Make a cylinder with an elliptical base or translate an area

I have to make an elliptical base cylinder. As an idea I thought of making the outer coat + the two bases with different graphics. For the base I did:

area(x,y)

for the cloak:

surf([x;x],[y;y],z)

for the upper base I don't know how to do it (is there a way to translate the area for example? or a command to do everything more simply?)

Where x and y are the point of ellips, and z is a matrix whit first row is 0 and second is 1.

Answer 1

[Abhishek]

Hi @Matteo Novello,

To complete the figure and plot the upper base of the elliptical cylinder, a simple way is to reuse the same 'x' and 'y' coordinates from the bottom base and just shift them upward along the z-axis. Since the bottom is at 'z = 0', one can place the top at 'z = 1' by setting all the z-values to 1.

'fill3' function can be used for this purpose. This particular function allows to draw a filled polygon in 3D space.

Let’s assume a base ellipse defined using this

x = a * cos(theta); 
y = b * sin(theta); 

Then the top base can be defined like this:

fill3(x, y, ones(size(x)), 'blue');  

This line uses the 'fill3' function to draw a filled 3D polygon—specifically, the top elliptical base of the cylinder.

• 'x' and 'y' are the coordinates of the ellipse in the horizontal plane.
• 'ones(size(x))' creates a vector of ones the same size as 'x', meaning all the 'z' values are set to 1—so the entire shape lies in the horizontal plane at 'z = 1'.
• 'blue' sets the color of the filled surface to blue

This complements the bottom base ('z = 0') and the vertical surface created with 'surf'. 'fill3' is useful here because it directly accepts the 'x', 'y', and 'z' coordinates variables and renders a filled 3D shape.

I tested this approach in MATLAB R2024b, here is the output:

For more details, please refer the following documentations:

• ‘fill3’: https://www.mathworks.com/help/releases/R2024b/matlab/ref/fill3.html
• ‘surf’: https://www.mathworks.com/help/releases/R2024b/matlab/ref/surf.html

Hopefully, this helps resolve the issue. If the problem persists, feel free to share more details.

[Rudraksh]

I was facing somewhat similiar issue. Thanks for helping out @Abhishek! On a side note, I would like to ask, that can fill3 also be used for the bottom base (z = 0) instead of area(x, y) to keep the code consistent?

[Abhishek]

Hi @Rudraksh,

Yes, you can use 'fill3' for the bottom base as well. Just set the 'z-values' to 0 like this:

fill3(x, y, zeros(size(x)), 'blue');