Media type name: model

Media subtype name: u3d

Required parameters: None

Optional parameters: None

Encoding considerations: binary

Security considerations: U3D, like many 3D models, may contain 
   sensitive industrial or intellectual property information. U3D 
   files cannot contain active content nor does U3D support 
   general-purpose programming language code. U3D files can contain 
   references to external data using HTTP and FTP URLs. Block 
   Metadata keys can also contain MIME data and external file 
   references as values, but interpretation of Metadata key/value 
   pairs is not defined by the U3D specification. U3D defines its own 
   platform independent domain-specific custom lossless bit encoding 
   algorithm. The encoding allows conditional reading and reading 
   data in cycles based on provided data, but infinite looping should 
   not be possible. Infinite loops are possible only by defining 
   wrong parent-child relationship in the node data, but this is 
   prohibited by the U3D spec and can be defensively coded. Many U3D 
   models can also be large and complex so protection against 
   resource exhaustion is a standard requirement. U3D files specify 
   their own file length in the Header Block, but do not contain any 
   further security or integrity controls.

Interoperability considerations: The U3D specification fully defines 
   the execution architecture that facilitates optimal run-time 
   modification of geometry, continuous-level-of-detail, a 
   domain-specific compression algorithm, progressive data streaming 
   and playback, key-frame and bones-based animation, and 
   extensibility of the U3D binary block-based format and run-time. 
   The Header Block of U3D files contain Major and Minor Version 
   numbers, and optionally a Profile Identifier that identifies the 
   profile used by a file and any optional or extension features. 
   There are multiple editions of the U3D specification, but all are 
   identified by Major Version 0 (zero) with the Minor Version being 
   implementation dependent. The Profile Identifier (when present) 
   along with Block Type identifiers enumerate data blocks data and 
   extensions such that an implementation can perform all necessary 
   interoperability checks. Extension blocks are allowed for some 
   profiles and this is indicated in those U3D files.

Published specification: 

   U3D is defined by "ECMA-363 Universal 3D file format" 
   (https://www.ecma-international.org/publications-and-standards/standards/ecma-363/). 

   There are 4 editions of the U3D ECMA-363 specification, with the 
   3rd edition (dated June 2006) being the most widely used. ISO 
   32000-2 (PDF 2.0) only supports U3D as defined by ECMA-363 3rd 
   Edition. See also 
   https://www.loc.gov/preservation/digital/formats/fdd/fdd000491.shtml

Applications which use this media: U3D was the original 3D data 
   visualization format used by PDF. It was first defined for use in 
   PDF by Adobe PDF 1.6 and continues to be supported in ISO 32000-1 
   (PDF 1.7) and ISO 32000-2 (PDF 2.0). U3D is also an exportable 
   file format from many CAD and 3D authoring applications.

Fragment identifier considerations: None

Restrictions on usage: None

Additional information:

   1. Deprecated alias names for this type: n/a 
   2. Magic number(s): First 4 bytes of the file are Hex: 55 33 44 00 
      (ASCII: "U3D"+\000)
   3. File extension(s): .u3d
   4. Macintosh file type code: n/a
   5. Object Identifiers: n/a

General Comments: Note that ECMA Technical Committee 43 that 
   originally defined U3D is no longer active, but U3D remains a 
   critical file format for use with PDF and thus MIME media type 
   registration change control will be managed by the PDF Association 
   as a registered ANSI standards development organization and as the 
   main industry body overseeing PDF standardization.

Person to contact for further information:

   1. Name: Peter Wyatt
   2. Email: peter.wyatt&pdfa.org

Intended usage: Common

   U3D is a 3D model format that can be embedded inside PDF 1.6 and 
   later files.

Author/Change controller: info&pdfa.org, Chief Technology Officer, 
   PDF Association. Note that ECMA Technical Committee 43 that 
   originally defined U3D is no longer active, but U3D remains a 
   critical file format for use with PDF and thus MIME media type 
   registration change control will be managed by the PDF Association 
   as a registered ANSI standards development organization and as the 
   main industry body overseeing PDF standardization.