cadmpeg-codec-step

cadmpeg-codec-step reads and writes ISO 10303-21 Part 21 exchange structures for AP203 editions 1–2, AP214, and AP242 editions 1–3. Schema selection uses StepSchema through StepWriteOptions. StepCodec implements both Codec decode and Encoder write. The cadmpeg CLI uses the same model.

Support level: L9 for AP242 editions 1–3 and AP203 editions 1–2/AP214.

Install

cargo add cadmpeg-codec-step cadmpeg-ir

Decode a Part 21 file

use cadmpeg_ir::{Codec, DecodeOptions};
use cadmpeg_codec_step::StepCodec;
use std::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut input = File::open("part.step")?;
    let result = StepCodec::default().decode(&mut input, &DecodeOptions::default())?;

    for loss in &result.report().losses {
        eprintln!("{:?}: {}", loss.severity, loss.message);
    }
    println!("{} bodies", result.ir().model.bodies.len());
    Ok(())
}

Decode transfers millimeter-normalized analytic and NURBS geometry, connected solid, sheet, and wire topology with pcurves, product identity and occurrences, AP242 tessellation where present, layers, colors, visibility, and PMI. Named opaque application records retain identity and byte spans when retained.

Write a document

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_codec_step::{
    write_step, StepSchema, StepUnsupportedPolicy, StepWriteOptions,
};

let ir = unit_cube();
let file = File::create("cube.step")?;
let mut output = BufWriter::new(file);
let options = StepWriteOptions {
    schema: StepSchema::Ap242Edition3,
    unsupported: StepUnsupportedPolicy::Reject,
    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 Part 21 envelope for the selected schema, product and representation context, and reachable shape. Coverage includes solid, sheet, and wire bodies plus standalone geometry; coedge pcurves; rigid body placement; products and occurrences; AP242 tessellation; visibility; layers; named colors; and semantic or presentation PMI where the target application protocol carries them. 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 and the target StepSchema. 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 ExportReport::losses. Review these notes before accepting the file. StepUnsupportedPolicy::Report writes the representable subset. StepUnsupportedPolicy::Reject returns StepError::Unsupported before any output byte is written.

In particular:

faces on unknown surfaces and edges without typed 3D curves are omitted;
non-rigid body transforms and non-identity root occurrence placements report losses;
coedge pcurves emit their geometry; native-only pcurve metadata is not represented in STEP;
textures, shaders, source attributes, and retained opaque records report losses or take the refusal path under Reject;
unsupported procedural definitions emit their solved carrier with a machine-readable loss, or fail under Reject;
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 under Report policy. StepError covers StepError::Unsupported under Reject and StepError::Io from the output sink. Because output is streamed after the Reject gate, an I/O failure can leave a partial file.

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

References

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