PRC 3D Format
PRC (Product Representation Compact) is a 3D data structure and file format, one of two systems used in 3D PDF documents. Along side U3D, PRC is now the preferred and most feature-rich method to embed 3D interactive data and models into a PDF file. A PDF file containing PRC based 3D model can be viewed in using the Adobe Reader as well as other tools. PRC is the recommended encoding method for PDF/E documents.
PRC is a compact representation for 3D models and assemblies, for the display and visual representation of various kinds of 3D data. It includes structure, geometry and product manufacturing information ( PMI ) metadata.
The format allows for either highly compressed geometric and visual representations, with varying levels of tessellated surface geometry spatial tolerance, or an exact form of representation including precise BREP data types. Dimensional and associated metadata may also be included as PMI annotations within the PRC encoding.
PRC is Used For
The PRC encoding method in 3D PDF is used for most 3D PDF application areas, including technical reports used in engineering, manufacturing, numerical modelling, medical, aerospace, geology, geophysics, oil & gas exploration, civil engineering, environmental surveys, and as an interoperable file format for Computer-Aided Manufacturing (CAM), Computer-Aided Engineering (CAE), and Product Life-Cycle Management (PLM) for supply-chain, training, marketing, archiving and engineering reports.
PRC Benefits over U3D
Although both U3D and PRC are available as 3D systems in a PDF, PRC is generally preferable due to:
- More geometric shape definitions, including NURBS
- Much better triangle mesh compression
- Annotations, PMI, Markup (absent from U3D)
- Internationally Agreed ISO Standard
- Scales to Complex Assemblies
PRC as File Format
PRC can be used as a 3D file type for storage and interchange. Such 3D binary files can be interchanged with other PRC compatible applications. PRC files may be “wrapped” into a PDF file for display using the Adobe Reader by tools such as media9 and Acrobat Pro. Today, PRC is primarily used for 3D PDF internal encoding, rather than an interchange format.
PRC Generation Tools
PDF3D products include PRC for highly effective compression and 3D representations in 3D technical documents. Note that aspects of the PDF3D implementation of PRC generation are the subject of granted and pending patents. Products including PRC encoding include:
Examples of 3D PDF files with PRC encoding are available on the sample Gallery page.
PRC ISO Standard
PRC is referenced in three related ISO standards. First and foremost, PRC is defined by ISO-14739 as a stand-alone data structure and file definition. The PRC format definition is not owned by any one commercial entity, although was established and submitted to ISO by Adobe.
PRC is an explicitly allowed annotation & multimedia type in the core PDF file standard ISO-32000.
In addition, the PRC encoding scheme is part of the ISO specification PDF/Engineering ISO-24517 International Standard for how PRC plays a part of a PDF document under a strict subset for engineering archive purposes.
The ISO standardization process, committee work, publications and the process of moving these standards forward is an active and ongoing process. Visual Technology Services is actively involved in the PRC standardization effort, with representation through the ISO-TC171-SC2-WG7 committee.
PRC Technical Summary
The technical specification for the internal structure of PRC is defined in ~300 page ISO-14739, so a brief technical summary hardly does it justice. The data structure is composed of a collection of linked tables, in a machine and language independent binary structure or file. Various geometric types may be specified, from points, lines, polygons to curved surfaces. Line curves, smooth curved surfaces including trimming curves using a lattice of control points and weights are included. A small collection of pre-defined shapes such as spheres and cylinders are included for convenience.
The structure includes a full model tree, part assembly or graphical scene graph hierarchy, supporting thousands of parts. Repeated (instanced) structures are well supported, with material types including optional texture images on any tessellated 3D part.
Annotations such as PMI, part labels, dimensions may also be specified within the PRC structure and associated with 3D parts. This allows for a rich set of 3D reporting options to include quantitative and meaningful annotations where needed.
Both full-resolution precise model definitions and high compression modes are available. In the case of tessellated geometry highly compressed modes, a very compact triangle mesh structure is used, with a cascade of efficient compression methods including run-length encoding, adaptive Lempel-Ziv, and frequency table Huffman coding compression schemes. In high compression, the model is accurate to a specific geometric vertex location tolerance, while still preserving every vertex and face without re-meshing or simplification.
PRC Format History
The PRC was first announced by Trade and Technologies France (TTF) in 2002. In 2006, Adobe Systems Inc. acquired TTF including rights to the PRC technology. The PRC format was introduced into Acrobat and the Adobe Reader at version 8, supplied as “Acrobat 3D” and “Acrobat Pro Extended 9”.
In 2009, the PRC Format was submitted to ISO as an open 3D data structure standard for 3D PDF, no longer controlled by a single vendor as a proprietary format. The PRC format ISO-14739 is now accepted and in the publication process.
In 2010, Adobe transferred responsibility to several 3rd party organizations, whereby at Acrobat versions 10 and 11, PRC generation was no longer integrated within Acrobat; the capability is packaged as plugins and external file converters from 3rd party vendors.
Visual Technology Services developed independent PRC generation, released in 2010, not based on TTF, Adobe or any 3rd party software.
The ISO Standards effort for PDF/E for engineering archive applications is progressing with full reference to PRC as the preferred 3D embedding mechanism.