Augmented Reality Roadmap for X3D

Abstract

Augmented Reality (AR) and Mixed Reality (MR) operate across many devices, ranging from small hand-held mobile phones to laptops, desktop, and full-blown walk-around CAVES. There is always a mix of both 2D imagery and 3D graphics, plus a mix of the real world and the virtual world.

X3D is a mature standard with many implementations and many converters. It collects numerous proven technologies together in a workable way, providing a simple and coherent way for authors to create 3D models and VR applications. Multiple implementations and extensions for AR have already been demonstrated in X3D. It has also been proven that mobile X3D can fit well with HTML5 and DOM improvements. X3D’s extensibility gives us the advantage to define component levels and profiles as easily expanded extensions. This all "plays well" when moving from simple mobile applications to bigger models and spaces.

Current work in AR is focused on harmonizing proven capabilities into best practices for AR and 3D graphics, implementable by multiple X3D viewers and usable by content authors. The X3D group is thinking in terms of the larger 2D + 3D space that authors and users want. X3D,a reliable and viable standard can save a lot of time for developers looking to design new AR applications.

Motivation: Value of X3D Standard for AR

Augmented Reality (AR) and Mixed Reality (MR) operate across many display devices, ranging from small hand-held mobile phones to tablets, laptops, desktops, and full-blown walk-around CAVE spaces. There is always a combination of both 2D imagery and 3D graphics, plus a mix of the real world and virtual worlds. Many people are especially interested in lightweight AR that they can use as part of the GPS-aware mobile devices.

Extensible 3D graphics(X3D) a roylaty free and ISO certified Standard developed by the Web3D Consortium (www.web3d.org) that originated from VRML, now in XML already has capabilities to support AR and MR applications. X3D is a mature standard with many implementations and many converters. It collects numerous proven technologies together in a workable way, providing a simple and coherent way for authors to create 3D models and VR applications. Current X3D efforts include identification of critical lightweight components suitable for mobile devices and AR applications. X3D can save a lot of time for developers looking to design new AR applications.

Because there are multiple implementations and extensions for AR that have already been demonstrated for X3D, it is clear that we can build an AR component for X3D. It will have lightweight capabilities suitable for mobile devices, plus additional compatible capabilities that work with larger 3D scenes and spaces. We will take advantage of X3D extensibility to define component levels and profiles that capture these palettes as easily expanded extensions.

It is sometimes tempting to think of a mobile device as simply a rotatable 2D display situated within the 3D real world. However 2D displays by themselves can be pretty limiting and oversimplified. The X3D group is thinking in terms of the larger 2D + 3D space that many authors and users want. Demonstrations are also showing that mobile X3D can fit well with HTML5 and DOM improvements. This all "plays well" when moving from simple mobile applications to bigger models and spaces.

Now is the time for serious AR developers to consider these essential challenges. Our current work is focused on harmonizing proven capabilities into best practices for AR and 3D graphics, implementable by multiple X3D viewers and usable by content authors. Collaborative work is happening to extend X3D to make AR/MR capable. Numerous innovative AR activities are ongoing by many researchers, companies and study groups. Web3D is engaged is all these efforts. Coordination and collaboration between numerous developers and standards organizations is necessary for AR to eventually become a seamless part of the Web infrastructure.

Architecture and Features of X3D

X3D has been developed to meet a specific set of market and technical requirements. To meet these requirements, X3D adopts the following design objectives:

• Separate the runtime architecture from the data encoding
• Support a variety of encoding formats, including the Extensible Markup Language (XML)
• Add new graphical, behavioral and interactive objects
• Provide alternative application programmer interfaces (APIs) into the 3D scene
• Define subsets of the specification ("Profiles") that meet different market needs
• Allow for the specification to be implemented at varying levels of service
• Eliminate, where possible, unspecified or underspecified behaviors

Features present in X3D

Not only are X3D features numerous and selectable, they are also fully integrated in a consistent way so that tools and authors might easily use them. For example:

