonder if there is a easy way to obtain these coordinates just by using the 'ButtonDownFcn' assigned to the specific point.

[Fangjun Jiang]

Okay, then I guess you could write a few more lines to compare the current point to see which data point is the closest.

[Fangjun Jiang]

Wait a minute! Can't you do this?!

plot(0, sin(0), 'bx', 'ButtonDownFcn', 'disp([0,sin(0)])');

[BF83]

Ok! Perhaps I can pass the coordinates to a function, for instance to @getPoint?

[Fangjun Jiang]

Yes. Like:

plot(0, sin(0), 'bx', 'ButtonDownFcn', 'getPoint(0,sin(0))')

[BF83]

Okay, great. I'm sure that it will solve my problem. I'm gonna test it tomorrow.

Thank you for coming up with this easy and elegant solution.

[Trishank Sharma]

Hi what if I have a set of 60 points (n=60), where x and y are real and imaginary parts of a complex number Z. Can I know the point number (the 'n'th point) beside the coordinates or do I have to do it manually?

[maziar]

Thanks

Answer 2

[BF83]

A working example for completion:

function getPlotPointCoord()
clc;
figure(1);

x = -2*pi:0.05:+2*pi;

subplot(1,2,1);
hold on;

plot(x, sin(x));
plot(0, sin(0), 'bx', 'ButtonDownFcn', {@getPoint, 0, sin(0)});

      function getPoint(src, eventdata, x, y)
          currentPoint = get(gca, 'CurrentPoint');
          fprintf('Hit Point! Mouse Coordinates: %f, %f \n', ...
                   currentPoint(1), currentPoint(3));
          fprintf('Hit Point! Real Coordinates: %f, %f \n', x, y);
      end

end

Answer 3

[Tarami Readus]

Where in the code does he add the marker, and to what specific point? I would like to know how to do that

Answer 4

[Adam Albayati]

function getPlotPointCoord()

clc;

figure(1);

x = -2*pi:0.05:+2*pi;

subplot(1,2,1);

hold on;

plot(x, sin(x));

% plot point at (x=0, y=0)

plot(0, sin(0), 'bx', 'ButtonDownFcn', @getPoint);

function getPoint(varargin)

currentPoint = get(gca, 'CurrentPoint');

fprintf('Hit Point! Coordinates: %f, %f \n', ...

currentPoint(1), currentPoint(3));

end

end