Chap 4' Representation and Modeling landscape specialisation

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Chap 4. Representation and Modeling landscape
specialisation

• 4-1. Intro
• 4-2. Simple height field landscape
• 4-3. Procedural modeling of landscapes - fractals
• 4-4. Terrain LODs triangle bintrees
• 4-5. Rendering of landscape by ray casting

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4-1. Intro

• Feature
• Very large data
• Superimposing a height field on a regular grid
  pattern in the xy plane.
• LOD Problems
• View dependent LODs
• Data Type
• Generally height field based on a uniform grid.
  (MxN)
• Consideration of landscape models
• Ease of following

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4-1. Intro

• Terrain data Acquisitions
• Draw the height map (4-2)
• Fractal Terrain (4-3)
• Real Terrain data
• Terrain Rendering Methods
• TIN ( Triangulated-Irregular-network )
• Regular Grids
• ROAM (Real-time Optimally Adapting Meshes )
  Using bintree methods (4-4)
• Lindstrom Using Quadtree methods
• Volumetric Representation ( Ray-casting ) (4-5)

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4-2. Simple height field landscapes

• Easiest way to generate a height field
• To paint gray scales to represent height.

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4-3. Procedural modeling of landscapes - fractals

• Midpoint displacement methods
• Simulate uplift phenomenon
• Plasma fractal, diamond(or square) algorithm
• 1-D
• Height Random value from - dHeight/2r to
  dHeight/2r

C
Height
A
A
B
B
A
B
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• 2-D
• Diamond step E(ABCD)/4random(-dHeight/2r
  ,dHeight/2r )
• Square step L(FEJK)/4random(-dHeight/2r
  ,dHeight/2r )

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4-4. Terrain LODs Triangle bintree

• TIN(Triangulated-Irregular Network)

Texture mapped
Underlying triangle mesh
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Regular Grids Methods

• ROAM( Real-Time Optimally Adapting Meshes )
• By Duchaineau Triangle bin tree

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Split and Merge
Split and Merge Operations on a bintree
triangulation
Forced Splitting of Triangle T
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• Vertex morphing ( or Geo-Morphing)
• Visual pop that occurs when triangles are
  inserted or removed from the mesh
• Gradual rise or fall of vertexs height from the
  un-split position to its new split position over
  course of several frames.
• Wm(W(v0)W(v1))/2, WcW(vc) gt Wa(t)(1-t)WmtWc
• Error Metrics
• eTmaxe0, e1 z(vc)-(z(v0)z(v1))/2
• Projected eT in screen space is compared maximum
  projected thickness.

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• Methods
• Find the highest-priority triangle T in the queue
• Force split T
• Update the queue by removing T and other split
  triangles
• Add any new triangles to the queue.

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4-5. Rendering of landscapes by ray
casting

• Voxel volume data
• Textured mapped uniform height fields are similar
  to voxel-based data.
• Basic algorithm ray casting

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• Intersection calculation using ray coherence

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• Multi-resolution representation