• XML Integration enables simple X3D use with HTML, Web Services, etc.
• Distributed Networks accessibility
• Cross-platform, inter-application file and data transfer
• Componentized: allows lightweight core 3D runtime delivery engine
• Extensible: allows components to be added to extend functionality for vertical market applications and services
• Profiled: standardized sets of extensions to meet specific application needs
• Evolutionary: easy to update and preserve VRML97 content as X3D
• Broadcast/Embedded Application Ready: from mobile phones to supercomputers
• Real-Time: graphics are high quality, real-time, interactive, and include audio and video as well as 3D data.
• Well-Specified: makes it easier to build conformant, consistent and bug-free implementations
• 3D graphics and programmable shaders - Polygonal geometry, parametric geometry, hierarchical transformations, lighting, materials, multi-pass/multi-stage texture mapping, pixel and vertex shaders, hardware acceleration
• 2D graphics - Spatialized text; 2D vector graphics; 2D/3D compositing
• CAD data - Translation of CAD data to an open format for publishing and interactive media
• Animation - Timers and interpolators to drive continous animations; humanoid animation and morphing
• Spatialized audio and video - Audio-visual sources mapped onto geometry in the scene
• User interaction - Mouse-based picking and dragging; keyboard input
• Navigation - Cameras; user movement within the 3D scene; collision, proximity and visibility detection
• User-defined objects - Ability to extend built-in browser functionality by creating user-defined data types
• Scripting - Ability to dynamically change the scene via programming and scripting languages
• Networking - Ability to compose a single X3D scene out of assets located on a network; hyperlinking of objects to other scenes or assets located on the World Wide Web
• Physical simulation and real-time communication - Humanoid animation; geospatial datasets; integration with Distributed Interactive Simulation (DIS) protocols

X3D's layered Components and Profiles

The modular architecture of X3D allows for layered "profiles" that can provide increased functionality for immersive environments and enhanced interactivity or focused data interchange formats for vertical market applications within a small downloadable footprint composed of modular blocks of functionality ("Components"), that can be easily understood and implemented by application and content developers. Components can be individually extended or modified through adding new "levels", or new components can be added to introduce new features, such as streaming. Through this mechanism, advancements of the specification can move quickly because development in one area doesn't slow the specification as a whole. Importantly, the conformance requirements for a particular piece of content are unambiguously defined by indicating the profiles, components and levels required by that content.

• Interchange is the basic profile for communicating between applications. It support geometry, texturing, basic lighting, and animation. There is no run time model for rendering, making it very easy to use and integrate into any application.
• Interactive enables basic interaction with a 3D environment by adding various sensor nodes for user navigation and interaction (e.g., PlaneSensor, TouchSensor, etc.), enhanced timing, and additional lighting (Spotlight, PointLight).
• Immersive enables full 3D graphics and interaction, including audio support, collision, fog, and scripting.
• Full includes all defined nodes including NURBS, H-Anim and GeoSpatial components.

The X in X3D stands for Extensible. X3D is highly modular in order to allow both authors and implementers to choose the palette of capability they might need for a given application area. This flexibility is a major virtue which lets the 3D content declare how much implementation support is needed.

                8 Profiles                    for common use cases    X3D Profiles
               
            35 X3D Components                 for modular design      X3D Components
      
       Two Hundred Eighteen X3D Nodes         for every little thing! X3D Nodes

For comparison purposes, 68 nodes are in the X3D Interactive profile which is lightweight already runs on mobile devices. Approximately 10 new nodes are being considered for AR, of which only a portion are suitable for mobile. This is an area of active work: minimizing software footprint while maximizing user capability. Modular X3D

Multiple implementations and extensions for AR have already been demonstrated in X3D. X3D’s extensibility provides the advantage to define component levels and profiles as extensions, allowing applications to not have to implement the entire specification. It has also been demonstrated that mobile X3D can fit well with HTML5 and DOM improvements. This all "plays well" when moving from simple mobile applications to bigger models and spaces.

Current Web3D Consortium AR working group activities are focused on harmonizing proven capabilities into best practices for AR and 3D graphics, implementable by multiple X3D viewers and usable by content authors. This Working Group is thinking in terms of the larger 2D + 3D space that authors and users want. We will harmonize lightweight AR components within an easily implementable X3D Mobile Profile. Heavyweight requirements for MR and CAVEs can be compatibly defined.

X3D Lightweight/Mobile profile

Recent work in HTML5/DOM, geospatial GpsSensor, and palettes for interactive scenes has lead to a propostion of a new lightweight (Mobile) Profile for X3D. A lightweight profile is valuable for author creation of simple but dramatic content. This approach allows a small-footprint and efficient operation of X3D on mobile devices, easy export from other formats, and a simple vocabulary for new authors.

This extension, optimization, and refinement process can unlock carefully chosen X3D capabilities for important new areas:

• Mobile applications
• Lightweight HTML5 web pages
• Augmented Reality (AR)

Heavyweight advanced capabilities for mixed reality, CAVEs etc. are defined and kept separate from lightweight/Mobile profile but available in the other AR-related X3D components.

