B582 - Lecture 6.1
VRML for Virtual Environments & Visualization

Outline

Brief history of VRML
Examples of VRML for Vis & VE
VRML - Pros and Cons for VR & Vis
Comparison of low level and high level graphics
Modeling with VRML
Animation & Interaction with VRML
Extending VRML
VRML Software
VRML Repositories & Information Sources

Brief History of VRML

(dates are approximate)

1993 - first discussions of a 3D web standard
1994 - VRML 1.0 standard based on SGI's Open Inventor developed
1995 - first VRML browser, WebSpace
1996 - VRML 2.0 spec (from SGI, Sony, etc.'s "Moving Worlds" proposal)
1997 - VRML 2.0 spec finalized as VRML'97; SGI develops Cosmosoftware subsidary
1998 - Cosmosoftware sold to Platinum; SGI's committment to standard uncertain
1999 - The saga continues (Platinum acquires Intervista; Computer Associates acquires Platinum)
1999 - discussion begins on next generation of VRML standard - X3D
1998-99 - Blaxxun and ParallelGraphics release VRML browsers (Contact & Cortona, respectively)

Examples of VRML in Vis & VE

Visualization

Mathematical Surface Server at Transaction Information Systems
Molecules from the IU Molecular Structure Center
Groundwater Flow Visualization from Iris Explorer
Interactive Phong Lighting Model

Virtual Environments

Dave Pape's VRML models of CAVE applications
The Miller Project at ICEMT - Significant Historical Buildings
IU Football Simulation
IU CAVE room study

Pros & Cons of VRML for VR & Vis

Pros

platform independent
web-based; possible to set up visualization servers
quick prototyping
abundant resources available
reasonably flexible
open standard

Cons

rendering is most likely slower than pure OpenGL
programming for complex interaction and manipulation is awkward or impossible
modifying geometry, parameters, etc. on the fly is awkward
less flexible than OpenGL/C; no low-level control
limited interface, widgets
uncertain future

Comparison of low-level & high-level graphics

Low-level graphics

High-level graphics

examples: OpenGL, DirectX, QuickDraw
built around hardware implementation - direct access to hardware features
possible to create very efficient or very inefficient code
limited set of primitives: points, lines, polygons
must specify all parameters (e.g. material, lights, texture coordinates, normals, etc.)
good for visualization - geometry derived algorithmically from data at run time
programmer devises and maintains own data structure
immediate mode rendering - programmer must detect events and re-draw scene and swap buffers when appropriate
no fundamental object-oriented paradigm
programmer develops all interaction

examples: VRML, Open Inventor, Iris Performer
independent of hardware - indirect or limited access to hardware features
built-in optimizers assure some minimal level of efficiency
rich set of primitives: cones, spheres, indexed face sets, etc.
usually provides reasonable default behaviors if parameters are not specified explicitly
good for simulation or environments - geometry designed by hand prior to run time
specific scene graph data structure enforced by language
retained mode rendering - system handles all drawing, buffer swaps, and exposure events
fundamental object-oriented paradigm
default interactors usually provided

Homebuilder analogy from Open Inventor manual: work with raw materials vs. pre-fabricated components

Modeling with VRML

VRML2.0 supports a hierarchical scene graph, similar to Open Inventor or Iris Performer. (Actually, VRML2.0 is more like Performer and less like Inventor and VRML1.0 in that it does not permit state inheritance between siblings.) The modeling units are meters; angles are specified in radians.

VRML 2.0 Modeling Nodes

Geometry Primitive Shapes Box Cone Cylinder Sphere Text Vertex-based Shapes IndexedLineSet IndexedFaceSet PointSet Other Shapes ElevationGrid Extrusion	Appearance Material OpenGL-style Texture ImageTexture MovieTexture PixelTexture	Appearance-modifying Geometry Normal* TextureCoordinate* TextureTransform * explicit for vertex-based shapes; implicit for primitives
Grouping Nodes Group Transform scale rotation translation Billboard Anchor (WWW Link) LOD (Level of Detail) Inline Switch Collision	Lights & Camera Lights DirectionalLight PointLight SpotLight Camera Viewpoint NavigationInfo	Environment Background Fog Sound Sound (ambient) AudioClip (file access)

Instancing Method

any node may be given a name (defined with DEF keyword) and then instanced again later in the file (using the USE keyword)

e.g.
        DEF RED_CUBE Shape {
                appearance Appearance {
                        material Material {
                            diffuseColor 1 0 0
                        }
                }
                geometry Cube {}
        }
        :
        :
        Transform {
            translation 10 0 0
            children [
                USE RED_CUBE
            ]
        }
        Transform {
            translation 20 0 0
            children [
                USE RED_CUBE
            ]
        }

Translating Models into VRML2.0

Use Inventor (~VRML1.0) as an intermediate file format.

