JT (visualization format)
JT is a 3D data format developed by Siemens PLM Software (formerly UGS Corp.) and is used for product visualization, collaboration, and CAD data exchange. It can contain any combination of approximate (faceted) data, exact boundary representation surfaces (NURBS), Product and Manufacturing Information (PMI), and Metadata (textual attributes) either exported from the native CAD system or inserted by a product data management (PDM) system. It is probably the most widely used 3D visualization format for discrete manufacturing with over 4,000,000 JT-enabled licenses of software in use.
JT files are used in product lifecycle management (PLM) software programs such as Teamcenter (Lifecycle Visualization) by engineers and other professionals that need to analyze the geometry of complex products. The format and associated software is structured so that extremely large numbers of components can be quickly loaded, shaded and manipulated in real-time. Because all major 3D CAD formats are supported, a JT assembly can contain a mixture of any combination which has led to the term "multi-CAD". As JT is typically implemented as an integral part of a PLM solution, the resulting multi-CAD assembly is managed such that changes to the original CAD product definition files can be automatically synchronized with their associated JT files resulting in a multi-CAD assembly that is always up-to-date.
Because JT files are inherently "lightweight" (~1-10% of the size of a CAD file) they are ideal for internet collaboration. With the growing trend toward globalization, more companies are leveraging resources wherever they are available in the world. Collaboration using JT allows companies to send 3D visualization data to suppliers and partners much more easily than sending the associated "heavy" CAD files. In addition, real-time, on-line collaboration is easier because the amount of information sent back-and-forth across the internet is reduced. Finally, JT provides an inherent security feature such that intellectual property does not have to be shared with inappropriate parties. As indicated above, JT can contain any combination of data such that the right amount of information can be shared without exposing the underlying proprietary design definition information.
JT is often used for Digital mockup (DMU) work, which allows engineers to validate that a product can be assembled together without interferences long before a physical prototype could be produced. This "spatial validation" is enabled by precise measurements and cross-sectioning as well as sophisticated clearance/interference detection. Leveraging JT for digital mockup allows users to reduce or eliminate costly physical prototypes and enables decision-making to occur much earlier in the development process.
Finally, JT is used as a CAD interoperability format for exchanging design data for Collaborative Product Development, where JT files are created by translating data from CAD systems such as NX (Unigraphics), I-DEAS, Solid Edge, Catia, Pro/Engineer, or Autodesk Inventor. JT is supported by an open industry forum, the JT Open Program, that is an open, influential community of users, software vendors, and interested parties advocating the use of JT as the visualization, collaboration and data-sharing standard for the PLM industry. The JT Open members have even advocated JT as suitable for use as a long-term data archival format.
JT was originally developed by Engineering Animation, Inc. as the DirectModel toolkit. When EAI was purchased by UGS, JT became a part of UGS Corp.’s suite of products. Early in 2007 UGS announced the publication of the JT data formateasing the adoption of JT as a master 3D format. Also in 2007, UGS was acquired by Siemens A.G. and became Siemens PLM Software. JT is the common interoperabilty format in use across all of Siemens PLM Software and has been adopted as the long term data archival format across all of Siemens.
Large Model Rendering
JT was created to support the interactive display of very large assemblies (i.e. those containing tens of thousands of components). The JT file format is capable of storing an arbitrary number of faceted representations with varying levels of detail (LODs). When the whole product is displayed on the computer screen the hosting application displays only a simple, coarse, model. However, as the user zooms into a particular area, progressively finer representations are loaded and displayed. Over time, unused representations are unloaded to save memory.
The JT data model is capable of representing a wide range of engineering data. This data can be very lightweight, holding little more than facet data or it can be quite rich, containing complete NURBS geometry representations along with product structure, attributes, meta data and PMI. It also supports multiple tessellations and level-of-detail (LOD) generation.
- Product Structure - assembly, part, instance
- Facet - polygon, polygon set
- Lighting - light set, point light, infinite light
- Precise Geometry and Topology - point, curve, surface, face, loop, edge, vertex
- Geometry Primitives - box, cylinder, pyramid, sphere
- Product Manufacturing Information (PMI) - FD&T, 3D annotations
- Attributes / Properties - text, integer, float, date, layers
- Meta data - property filters, transforms, bounding box definitions
The relationship of product structure hierarchy to exported JT file structure is arbitrary. Any node in the hierarchy may be specified as the start of a new JT file. Thus, product structure may be represented in a variety of JT file configurations.
JT supports three common product structure-to-file structure mappings. These include:
- Per part - All assembly nodes in a product structure hierarchy are stored in a single JT file, and each part node in the hierarchy is stored in an individual JT file in a subdirectory that is of the same name as the assembly JT file.
- Fully shattered - Each product structure node in the hierarchy is stored in an individual JT file.
- Monolithic - All product structure is stored in a single JT file.
Client applications may use these mappings, or choose to define their own custom mapping.
To help shrink the storage and transmition bandwidth requirements of 3D models, JT files may take advantage of compression. Use of compression is transparent to the user of the JT data, and a given model may be composed of JT files using different compression settings (including none).
To date, the JT file format has evolved through two forms of compression, exposed in JT Open Toolkit as standard and advanced compression. These differ in that the former employs a simple, lossless compression algorithm, while the latter employs a more sophisticated, domain-specific compression scheme supporting lossy geometry compression. Client applications are encouraged to take advantage of advanced compression over standard compression, as attainable compression ratios are much greater. Support for standard compression is maintained only in the interest of backward compatibility with legacy JT file viewing applications.
The compression form used by a JT file is related to the JT file format version in which it was written. This version is readily viewable by opening a JT file in a text editor and looking at its ASCII header information. The following table summarizes the how this version information relates to compression:
JT Open is a community of users, software vendors, OEMs, and interested parties who, through an open distribution agreement of JT technology under a "level playing field" business model, are able to exchange 3D data for the purposes of visualization, collaboration and data sharing.
JT Open Toolkit
The JT Open Toolkit is a C++ library that provides read and write access to JT data. It allows applications to dramatically reduce coding and maintenance effort needed to create JT-enabled applications. Using the toolkit also ensures 100% data compatibility.
JT2Go is a no-charge, lightweight viewer that enables anyone to view JT files for free. With the inclusion of Microsoft Office plug-ins, JT2Go also enables 3D JT data to be embedded in Microsoft Office documents.
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