How to draw a cylinder that has an irregular cross section and changing along the cylinder length?

I need to draw a cylinder that has a different radius around the rotation axis, and these radii change along that cylinder, these data may be helpful to get the point.

[Adam Danz]

What's preventing you from creating multiple cylinders and then concatenating them together graphically?

[Muhamed Sewidan]

how can I concatenate them?

Answer 1

[John D'Errico]

You essentially have radius, as a function of theta, and z. And I don't have your data, since all you gave us is a picture. It is just as easy to attach a .mat file, or even a text file! A picture of numbers is NOT worth a thousand words. It is almost worthless.

So I'll make up some data.

theta = (0:30:360)';
z = 0:.5:1.5;
r = rand(12,4)*3 + 20;
r(end+1,:) = r(1,:);
r
r =
       22.128       22.254       22.443       22.752
       22.264       20.765       20.731       20.858
       20.828       21.518       22.788       22.272
       22.039       22.097        21.05       22.261
       21.965       22.673        20.59       21.141
       20.488       22.878       20.753       21.703
       20.357       21.642       21.848       20.228
       21.495       20.416        21.42       20.162
       22.879       20.448       21.055       21.592
       21.021       20.773       22.492       22.338
       21.756       22.522       21.756       22.802
       20.671       20.763       21.649        20.39
       22.128       22.254       22.443       22.752

The only thing of importance is I made sure the first and last radii are the same at 0 and 360 degrees. Note my use of sind and cosd, because you used degrees. Now just call surf.

surf(r.*cosd(theta),r.*sind(theta),ones(size(theta)).*z)

This will work as long as you have R2016b of MATLAb or later. Easy enough to fix using bsxfun or even repmat if you have an older release.

Would not even be that difficult to put an end cap on the ends. Just a pair of polygonal patches.

[Muhamed Sewidan]

I have Matlab 2014a, and this code is not working due to an error in the 7th row, could you please tell me or fix it to me because I'm a little beginner in using matlab

[Muhamed Sewidan]

r =  [22.128       22.254       22.443       22.752
       22.264       20.765       20.731       20.858
       20.828       21.518       22.788       22.272
       22.039       22.097        21.05       22.261
       21.965       22.673        20.59       21.141
       20.488       22.878       20.753       21.703
       20.357       21.642       21.848       20.228
       21.495       20.416        21.42       20.162
       22.879       20.448       21.055       21.592
       21.021       20.773       22.492       22.338
       21.756       22.522       21.756       22.802
       20.671       20.763       21.649        20.39
       22.128       22.254       22.443       22.752]
   
   surf(r.*cosd(theta),r.*sind(theta),ones(size(theta)).*z)

It says error in the row of surf, (Error using .* Matrix dimensions must agree.)

[John D'Errico]

Easy enough to fix, although there are many good reasons to upgrade.

theta = (0:30:360)';
z = 0:.5:1.5;
r = rand(12,4)*3 + 20;
r(end+1,:) = r(1,:);

X = bsxfun(@times,r,cosd(theta));
Y = bsxfun(@times,r,sind(theta));
Z = ones(size(theta)).*z;
surf(X,Y,Z)

REALLY old releases might use repmat instead of bsxfun.

[Muhamed Sewidan]

I think I should listen to your advice

One more thing please, if I want to add my data from the table how can I add them rather than the random values?

[Muhamed Sewidan]

Thanks, I only need to know how can I add my values in r rather than the random values

[John D'Errico]

Your table is what, a spreadsheet? Use a tool like xlsread. Then reshape the array to be 13x4, or whatever shape is appropriate for your problem.

[Muhamed Sewidan]

yes it is a spreadsheet, ok thanks a lot.

One more thing is it possible to make this cylinder closed?

[John D'Errico]

Well, I did mention how to do that, but only briefly. You have the data for the lower and upper values of z in the cylinder. So you can create a polygonal region in x and y, with a fixed z. Then just call patch or fill3 with the coordinates of those points, and whatever color you wish to fill it in with. So one call per end of the cylinder.

[Muhamed Sewidan]

Thank you a lot, you saved me :D