3D cylinder code debugging

Hi, I am trying to implement a 3D cylinder code, and here is the code:

nCS = 2; %number of cross section of cylinder
nNodes = 50; %number of nodes per cross section

rSC = size * ones(1, nNodes);       %set length of each vertices
theta = linspace(0, 2* pi, nNodes); %set angle of each vertices
polar(theta, rSC) 

zSC = linspace(0, hSC, nCS)';   %create z coordinates, with height hSC

[xSC,ySC] = pol2cart(theta, rSC);   %transform from polar to cartisen
XSC = repmat(xSC, nCS, 1);      %repeat for array of number of cross sections
YSC = repmat(ySC, nCS, 1);
ZSC = repmat(zSC, 1, nNodes);   %repeat for number of z-layers

xSC_lid = zeros(2, nNodes);     %creating the top and bottom lid
ySC_lid = zeros(2, nNodes);
zSC_lid = repmat([0, hSC], 1, nNodes);

X = [xSC_lid(1,:); XSC; xSC_lid(2,:)];
Y = [ySC_lid(1,:); YSC; ySC_lid(2,:)];
Z = [zSC_lid(1,:); ZSC; zSC_lid(2,:)]; 

surf(X, Y, Z)

The error message is

What is wrong and how to solve this?

Answer 1

[Matt J]

Much of your code seems to be an unnecessary reinvention of the cylinder() command.

nCS = 2; %number of cross section of cylinder
nNodes = 50; %number of nodes per cross section

[X,Y,Z]=cylinder(ones(1,nCS),nNodes);

surf(X,Y,Z,'FaceAlpha',0.7)
patch('XData',X(1,:),'YData',Y(1,:), 'ZData',Z(1,:),'FaceColor','r');
patch('XData',X(nCS,:),'YData',Y(nCS,:), 'ZData',Z(nCS,:),'FaceColor','r');

[Miles Hao Peng Su]

I see, however I wish to stack 2 cylinders together, which I am thinking hard to implement through cylinder(m).

May I know if you know how to implement this?

say cylinder1 has a height of 2, and I want to have the base of cylinder2 (height 3) to be ontop of cylinder1?

[Matt J]

Do they have different radii? Otherwise, the stacking is equivalent to taking nCS=3.

[Miles Hao Peng Su]

Oh you're right! I never thought of this. My model also has an ring on top of the cylinder, which has a different radii than the cylinder. Can I also use the cylinder(m) function? How do you stack the ring onto the cylinder?

[Matt J]

Just add shifts and scalings to the X,Y,Z coordinates as appropriate

cappedCylinder(2,4,0)
cappedCylinder(4,1,4)

function cappedCylinder(r, h, z0)

 nCS = 2; %number of cross section of cylinder
 nNodes = 50; %number of nodes per cross section
 [X,Y,Z]=cylinder(ones(1,nCS),nNodes);

 X=r*X; Y=r*Y; Z=h*Z+z0;
 
 surface(X,Y,Z,'FaceAlpha',0.5,'FaceColor','g')
 patch('XData',X(1,:),'YData',Y(1,:), 'ZData',Z(1,:),'FaceColor','r');
 patch('XData',X(nCS,:),'YData',Y(nCS,:), 'ZData',Z(nCS,:),'FaceColor','r');
 view(3); axis equal
end

[Miles Hao Peng Su]

Hi! May I ask what is the function of the ones(1,nSC) in the code?

[X,Y,Z]=cylinder(ones(1,nCS),nNodes);

I am curious, because when I pass just 1 through returns me the same result. Like so:

[XSC,YSC,ZSC]=cylinder(1,nNodes);

Why do we need to pass radius 2 times? Oh and anyway I only need the top and bottom 2 slices, so I don't really know if I need the nCS there.

[Miles Hao Peng Su]

Hi, I got any other qusetion >< with this method is it possible to generate a hollow cylinder? like the walls have a certain thickness and the middle is void. Or would you suggest to use multicylinder for this?

Answer 2

[Torsten]

zSC_lid is an 1 x nNodes vector:

zSC_lid = repmat([0, hSC], 1, nNodes);

Thus it has only one row.

But you reference the second row in the command

Z = [zSC_lid(1,:); ZSC; zSC_lid(2,:)];

which does not exist.

Thus MATLAB throws an error.

[Miles Hao Peng Su]

I see! I will try to fix this. Thank you!!