OFF (.off)

The Object File Format: a minimal ASCII surface format — a vertex/face/edge count header, the vertex coordinates, then one line per face (leading vertex count + indices).

Format name	off
Extensions	.off
Read / Write	✓ / ✓
Extra dependencies	—

Reading & writing

import meshioplusplus

mesh = meshioplusplus.read("surface.off")
meshioplusplus.off.write("out.off", mesh)

write takes no keyword arguments.

File structure

OFF
<nverts> <nfaces> <nedges>
x y z              # nverts lines
3 i j k            # nfaces lines: leading vertex count (must be 3) + indices

The first line must be exactly "OFF" (ReadError otherwise). The counts line's edge count is parsed but discarded. Every face row's leading count must be 3 — any other value raises ReadError("Can only read triangular faces").

Cell types

triangle only.

Data mapping

None — OFF carries no point_data, cell_data, or field_data; Mesh(points, cells) only.

Quirks & limitations

• Text-mode strictness: the Python reader requires a text-mode stream (raises if given bytes); the writer always opens the file itself in binary mode regardless of the caller's context.
• No boundary/edge data is ever produced — the edge count is read-and- discarded on read, and always written as 0.

Notes

• Fully handled by the C++ core.
• No reference fixture exists under tests/meshes/off/; tests round-trip a synthetic tri_mesh and check .off/.0.off extension dispatch.