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Virtual Reality Modeling

Language (VRML)

Peter O’Grady

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VRML

Background Example VRML Versions VRML language Creating a VRML world

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VRML - Background

Sometimes pronounced “vermel”. A language for building 3-D worlds on the

WWW. Use a VRML browser to walk around virtual

world. Browser downloads file containing

description of world (in VRML format). Browser interprets scene descriptions and

renders the resulting image.

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VRML - Background (2) Manipulation is performed on client (host)

computer. Use of 3-D cards can speed performance. Rendering performed through lens of a

virtual camera. Can move, twist and twirl. Can alter lighting.

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Using VRML

VRMLtext file

*.wrl

VRMLRenderer

usually browser plug-in or

ActiveX control

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VRML - History WWW conference in March 1994 -

basic requirements defined. WWW conference October 1994 - draft

specification of VRML 1.0 presented. Used language from a 3-D modeler Version 1.0 introduced April 1995. Version 97 now available and in use

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VRML Versions 1.0 Initial version. Static images. 97 aims to be multi-user, objects

defined their behavior, “participants” can see each other

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VRML Language

VRML 97 provides these extensions and enhancements to VRML 1.0:– Enhanced static worlds – Interaction – Animation – Scripting – Prototyping

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VRML Language Script-like language in ASCII text Given extension .wrl For easy identification of VRML files,

every VRML 97 file must begin with the characters: #VRML V2.0 utf8

Scene graphs consist of “nodes” Each node has attributes See example on web site

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VRML Working Process

Generation of a VRML file Transmission of VRML file to viewer Viewing of VRML world Interacting with the VRML world

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The Structure of VRML VRML can be viewed at a high level of

abstraction as a collection of objects which are called nodes.

These objects, or nodes, are defined for 3D graphics

Nodes are arranged in hierarchical structures called scene graphs, which define an ordering for the nodes.

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The Structure of VRML This was originally based on the Open

Inventor 3D toolkit developed by SGI, for VRML 1.0.

The scene graph represents such aspects of a 3D world as geometry, materials, textures, geometric transformations, lights, viewpoints, and nesting structures.

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Characteristics of a Node

A node might be a cube, a sphere, a texture map, a transformation, etc.

The node has parameters that distinguish the node from other nodes of the same type.

The node has a name. The node can be part of a hierarchy.

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Enhancement of VRML VRML 97 adds five constructs to VRML

1.0 that can significantly improve a 3D world.

Four of these (namely node event field, routes, sensors, interpolators) connect and control animations, actions and reactions.

The fifth (script nodes) allows for the interface with JavaScript or Java programs.

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Enhancement of VRML

In addition, VRML 97 allows for video images (in MPEG format) to be mapped to a surface, collision detection, fog, text that always points to the user, contoured terrains, and texture mapped backgrounds.

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VRML Language -Nodes Cylinder {

bottom TRUE

height 2

radius 1

side TRUE

top TRUE

}

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VRML Language -Nodes Cone {

bottomRadius 1

height 2

side TRUE

bottom TRUE

}

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VRML Language -Nodes Box {

size 2 2 2

}

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VRML Language -Nodes

Sphere { radius 1}

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Coordinate Systems and Transformations

VRML uses a Cartesian, right-handed, 3-dimensional coordinate system.

By default, objects are projected onto a 2-dimensional display device by projecting them in the direction of the positive Z-axis, with the positive X-axis to the right and the positive Y-axis up.

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VRML Language -Nodes

Transform { children [ ]

scale 1 1 1

translation 0 0 0

}

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VRML Language -Nodes Coordinate {

point [ ]

}

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VRML Language -Nodes

Color {

color [ ]

}

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VRML Language -Nodes

PointSet { color NULL coord NULL}

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VRML Language -Nodes IndexedFaceSet {

color NULL

coord NULL

coordIndex [ ]

normalIndex [ ]

normalPerVertex TRUE

solid TRUE

}

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VRML Language -Nodes

Appearance { material NULL

texture NULL

textureTransform NULL

}

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VRML Language Material - with attributes such as diffuseColor,

and shininess diffuseColor 0 0 0 is black, 1 1 1 is white shininess 1.0 is highly reflective Translation - to specify position of object Level of Detail (LOD) nodes allow varying level

of detail with distance WWWAnchor creates link to another VRML

world

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Example 1 - source code#VRML V2.0 utf8

DEF Machine3 Transform { translation 2 0 0 rotation 0 1 0 0 children [ Shape { geometry Box { size 6 10 6 } appearance Appearance { material Material { diffuseColor 0.2 0 0.8 } }

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Example 2 - source code#VRML V2.0 utf8Transform {

scale 5 5 5children [

Shape {appearance Appearance {material Material {

ambientIntensity 0.8 diffuseColor 1 0 0 emissiveColor 1 0 0 #shininess 1 specularColor 0 0 0 transparency 0 }

}

geometry IndexedFaceSet {coord Coordinate { point

[-0.106390.50.153638,-0.10757

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Example 2 - VRML World

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Creating VRML Worlds

Free formed surfaces, such as that arising from imaging, are not included in the VRML specification.

Therefore, a set of polygons should approximate to a free-formed surface or curve.

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Creating VRML Worlds

For the purpose of rendering and shading the created polygons, their normal vectors are calculated and given to the respective polygons.

Suppose that the surface is an imaging object. Then, the surface is translated into a VRML file format.

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Creating VRML Worlds - One Proposal

Maxi

iP(||||)

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Working With VRML Native code Converters Software that produces VRML code Can be large files - problem is to make

the code efficient IIL work gives about 100:1 reduction

from original data set.

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Examples - See IIL Site Data from MRI Data from CT

– Lung– Lung and tumor

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VRML and Medical Applications

Visualization over WWW Need advanced methods to map from

data to VRML. Acceleration

– 3D boards– Better software

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Medical Applications - Creation of Virtual Reality Worlds from Medical Imaging Data

Image Segmentation VRML Mapping

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Literature on Medical Image Segmentation

Manually Automatically Semi-automatically

– Thresholding– Boundary finding– Mathematical Morphology– Region Growing

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Literature on Medical Image Segmentation

Segmentation is a challenging task, especially considering an organ like the lung.

Much of the work on lung segmentation has involved manual segmentation (Naidich et al, 1993) but this involves considerable labor and can be prone to bias.

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Literature on Medical Image Segmentation

Two Dimensional (2D) images require that the physician mentally determine 3D images from 2D slices, and this is difficult and error prone.

The fundamental problems with current approaches to 3D display of scans are that they are not interactive once reported.

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Boundary Identification (2D Segmentation)

Grouping Analysis

Vx(Px,y,z) = ABS((MEAN (Px-p,y,z ,…. Px-2,y,z , Px-1,y,z )-MEAN (Px+1,y,z , Px+2,y,z , …Px+p,y,z ))

0

20

40

60

80

100

120

140

pixel

valu

e o

f p

ixel

Pr,s,t

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Case Study - Lung/Tumor

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Case Study - Lung/Tumor

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Other Considerations Variety of VRML browsers available. Netscape uses Cosmo player (from SGI,

CA) for VRML Microsoft new browser with IE 4 For Windows 9x, Direct3D has been defined. 3D Boards now have Direct3D drivers Need to have VRML browser with Direct3D

support.