DXF (.dxf)

Drawing Exchange Format output for sketches and outlines: the format every CAD sketcher, laser cutter and CNC post-processor imports. A section of a scan chained by slice(chain=True) or sections, then fitted by fit_curves, crosses to CAD and CAM at 1:1 as a DXF drawing of lines, arcs and circles (roadmap 7.6.4). It is a drawing, not a mesh format: only line meshes and sketches are written, and only the curves come back.

Format name	dxf
Extensions	.dxf
Read / Write	✓ (a drawing: LINE, ARC, CIRCLE, LWPOLYLINE, SPLINE) / ✓
Extra dependencies	—

Writing

meshioplusplus.dxf.write(path, mesh) takes no options.

import meshioplusplus

profile = meshioplusplus.sections(scan, direction=(0, 0, 1), offsets=[2.0])
sketch = meshioplusplus.fit_curves(profile, tolerance=0.01)
meshioplusplus.write("profile.dxf", sketch)

The file is ASCII DXF R2000 ($ACADVER AC1015), the oldest release that has LWPOLYLINE and SPLINE, with what an R2000 reader expects around the entities: a HEADER ($ACADVER, $HANDSEED, $INSUNITS), the nine symbol tables (one layer, 0; the ByBlock, ByLayer and Continuous line types; the Standard text and dimension styles; the ACAD application), the model and paper space block records and blocks, and an OBJECTS section with the root dictionary and the two layouts. Every object carries a handle and its owner. ezdxf's audit of each file the tests write finds no error and nothing to fix.

• A sketch (a mesh carrying fit_curves' sketch:type, sketch:params and sketch:frame field data) is written as its pieces. A line becomes a LINE between its ends in world coordinates. An arc or a full circle becomes an ARC or CIRCLE in the object coordinate system (OCS) of the sketch plane's normal, built by DXF's arbitrary-axis algorithm, with that normal as its extrusion direction (210/220/230); a clockwise arc is written with its start and end angles swapped, since DXF arcs run counterclockwise about the extrusion.
• Any other line mesh is written as one LINE per segment. Vertex cells are skipped. Surface and volume cells are refused by name (slice or section a surface first).
• Units: $INSUNITS is the code of field_data["meshio:length_unit"] (inches 1, feet 2, miles 3, millimetres 4, centimetres 5, metres 6, kilometres 7, yards 10, nanometres 12, micrometres 13, decimetres 14), or 0, unitless, for no unit or any other. Coordinates are written as they are, so a sketch in millimetres is 1:1 in a millimetre drawing.
• Numbers are written with 17 significant digits (-0 as 0), so every coordinate reads back to the same double.
• Provenance: the provenance block leads the file as 999 comment pairs, which DXF readers skip.

SPLINE and LWPOLYLINE are read but not written: a fit_curves sketch has no B-spline pieces, and a polyline is written as its LINEs.

Reading

meshioplusplus.read("part.dxf") returns the drawing's curves as a line mesh, in world coordinates:

Entity	Read as
LINE	one segment
ARC	segments, 64 per full turn, through the OCS of its extrusion direction
CIRCLE	a closed chain of 64 segments
LWPOLYLINE	its vertices at the polyline's elevation, in its OCS; a bulge span sampled as an arc (64 segments per full turn); 70 bit 1 closes it
SPLINE	8 samples per control point along the B-spline (de Boor, with weights when given)

Points are shared where entities meet at exactly the same coordinates. The cell data dxf:entity holds each segment's entity index and dxf:type its kind (1 line, 2 arc, 3 circle, 4 polyline, 5 spline); $INSUNITS becomes meshio:length_unit. Any other entity in the ENTITIES section (TEXT, INSERT, HATCH, POLYLINE, 3DFACE, …) is refused by name, as are inconsistent SPLINE knots and a non-positive radius: the svg and tikz rule, a reader limited to what the writer emits.

Engines

The C++ core (formats/dxf.cpp) and the Python reference (dxf/_dxf.py) write the same bytes and read the same mesh, pinned by tests/python/test_dxf.py. The native reader returns a mesh or throws ReadError on any input, every number going through detail::parse_double; the fuzz seed corpus carries a line drawing.