Reference Data Geometry

Relevant source files

The following files were used as context for generating this wiki page:

• src/convert/adapters/solidworks/container/Parasolid.py
• src/convert/adapters/freecad/Archive.py
• src/convert/adapters/solidworks/core/Adapter.py
• re/solidworks/README.md
• re/solidworks/archive/Grammar.md
• re/solidworks/features/Revolve.md

Geometry Translation (Parasolid & OpenCASCADE)

Kit provides bidirectional translation between CAD-neutral B-rep models and vendor-specific geometry formats, primarily focusing on Parasolid (used by SOLIDWORKS) and OpenCASCADE (used by FreeCAD). The system handles the extraction, transformation, and re-injection of B-rep data into proprietary containers.

Parasolid Translation

Parasolid translation manages the extraction and encoding of .x_t (text) and .x_b (binary) geometry data within SOLIDWORKS .SLDPRT and .SLDASM files.

Geometry Extraction

Kit identifies Parasolid payloads by scanning compound stream records for specific magic numbers or headers. It identifies native Parasolid content within raw-deflate streams. The decoder extracts compressed Parasolid transmit blobs and converts them into neutral BrepModel structures.

Payload Management

The following diagram illustrates the flow of Parasolid data during a SOLIDWORKS part read:

flowchart TD
    A[SLDPRT Archive] --> B{Scan Records}
    B -->|Match Magic| C[Extract Partition Stream]
    C --> D[Decompress Zlib Blob]
    D --> E[Parse Parasolid Transmit File]
    E --> F[Neutral BrepModel]

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The system identifies Contents/Config-0-Partition as the primary Parasolid body cache in SOLIDWORKS files.

Feature-Based Rebuilds

Kit can drop the Parasolid geometry cache entirely in SOLIDWORKS files. If the cache is absent, SOLIDWORKS rebuilds the identical solid geometry from the feature history records (Contents/Config-0-ResolvedFeatures) and XML metadata.

OpenCASCADE Translation

OpenCASCADE translation facilitates B-rep interchange for FreeCAD .FCStd files, typically using the BREP format.

BREP Serialization

The system converts neutral B-rep models into OpenCASCADE-compatible ASCII BREP strings. These strings start with the standard header: CASCADE Topology V1, (c) Matra-Datavision.

FreeCAD Geometry Logic

FreeCAD adapters handle geometry through Part::PropertyPartShape properties. Kit manages primary .brp (BREP) files and associated sidecar files like .Map.txt (Element Maps) to preserve topological naming and entity mappings.

Comparison of Geometry Formats

Format	Native CAD	Storage Method	Neutral Representation
Parasolid	SOLIDWORKS	Compressed blobs in streams	BrepModel / ParasolidPayload
OpenCASCADE	FreeCAD	ASCII .brp files in ZIP	BrepModel / ProvenAsciiBrep

Cross-Format Data Flow

Conversion between formats utilizes a central neutral model.

sequenceDiagram
    participant S as SOLIDWORKS (.SLDPRT)
    participant K as Kit Neutral (BrepModel)
    participant F as FreeCAD (.FCStd)

    S->>K: Extract Parasolid Blob
    Note over K: Convert to Neutral Topology
    K->>F: Serialize to OCC BREP (.brp)
    Note over F: Insert into FCStd ZIP

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Geometry Consistency Rules

• Stale Caches: Stale derived caches (like bounding boxes or Parasolid face blobs) are generally safe to leave in the document; the vendor application recomputes them on load.
• Incorrect Caches: Writing plausible but mathematically incorrect geometry caches often leads to application crashes or zero-volume bodies.
• Feature Identity: SOLIDWORKS identifies bodies via a final_feature_id which must correlate with the B-rep bodies stored in the Parasolid partition.

Implementation Details

Parasolid Payload Schema

The BrepPayload object for Parasolid data includes specific attributes used for reconstruction:

Attribute	Type	Description
format_id	string	Set to "parasolid"
kind	string	e.g., "partition" or "shape"
wrapper_offset	integer	Byte offset of the vendor wrapper
compressed_size	integer	Size of the zlib-compressed payload

Code Snippet: OpenCASCADE BREP Header Validation

Kit validates OpenCASCADE ASCII BREP strings by checking for the structural header.

Consult the linked source file for the exact implementation; this reference does not duplicate executable code.