VRML Scene Graphs

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VRML Scene Graphs
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Learning Objectives

• Understand the concept of a scene graph
• Understand how VRML defines transformations
  (translations, rotations, and scaling)
• Understand how to define children of transform
  nodes
• Understand how to create a VRML file with a scene
  graph using a text editor.

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A Scene Graph
Root
T1
T2
T3
T4
Geom 3
Geom 4
Geom 1
Geom 2
Geom 5
Affected By T2
Affected By T1
Affected By (T4)(T3)
Affected By T2
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What is a Transform?

• Transform
• SFVec3f center 0 0 0  (- , )
• MFNode children
• SFRotation rotation 0 0 1 0 -1,1,(- , )
• SFVec3f scale 1 1 1  (0, )
• SFRotation scaleOrientation 0 0 1 0 -1,1,(- ,
  )
• SFVec3f translation 0 0 0  (- , )
• SFVec3f bboxCenter 0 0 0  (- , )
• SFVec3f bboxSize -1 -1 -1  (0, ) or -1,-1,-1

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How Does The Transform Work?

• Given a 3-dimensional point P and Transform node,
  P is transformed into point P' in its parent's
  coordinate system by a series of intermediate
  transformations. In matrix transformation
  notation, where C (center), SR (scaleOrientation),
  T (translation), R (rotation), and S (scale) are
  the equivalent transformation matrices,
• P' T C R SR S -SR -C P
• (Note that this matrix notation is a transposed
  form of the material we studied earlier this
  semester)

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In VRML, this would be

• Transform
• translation T
• children Transform
• translation C
• children Transform
• rotation R
• children Transform
• rotation SR
• children Transform
• scale S
• children Transform
• rotation -SR
• children Transform
• translation -C
• children ...

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What Do You Need To Remember?

• FIRST TRANSLATE
• THEN ROTATE

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What About The Children?

• Anchor
• Background
• Billboard
• Collision
• ColorInterpolator
• CoordinateInterpolator
• CylinderSensor
• DirectionalLight
• Fog
• Group
• Inline

• LOD
• NavigationInfo
• NormalInterpolator
• OrientationInterpolator
• PlaneSensor
• PointLight
• PositionInterpolator
• ProximitySensor
• ScalarInterpolator
• Script
• Shape

• Sound
• SpotLight
• SphereSensor
• Switch
• TimeSensor
• TouchSensor
• Transform
• Viewpoint
• VisibilitySensor
• WorldInfo

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How Do You Define Children?

• children
• Shape geometry Sphere
• Transform
• translation 2 0 0
• children
• DEF Joe Shape geometry Sphere radius .2
• Transform
• translation -2 0 0
• children USE Joe

Sphr 1
Trans (-2 0 0)
Trans (2 0 0)
Joe 2
Joe
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Example 1
Group

• VRML V2.0 utf8
• Group
• children
• Shape geometry Sphere radius 1
• Transform
• translation 5 0 0
• children
• Shape geometry Sphere radius 2
• Transform
• translation -5 5 0
• children
• Shape geometry Sphere radius 3
  

Sph 1
Trans (5 0 0)
Sph 2
Trans (-5 5 0)
Sph 3
.WRL file containing this example
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Example 2

• VRML V2.0 utf8
• Group
• children
• Shape geometry Sphere radius 1
• Transform
• translation 5 0 0
• children
• Shape geometry Sphere radius 2
• Transform
• translation 0 5 0
• children
• Shape geometry Sphere radius 3
  

Group
Sph 1
Trans (0 5 0)
Trans (5 0 0)
Sph 3
Sph 2
.WRL file containing this example
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Lets Make This
y
y
3
3
10
2
2
x
z
3
5
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Learning Objectives

• Understand the concept of a scene graph
• Understand how VRML defines transformations
  (translations, rotations, and scaling)
• Understand how to define children of transform
  nodes
• Understand how to create a VRML file with a scene
  graph using a text editor.

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