How can I add a face to a 3D geometry without defining edges in advance?

By using code like the following, a cuboid can be created as a 3D geometry:

gm = multicuboid(1,1,1);

This cuboid can be used as geometry for a PDE model. In order to obtain the discretized output matrix for an output which contains a part of one face of the cuboid using the function linearizeOutput of the PDE toolbox, I want to define an additional face on a part of one face of the cuboid. This could theoretically be done by using the function addVertex, but addVertex can't be used here because it needs edges that have been defined in advance. But I could not find a MATLAB function that can be used to define edges arbitrarily, but only for defining vertices. So does anyone have an idea how I can add the face without defining edges in advance or how I can define edges from vertices?

Thanks!

Answer 1

[Avni Agrawal]

Hi,

I understand that you are trying to add a face to a 3D geometry without defining edges in advance in MATLAB. To achieve this, you can use the `patch` function. The `patch` function allows you to create a surface by specifying the vertices and faces of the geometry.

Here's an example that demonstrates how to add a face to a 3D geometry in MATLAB:

% Define the vertices of the geometry
vertices = [0, 0, 0; 1, 0, 0; 1, 1, 0; 0, 1, 0; 0, 0, 1; 1, 0, 1; 1, 1, 1; 0, 1, 1];

% Define the faces of the geometry 
faces = [1, 2, 3, 4; 5, 6, 7, 8; 1, 2, 6, 5; 2, 3, 7, 6; 3, 4, 8, 7; 4, 1, 5, 8]; 

% Plot the initial geometry 
figure; 
patch('Vertices', vertices, 'Faces', faces, 'FaceColor', 'blue', 'EdgeColor', 'black'); 
axis equal; 
grid on; 

% Add a new face to the geometry 
newFace = [2, 6, 7, 3]; % Define the new face vertices 

hold on; 
patch('Vertices', vertices, 'Faces', newFace, 'FaceColor', 'red', 'EdgeColor', 'black'); 
hold off; 

In this example, we first define the vertices and faces of the initial geometry. Then, we plot the initial geometry using the `patch` function. Finally, we add a new face to the geometry by specifying the vertices of the new face and plotting it using the `patch` function again.

The resulting figure will show the initial geometry (a cube) in blue and the added face (a triangular face on one side of the cube) in red.

Please refer to the below documentation for further assistance: https://in.mathworks.com/help/matlab/ref/patch.html

I Hope this helps.