Virtual Reality Modeling
Language (VRML)
Peter O’Grady
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VRML
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Background
Example VRML
Versions
VRML language
Creating a VRML world
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VRML - Background
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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)
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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
VRML
text file
*.wrl
VRML
Renderer
usually browser
plug-in or
ActiveX control
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VRML - History
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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
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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
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VRML 97 provides these extensions
and enhancements to VRML 1.0:
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Enhanced static worlds
Interaction
Animation
Scripting
Prototyping
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VRML Language
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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
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Scene graphs consist of “nodes”
Each node has attributes
See example on web site
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VRML Working Process
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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
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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
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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
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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
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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
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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
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Cylinder {
bottom TRUE
height 2
radius 1
side TRUE
top TRUE
}
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VRML Language -Nodes
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Cone {
bottomRadius 1
height
2
side
TRUE
bottom
TRUE
}
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VRML Language -Nodes
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Box {
size 2 2 2
}
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VRML Language -Nodes
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Sphere {
radius 1
}
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Coordinate Systems and
Transformations
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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
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Transform {
children
scale
translation
[]
111
000
}
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VRML Language -Nodes
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Coordinate {
point [ ]
}
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VRML Language -Nodes
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Color {
color [ ]
}
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VRML Language -Nodes
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PointSet {
color
NULL
coord
NULL
}
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VRML Language -Nodes
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IndexedFaceSet {
color
NULL
coord
NULL
coordIndex
[]
normalIndex
[]
normalPerVertex TRUE
solid
TRUE
}
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VRML Language -Nodes
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Appearance {
material
NULL
texture
NULL
textureTransform NULL
}
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VRML Language
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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 utf8
Transform {
scale
children [
Shape {
5 5 5
appearance Appearance {
material Material {
ambientIntensity
diffuseColor
emissiveColor
#shininess
specularColor
transparency
0.8
1 0 0
1 0 0
1
0 0 0
0
}
}
geometry
IndexedFaceSet {
coord Coordinate {
point
[
-0.10639
0.5
0.153638
,
-0.10757
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Example 2 - VRML World
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Creating VRML Worlds
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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
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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
Max(|| Pi ||)  
i
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Working With VRML
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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
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Data from MRI
Data from CT
– Lung
– Lung and tumor
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VRML and Medical Applications
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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
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Image Segmentation
VRML Mapping
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Literature on Medical Image
Segmentation
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Manually
Automatically
Semi-automatically
– Thresholding
– Boundary finding
– Mathematical Morphology
– Region Growing
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Literature on Medical Image
Segmentation
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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
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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)
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Grouping Analysis
140
120
value of pixel
100
80
60
40
20
0
pixel
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Pr,s,t
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 ))
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Case Study - Lung/Tumor
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Case Study - Lung/Tumor
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Other Considerations
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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.
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