散点图上的 datacursormode 数量有限 - Matlab

Question

我有一个椭圆图（散点图），我希望只有两个数据光标模式，然后得到它们各自的 X 和 Y 坐标。附加的代码绘制了椭圆并标记了一个点，但是我如何限制它并获取坐标？

代码：

clc;
clear;

a=3;  
b=7; 
x0=0;
y0=0;
t=-pi:0.01:pi;
x=x0+a*cos(t);
y=y0+b*sin(t);
sz = 5;
scatter(x,y,sz)

dcm_obj = datacursormode;
set(dcm_obj,'UpdateFcn',@myupdatefcn)

function txt = myupdatefcn(empt,event_obj)
pos1 = get(event_obj,'Position');
txt = {['X position ',num2str(pos1(1))],...
          ['Y position: ',num2str(pos1(2))]};
end    

Answer 1

您可以使用 while 循环来选择两个点，并使用嵌套函数来共享变量。

使用嵌套函数是将选定坐标和计数器传递给父函数的一种可能解决方案。

您可以使用 while 循环将选定（标记）点的数量限制为两个。
在 while 中放置 pause 对于响应能力很重要。

这是一个工作代码示例：

function ellip()
%Parent function (use a function instead of a script, 
%allows sharing variables with internal function).

clc;
%clear;

a=3;  
b=7; 
x0=0;
y0=0;
t=-pi:0.01:pi;
x=x0+a*cos(t);
y=y0+b*sin(t);
sz = 5;
h = figure; %Open new figure, and keep the handle.
scatter(x,y,sz);

dcm_obj = datacursormode;
dcm_obj.Enable = 'on';
set(dcm_obj,'UpdateFcn',@myupdatefcn)

%pos_x, pos_y and pos_counter are known both in scope of myupdatefcn and in ellip
pos_x = zeros(1,2);
pos_y = zeros(1,2);
pos_counter = 0;

%Loop until two points are selected
while (pos_counter < 2) && isvalid(h)
    pause(0.01);
end

if isvalid(h)
    close(h); %Close the figure;

    %Display position of the two selected coordinates.
    fprintf('pos1 = (%f, %f), pos2 = (%f, %f)\n', pos_x(1), pos_y(1), pos_x(2), pos_y(2));
end

dcm_obj.delete() %Delete the object (cleanup)

    %myupdatefcn is a nested function, inside ellip function
    function txt = myupdatefcn(empt, event_obj)      
        pos1 = get(event_obj,'Position');
        txt = {['X position ',num2str(pos1(1))],...
               ['Y position: ',num2str(pos1(2))]};
        disp(txt);

        pos_counter = pos_counter + 1; %Increase counter.
        pos_x(pos_counter) = pos1(1);  %Store position
        pos_y(pos_counter) = pos1(2);        
    end

end

我希望我没听错，很难理解你在问什么......

---

更新评论：

• 在函数外部创建散点图很简单。
• 保存 4 个位置很简单 - 函数可以返回点数。
• 我找不到一种优雅的方式将工具提示信息留在绘图上。
  问题是调用createDatatip 会触发事件并多执行几次myupdatefcn。
  你可以看看Set data tips programmatically?

更新代码：

clc
clear
close all

a=3;  
b=7; 
x0=0;
y0=0;
t=-pi:0.01:pi;
x=x0+a*cos(t);
y=y0+b*sin(t);
sz = 5;
scatter(x,y,sz);

[pos_x, pos_y] = ellip();

%Display position of the two selected coordinates.
fprintf('pos1 = (%f, %f), pos2 = (%f, %f)\n', pos_x(1), pos_y(1), pos_x(2), pos_y(2));


function [pos_x, pos_y] = ellip()
%Parent function (use a function instead of a script, 
%allows sharing variables with internal function).

dcm_obj = datacursormode;
dcm_obj.Enable = 'on';
set(dcm_obj,'UpdateFcn',@myupdatefcn)

h = dcm_obj.Figure; %Get hendle to the figure.
hScatter = findobj(h, 'Type', 'scatter'); %Handle to scatter plot

%pos_x, pos_y and pos_counter are known both in scope of myupdatefcn and in ellip
pos_x = zeros(1,2);
pos_y = zeros(1,2);
pos_counter = 0;

%Loop until two points are selected
while (pos_counter < 2) && isvalid(h)
    pause(0.01);   
end

% if isvalid(h)
%     close(h); %Close the figure;    
% end


%dcm_obj.delete() %Delete the object (cleanup)
if isvalid(h)
    dcm_obj.Enable = 'off';
    set(dcm_obj,'UpdateFcn',[]) %Replace the callback with an empty function instead of deleting the object
end

    %myupdatefcn is a nested function, inside ellip function
    function txt = myupdatefcn(empt, event_obj)      
        pos1 = get(event_obj,'Position');

        txt = {['X position ',num2str(pos1(1))],...
               ['Y position: ',num2str(pos1(2))]};

        if (pos_counter > 0) && (pos_x(pos_counter) == pos1(1)) && (pos_y(pos_counter) == pos1(2))
            return %Return if pod1 is already selected.
        end

        disp(txt);

        pos_counter = pos_counter + 1; %Increase counter.
        pos_x(pos_counter) = pos1(1);  %Store position
        pos_y(pos_counter) = pos1(2);

        %Try keeping the tool-tip data
        hdtip = dcm_obj.createDatatip(hScatter);
        set(hdtip, 'MarkerSize',5, 'MarkerFaceColor','none', 'MarkerEdgeColor','r', 'Marker','o', 'HitTest','off');                    
    end
end