Customize data cursor for 3D objects

Question

Let's say, I have many spheres drawn with surf/mesh function in MATLAB.

I want to display customize data values rather than x,y,z. All values will be different for different spheres and clicking on any point on a particular sphere should display the same data. Refer figure. How do I achieve it?

So far, I'm thinking of using Surface property 'tag' to assign unique string to each sphere. Is there any better way to do it?

[x,y,z] = sphere;
a=[3 1 3 1];
s1=surf(x*a(1,4)+a(1,1),y*a(1,4)+a(1,2),z*a(1,4)+a(1,3),...
        'FaceColor', [1 0 0],'FaceLighting','flat','EdgeColor','none');
s1.Tag = '1';

How should I proceed with custom datacursor function for custom functionality ?

Answer 1

The datacursor function is an attribute of the figure, so the trick is to assign the datatip update function to the figure.

Placing the custom information for each sphere/graphic object in its Tag property is a good idea for what you want to achieve.

Let's define the update function first. Save the following file under datatip_sphere.m and make sure it is visible in the Matlab path:

function output_txt = datatip_sphere(~,event_obj)
% Display the tag of the cursor target
% obj          Currently not used (empty)
% event_obj    Handle to event object
% output_txt   Data cursor text string (string or cell array of strings).

output_txt = { event_obj.Target.Tag };

---

Armed with that, now let's draw two spheres and make sure the cursor function displays what you want:

% retrieve the handle of the figure used for sphere display
% (better than calling 'gca' in datacursormode(hfig)
hfig = figure ;

% Draw your objects
[x,y,z] = sphere;
a=[3 1 3 1] ;
b=[5 6 4 1] ;
s1 = surf(x*a(1,4)+a(1,1),y*a(1,4)+a(1,2),z*a(1,4)+a(1,3),...
        'FaceColor', [1 0 0],'FaceLighting','flat','EdgeColor','none','Facealpha',0.5);
hold on 
s2 = surf(x*b(1,4)+b(1,1),y*b(1,4)+b(1,2),z*b(1,4)+b(1,3),...
        'FaceColor', [0 0 1],'FaceLighting','flat','EdgeColor','none','Facealpha',0.5);
axis equal
    
% Add a tag to each object
s1.Tag = 'This is sphere 1';
s2.Tag = 'This is sphere 2';

% Now force the figure datatip function to your custom version
dcm = datacursormode(hfig) ;
dcm.UpdateFcn = @datatip_sphere ;

Obviously, the important lines are the last 4 lines, where you assign a Tag for each of your graphic object, and specially the last two lines where you assign your custom cursor update function to the figure.

---

Cool, now your datatip will always display the name/tag assigned to the object, regardless of their position: