IFCCAD and OCDraw

Website: IFCCAD & OCDraw Explorer

OpenAEC develops two experimental, open CAD drawing formats in parallel. IFCCAD is a CAD drawing profile built on IFCX structure and composition. OCDraw is a standalone, application-independent drawing model and exchange format, with direct control over storage and performance.

Format	Direction	Contract and implementation
OCDraw	A standalone, application-independent CAD drawing model, with direct control over storage and performance	Contract, core, CAD conversion
IFCCAD	A CAD drawing profile using IFCX structure and composition, exploring a place for drawings in the evolving IFCX ecosystem	Experimental contract, core, CAD conversion

Both routes develop typed drawing content, strict validation and explicit CAD conversion diagnostics. Their models, schemas and encoding routes stay separate. OCDraw opens independently of IFCX. Current capabilities differ; support in one route does not establish support in the other. IFCCAD is a provisional profile, not an official buildingSMART CAD standard.

An OCDraw drawing contains typed geometric entities, layers, layouts, entity appearance choices, named simple line patterns, shared block definitions, and drawing-bound state. It opens without IFCX. The JSON format marker is open_cad_drawing. The initial 0.1.0 contract and entity schema v1 are provisional until contract completion and verification.

Architecture

• schemas/ocdraw: language-neutral logical registry, logical rules, JSON mapping and document schema.
• conformance/next/ocdraw: candidate valid and invalid drawings.
• src/ocdraw/logical: typed model and shared semantic validation.
• src/ocdraw/codec/json: physical fields, column packing, decoding and encoding.
• src/ocdraw/read.rs, build.rs, build/: validated access and typed construction.
• IFCCAD profile rules: ordinary IFCX declarations, temporary local-value supplements and graph/domain obligations.
• src/ifccad and schemas/ifccad: separate IFCCAD model, source graph, validation, profile and encoding.
• src/geometry_kernel: shared primitive geometry, placement, validation, bounds and analytic clip calculations, independent of CAD runtimes.
• Both cores separate encode.rs orchestration, codec/ physical mapping and storage.rs file IO; see API conventions and migration.
• crates/ocdraw-convert: conversion between OCDraw and pinned opencadcodec CadDocument; DXF/DWG IO remains a CAD codec responsibility. Both converters use pinned upstream opencadcodec under its upstream name.
• crates/ifccad-convert: the independent IFCCAD conversion route.
• crates/cad-preservation: audited codec-specific spline byte snapshots shared by the converters; envelopes and predicates stay format-specific.
• crates/cad-presentation-convert: CAD-only color/quantization rules and strict viewport XRecord grammar; native reference binding stays in each adapter.
• crates/cad-geometry-convert: shared CAD geometric preparation, tolerance resolution and primitive/nested occurrence accuracy proofs for both routes.
• crates/viewer, crates/browser: file inspection/conversion adapters. The inspector presents data and can embed Open CAD Studio to view original CAD and generated CAD through either route; see website.

Reader and writer use shared logical validation. Generated outputs are loaded through the production reader. CAD conversion consumes typed drawing values, without JSON inspection. Core has no CAD runtime dependency.

OcdrawDocument is the complete mutable logical drawing. The builder can return it with build_document(); finish() uses that document and the common encoder. Reading exposes an immutable document snapshot, which can be consumed for edits. encode_ocdraw_document() retains IDs, allocation watermarks and valid supplied bounds; bounds recomputation is explicit. See the document lifecycle.

Current geometry includes XYZ lines, oriented points, placed circles/arcs and ellipses, planar polylines with bulges, direct XYZ spatial polylines, and local shared block instances. Layouts, appearances, plot state, named/current UCS, model windows, paper canvases and paper viewports have typed records. Active viewport clips support circles, full ellipses and closed planar polylines with straight or bulged segments. Direct CAD conversion resolves clip references independently of draw order, preserving activation separately from stored boundaries. The new upstream pin includes clipping and DXF angle repairs; the remaining local codec patch retains the independent viewport-off bit. The DWG profile includes a paper canvas. See the dependency audit and the converter coverage contracts for limits. Named simple patterns retain their definitions, unused records, local references, scale and polyline generation. Complex text/shape patterns become named continuous patterns with loss evidence under Allow; Reject refuses this fallback. Both routes have independent native Text/MText, local font requests and text styles, rich paragraph/inline formatting, column/background state and explicit estimated bound quality. Their CAD routes separately qualify a bounded text profile and expose unverified glyph geometry separately from anchor accuracy. See text support.

Both routes also provide native Solid and LinePattern Hatch with stored planar boundaries, three area rules and optional same-owner source relations. Contour exchange and unassessed fill are separate evidence; see Hatch support. Embedded pattern families retain origin, rotation, scale, signed spacing and ordered dash/gap/dot definitions; CAD support uses qualified explicit families.

Unsupported conversion semantics are diagnosed or rejected. Numerical accuracy has a hard unit-aware tolerance, including nested block occurrences. See export coverage and import coverage for limits.

Parallel development

OCDraw and IFCCAD are active development tracks. CAD semantics are considered together and implemented against each format's own contract. Reference drawings, strict readback and comparable retained-content measurements inform both tracks. Each route can expand at its own pace while keeping coverage differences visible.

OCDraw focuses on standalone CAD functionality and measured storage/performance improvements. IFCCAD explores drawing integration with IFCX identity, relationships and composition. Future IFC associations, incremental collaboration and efficient IFCX storage require concrete designs and upstream coordination; they are not current capability claims.

