cad2d-ir

cad2d-ir is a typed intermediate representation and conversion toolkit for 2D CAD data.

It provides:

• a canonical JSON Schema for 2D CAD geometry and tables;
• native DXF, DWG, DGN, DWF/DWFx, JWW, MI/BI, and SXF import paths;
• DXF R12 (AC1009) and R2010 (AC1024) export;
• structured import/export diagnostics;
• deterministic IR-entity to DXF-handle correspondence.

Installation

pip install cad2d-ir
pip install "cad2d-ir[dwg]"
pip install "cad2d-ir[dgn]"
pip install "cad2d-ir[dwf]"
pip install "cad2d-ir[jww]"
pip install "cad2d-ir[mi]"
pip install "cad2d-ir[sxf]"
pip install "cad2d-ir[all]"

Python 3.10 or newer is required. The core wheel is pure Python; native format adapters are optional extras.

For development:

uv sync
uv sync --all-extras
uv run python -m pytest

Supported data

IR entities include LINE, CIRCLE, ARC, POINT, ELLIPSE, LWPOLYLINE, SPLINE, TEXT, MTEXT, INSERT, HATCH, and DIMENSION. Layer, linetype, text-style, dimension-style, and block tables are represented by the schema.

Import adapters:

Native adapters preserve source semantics and provenance rather than flattening through an intermediate DXF.

CLI

# Validate IR
cad2d-ir validate examples/ir/minimal.json

# DXF -> IR with BOM/codepage/UTF-8/CP932 detection
cad2d-ir dxf2ir drawing.dxf -o drawing.json --pretty
cad2d-ir dxf2ir drawing.dxf --encoding cp932 -o drawing.json

# Auto-detected DXF/DWG/DGN/DWF/DWFx/JWW/MI/BI/SFC/P21 -> IR
cad2d-ir import drawing.JWW -o drawing.json --pretty
cad2d-ir import drawing.dwg -o drawing.json --pretty
cad2d-ir import drawing.dgn -o drawing.json --pretty
cad2d-ir import drawing.dwfx -o drawing.json --pretty
cad2d-ir import drawing.mi -o drawing.json --pretty
cad2d-ir import drawing.p21 -o drawing.json --pretty

# IR -> R2010 or R12 DXF
cad2d-ir ir2dxf drawing.json --target-version AC1024 -o drawing-r2010.dxf
cad2d-ir ir2dxf drawing.json --target-version AC1009 \
  --encoding cp932 --curve-segments 128 -o drawing-r12.dxf

Python API

from cad2d_ir import convert_file_to_ir, convert_ir_to_dxf_text

imported = convert_file_to_ir("drawing.dxf", strict=False)
print(imported.statistics["encoding"])
for diagnostic in imported.diagnostics:
    print(diagnostic.code, diagnostic.as_dict())

exported = convert_ir_to_dxf_text(
    imported.document,
    target_version="AC1024",
    generic_dimensions="explode",
)
for entry in exported.entity_map:
    print(entry["ir_id"], entry["handle"], entry["dxf_type"])

R2010 output assigns deterministic handles and emits $HANDSEED. Re-importing the DXF records each handle in entity.source.id. R12 omits handles and retains deterministic index values in the entity map.

Export behavior

• TABLES contains LAYER, LTYPE, and STYLE records from IR tables.
• GENERIC dimensions expand to their preserved visual primitives by default.
• R12 declares $DWGCODEPAGE=ANSI_932 and file output uses CP932 by default; LWPOLYLINE becomes POLYLINE/VERTEX, MTEXT becomes TEXT, ELLIPSE/SPLINE become sampled polylines, and HATCH becomes boundary polylines.
• Every skip, approximation, explosion, and normalization is represented by an ExportDiagnostic.
• The same document and options produce byte-identical DXF and entity-map output within a package minor version.

Compatibility boundaries

• constraints are IR-only and are diagnosed when omitted from DXF.
• A complete affine INSERT.transform cannot be represented by plain DXF INSERT and is diagnosed when omitted.
• R12 has no true-color, lineweight, or $INSUNITS equivalent with the same semantics; downgrade diagnostics disclose those losses.
• HATCH support focuses on polyline-style loops.
• Ellipse start/end parameters are radians independently of header.angle_unit.
• DGN import covers V7 2D and native V8 documents. V7 text encoding auto-detection probes ASCII, CP932, then Latin-1 at file scope; V8 text arrives already decoded per element. ezdgn rejects V7 3D; V8 3D models and multi-model files are reduced to one projected model with explicit loss diagnostics, and V8 shared-cell definitions, fills, color tables, and spline knots are not decoded yet.
• DWF/DWFx import preserves sheet identity in metadata while placing supported 2D entities and markups in one IR modelspace. Raster payloads and complex brush semantics remain source metadata/diagnostics rather than invented IR geometry.
• MI import consumes ezmi2d>=0.2,<0.3 directly. Part definitions and shared occurrences become IR blocks and INSERTs; source radians are normalized to IR degrees. .bi dispatch covers the gzip-wrapped MI container verified by ezmi2d, not every historical Drafting/ME10 BI compression variant.

See:

• API guide
• Importer behavior
• Schema notes
• Diagnostic code catalog
• Contributing

Repository layout

src/cad2d_ir/
  api.py
  cli.py
  diagnostics.py
  schema.py
  codecs/dxf.py
  importers/
  data/ir_schema.json
ir_schema.json
tests/
examples/
docs/

License

MIT (LICENSE).