Importing STEP and IGES Data

Introduction#

STEP (Standard for the Exchange of Product Data, ISO 10303) and IGES (Initial Graphics Exchange Specification) are long-established neutral file formats for exchanging 3D CAD and geometric data between different engineering systems.
Unlike IFC, which encodes semantic and relational information for BIM and facility modeling, STEP and IGES primarily describe pure geometry — solids, surfaces, curves, and assemblies — without detailed object classification or material context.

Both formats are widely used in mechanical, manufacturing, and plant design domains, and FRI3D provides import support for them to facilitate integration of geometry-only models (e.g., mechanical enclosures, ducts, or equipment housings) into the simulation environment.

⚠️ Important Note:
STEP import functionality is currently limited in FRI3D. While basic geometry import is supported, advanced STEP features such as complex assemblies, advanced BREP operations, parametric data, and some STEP application protocols (APs) may not be fully supported. Import reliability may vary depending on the source CAD software and export settings. For production workflows requiring robust geometry import, consider using IFC format for building models or verify STEP import compatibility with your specific files.

Format Overview#

Format	Standard	Description	Typical Use
STEP (.stp, .step)	ISO 10303	Modern, extensible schema for 3D product data. Represents solids, assemblies, and topology with boundary representation (BREP).	Mechanical design, industrial parts, and equipment layouts
IGES (.igs, .iges)	ANSI Y14.26M / NIST	Legacy exchange format storing surfaces, wireframes, and annotations.	Older CAD data, wireframe and surface models

STEP files are structured as entities (e.g., ADVANCED_FACE, EDGE_LOOP, BREP_SOLID) referencing topology and geometry.
IGES files store lists of directory entries and parameter data sections defining curves, surfaces, and annotations.

Supported Entities and Classes#

FRI3D’s importer focuses on extracting geometry rather than full product semantics.
The following entity types are commonly recognized:

Category	STEP Entities	IGES Entities	Description
Solids	`ADVANCED_BREP_SHAPE_REPRESENTATION`, `MANIFOLD_SOLID_BREP`, `CLOSED_SHELL`	Type 186 (Manifold Solid BREP)	Closed solids used for volumetric representation
Surfaces	`ADVANCED_FACE`, `SURFACE_OF_LINEAR_EXTRUSION`	Type 128 (NURBS Surface)	Faces or patches representing part boundaries
Curves / Edges	`EDGE_CURVE`, `VERTEX_POINT`, `CIRCLE`, `LINE`	Type 126 (NURBS Curve), 100 (Circular Arc), 110 (Line)	Boundary edges and wireframes
Assemblies	`SHAPE_DEFINITION_REPRESENTATION`, `NEXT_ASSEMBLY_USAGE_OCCURRENCE`	—	Hierarchical organization of parts and sub-assemblies
Attributes (Limited)	`PRODUCT_DEFINITION`, `MATERIAL_DESIGNATION`	—	Optional naming or material metadata (often incomplete)

⚠️ Note:
Many STEP and IGES exporters differ significantly in how these entities are organized.
The same part may be represented as an ADVANCED_FACE group in one file and as a nested BREP_SOLID in another.
As a result, import reliability may vary between software sources.

Import Workflow in FRI3D#

File Detection
FRI3D automatically detects .stp, .step, .igs, or .iges extensions.
Parsing
Geometry is parsed using the Open Cascade (OCCT) kernel, which handles BREP and NURBS surfaces.
Topology Reconstruction
Solids, shells, and surfaces are reconstructed into watertight meshes suitable for simulation or visualization.
Tagging and Classification
Because STEP/IGES lack inherent semantic tagging, FRI3D infers categories based on naming conventions (e.g., part names, layer identifiers, or color attributes).
Simplification and Conversion
Geometry is optionally simplified to triangular meshes or bounding volumes for use in fire, smoke, or CFD modules.

Reliability and Limitations#

STEP and IGES import in FRI3D are considered best-effort features.

⚠️ Important:
STEP import functionality is currently limited in FRI3D. The following limitations apply:
Complex assemblies and hierarchical structures may not be fully preserved
Advanced BREP operations and complex surface definitions may be simplified or fail to import
Parametric data and feature-based modeling information are typically not preserved
Some STEP application protocols (APs) beyond AP203, AP214, and AP242 may have limited support
Import reliability varies significantly depending on the source CAD software and export settings
For production workflows requiring reliable geometry import, IFC format is strongly recommended for building models, or verify STEP import compatibility with your specific files before use.

General Limitations#

There is no guaranteed semantic consistency across files — identical parts exported from different CAD tools may have entirely different structures.
Many files include non-manifold geometry or incomplete topology that can lead to gaps or misclassified solids.
IGES often lacks surface orientation and volume closure, requiring post-processing or manual cleanup.
Attribute and material data are usually not preserved reliably.

Therefore, while FRI3D can import these formats for visualization and approximate geometric context, IFC import is recommended for robust and semantically consistent workflows.

Supported Versions#

Format	Supported Versions	Notes
STEP	ISO 10303-21 (AP203, AP214, AP242)	Best results with AP214 or AP242 files containing solid BREP definitions
IGES	Version 5.3 and later	Limited to surface and solid entity types only