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. [StepCodec::plan] resolves the requested StepSchema from the encoder catalog. StepCodec implements both Codec decode and Encoder write. The cadmpeg CLI uses the same model.

Support: L8 (ladder).

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

Use StepCodec through [Encoder::plan]. The plan resolves and validates a catalog target before producing bytes and an export report.

The encoder emits the Part 21 envelope for the named 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.

Bodies absent from every product definition's body list are written once in model coordinates in a representation linked to the root product. Claimed bodies keep their component ownership and occurrence placements. Without a unique local root product, the writer creates a separate model product for the unclaimed bodies. The stable step/product.body-without-representation loss code reports the count of bodies assigned to the root. Its message states this assignment. The code, taxonomy, and severity remain unchanged, so --reject-lossy still refuses this assignment.

A procedural surface or curve with no STEP construction and no writable solved carrier is written as a sampled cubic B_SPLINE_SURFACE_WITH_KNOTS or B_SPLINE_CURVE_WITH_KNOTS carrier when cadmpeg can evaluate it over a finite parameter domain. This covers ruled and sum surfaces, surfaces whose domain comes from their trim pcurves, and curves other than helices. Helix curves and helix surfaces without a solved carrier take the fitted-helix path instead and are never sampled. The knots keep the source parameters, so the trim pcurves of the face keep their chart. Each carrier is a chain of cubic Bézier patches that interpolate the procedural points. The writer doubles the patch count of an axis until residual probes on the knot lines and inside each patch are at most one quarter of the model linear tolerance. A sampled edge curve and its sampled surface are then within one half of that tolerance at the probes; the probes do not give a global bound between them. Before sampling, each trim pcurve of any kind must evaluate at both ends, inside the domain and onto its edge vertex. Refinement stops at 1,024 patches per axis. One export permits 1,048,576 approximation poles, 8,388,608 point samples, and 67,108,864 evaluation work units. The writer reports the sampled carriers once, as geometry.procedural-sampled-to-bspline. A carrier with no evaluator, no finite domain, inconsistent trims, a failed fit, or an exhausted budget keeps the omission report, and a surface whose fit failed is not sampled again; none of these fails the export.

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; the target StepSchema is selected by Encoder::plan, not stored in the options. 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.

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;
unsupported procedural definitions emit their solved carrier with a machine-readable loss;
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 covers StepError::Io from the output sink. Because output is streamed, 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. Inspect ExportReport::losses for each loss and its severity; lower-severity losses still require caller review.

References

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