X3D Binary Compression Capabilities and Plans

Synopsis. Lots of work has been accomplished towards proper support of X3D Binary Compression for a wide variety of potential uses.

X3D appears to have have an 80% solution already available that meets various requirements for a general 3D transmission format.

Existing Compression Standards

• Approved ISO standard Compressed Binary Encoding (CBE) for X3D
  • Based on ISO standard Fast Infoset (FI) for XML compression
• Optional, alternative gzip compression and MIME Type definitions
  • XML encoding (.x3dz/.x3d.gz), ClassicVRML encoding (.x3dvz/.x3dv.gz) and Compressed Binary encoding (.x3db.gz) file extensions
  • Original compression technique of gzip compression for .wrl VRML called .wrz. This is a common practice. (TODO need reference)

Polygon reduction and geometric compression

• CAD Distillation Filter (CDF) technique allowing successive refinement of large X3D scenes into tighter X3D scenes
• Extensible, repeatable compression and decompression algorithms for data-flow production chains
• A highly effective exemplar algorithm for Coding Polygon Meshes as Compressable ASCII is demonstrated in the Experimental Binary Compression examples.
• Multiple filters implemented in Xj3D and X3D-Edit as open-source
• Multiple other conversion and translation tools available with supporting capabilities
• X3D Canonicalization (C14N) provides standardized formatting so that digital signatures are not thwarted by whitespace variations

Binary encodings

• Plan to add a further-improved X3D Compressed Binary Encoding using now-approved W3C Recommendation for Efficient XML Interchange (EXI)
• Web3D contributed to EXI working group and XML Binary Characterization working group efforts
  • 3D Model Compression, Serialization and Transmission use-case requirements are defined and met by EXI
• Design includes compatibility with CDF techniques, XML Encryption, and XML Digital Signature for author authentication
  • Relevant example scenes maintained as part of X3D Basic Examples Archive - Security
• These capabilities meets most needs of digital authors for digital rights management (DRM)

Network streaming

• Multiple capabilities are already available in X3D for flexible network transmission
  • Anchor, Inline, LOD, LoadSensor, Script and Prototype nodes support successive retrieval of content once initial model is displayed
• TODO: Willing to consider further addition of progressive-mesh geometric streaming technologies, perhaps by a public Call for Contributions. Note however that an effective progressive-mesh approach is likely dependent on the availability of a corresponding mesh compression algorithm.
  • For example, the original August 2003 X3D Compressed Binary Encoding Request For Proposals (RFP)
• Intellectual Property Rights (IPR) protections for X3D specification
  • Patented technologies can be considered, but only when eventual use will be royalty free for X3D use (if eventually accepted)
  • Submitters can restrict access to patented submissions during member-only working group review, if desired
• TODO: Use cases and test examples can demonstrate whether http/https and local-file url retrieval are sufficient for a network protocol
  • Other network protocols (Web sockets, P2P channels, etc.) might be possible, but only if security restrictions can be handled satisfactorily

X3D Implementations

The following tools implement the X3D Compressed Binary Encoding (CBE) standard.

• Two independent open-source implementations available
  • C++ codebase: XIOT X3D Input Output Tool library
  • Java codebase: Xj3D
• Ongoing status is maintained on Web3D-member wiki pages:
  • Player_support_for_X3D_components
  • Tool_support_for_X3D_components
• Several thousand X3D Examples are available in .x3db form, encoded by Xj3D
  • TODO: Plan to similarly automate conversions and comparisons, using both Xj3D and XIOT, for cross-check interoperability and validation testing

Looking ahead

• Web3D's X3D and CAD Working Groups each have member commitments to pursue this continued innovative work in 2012
• TODO: An open workshop on 3D Transmission Formats might be a thorough way to compare candidate technologies to complete these capabilities
• Consider common, sharable technical strategies with MPEG-4 and Collada