X3D Binary Compression Capabilities and Plans

Synopsis: Lots of work has been accomplished using X3D Compressed Binary Encoding standard for a wide variety of potential uses. X3D has an 80%-complete solution already available that meets various requirements for a general 3D transmission format. Further improvements and standards-based partnerships are possible.

In progress: We are building a draft 2013 Call For Contributions to further advance these technical capabilities for X3D.

Existing Compression Usage for X3D and VRML97

• 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 for X3D.
  • XML encoding (.x3dz/.x3d.gz), ClassicVRML encoding (.x3dvz/.x3dv.gz) and Compressed Binary encoding (.x3db.gz) file extensions.
• Optional, alternative gzip compression for VRML97.
  • Original compression technique of applying gzip to .wrl compressed VRML97 files was called .wrz.
  • This emerged as a common practice when gzip was originally used. No formal specification of .wrz or corresponding mime type was produced.
  • Occasionally authors might also gzip .wrl files while retaining the .wrl file extension.

Polygon Reduction and Geometric Compression

Formal specifications:

• The X3D Compressed Binary Encoding defines extensible, repeatable compression and decompression algorithms for data-flow production chains. Multiple type-specific field encoders and geometric compression algorithms can be used in concert, but no specific geometric compression algorithms are referenced or required.
• X3D Canonicalization (C14N) provides standardized formatting so that digital signatures are not thwarted by whitespace variations.

Best practices:

• CAD Distillation Filter (CDF) technique allowing successive refinement of large X3D scenes into tighter X3D scenes.
• A highly effective exemplar algorithm for Coding Polygon Meshes as Compressable ASCII is demonstrated in the Experimental Binary Compression examples.
• Multiple CAD Distillation Filter (CDF) algorithms implemented in Xj3D and X3D-Edit as open-source.
• The Chisel VRML Optimisation Tool has an excellent set of data-reduction tools for VRML that are worth repeating for X3D.
• Multiple other conversion and translation tools available with supporting capabilities.

Data-Centric 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.
  • Javascript Object Notation (JSON) might be suitable for simple streaming of X3D scene-graph data via Script node or external HTML page, which can be useful for progressive mesh and other incremental network-update approaches.
  • JSON might have other uses as well, see Khronos work on Collada2JSON and glTF.
  • Further investigation needed.

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 2013.
• 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.