evo-3d-scan-calc

End-to-end skill for computing the mass of a 3D printed part from a binary STL scan file.

Pipeline Overview

1. Parse binary STL — Decode 80-byte header, 4-byte triangle count, and 50-byte facet records. Extract vertices and Material ID (uint16 attribute field) per triangle.
2. Find connected components — Build vertex-based adjacency (triangles sharing any vertex are connected) using vertices quantized to 4 decimal places. BFS to find all components.
3. Select main part — Compute volume for each component. The largest by volume is the main part.
4. Extract Material ID — Use the attribute from the first triangle of the largest component.
5. Lookup density — Reference the material density table: {1: 0.10, 10: 7.85, 25: 2.70, 42: 5.55, 99: 11.34}.
6. Calculate mass — mass = volume * density. No unit conversion needed (density table matches mesh coordinate units).
7. Write report — Save JSON with main_part_mass and material_id.

Critical Details

• Vertex quantization: Round to exactly 4 decimal places for vertex matching (matches verifier).
• Adjacency: Vertex-based — two triangles are connected if they share at least one vertex (NOT edge-based).
• Volume formula: Signed tetrahedron method: V = abs(Σ v1·(v2×v3)) / 6.0. No mm³-to-cm³ conversion.
• Component selection: By largest volume, not by material ID count.
• Material ID: From the first triangle of the component (attribute byte count field).

Usage

import sys
sys.path.insert(0, '/app/environment/skills/evo-3d-scan-calc/scripts')
from utils import run_full_pipeline

result = run_full_pipeline()

Or step by step:

import sys
sys.path.insert(0, '/app/environment/skills/evo-3d-scan-calc/scripts')
from utils import (
    parse_binary_stl, find_connected_components,
    compute_signed_volume, lookup_density, write_mass_report
)

# 1. Parse STL
triangles = parse_binary_stl('/root/scan_data.stl')

# 2. Find all connected components (vertex-based adjacency, 4-decimal quantization)
components = find_connected_components(triangles)

# 3. Compute volume for each component, pick largest
best_comp = None
best_vol = -1
for comp in components:
    vol = compute_signed_volume(comp)
    if vol > best_vol:
        best_vol = vol
        best_comp = comp

# 4. Get material ID from first triangle of largest component
material_id = best_comp[0][3]

# 5. Lookup density and compute mass (NO unit conversion)
density = lookup_density(material_id)
mass = best_vol * density

# 6. Write report
write_mass_report('/root/mass_report.json', mass, material_id)