STEP (ISO 10303-21)

@modelscript/step (languages/step) provides a native WebAssembly GLR parser, assembly hierarchy extractor, AP242 Geometric Dimensioning & Tolerancing (GD&T / PMI) analyzer, and Modelica MultiBody kinematic synthesizer for ISO 10303-21 Clear Text Encoding of the Exchange Structure (.step, .stp, .p21).

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Supported Extensions & Standards

Extension	Standard	Scope
.step, .stp, .p21	ISO 10303-21 (AP203, AP214, AP242)	B-Rep solid geometry, product assembly trees (NEXT_ASSEMBLY_USAGE_OCCURRENCE), kinematic joints, and PMI/GD&T tolerances

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Capabilities

1. Zero-Dependency STEP Part 21 Parser: Parses HEADER; and DATA; sections, #id = ENTITY_NAME(...) instances, nested typed parameters, and enumeration tokens into linear memory.
2. Assembly Hierarchy & Mass Properties (extractStepAssembly): Extracts PRODUCT_DEFINITION parts, NEXT_ASSEMBLY_USAGE_OCCURRENCE parent–child assembly trees, AXIS2_PLACEMENT_3D rigid-body frames, bounding boxes, and mass/inertia properties.
3. AP242 PMI & GD&T Extraction (extractStepAssembly): Extracts datum features (DATUM, DATUM_FEATURE, DATUM_SYSTEM) and 10 geometric tolerance categories (StepGeometricTolerance in languages/step/src/extractor.ts) for 3D tolerance stack-up analysis (ToleranceStackOracle):

GD&T Tolerance Kind	STEP AP242 Entity Name
flatness	FLATNESS_TOLERANCE
roundness	ROUNDNESS_TOLERANCE / CIRCULARITY_TOLERANCE
cylindricity	CYLINDRICITY_TOLERANCE
perpendicularity	PERPENDICULARITY_TOLERANCE
parallelism	PARALLELISM_TOLERANCE
position	POSITION_TOLERANCE
surface_profile	SURFACE_PROFILE_TOLERANCE
concentricity	CONCENTRICITY_TOLERANCE / COAXIALITY_TOLERANCE
runout	CIRCULAR_RUNOUT_TOLERANCE / TOTAL_RUNOUT_TOLERANCE
general	GEOMETRIC_TOLERANCE (with TOLERANCE_VALUE / LENGTH_MEASURE_WITH_UNIT)

4. Modelica MultiBody Kinematic Synthesis (mapStepToMultiBody): languages/step/src/multibody-mapper.ts translates STEP kinematic joints and AXIS2_PLACEMENT_3D transforms directly into Modelica.Mechanics.MultiBody components:
   • Kinematic Joints: Maps REVOLUTE_PAIR $\to$ Modelica.Mechanics.MultiBody.Joints.Revolute, PRISMATIC_PAIR $\to$ Joints.Prismatic, CYLINDRICAL_PAIR $\to$ Joints.Cylindrical, SPHERICAL_PAIR $\to$ Joints.Spherical, and PLANAR_PAIR $\to$ Joints.Planar with axis vectors n and connect(...) equations.
   • Static Frame Placements (MultiBodyFixedTranslation): Computes exact translation vectors r = {x, y, z} (converting MILLI to meters) and $3\times 3$ orthonormal orientation matrices from AXIS2_PLACEMENT_3D axis ($\hat{z}$) and ref_direction ($\hat{x}$) vectors to emit Modelica.Mechanics.MultiBody.Parts.FixedTranslation and Parts.BodyBox / Parts.BodyCylinder components.

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IDE & CAE Mesh Generation Actions

stepLanguage.actions (languages/step/src/language.ts) provides 6 built-in CAD/CAE workflows:

Action ID	Description
open_cad_viewer	Opens the interactive 3D B-Rep & assembly viewer for the .step model
generate_multibody	Synthesizes a Modelica.Mechanics.MultiBody .mo model from STEP assembly frames and joints
generate_fea_mesh	Tessellates the STEP B-Rep solid into a 3D tetrahedral CalculiX .inp finite element mesh
generate_cfd_mesh	Generates an unstructured .su2 surface/volume fluid mesh from the STEP geometry
create_fea_setup	Scaffolds a parametric .inpt CalculiX structural study linked to the STEP part
create_cfd_setup	Scaffolds a parametric .cfgt SU2 aerodynamic study linked to the STEP part

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Dedicated step-mcp Server Tools

The @modelscript/step MCP server (languages/step/src/mcp/server.ts) exposes two specialized tools for AI engineering agents:

• step_extract_entities: Parses a .step / .stp file and returns the structured assembly tree, AXIS2_PLACEMENT_3D coordinate frames, kinematic joints, and AP242 GD&T geometric tolerances.
• step_to_multibody: Generates complete Modelica.Mechanics.MultiBody code (including World, Parts.Body, Parts.FixedTranslation, Joints.*, and connect(...) equations) from a STEP assembly.

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Polyglot TGG Rules

@modelscript/step registers 5 bidirectional Triple Graph Grammar (TGG) rules in languages/step/src/language.ts:

Rule Name	Source (step)	Target Language	Target Construct
StepProductToSysML2Part	DataEntity (PRODUCT)	sysml2	PartDef
StepPropertyToSysML2Attribute	DataEntity (PROPERTY_DEFINITION)	sysml2	AttributeUsage
StepPlacementToSysML2Port	DataEntity (AXIS2_PLACEMENT_3D)	sysml2	PortUsage
StepRevoluteJointToModelicaRevolute	DataEntity (REVOLUTE_PAIR)	modelica	ComponentClause (Modelica.Mechanics.MultiBody.Joints.Revolute)
StepPrismaticJointToModelicaPrismatic	DataEntity (PRISMATIC_PAIR)	modelica	ComponentClause (Modelica.Mechanics.MultiBody.Joints.Prismatic)

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CLI Usage

# Parse and inspect the CST of an ISO 10303-21 STEP file
npx msx parse chassis.step

# Project a STEP assembly into a Modelica MultiBody model via TGG rules
npx msx polyglot project chassis.step --target modelica --out chassis.mo

# Verify cross-domain alignment between STEP CAD geometry and SysML v2 architecture
npx msx align chassis.step architecture.sysml

Diagnostic Rules

8 rules5 error3 warning Run with msx lint

Code	Rule	Severity	Message
M1001	step-syntax-error	error	STEP file syntax error: <detail>.
M1002	missing-header-section	error	STEP exchange file is missing mandatory 'HEADER;' section.
M1003	missing-schema-declaration	warning	STEP header lacks a recognized 'FILE_SCHEMA' declaration (e.g. AP203, AP214, AP242).
M1004	missing-data-section	error	STEP exchange file is missing mandatory 'DATA;' section.
M1005	unresolved-entity-reference	error	Referenced STEP entity '#<entityId>' is not defined in the DATA section.
M1006	duplicate-entity-id	error	Entity ID '#<entityId>' is declared more than once in the DATA section.
M1007	empty-data-section	warning	STEP DATA section contains no entity records.
M1008	unsupported-ap-schema	warning	Application Protocol schema '<schema>' may not support complete PMI or B-Rep extraction.

Generated from languages/step/src/errors.ts. All languages →