Integrating X3D into HTML (X3dom)

The traditional way to embed a X3D augmented reality scene into a webpage uses a plug-in that needs to be installed by the user. The plug-in approach has always been an issue for web developers and users. Several efforts have been initiated by Web3D on how to integrate X3D with HTML. Our goal is to bring 3D to Web developers by fully integrating 3D content into HTML documents. Today Web pages exist as large collections of hierarchical elements that are rendered to the page; all content appears in the Document Object Model (DOM). Several tools are available to allow programmers to manipulate the DOM, in particular tools and frameworks based on JavaScript. Placing 3D graphics in the DOM, allows these JavaScript tools to access and manipulate 3D graphics. Web3D and Fraunhofer IGD‘s recent efforts – X3DOM (www.x3dom.org), integrating X3D with HTML and the DOM, have proven this capability. X3dom's design goals are to have a live X3D scene in your HTML DOM, allowing you to manipulate the 3D content by only adding, removing, or changing DOM elements. No specific plugin or plugin interface (like the X3D-specific SAI) is needed. It also supports HTML events (like “onclick”) on 3D objects. X3dom Showcase

X3DOM uses three basic approaches to display an X3D scene inside an HTML page without a plug-in. X3dom Fallback model

• External reference: HTML page includes an object element tag that refers to an .x3d scene, implemented via an X3D plug-in. Data might be passed within the page using DOM events.
• X3D as XML in HTML: HTML page directly includes X3D source, likely with an XML namespace prefix, presumably implemented via an X3D plug-in or the browser itself. Again data might be exchanged within the page using DOM events.
• API access: HTML page includes some form of canvas (or maybe Canvas3D) element that allows programmatic access to the page, so that X3D Scene Access Interface (SAI) might draw a bitmap.

The X3dom model provides an experiment environment to develop an integration model for declarative 3D in HTML and has triggered several discussion in the HTML and X3D communites, and maybe finally become a part of the HTML standard supported by every major browser.

The recently formed “Declarative 3D” W3C Community Group is working to define requirements to integrate 3D with HTML and the DOM (Declarative 3D in HTML). Efforts include in-depth consideration of X3DOM as one possible exemplar solution. The Declarative 3D effort has strategic importance for Web3D and indeed for all 3D graphics, especially since X3D is already a portable interchange format for a wide variety of models and technical approaches. We intend to establish a solid foundation for X3D to properly support 3D graphics for the native Web page, which definitely includes enhancements for AR capabilities and experiences.

X3dom and AR

X3dom AR efforts are experimenting on multiple new possibilities. In addition to HTML–WebGL integration, the Flash version of AR Toolkit (FLART) layers an X3D scene on top of Flash viewport. This provides a good platform for experimenting and implementing AR/MR functions as potential standards candidates. Users might also benefit more if the functions provided by FLARToolkit eventually become consolidated as standard in X3D, so that authors and tools might avoid needing to handle repetitive wiring between Flash and X3D.

X3D Strategy for AR

Multiple experimental AR nodes have been proposed and implemented for X3D by Web3D Consortium members. A comprehensive list of AR nodes is being considered by the X3D AR Working Group and formally written up as the Augmented Reality (AR) component for the X3D Specification. Establishing common implementations and examples to demonstrate successful interoperability for the spec is of primary importance. Recent work in HTML/DOM, geospatial GpsSensor, and palettes for interactive scenes has led to a proposal for a new lightweight (Mobile) Profile for X3D. Heavyweight advanced capabilities for mixed reality, CAVEs etc. will be kept separate from Mobile but available in AR-related X3D components.

Continued collaboration and reaching out to the ISO-SC24 Working Group, W3C Augmented Reality Community Group, newly formed OGC ARML Working Group, KHRONOS, and the AR Standards Group is crucial. The common goal for Web3D Consortium remains maximum interoperability with all AR and Web standards.

X3D Relation to Reality–Virtuality Continuum

The Reality–Virtuality Continuum is often used to describe the range of functionality involved. The goals for X3D capabilities are broad.

         | - - - - - - - - - Mixed Reality (MR) - - - - - - - - |
     
   <<================================================================>>
     
     Real          Augmented                 Augmented         Virtual
     Environment  Reality (AR)           Virtuality (AV)   Environment
     
   <<================================================================>>
   
                  | - - - - - - X3D AR-Related Nodes - - - - - - - - |

Extending X3D for AR/MR applications

Many capabilities are possible and relevant for adding AR/MR functionality to Web-based 3D graphics. Most have already been demonstrated as feasible, and some have been shown several times. The current challenge facing the X3D AR Working Group is deciding how to best merge and harmonize these capabilities consistently with the X3D Specification and X3D best practices.

