Create surface consisting of two implicitly surfaces

Dear Community,

I would like to create surfaces consisting of two implicitly described surfaces (see figure).

https://images4.sw-cdn.net/product/picture/674x501_21915173_12299065_1516271298.jpg

With the functions isosurface and isocaps I only manage to create a full body (see figure).

https://www.researchgate.net/profile/Ajit_Panesar/publication/321076296/figure/fig5/AS:667675449647111@1536197640334/Library-of-implicit-surface-based-unit-cells-Network-phase-representatives-a-G.jpg

So far, I have to create two separate full bodies and then subtract them in another program by boolean subtract. Unfortunately, this route is complex and only works to a limited extent. Therefore, I would like to be able to use Matlab to create the surface limited by two implicit surfaces and the edge surfaces.

To create the stl-files I use as code (Note: This requires the stlwrite.m function):

clc
clear
close all


n=200;
t=pi/n;

x_max=1;
y_max=1;
z_max=1;

xi = 0:t:x_max;
yi = 0:t:y_max;
zi = 0:t:z_max;

[x,y,z] = meshgrid(xi,yi,zi);

F=-1.*(cos(2.*pi.*x)+cos(2.*pi.*y)+cos(2.*pi.*z))+0;

[fs,v]=isosurface(x,y,z,F,0);
[fc,v2,c] = isocaps(x,y,z,F,0);
fn = [fs ; fc+length(v(:,1))];
vn = [v ; v2];
 
stlwrite('geometry.stl',fn,vn);

Can anyone help me with this question?

Thank you very much and best regards

Answer 1

[Bruno Luong]

"Can anyone help me with this question?"

Not clear to me what exactly is the question.

If you have two implicit equations for two surfaces F1==c1 and F2==c2, you might combine the surfaces of both by

(F1-c1).*(F2-c2) == 0.

[Fabian Günther]

Wonderful, your proposal works exactly as I imagined it would.

It was not clear to me that I can unite the two surfaces by multiplying them.

Thanks alot Mr. Luong.