combine two stl into one

I have two 3D geometries ('sol_1.stl' and 'sol_2.stl') and their corresponding nodes and faces.

I would like to combine the two STL geometries into a single geometry, or merge the nodes and faces of the two geometries into one.

• sol_1.st + sol_2.st -> sol_fin.stl
• nodes_sol_1 + nodes_sol_2 -> nodes_sol_fin (simple)
• faces_sol_1 + faces_sol_2 -> faces_sol_fin

Answer 1

[Avni Agrawal]

Hi @Alberto Acri,

I understand that you are trying to combine two STL geometries into a single geometry by merging their nodes and faces in MATLAB, you can follow these steps:

1. Read the STL files to get the nodes and faces.
2. Merge the nodes and faces from both geometries.
3. Write the combined geometry to a new STL file.

Below is a MATLAB script that demonstrates how to do this:

% Read the STL files
fv1 = stlread('../sol/sol_1.stl');
fv2 = stlread('../sol/sol_2.stl');

% Extract nodes (vertices) and faces from the first geometry
nodes1 = fv1.Points;
faces1 = fv1.ConnectivityList;

% Extract nodes (vertices) and faces from the second geometry
nodes2 = fv2.Points;
faces2 = fv2.ConnectivityList;

% Merge nodes
% Note: We need to adjust the face indices of the second geometry
% by adding the number of nodes in the first geometry

% Combine nodes
combinedNodes = [nodes1; nodes2];

% Adjust face indices for the second geometry
adjustedFaces2 = faces2 + size(nodes1, 1);

% Combine faces
combinedFaces = [faces1; adjustedFaces2];

% Create a new triangulation object for the combined geometry
combinedGeometry = triangulation(combinedFaces, combinedNodes);

% Write the combined geometry to a new STL file
stlwrite(combinedGeometry, 'combined_geometry.stl');

I hope this helps.

[DGM]

Note that this doesn't actually do any CSG to combine the geometry (e.g. the union). This just creates a model with two independent connected components.

If the objects intersect, there will be no new vertices or edges formed at their intersection, and the model will have interior and/or tangential faces and edges.

Answer 2

[DGM]

Perhaps this will be easier to use. Say we have multiple files or other representations of triangulated surfaces:

% if you have files or other things, just throw them into a cell array

unzip stlpile.zip % prepare things for the forum

% model 1 (a triangulation object)
Tc{1} = stlread('stlpile/stepholecube.stl');

% model 2 (F,V lists)
Tc{2} = stlread('stlpile/sphere_20.stl');
[F V] = t2fv(Tc{2});
V = V/25;
V(:,1) = V(:,1) + 1.5;
Tc{2} = {F V};

% model 3 (an FV struct)
[x y z] = peaks(21);
Tc{3} = surf2patch(x/2,y/2 + 3,z/6,'triangles');

% model 4 (a TriRep object)
% pretend for a moment we're using an old version
[F V] = stlread_2011('stlpile/btpyramid.stl'); % prior to R2018b (FEX #22409)
V = bsxfun(@minus,V,[2 0.5 0.5]); % prior to R2016b
Tc{4} = TriRep(F,V); %#ok<DTRIREP> % prior to R2013a

At this point, we have a cell array of four models in different formats. Combining them is easy.

% concatenate the models and write to a file
T = tricat(Tc); % attached
stlwrite(T,'test.stl')

% display the composite model
trisurf(T,'facecolor','w','edgecolor','k')
view(3); view(-45,25); camlight; 
axis equal; grid on

As before, this does not do any CSG on the models. It just concatenates and does index offsets and some cleanup.

The input to tricat() is a cell array containing surface data in any of the following formats:

• triangulation objects
• delaunayTriangulation objects
• legacy TriRep or DelaunayTri objects
• FV structs
• cell arrays containing F,V lists

The combined data is pruned and returned as either a triangulation object or as F,V lists.

While tricat() itself should run on older versions, the rest of this example isn't version-agnostic. If we were truly running an old version, as in example 4, T would be a TriRep object, and we would need to use a third-party encoder.

See also:

https://www.mathworks.com/matlabcentral/answers/1567423-how-to-write-multiple-object-surfaces-solids-to-a-single-stl-file#answer_1567955