DXF Drawing Inspection

Analyze a CAD drawing and report what's in it: layers, entity inventory, extents, and common hygiene problems. The standard first pass before any CAD task (redlining, cleanup, conversion, quantity counting).

When to use

• "What's in this .dxf/.dwg file?"
• Checking a submission against the office layering standard
• Finding problems before conversion (off-origin, exploded blocks, empty layers)
• Estimating drawing size/complexity

Workflow

1. Prefer ezdxf for accurate results:

   pip install ezdxf

   import ezdxf
   
   doc = ezdxf.readfile("plan.dxf")
   msp = doc.modelspace()
   
   layers = {l.dxf.name for l in doc.layers}
   entities = {}
   for e in msp:
       entities[e.dxftype()] = entities.get(e.dxftype(), 0) + 1
   print(f"Layers ({len(layers)}): {', '.join(sorted(layers))}")
   print("Entities:", ", ".join(f"{k}: {v}" for k, v in sorted(entities.items())))

2. Fallback (stdlib only): DXF is a text format. Pair-group lines where even offsets are group codes and odd offsets are values. 0 group code = entity start. See scripts/inspect_dxf.py for a complete dependency-free parser.
3. Report (see output format below).
4. Hygiene checks (the valuable part):
   • Geometry outside a sane coordinate range (e.g. |x| or |y| > 1e6) — likely off-origin
   • 0 layer usage (everything on layer 0 is a red flag)
   • Empty layers (declared, never used)
   • Layers named "Layer1", "aaa", etc. — not renamed
   • Duplicate/overlapping entities (e.g. identical LINE entities)
   • Missing or non-ASCII drawing units header

Output format

DXF: plan.dxf (AC1027, 4.2 MB)
Layers: A-WALL, A-DOOR, A-GLAZ, A-ANNO, A-DIMS (5)
Entities: LINE 1,204 | TEXT 312 | INSERT 186 | LWPOLYLINE 84 | HATCH 96
Extents: (-125.00, -86.00) to (4,120.00, 3,240.00)  [units: mm]
Hygiene: 12 entities at origin (0,0); 3 empty layers (A-AREA, A-FURN); everything on layer 0

Edge cases

• Binary DXF: starts with AutoCAD Binary DXF — requires ezdxf; the stdlib parser should report this clearly.
• DWG: not text-readable. Use ezdxf.readfile with the ODA File Converter, or tell the user DWG needs AutoCAD/ODA; ask for a DXF export.
• AC1009 (R12) and older: ezdxf handles them, but some entity types (HATCH/MTEXT) are newer; expect counts to differ from modern versions.
• Huge files (100MB+): prefer ezdxf; warn before the fallback parser on large files.
• Units: the $INSUNITS header variable is often 0 (unitless). Don't guess — report "units: unknown" and let the user confirm.

Files

• references/dxf-quick-reference.md — entity types, group codes, and layering conventions.
• scripts/inspect_dxf.py — dependency-free inspector producing the report above.