Compact, directly openable files are an adoption goal for both routes. Physical encoding choices follow measured size, opening time and memory use. Binary storage and compression per part remain options to investigate, not selected contracts.

Development sequence

The typed model/JSON boundary, standalone parity and package retirement are implemented. The complete document lifecycle supports direct logical conversion, shared validation and identity-preserving core encoding. Scope lists now define ownership and order; the JSON mapping uses present stream names without a stream directory. Rust gates, candidate conformance and the standalone primitive exchange experiment pass. Recording 0.1.0 and schema v1 as the first supported version remains a separate step. ROADMAP.md defines sequencing and exit criteria.

OCDraw's first bounded preservation slice stores complete typed spline snapshots with editable native common properties, ordinary ownership/order, durable readback and separately qualified CAD restoration. Capture is opt-in; it does not add native spline geometry. Broader providers, raw/private/shared codec storage and external links such as IFC associations remain future work. See preservation. No generic foreign-semantic extension protocol or IFCPR resource is introduced. IFCCAD is integrated on main as an independent experiment alongside OCDraw, with separate models, schemas, validation and direct conversion routes. The explorer opens either native format and converts DWG/DXF through the chosen route. IFCCAD geometry now includes points, signed arcs, full/partial ellipses, bulged planar and straight spatial paths, optional scope bounds and expanded viewport clips. Both converters share adjustable accuracy with independent coordinate-domain evidence. This remains a provisional 0.1.0 revision; see shared geometry. Both formats now retain layout media independently of plot settings. IFCCAD adds effective plot output, limits, plot-style mode and Paper-space linetype-scaling parity; both CAD routes assess Paper accuracy through each fixed physical plot mapping. The provisional contract removes IFCCAD's independent Paper coordinate unit. See layout output for numeric/raster restrictions. Both routes now offer independent opaque SPLINE preservation pilots: durable storage, optional exact native common properties, guarded fresh CAD restoration and explicit incomplete geometry evidence. IFCCAD Paper guards use exact effective physical mapping. Broader raw/private/shared preservation and native spline geometry remain separate follow-up work; see preservation.

Both formats now retain UCS, Model windows, Paper canvases and per-viewport grid/snap state, including unspecified choices and dormant values. Known active Paper layouts survive DXF/DWG exchange through consistent reserved-block roles. Qualified CAD limitations remain explicit; see workspace state. Both native presentation models now retain concrete color identity, layer/common visibility, PointDisplay and ordinary block metadata. Relational viewport appearance overrides map through qualified CAD XRecords. OCDraw now also converts perspective Paper cameras; quality/DPI stays on layouts while viewport ShadePlot stores mode only. The Paper grid and DXF ShadePlot repairs remain upstream-gated; see presentation and transport coverage.

Using the implementation

cargo run --example write_ocdraw -- drawing.ocdraw.json
cargo run -p viewer -- drawing drawing.ocdraw.json
cargo run -p ocdraw-convert --example minimal_to_dxf -- drawing.ocdraw.json drawing.dxf

New drawing files refuse to overwrite existing files. The crate and companion README documents describe public APIs. Implementations can independently use the published schemas and conformance materials.

Verification

cargo fmt --all -- --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace

Controlled measurements have separate reproduction instructions under docs/benchmarks; historical IFCCAD ratios do not measure standalone OCDraw. The repeatable four-format experiment compares OCDraw, IFCCAD, DXF and DWG with identical retained content. See the synthetic/foundation report and large DXF report. Size measurements are run only on explicit user request, for the full experiment or a requested selection. They are never automatic checks for a new main revision or converter/encoding/dependency changes. Focused correctness tests still apply. Licensed under MPL-2.0.

IFCCAD capabilities and resources

The independent IFCCAD proof is available in src/ifccad, with its experimental contract, sample and evaluation. Its direct converter connects the supported subset to opencadcodec CadDocument, including named simple line patterns, scales and polyline pattern generation. See the geometry sample and line-pattern sample. Geometry validation and length-unit tokens use shared neutral helpers; the two drawing models, schemas and encoding routes remain separate. The IFCCAD & OCDraw Explorer now opens IFCCAD and roundtrips through DXF/DWG using its own converter. Model and multiple Paper layouts convert with explicit tab order, optional media and explicit output mappings. Paper viewports now retain orthographic/perspective camera, depth/display state and circle/full-ellipse/closed straight-or-bulged path clipping. CAD viewport exchange uses the explicit development codec repairs described in the converter; effective plot settings retain the documented CAD limits.

History and naming

The current IFCX-native CAD profile was previously called IFCX-CAD and is now named IFCCAD. Its Rust module, public types, converter crate, schema files and browser APIs use IFCCAD names. See the API migration for the previous-to-current names. The underlying IFCX syntax, .ifcx file extension and ifccad:: schema namespace retain their meaning.

The IFCCAD name also belonged to an earlier package experiment combining an IFCX semantic graph with IFCDR drawing resources and optional IFCPR source preservation. That package architecture, its readers and writers, and its active schemas are retired. Today's IFCCAD and OCDraw are independent drawing models with their own schemas, validation and conversion routes.

Numbered conformance collections remain immutable. The historical package design and Git history retain the earlier experiment's context.

Local maintenance

Run pwsh -NoProfile -File scripts/cleanup_local.ps1 to audit local worktrees and build caches. Removal requires an explicitly selected, unused worktree; the script retains local changes and unfamiliar files for review.