Draw surface of a football (American)

Question

Szabolcs Simon-Guth 2021-11-5

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https://ww2.mathworks.cn/matlabcentral/answers/1579689-draw-surface-of-a-football-american

评论： Szabolcs Simon-Guth 2021-11-5

采纳的回答： DGM

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Hi everyone!

I got the following assignment:

Draw the surface of an american football which can be described with the following equation:

within the interval

The surface should look like this:

I have the following code:

r = linspace(-1,1,21);
a = linspace(0,2*pi,63);
[R,A] = meshgrid(r,a);
X = R.*cos(A);
Y = R.*sin(A);
Z = acos(R);
surf(X,Y,Z);
axis equal

But every time I run the code, I get the following surface:

What is it that I am doing wrong?

Thank you for any help that anyone could provide, in advance!

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Answer 1

DGM 2021-11-5

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1579689-draw-surface-of-a-football-american#answer_824574

编辑：DGM 2021-11-5

在 MATLAB Online 中打开

Two things to notice: note the way your points are spaced unevenly along z compared to the reference image. Also note the restricted domain of acos(). This problem would be easier approached by using z as the parameter instead of r.

z = linspace(-pi/2,pi/2,21);

th = linspace(0,2*pi,63).';

X = cos(z).*cos(th);

Y = cos(z).*sin(th);

Z = repmat(z,numel(th),1);

surf(X,Y,Z);

axis equal

colormap(jet)

If you really wanted to do it your way, you could ...

clf; % reset web-plot

r = linspace(0,1,21);

a = linspace(0,2*pi,63);

[R,A] = meshgrid(r,a);

X = R.*cos(A);

Y = R.*sin(A);

Z = acos(R);

surf(X,Y,Z); hold on

surf(X,Y,-Z)

axis equal

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Szabolcs Simon-Guth 2021-11-5

Thank you very much for your guidance! I'm new to MATLAB and I didn't think of the fact that the restricted domain, because I concentrated too much on the coding aspect, instead of the maths. Thank you again for all the help! :)

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