Plot only the surfaces within a bounding surface?

Question

iontrap 2023-5-30

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https://ww2.mathworks.cn/matlabcentral/answers/1975874-plot-only-the-surfaces-within-a-bounding-surface

评论： Mathieu NOE 2023-5-31

I have a large cylinder with base in the x-y plane intersected by smaller cylinders with base in the x-z plane. I'd like to plot only the surfaces belonging to the larger cylinder, however my smaller cylinder sticks out of the larger volume. How can I make the surface of the small cylinder bounded by the large cylinder?

Below is the code.

rs = 9.0;

Cxt = -6.0;

Czt = 3.0;

dia_tube = 1.0;

% for the larger cylinder plotting

[xs1 ys1] = GetCircle(rs, 0, 0, 0, 2*pi);

Ns = length(xs1);

zmins = zeros(1,Ns);

zmaxs = zeros(1,Ns) + 6;

xs = [xs1;xs1];

ys = [ys1;ys1];

zs = [zmins;zmaxs];

surf(xs,ys,zs);

alpha 0.5;

hold on

% for smaller cylinder(s)

[xt zt] = GetCircle(dia_tube*0.5, Cxt, Czt, 0, 2*pi);

for i = 1:Ns

ymin = -(rs^2 - xt(i)^2)^(1/2);

ymax = (rs^2 - xt(i)^2)^(1/2);

end

xt = [xt;xt];

yt = [ymin;ymax];

zt = [zt;zt];

surf(xt,yt,zt);

axis equal

% with the circle generator

function [x y] = GetCircle(r, h, k, a, b)

t = linspace(a, b, 40);

x = r*cos(t) + h;

y = r*sin(t) + k;

end

I was hoping ymin and ymax would allow me to do this, but we just find the min and max of the x data such that the edge of the tubes are aligned.

I also tried changing

yt = [ys1;ys1];

to match the cylinder case, but this left me with a weird 2D shape. Thanks for your help.

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Answer 1

iontrap 2023-5-31

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https://ww2.mathworks.cn/matlabcentral/answers/1975874-plot-only-the-surfaces-within-a-bounding-surface#answer_1247704

编辑：iontrap 2023-5-31

在 MATLAB Online 中打开

I was able to figure out the solution:

[xt zt] = GetCircle(dia_tube*0.5, Cxt, Czt, 0, 2*pi); %% make a circle for the small cylinder
for i = 1:Ns
    y_temp(i) = sqrt(rs^2 - (xt(i))^2); %% the y value belonging to the large cylinder corresponding to a given x value of small cylinder.
end
xt3 = [xt;xt]; %% change this to a different variable for clarity.
yt3 = [y_temp;-y_temp];
zt3 = [zt;zt];
surf(xt3,yt3,zt3);

gives the result -

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iontrap 2023-5-31

Great! Thanks for your help.

Mathieu NOE 2023-5-31

my pleasure !

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Answer 2

Mathieu NOE 2023-5-31

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1975874-plot-only-the-surfaces-within-a-bounding-surface#answer_1247429

在 MATLAB Online 中打开

hello

seems to me there is no need for a for loop to compute ymin & ymax

also ymin = - ymax , so we can avoid creating yet another variable in the workspace

and ymax can be directly computed as

ymax = (rs^2 - (abs(Cxt)+0.5*dia_tube)^2)^(1/2);

final result :

rs = 9.0;

Cxt = -6.0;

Czt = 3.0;

dia_tube = 1.0;

% for the larger cylinder plotting

[xs1, ys1] = GetCircle(rs, 0, 0, 0, 2*pi);

Ns = length(xs1);

zmins = zeros(1,Ns);

zmaxs = zeros(1,Ns) + 6;

xs = [xs1;xs1];

ys = [ys1;ys1];

zs = [zmins;zmaxs];

surf(xs,ys,zs);

alpha 0.5;

hold on

% for smaller cylinder(s)

[xt, zt] = GetCircle(dia_tube*0.5, Cxt, Czt, 0, 2*pi);

ymax = (rs^2 - (abs(Cxt)+0.5*dia_tube)^2)^(1/2);

xt = [xt;xt];

yt = [ymax;-ymax];

zt = [zt;zt];

surf(xt,yt,zt);

axis equal

% with the circle generator

function [x, y] = GetCircle(r, h, k, a, b)

t = linspace(a, b, 40);

x = r*cos(t) + h;

y = r*sin(t) + k;

end

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iontrap 2023-5-31

Thanks for your response. The reason I tried to use a loop was to create a curved bounding surface rather than a planar bounding surface. There is still the problem shown in the attached picture.

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