three-iges-loader

Architecture

This repository is a pnpm monorepo implementing IGES → Three.js in layers. Each layer has one job; only the top layer imports three.

Packages

Package	Path	Depends on	Responsibility
iges-core	packages/iges-core	—	Parse IGES 5.3, build entity map, resolve pointers/transforms, decode wireframe geometry
three-iges-loader	root src/	iges-core, three (peer)	IGESLoader, toThreeGroup() tessellation

Data flow

.iges file (80-column ASCII)
        │
        ▼
  splitSections()          ← packages/iges-core/src/parse/sections.ts
        │
        ├── GlobalSection
        ├── DirectoryEntry[]  (2 lines per entity)
        └── Parameter records
        │
        ▼
  parseIGES() → IGESModel    Map<deSequence, RawEntity>
        │
        ▼
  resolveReferences() → ResolvedIGESModel
        │                  • Type 124 transforms
        │                  • ENTITY_DECODERS → GeometryEntity[]
        ▼
  toThreeGroup() → THREE.Group   (root src/three/toThree.ts)

Adding a new entity type

1. Read the parameter table in ENTITY_IMPLEMENTATION.md.
2. Add packages/iges-core/src/entities/decoders/typeNNN.ts.
3. Register in packages/iges-core/src/entities/registry.ts.
4. Add geometry to types.ts if needed.
5. Handle tessellation in src/three/toThree.ts (or defer if surface).
6. Add a fixture under test/fixtures/ and tests in packages/iges-core/test/.

Coordinate systems

• IGES model space is typically Z-up.
• Three.js is Y-up.
• A single root rotation (rotation.x = -π/2) is applied in toThreeGroup(), not per entity.

Out of scope (for now)

Surface entities (128, 144, B-rep 186, etc.) live on the ROADMAP under Phase C/D.

Optional future package: iges-occt using Open CASCADE WASM for full B-rep tessellation.

AI / contributor entry points

• AGENTS.md — rules for automated contributors
• ENTITY_IMPLEMENTATION.md — per-type checklist
• ROADMAP.md — phased delivery plan

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