Building cylinder using isosurface

Question

Vittorio 2014-7-29

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https://ww2.mathworks.cn/matlabcentral/answers/143767-building-cylinder-using-isosurface

编辑： Vittorio 2014-7-29

Hello everyone,

I'm trying to create a cylindric patch using the isosurface command. Using this tutorial I created my own structure. The code is the following:

[x,y,z] = meshgrid(-1:.02:1);
blob = z <= 0 & z >= -1 & x.^2 + y.^2 <= sqrt(0.18) & x.^2 + y.^2 >= sqrt(0.15);
p = patch(isosurface(blob,0.5));
set(p, 'FaceColor', 'red', 'EdgeColor', 'none');
view(3)
camlight
alpha(0.3)
lighting gouraud

Now, I want to specify for every level of the cylinder a different radius. The values of the radii for every level are stored in a vector 1x36.

How can I modify the blob accordingly?

Thanks for any suggestions.

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Answer 1

Matz Johansson Bergström 2014-7-29

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I would try using a function

test = @(x) abs( cos(4*x) );
[x,y,z] = meshgrid(-1:.02:1);
blob = z <= 0 & z >= -1 & x.^2 + y.^2 <= ...
    sqrt(0.18*test(z)) & x.^2 + y.^2 >= ...
    sqrt(0.12*test(z));

In this way you will get a wobbly thing depending on the z coordinate.

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Vittorio 2014-7-29

在 MATLAB Online 中打开

Good solution, but the radius is not changing accordingly to a function. The vector which is storing the radii values is:

Vittorio 2014-7-29

编辑：Vittorio 2014-7-29

在 MATLAB Online 中打开

I did it! :)

Probably not an elegant solution, but here is the code:

i = 1;
[x,y,z] = meshgrid(-1:.02:1);
r1 = zeros(length(z),length(z),length(z));
step = round(length(z)/length(r));
for j = 1:step:length(z)
    r1(:,:,j) = r(i);
    if j+1>length(z)
        break
    end
    r1(:,:,j+1) = r(i);
    if j+2>length(z)
        break
    end
    r1(:,:,j+2) = r(i);
    if i>length(r)
        break
    end
    i = i+1;
end
blob = z <= 0 & z >= -1 & x.^2 + y.^2 <= sqrt(0.18*r1) & x.^2 + y.^2 >= ...
    sqrt(0.12*r1);
p = patch(isosurface(blob,0.5));
set(p, 'FaceColor', 'red', 'EdgeColor', 'none');
view(3)
camlight
alpha(0.3)
lighting gouraud