Using current points instead of ginput to get locations on axes

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Hi. I am currently using ginput to select two points on an image to then draw a line. The problem is that my image is mainly black with white spots and the cross hairs for ginput are black, so its hard to use.
So after investigating I thought I could use the following
axes(handles.axes4); %my image is on axes4
cp = get(handles.axes4,'CurrentPoint')
x = cp(1,1)
y = cp(1,2)
plot(x,y,'ro'); drawnow;
The point I selected on is the red circle below at coordiantes 244, 605 on that axes. However, the returned values of cp are
cp =
1.0e+03 *
-1.2142 1.3601 5.6639
-1.2142 1.3601 0.0000
What do these cp values correspond to, I thought x = cp(1,1) and y = cp(1,2), but they don't seem to be.
Also is this the best way or is there another way?
Thanks Jason

Accepted Answer

Walter Roberson
Walter Roberson on 3 Oct 2017
cp(2,:) is for the back points, which is more meaningful for 3D.
The values are in axes data units.
"The two points indicate the location of the last mouse click, unless there is a WindowButtonMotionFcn callback defined for the figure. If the WindowButtonMotionFcn callback is defined, then the points indicate the last location of the mouse pointer."
My speculation is that you do not have WindowButtonMotionFcn active and that your last click was to the left of the current mouse position.
  2 Comments
Jason
Jason on 3 Oct 2017
So I would use something like this:
axes(handles.axes4)('WindowButtonDownFcn',@myMouseclickFunction)
Jason
Jason on 3 Oct 2017
I think I've done it, I just put a waitforbuttonpress!!
w = waitforbuttonpress
if w == 0 %0 for mouse click, 1 for button press
disp('Button click')
cp = get(gca,'CurrentPoint')
x = cp(1,1)
y = cp(1,2)
plot(x,y,'ro'); drawnow;
end

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