JT Import-Export Component

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JT reader and writer for CAD applications

The JT Import-Export SDK reads and writes JT models and connects them to Open CASCADE document structures. It supports assembly trees, triangulation at multiple levels of detail, names, colors and transparency. Late loading and part processing options support applications that work with larger assemblies.

Work directly with JT models

The SDK exposes JT model structures for creating, exploring and modifying data programmatically, as well as reading and writing files. Assembly trees, part names, colors, transparency and triangulation at multiple levels of detail remain available to the application.

Late loading defers data access until the relevant content is needed. Parallel part processing, LOD management and object culling can be used when implementing a viewer for large assemblies. The reader and writer also support conversion between their supported JT versions.

JT structures, properties and compression

The documented structure coverage includes:

• LOD geometry represented by Vertex, Tri-Strip Set and Primitive Set elements.
• Geometric Transform and Material attributes.
• Late Loaded and String properties.
• PMI information, with the required presentation and semantic scope to establish during integration.
• Node elements other than Switch.
• Standard JT compression and encoding, including ZLIB and LZMA.

OCAF converters and programming examples

The OCAF-to-JT converter transfers document hierarchy, names and labels, colors and mesh representations. The reverse converter brings JT hierarchy, visual attributes and supported geometric representations into OCAF. Precise BRep import uses the Parasolid interface when the JT file contains embedded Parasolid BRep data.

DRAW command examples accompanying the SDK demonstrate these converters. They provide an integration reference for connecting a source CAD reader, the document representation and a JT writer.

Convert STEP to JT

A STEP-to-JT integration uses the OCCT STEP reader, prepares the model’s tessellation and visual attributes, then writes the JT document with this commercial component. Decide which assembly structure, names, colors and mesh levels of detail the receiving application needs.

Other source formats can use the same route through their respective readers. Parasolid input, ACIS input and DXF input require their corresponding commercial components.

Import JT BRep through the Parasolid interface

A JT file may carry visualization meshes, precise geometry, or both. JT BRep import is supported through the Parasolid interface when the file contains Parasolid BRep data. This route reads the embedded precise geometry into OCCT BRep shapes, which can be processed or exported to STEP through the OCCT workflow. Include the Parasolid interface in the integration for this capability.

For JT-to-STEP conversion, select the embedded BRep representation when precise CAD geometry is required. A JT file containing only tessellation can still supply mesh data, but has no embedded Parasolid BRep to import.

Tessellation does not establish recovery of the original analytic or NURBS surfaces. Specify whether the output must contain precise CAD geometry or whether a mesh representation is sufficient before selecting this conversion route.

JT to STL, glTF / GLB or USD

For USD / USDZ scenes, glTF / GLB or STL, import the JT content into the OCCT document workflow and use the appropriate downstream writer. Check how hierarchy, appearance and levels of detail map to the target format. STL is a triangle-mesh target; it does not retain the full JT assembly and attribute model.

For precise geometry, see reading Parasolid BRep embedded in JT, native BRep storage and JT-to-ACIS conversion. Browse the conversion catalog for other JT destinations.

Supported versions and evaluation checks

The published interface description lists JT reading for 8.1, 9.5, 10.0 and 10.5, and writing for 8.1, 9.5 and 10.0. Confirm the supported versions for the component delivery being evaluated.

Check	Why it matters
Source representation	Determines whether the workflow starts from mesh, BRep or both
Parasolid BRep import	Requires embedded Parasolid BRep in the JT file and the Parasolid interface
Output version	Must match the receiving application’s JT support
Assembly and appearance	Verify hierarchy, transforms, names, colors and transparency
Mesh quality and LOD	Balance visual detail, file size and application performance
PMI requirements	Identify the information needed and verify its handling separately

Review the CAD exchange format matrix and surface meshing SDK. Request a JT conversion evaluation with your source format, target, OCCT version and geometry requirements.