Design an algorithm to detect missing triangles in a STL file

[JaysonJ9Cummins]

Body

Folks,
I'm in a Masters Level AM course where one of the projects is to create an algorithm to detect missing triangles in a STL file. I haven't a slightest clue to search for this. I've googled it, I've YouTube'd it and I am so lost on where to go.. Can someone just point me in a direction to go?

Guidelines

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[abdulrehmanwaseem]

`import numpy as np
from collections import defaultdict

def parse_stl(file_path):
"""
Parses an ASCII STL file and extracts the triangles (three vertices per triangle).
Returns a list of triangles (each triangle is a 3x3 numpy array).
"""
triangles = []
with open(file_path, 'r') as f:
lines = f.readlines()
for i, line in enumerate(lines):
if 'vertex' in line:
vertex1 = np.array([float(x) for x in lines[i].split()[1:]])
vertex2 = np.array([float(x) for x in lines[i+1].split()[1:]])
vertex3 = np.array([float(x) for x in lines[i+2].split()[1:]])
triangles.append((vertex1, vertex2, vertex3))
return triangles

def add_edge(edge_dict, v1, v2):
"""
Adds an edge to the edge dictionary.
Edges are stored in a consistent order (min(v1, v2), max(v1, v2)).
"""
edge = tuple(sorted([tuple(v1), tuple(v2)]))
edge_dict[edge] += 1

def detect_missing_triangles(stl_file_path):
"""
Detects missing triangles in an STL file by analyzing edge occurrences.
"""
triangles = parse_stl(stl_file_path)
edge_dict = defaultdict(int)

# Loop through each triangle and record its edges
for tri in triangles:
    v1, v2, v3 = tri
    add_edge(edge_dict, v1, v2)
    add_edge(edge_dict, v2, v3)
    add_edge(edge_dict, v3, v1)

# Identify edges that appear only once (indicating a missing triangle)
missing_edges = [edge for edge, count in edge_dict.items() if count == 1]

if missing_edges:
    print(f"Detected missing triangles along the following edges:")
    for edge in missing_edges:
        print(edge)
else:
    print("No missing triangles detected, the mesh appears to be closed.")

Example usage

stl_file_path = 'example.stl'
detect_missing_triangles(stl_file_path)
`