MATLAB：如何在使用 "fill" 函数时保持填充椭圆的纵横比？

Question

我正在 x-y 图上绘制实心圆和椭圆。椭圆源自 2x2 张量数据。根据我绘制的数据类型，x 方向和 y 方向的单位截然不同。我想在图上的某个 (x,y) 位置绘制一个椭圆，但我希望无论 x 和 y 轴单位如何，都保持绘制的椭圆的纵横比。请注意，axis equal 不是此处的选项，因为 x 和 y 比例非常不同。如果我尝试做 axis equal 它只会让剧情变得很小。

下面是一个简单的例子。在这个例子中，第一个椭圆始终是一个完美的圆，以供参考以查看图形如何扭曲它。感谢任何帮助。

x = 100*[1 2 3 4]; %x direction is several orders of magnitude larger than y direction
y = [1 2 3 4]; %y direction
data = randn(4,1); %data to fill ellipse (irrelevant to the question)

nrot = 36; %Number of points on each ellipse

for i = 1:4
    %Elements of 2x2 tensor to make the ellipse
    r1 = randn; r2 = randn; r3 = randn; r4 = randn;

    for irot=1:nrot %Loop to get ellipse points

        rot_ang = (irot-1)*360/(nrot-1);
        v = [cosd(rot_ang),sind(rot_ang)]; %Rotating vector components

        if i == 1 %Ensure that the first ellipse is a perfect circle
            r1 = 0; r4 = 0; r3 = r2;
        end

        plot_vec = [r1 r2; r3 r4]*v';

        %x component of ellipse to plot
        ex(irot) = plot_vec(1);

        %y component of ellipse to plot
        ey(irot) = plot_vec(2);  
    end 

    %Plot the ellipse at the x-y location
    xp = x(i)+ex;
    yp = y(i)+ey;

    fill(xp,yp,data(i)); hold on %Plot ellipses filled with "data".


end

%"Axis equal" does not work in this case
%axis equal

Answer 1

听起来您希望椭圆的显示数据纵横比为 1:1，即使轴的数据纵横比不是。一种选择是首先选择您想要的轴 data aspect ratio，然后在平移和绘制它们之前相应地缩放椭圆的 y 值：

x = 100*[1 2 3 4];
y = [1 2 3 4];
aspectRatio = 100;  % Choose an aspect ratio of 100
data = randn(4, 1);
nrot = 36;

for i = 1:4

  r1 = randn; r2 = randn; r3 = randn; r4 = randn;

  for irot = 1:nrot

    rot_ang = (irot-1)*360/(nrot-1);
    v = [cosd(rot_ang), sind(rot_ang)];

    if i == 1
      r1 = 0; r4 = 0; r3 = r2;
    end

    plot_vec = [r1 r2; r3 r4]*v';
    ex(irot) = plot_vec(1);
    ey(irot) = plot_vec(2);

  end

  xp = x(i)+ex;
  yp = y(i)+ey./aspectRatio;  % Scale ellipse y data by aspect ratio

  fill(xp, yp, data(i));
  hold on;
  daspect(gca, [aspectRatio 1 1]);  % Set aspect ratio of axes

end

结果如下：

椭圆很小，但如果放大，您会发现它们的宽高比正确（即第一个看起来像圆）。

MATLAB：如何在使用 "fill" 函数时保持填充椭圆的纵横比？

MATLAB: How to maintain aspect ratio of filled ellipses when using "fill" function?

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axis

ellipse

fill

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