Scripts/mesh_to_step.py

#!/usr/bin/env python3
"""
=============================================================================
STL Mesh to Parametric STEP Solid Converter (OpenCASCADE Backend)
=============================================================================
Requirements (Run inside your environment before executing):
    pip install trimesh scipy cadquery

Usage:
    python mesh_to_step.py <path_to_mesh.stl>
=============================================================================
"""

import sys
from pathlib import Path

try:
    import trimesh
    import cadquery as cq
    from OCP.BRepBuilderAPI import BRepBuilderAPI_MakeFace, BRepBuilderAPI_Sewing, BRepBuilderAPI_MakeSolid, BRepBuilderAPI_MakeEdge, BRepBuilderAPI_MakeWire
    from OCP.gp import gp_Pnt
except ImportError as e:
    print(f"[fucking error] Missing dependencies. Run: pip install trimesh scipy cadquery")
    print(f"Details: {e}")
    sys.exit(1)

def mesh_to_step(input_path):
    input_file = Path(input_path)
    if not input_file.exists():
        print(f"[fucking error] File not found: {input_file}")
        sys.exit(1)
        
    output_step = input_file.with_suffix('.step')
    
    print(f"[*] Loading mesh: {input_file}")
    mesh = trimesh.load(input_file, force='mesh')
    
    print("[*] Running geometry healing filters...")
    mesh.update_faces(mesh.unique_faces())
    mesh.fill_holes()
    
    print(f"[*] Extracting {len(mesh.faces)} facets and building faces...")
    # 0.1mm tolerance to sew loose vertices and fix misaligned triangle normals
    sewing = BRepBuilderAPI_Sewing(0.1)
    
    success_faces = 0
    for face in mesh.faces:
        p1 = gp_Pnt(float(mesh.vertices[face[0]][0]), float(mesh.vertices[face[0]][1]), float(mesh.vertices[face[0]][2]))
        p2 = gp_Pnt(float(mesh.vertices[face[1]][0]), float(mesh.vertices[face[1]][1]), float(mesh.vertices[face[1]][2]))
        p3 = gp_Pnt(float(mesh.vertices[face[2]][0]), float(mesh.vertices[face[2]][1]), float(mesh.vertices[face[2]][2]))
        
        try:
            ocp_face = BRepBuilderAPI_MakeFace(p1, p2, p3).Face()
            sewing.Add(ocp_face)
            success_faces += 1
        except Exception:
            try:
                # Fallback path if raw surface generation hits a localized coordinate breakdown
                e1 = BRepBuilderAPI_MakeEdge(p1, p2).Edge()
                e2 = BRepBuilderAPI_MakeEdge(p2, p3).Edge()
                e3 = BRepBuilderAPI_MakeEdge(p3, p1).Edge()
                wire = BRepBuilderAPI_MakeWire(e1, e2, e3).Wire()
                ocp_face = BRepBuilderAPI_MakeFace(wire).Face()
                sewing.Add(ocp_face)
                success_faces += 1
            except Exception:
                continue

    print(f"[*] Successfully added {success_faces}/{len(mesh.faces)} faces to the engine.")
    if success_faces == 0:
        print("[fucking error] All faces rejected by OpenCASCADE geometry constraints.")
        sys.exit(1)

    print("[*] Sewing facets together via OpenCASCADE engine...")
    sewing.Perform()
    
    print("\n=== OpenCASCADE Sewing Diagnostics ===")
    print(f"Free edges (gaps): {sewing.NbFreeEdges()}")
    print(f"Multiple edges: {sewing.NbMultipleEdges()}")
    print("======================================\n")

    sewed_shape = sewing.SewedShape()
    
    print("[*] Computing solid volume...")
    solid_builder = BRepBuilderAPI_MakeSolid()
    
    from OCP.TopExp import TopExp_Explorer
    from OCP.TopAbs import TopAbs_SHELL
    from OCP.TopoDS import TopoDS
    
    explorer = TopExp_Explorer(sewed_shape, TopAbs_SHELL)
    shell_count = 0
    
    while explorer.More():
        shell = TopoDS.Shell(explorer.Current())
        solid_builder.Add(shell)
        shell_count += 1
        explorer.Next()
        
    if shell_count == 0:
        print("[fucking error] Sewing failed to produce a valid shell structure.")
        sys.exit(1)
        
    if not solid_builder.IsDone():
        print("[fucking error] OpenCASCADE sewed the shell but cannot compute a closed solid volume.")
        sys.exit(1)
        
    ocp_solid = solid_builder.Solid()
    
    # Cast directly into CadQuery's core Shape object to handle pristine STEP output
    cq_shape = cq.Shape.cast(ocp_solid)
    
    print(f"[*] Exporting pristine STEP file: {output_step}")
    cq.exporters.export(cq_shape, str(output_step), cq.exporters.ExportTypes.STEP)
    print("[+] Done!")

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: python mesh_to_step.py <path_to_mesh.stl>")
        sys.exit(1)
        
    mesh_to_step(sys.argv[1])