The following list shows the functions and features under consideration for supporting AR and MR visualization in X3D:

• Adding real world view
  • Access to live video (e.g. local camera on the user's portable device)
    • Live video stream as a texture on geometry within the X3D scene
    • Live video stream as a background of the X3D scene
• Merging real and virtual images correctly
  • Access to calibration information of the camera device providing the video stream
  • Viewpoint nodes using calibration information to set projection parameters
  • Chroma keying of live video stream texture (rendering pixels in key color transparent)
  • Correct occlusion between real and virtual objects
    • Depth masking with virtual representation of physical object
    • Support for depth image and depth imaging devices
• Tracking, registration and real-time interaction
  • Access to motion tracking information
  • Camera for registration between real and virtual spaces
  • Other physical objects for real-time interactivity

Why X3D is a viable and proven standard platform for implementing AR/MR

The Web3D Consortium is a standardization group that has been producing and maintaining the X3D standard for ISO for more than 10 years. Today, the Web3D Consortium is utilizing its broad-based industry support to extend the X3D specification for AR. Through well-coordinated efforts with the ISO, OGC, AR standards Group and W3C, the Web3D Consortium is extending its standardization activities for AR capabilites. Our common goal remains maximum interoperability with all AR and Web standards.

The Web3D AR working group activities are focused on developing proven capabilities into best practices for AR and 3D graphics, implementable by multiple X3D viewers and usable by content authors. This Working Group is thinking in terms of the larger 2D + 3D space that authors and users want. We will harmonize lightweight AR components within an easily implementable X3D Mobile Profile. Heavyweight requirements for MR and CAVEs can be compatibly defined. Current technical work includes harmonizing proposals from Web3D members for best fitting AR capabilities into X3D scenes. This work will be formally written up as the Augmented Reality (AR) Component for the X3D Specification.

X3D is a mature standard with many examples, many players and many converters. Multiple implementations and extensions for AR have already been demonstrated in X3D. These efforts have been successful because X3D collects numerous proven technologies together in a workable way, providing a simple and coherent path for authors to create 3D models and VR applications. X3D’s extensibility provides the advantage to define component levels and profiles as extensions, allowing applications to avoid having to implement the entire specification. It has also been demonstrated that mobile X3D can fit well with HTML5 and DOM improvements. This all "plays well" when moving from simple mobile applications to bigger models and spaces. X3D is definately becoming a viable and reliable standard for AR developers looking to save time when designing new AR applications.

Interoperability with other AR and Web Standards

For the past 10 years the Web3D Consortium is extending its standardization activities through formal collaboarative efforts with the ISO, OGC, and W3C standards organization. Several discussions at the Web3D Conference, SIGGRAPH, ISO-SC24 and OGC meeting about the recent developments in AR Standards continue to improve and refine our strategy on interoperability with other standards.

ISO Standards Committee (SC24) which administers X3D review as an International Standard has established a new Working Group for Augmented and Mixed Reality. The group proposes a AR content model as an extension of a virtual world with provisions for representing the physically-sensed objects. The ISO JTC1/SC24 report by Dr. Gerry Kim summarizes the group's findings of the current state of the art in AR/MR and proposals on standardization AR/MR functionalities.

Recent discussions at ARML SWG meeting focused on the OGC ARML SWG work mainly targeted for mobile platforms resulting in a standard build on KML. It will also define the element attributes to send and receive JavaScript events. KML is an OGC standard that allows X3D to be embedded. Web3D and OGC have successfully worked together formally under a MOU agreement since 2006. Our common gaol is to advance standards-based, interoperable web-enabled 3D geospatial content sharing, modeling and visualization. Our collaboration with OGC will continue to provide interoperability with OGC and X3D standards for AR capabilities too.

As we achieve clarity on the larger strategy for AR, we plan to outreach and collaborate with AR standards groups in establishing compatibility of X3D with other AR models.

Invitation to Participate

Much work has been accomplished already towards integrating AR capabilities in X3D. Current efforts are focused on harmonization of options, lightweight deployability, heavyweight consistency, and interoperability with all Web standards.

Web3D Consortium membership is open to companies, government agencies, educational institutions, and individuals. All X3D Specification capabilities can be implemented on a royalty free basis. We look forward to further participation and collaboration by the AR community to achieve long-term success for AR content on the Web.