cadmpeg-step

cadmpeg-step serializes a CadIr document as an ISO 10303-21 exchange file using the STEP AP214 AUTOMOTIVE_DESIGN schema. It is the library interface for STEP export; the cadmpeg CLI uses the same model and writer.

Export a document

Add the writer and IR crates:

cargo add cadmpeg-step cadmpeg-ir

Pass any std::io::Write sink to write_step:

use std::fs::File;
use std::io::BufWriter;

use cadmpeg_ir::examples::unit_cube;
use cadmpeg_step::{write_step, StepWriteOptions};

let ir = unit_cube();
let file = File::create("cube.step")?;
let mut output = BufWriter::new(file);
let options = StepWriteOptions {
    product_name: "cube".into(),
    author: "Example Author".into(),
    organization: "Example Organization".into(),
    timestamp: "2026-07-11T09:00:00Z".into(),
    originating_system: "example-exporter".into(),
};

let report = write_step(&ir, &mut output, &options)?;
if !report.losses.is_empty() {
    for loss in &report.losses {
        eprintln!("{:?}: {}", loss.severity, loss.message);
    }
}

# Ok::<(), Box<dyn std::error::Error>>(())

write_step emits the complete Part 21 envelope, product-definition records, representation context, and reachable boundary-representation geometry. Each IR region becomes a MANIFOLD_SOLID_BREP; regions with additional shells become BREP_WITH_VOIDS. The topology walk continues through shells, faces, loops, coedges, edges, and vertices.

Supported surface carriers are planes, cylinders, cones, spheres, tori, and rational or non-rational NURBS surfaces. Supported curve carriers are lines, circles, ellipses, parabolas, hyperbolas, and rational or non-rational NURBS curves. The writer preserves shared carriers by reusing STEP instances.

Units and metadata

Coordinates are written without rescaling and the representation context declares millimetres. Supply geometry in millimetres before export. The context uses the IR linear tolerance as its uncertainty value; plane and solid angles use radians and steradians.

StepWriteOptions controls FILE_NAME metadata. An empty timestamp produces 1970-01-01T00:00:00, which keeps default output deterministic. The first body name, when present, supplies the STEP product name. product_name supplies the FILE_NAME name instead.

Losses and errors

The writer exports representable geometry and records reductions in StepReport::losses. Review these notes before accepting the file. In particular:

• faces on unknown surfaces and edges without typed 3D curves are omitted;
• body transforms are not applied, so affected coordinates remain in body-local space;
• coedge pcurves, colors, appearances, source attributes, passthrough records, and parametric history are not emitted;
• procedural geometry is reduced to its solved curve or surface carrier;
• signed sphere radii and nonstandard torus minor radii are normalized where required by the emitted STEP entity.

An empty or fully unrepresentable model still produces a syntactically complete file with an empty geometric representation and a warning. StepError reports only failures from the output sink. Because output is streamed, an I/O failure can leave a partial file.

StepReport::entity_counts groups DATA instances by entity keyword, and StepReport::total_entities gives the complete DATA instance count. StepReport::error_count counts loss notes whose severity is at least Error; lower-severity losses still require caller review.

References

• API documentation
• Format support
• Architecture and crate map
• Clean-room and legal policy
• Repository

Requires Rust 1.88 or later. Licensed under Apache-2.0.