Hi Sabyasachi,
Creating a valid STL file from overlapping spheres involves removing the intersecting parts and keeping only the outer boundary. Here’s a step-by-step approach to achieve this:
1. Generate the Spheres
First, create the two spheres using MATLAB's sphere function. You can translate one of them to ensure they overlap:
n = 50; % Resolution of the spheres
[x1, y1, z1] = sphere(n);
[x2, y2, z2] = sphere(n);
% Translate the second sphere
x2 = x2 + 1.5; % Adjust translation to ensure overlap
2. Convert to Point Clouds
Convert the surface data of the spheres into point clouds:
points1 = [x1(:), y1(:), z1(:)];
points2 = [x2(:), y2(:), z2(:)];
3. Use Alpha Shape for Boundary Extraction
Use the alphaShape function to extract the boundary of the combined spheres:
% Combine points
combinedPoints = [points1; points2];
% Create alpha shape
alphaValue = 1.0; % Adjust this value as needed
shp = alphaShape(combinedPoints, alphaValue);
% Extract boundary facets
[faces, vertices] = boundaryFacets(shp);
4. Create a Triangulation and Export to STL
Create a triangulation object and export it using a custom STL export function:
TR = triangulation(faces, vertices);
% Custom function to write STL
function writeSTL(filename, TR)
fid = fopen(filename, 'w');
fprintf(fid, 'solid OpenSCAD_Model\n');
for i = 1:size(TR.ConnectivityList, 1)
face = TR.ConnectivityList(i, :);
v1 = TR.Points(face(1), :);
v2 = TR.Points(face(2), :);
v3 = TR.Points(face(3), :);
normal = cross(v2 - v1, v3 - v1);
normal = normal / norm(normal);
fprintf(fid, ' facet normal %.7f %.7f %.7f\n', normal);
fprintf(fid, ' outer loop\n');
fprintf(fid, ' vertex %.7f %.7f %.7f\n', v1);
fprintf(fid, ' vertex %.7f %.7f %.7f\n', v2);
fprintf(fid, ' vertex %.7f %.7f %.7f\n', v3);
fprintf(fid, ' endloop\n');
fprintf(fid, ' endfacet\n');
end
fprintf(fid, 'endsolid OpenSCAD_Model\n');
fclose(fid);
end
% Write to STL
writeSTL('output.stl', TR);
5. Validate the STL File
After exporting, validate the STL file using software like MeshLab or an STL viewer to ensure there are no self-intersections and that the mesh represents only the outer boundary.
Notes
- Alpha Value Tuning: The alphaValue in alphaShape is crucial. It should be small enough to capture the detail but large enough to merge the two spheres correctly.
- Mesh Quality: You may need additional post-processing if the mesh quality is not satisfactory. Tools like MeshLab can help with smoothing and repairing meshes.
- Custom STL Export: The provided function is a simple ASCII STL writer. For large datasets, consider using binary STL for efficiency.
By following these steps, you should be able to create a valid STL file representing the outer boundary of the overlapping spheres.