Step 1. Convert or save file as Inventor or VRML 1.0

SGI converters: DxfToIv, ObjToIv, AliasToIv, SoftimageToIv, 3dsToIv
Iris Explorer, Showcase, ProEngineer: direct Inventor output
AVS: module to write VRML1.0

Step 2. Convert to VRML 2.0

use CosmoWorlds File Import
use /usr/sbin/vrml1ToVrml2 on command line

Tip: Inventor is an easier file format to read and modify, plus, you can use several SGI desktop tools to view and modify the file (ivview, SceneViewer, gview, showcase). Work with files as long as possible in Inventor format; commit them to VRML as late as possible.

Animation & Interaction with VRML

The VRML1.0 standard supported only static models and hyperlinks. The key additions for VRML2.0 (originally know as the Living Worlds or Moving Worlds standard) are nodes which support animation and interaction and mechanisms for extending VRML through scripting.

VRML2.0 Action & Interaction Nodes

Interpolators

ColorInterpolator
CoordinateInterpolator
NormalInterpolator
OrientationInterpolator
PositionInterpolator
ScalarInterpolator

Timer

TimeSensor

Sensors

CylinderSensor
PlaneSensor
ProximitySensor
SphereSensor
TouchSensor
VisibilitySensor

ROUTE-ing Mechanism

label nodes of interest with DEF

(DEF'ed nodes may also be instanced with USE)

ROUTE EventOut fields to EventIn fields of the same type

chain nodes together in a data-flow style, e.g.

ROUTE Timer.fraction_changed TO OrientationInterpolator.set_fraction
ROUTE OrientationInterpolator.valueOut TO Transform.set_rotation

fan-in and fan-out are permitted
loops are not permitted

initial events are propogated along routes (a.k.a. event cascade)
Example - IU football

Extending VRML

PROTOtypes

PROTO allows you to create a new node type which encapsulates standard nodes, scripts, and ROUTES
EXTERNPROTO allows that definition to be defined in an external file and incorporated in multiple VRML files
Example: Electric football - one player, the whole team

Scripting

Script nodes define short programs which may make logical decisions, maintain state, or perform calculations.
The VRML standard does not specify a specific scripting language.

CosmoPlayer 1.02 for Irix supports vrmlScript (an SGI-proposed extension of JavaScript)
CosmoPlayer 2.1 for Windows support vrmlScript and JavaScript
CAVE6U from EVL supports most of vrmlScript

An interface to the browser allows the loading of new URLs, the creation of VRML from a string, and the addition and deletion of ROUTEs.
Example: Solar System simulation

EAI - Interfacing Java and VRML

EAI = External Authoring Interface
Allows a Java applet to access fields of labeled nodes within the VRML plugin
Pros: more organized and more powerful than Script nodes for complex tasks; debugging is much easier
Cons: not all combinations of viewers and browsers work properly; some are flakey when they do work
Working EAI Combinations

IRIX: Netscape 3.01S & CosmoPlayer 1.02
NT: Netscape 4.05 & CosmoPlayer 2.01

Examples: Descent navigation, miscellaneous examples

VRML Software

CosmoPlayer - Netscape VRML viewing plugin

IRIX version is supported by SGI
Windows and Mac versions unsupported by CAI

CosmoWorlds - graphical world building and key-frame animating tool

IRIX version (1.03) is supported by SGI is free under varsity program
Windows version (2.0) from Cosmo Software is available for 30 day free trial

Cortona - VRML browser & screen saver from Parallel Graphics
Blaxxun Contact - VRML browser with multi-user capabilities from Blaxxun
cave6u - VRML2.0 browser for the CAVE

master's thesis project by EVL grad student (Swami Narayanan)
written with Iris Performer and pfCAVE libraries
covers ~90% of the standard
supports most of VrmlScript
problems include: not reading sensor configuration options (must relocate head sensor to top of glasses)
look in /usr/local/CAVE/demos/cave6u for executable and more info

Open-source VRML browsers

see VRML4Linux site
I've had some success with VRwave (Java based)

Commercial, extensible browsers and libraries

OpenWorlds - includes class libraries, browser source and Performer loaders

VRML Repositories & Information Sources

vrml.sdsc.edu - VRML Repository (San Diego SuperComputing Center)
www.vrml.org - official 3D Web
www.cosmosoftware.com - Cosmo Software
www.intervista.com - Intervista Software
VRML for Linux - good source for open source

Local versions of: (coming soon)

VRML97 Spec
VrmlScript Spec
Dave Nadeau's VRML97 course notes

B582 - Lecture 6.1 VRML for Virtual Environments & Visualization