Chap 04

Chap 4. Representation and Modeling – landscape specialisation : 

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

4-1. Intro : 

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’

4-1. Intro : 

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)

4-2. Simple height field landscapes : 

4-2. Simple height field landscapes Easiest way to generate a height field To paint gray scales to represent height.

4-3. Procedural modeling of landscapes - fractals : 

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 A B A B C Height A B

Slide 7: 

2-D Diamond step : E=(A+B+C+D)/4+random(-dHeight/2r ,+dHeight/2r ) Square step : L=(F+E+J+K)/4+random(-dHeight/2r ,+dHeight/2r )

4-4. Terrain LODs: Triangle bintree : 

4-4. Terrain LODs: Triangle bintree TIN(Triangulated-Irregular Network) Texture mapped Underlying triangle mesh

Regular Grids Methods : 

Regular Grids Methods ROAM( Real-Time Optimally Adapting Meshes ) By Duchaineau : Triangle bin tree

Split and Merge : 

Split and Merge Split and Merge Operations on a bintree triangulation Forced Splitting of Triangle T

Slide 12: 

Vertex morphing ( or Geo-Morphing) Visual ‘pop’ that occurs when triangles are inserted or removed from the mesh Gradual rise or fall of vertex’s height from the un-split position to its new split position over course of several frames. Wm=(W(v0)+W(v1))/2, Wc=W(vc) => Wa(t)=(1-t)Wm+tWc Error Metrics eT=max{e0, e1} + | z(vc)-(z(v0)+z(v1))/2| Projected eT in screen space is compared maximum projected thickness.

Slide 13: 

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.

4-5. Rendering of landscapes by ray casting : 

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

Slide 15: 

Intersection calculation using ray coherence

Slide 16: 

Multi-resolution representation