PMI Extraction System

Product Manufacturing Information (PMI) extraction from STEP AP242 files, with fallback support for AP203/AP214 legacy formats.

Overview

The PMI extraction system enables extraction and 3D visualization of manufacturing annotations embedded in CAD files. This includes:

Dimensions - Linear, angular, diameter, and radius measurements
Geometric Tolerances (GD&T) - Form, orientation, location, and runout controls
Datums - Reference features for tolerance specifications
Surface Finishes - Roughness parameters (Ra, Rz, etc.)
Weld Symbols - AWS A2.4 / ISO 2553 compliant symbols
Notes - Text annotations and callouts
Graphical PMI - Legacy presentation annotations

Architecture

┌─────────────────────────────────────────────────────────────┐
│                     Frontend (React)                        │
│  ┌─────────────────┐  ┌─────────────────┐                   │
│  │   STEPViewer    │  │ useCADProcessing│                   │
│  │   (Three.js +   │◄─│     (Hook)      │                   │
│  │   CSS2DRenderer)│  └────────┬────────┘                   │
│  └─────────────────┘           │                            │
│                                ▼                            │
│  ┌─────────────────────────────────────────────────────────┐│
│  │                   cadBackend.ts                         ││
│  │  Mode: 'custom' | 'byob' | 'frontend'                   ││
│  └─────────────────────────────────────────────────────────┘│
└────────────────────────────────┬────────────────────────────┘
                                 │ HTTP/JSON
                                 ▼
┌─────────────────────────────────────────────────────────────┐
│               Backend (Python/FastAPI)                      │
│  ┌─────────────────┐  ┌─────────────────┐                   │
│  │   step_parser   │  │  pmi_extractors │                   │
│  │   (Text Parser) │─▶│  (7 Extractors) │                   │
│  └─────────────────┘  └─────────────────┘                   │
└─────────────────────────────────────────────────────────────┘

Backend Components

1. Step Parser (`step_parser.py`)

Direct text parsing of ISO 10303-21 (STEP Part 21) files.

Key Features:

Regex-based entity extraction
Entity graph traversal
Reference resolution (#123 → entity)
Statistics and validation

Parsed Entity Types:

DIMENSIONAL_SIZE, DIMENSIONAL_LOCATION, ANGULAR_LOCATION
GEOMETRIC_TOLERANCE, POSITION_TOLERANCE, FLATNESS_TOLERANCE
PERPENDICULARITY_TOLERANCE, SURFACE_PROFILE_TOLERANCE
DATUM, DATUM_FEATURE, DATUM_REFERENCE
PLUS_MINUS_TOLERANCE, LIMITS_AND_FITS
SURFACE_TEXTURE_REPRESENTATION
EXTERNALLY_DEFINED_SURFACE_SIDE_STYLE
DRAUGHTING_PRE_DEFINED_COLOUR

2. PMI Extractors (`pmi_extractors.py`)

Seven specialized extractors for different PMI types:

Extractor	STEP Entities	Output
`DimensionExtractor`	DIMENSIONAL_SIZE, DIMENSIONAL_LOCATION, ANGULAR_LOCATION	Linear, angular, diameter, radius dimensions
`ToleranceExtractor`	GEOMETRIC_TOLERANCE, *_TOLERANCE	GD&T symbols with datum refs
`DatumExtractor`	DATUM, DATUM_FEATURE	Datum labels (A, B, C)
`SurfaceFinishExtractor`	SURFACE_TEXTURE_REPRESENTATION	Ra, Rz values
`WeldSymbolExtractor`	EXTERNALLY_DEFINED_*	Fillet, groove, spot welds
`AP203AP214Extractor`	DRAUGHTING_, ANNOTATION_	Graphical PMI for legacy files
`AnnotationExtractor`	ANNOTATION_PLANE, DRAUGHTING_*	Position enrichment

3. GD&T Symbol Mapping

Per ASME Y14.5 / ISO 1101:

Tolerance Type	Symbol
Flatness	⏥
Straightness	⏤
Circularity	○
Cylindricity	⌭
Profile (Line)	⌒
Profile (Surface)	⌓
Parallelism	∥
Perpendicularity	⊥
Angularity	∠
Position	⌖
Concentricity	◎
Symmetry	⌯
Circular Runout	↗
Total Runout	↗↗

Material Condition Modifiers:

Ⓜ - Maximum Material Condition (MMC)
Ⓛ - Least Material Condition (LMC)
(none) - Regardless of Feature Size (RFS)

Frontend Components

1. CAD Backend Configuration (`src/config/cadBackend.ts`)

Centralized configuration for backend switching:

type CADBackendMode = 'custom' | 'byob' | 'frontend';

// custom: Eryxon3D Docker backend (recommended)
// byob: Bring Your Own Backend (CAD Exchanger SDK, etc.)
// frontend: Browser-only via occt-import-js (fallback)

Environment Variables:

VITE_CAD_SERVICE_URL=http://localhost:8888
VITE_CAD_SERVICE_API_KEY=your-api-key
VITE_CAD_BACKEND_MODE=custom  # optional override

2. CAD Processing Hook (`src/hooks/useCADProcessing.ts`)

React hook for CAD processing and PMI management.

PMI Data Types:

interface PMIData {
  version: string;
  source?: string;          // 'text_parser' | 'xcaf'
  schema?: string;          // 'AP242' | 'AP203/AP214'
  dimensions: PMIDimension[];
  geometric_tolerances: PMIGeometricTolerance[];
  datums: PMIDatum[];
  surface_finishes?: PMISurfaceFinish[];
  weld_symbols?: PMIWeldSymbol[];
  notes?: PMINote[];
  graphical_pmi?: PMIGraphical[];
  statistics?: PMIStatistics;
}

3. STEP Viewer Component (`src/components/STEPViewer.tsx`)

Three.js-based 3D viewer with PMI overlay.

PMI Visualization:

CSS2DRenderer for labels positioned in 3D space
Leader lines connecting labels to geometry
Color-coded by PMI type:
- Cyan: Dimensions
- Purple: GD&T Tolerances
- Green: Datums
- Orange: Surface Finishes
- Red: Weld Symbols
- Slate: Notes
- Indigo: Graphical PMI

Filter Controls:

All / Dimensions / Tolerances / Datums / Surface / Welds / Notes / Legacy

Supported File Formats

Format	Schema	PMI Support
STEP AP242	ISO 10303-242	✅ Full semantic PMI
STEP AP214	ISO 10303-214	⚠️ Graphical PMI only
STEP AP203	ISO 10303-203	⚠️ Graphical PMI only
IGES	-	❌ No PMI

Test Data

NIST PMI test files located at: services/eryxon3d/NIST-PMI-STEP-Files/

Run batch test:

cd services/eryxon3d
python test_text_parser.py

Test Results - AP242 Files (17 NIST files):

Success Rate: 100%
Total Dimensions: 261
Total Tolerances: 360
Total Datums: 114
Average Processing Time: ~1.3 seconds/file

Test Results - AP203 Files with PMI (5 NIST files):

Success Rate: 100%
Total Graphical Dimensions: 43
Total Graphical Annotations: 60+ (FCF, datums, notes)
Average Processing Time: ~0.8 seconds/file

API Reference

Process Endpoint

POST /process
Content-Type: application/json
X-API-Key: your-api-key

{
  "file_url": "https://storage.example.com/part.stp",
  "file_name": "part.stp",
  "include_geometry": true,
  "include_pmi": true,
  "generate_thumbnail": false,
  "thumbnail_size": 256
}

Response:

{
  "success": true,
  "geometry": {
    "meshes": [...],
    "bounding_box": {...},
    "total_vertices": 12345,
    "total_faces": 4567
  },
  "pmi": {
    "version": "2.0",
    "source": "text_parser",
    "schema": "AP242",
    "dimensions": [...],
    "geometric_tolerances": [...],
    "datums": [...],
    "surface_finishes": [...],
    "weld_symbols": [],
    "notes": [],
    "graphical_pmi": [],
    "statistics": {
      "dimension_count": 21,
      "tolerance_count": 6,
      "datum_count": 3,
      "surface_finish_count": 0,
      "weld_count": 0,
      "is_legacy_format": false
    }
  },
  "processing_time_ms": 1423
}

Known Limitations

Position Accuracy: PMI positions are extracted from STEP annotation planes when available. For files without annotation placement data, positions default to origin (0, 0, 0).
Legacy Format Support: AP203/AP214 files only contain graphical (presentation) PMI, not semantic PMI. Dimension values may need to be parsed from text strings.
Complex Tolerance Zones: Composite tolerances and projected tolerance zones are extracted but may not fully render all modifier symbols.
Weld Symbol Complexity: Multi-pass welds and non-standard symbols may not be fully parsed.

References

Chen et al. (2025) “Three-Dimensional Visualization of PMI in a Web Browser”
ISO 10303-242:2020 (STEP AP242 Ed. 2)
ASME Y14.5-2018 (GD&T Standard)
ISO 1101:2017 (Geometrical Tolerances)
ISO 1302:2002 (Surface Texture Indication)
AWS A2.4 / ISO 2553 (Welding Symbols)

Changelog

v2.0 (Current)

Text-based parsing bypasses broken pythonocc bindings
Added surface roughness symbol extraction
Added weld symbol extraction
Added AP203/AP214 legacy format support
Configurable backend switching (custom/byob/frontend)
100% test coverage on NIST AP242 files

v1.0 (Previous)

XCAF-based extraction via pythonocc-core
Limited to basic dimensions and tolerances
Frequent crashes due to binding issues