Terrain

1
Terrain

• Fake Terrain

2
Fake Terrain

• Generate the heightfield
• Random process
• Reflects realistic terrain in some way

3
Random Terrain

• Simple
• Terrain(x,y) rand( MAX_HEIGHT )
• Results in random noise
• Next step
• Smooth the terrain generated above
• FIR filter

4
Filtering

• FIR (Finite Impulse Response) filter
• Pass a window over the data
• Multiply data in window by weights
• Result d1w1 d2w2 dNwN
• Window weights is called filter kernel
• Larger window grabs more data

5
Random Fault Lines

• Repeatedly
• Create a line that crosses terrain
• Add dHeight offset on one side of line
• dHeighti dHeight0 (i/n)(dHeightn -dHeight0)
• Select random endpoints to generate line
• Compute side of line by plugging X,Y into line
  equation

6
More Realistic Faults

• Apply FIR filter to faulted heightmap
• Smooth out abrupt fault transitions Erosion

7
Fractal Mountains

• Fournier Fussell (1980)
• Recursively subdivide geometry by random number
  d
• dHeight/2 lt d lt dHeight/2
• At each recursion
• dHeight 2-r
• r1 self-similar
• rgt1 large features early
• rlt1 large features late

8
Fractal Terrain

• Subdivision on quads

F
E
G
H
I
9
Fractal Terrain
10
Particle Deposition

• Drop particles in areas where you want volcanic
  mountains
• Particles flow downhill until they have cause to
  rest
• Move the drop point to create interesting peak

11
Particle Deposition

• Flow computation
• At given point, find lowest neighbor
• If local geometry is not flat enough, move new
  particle on top of lowest neighbor
• Flat enough 27 degrees or so
• Check 3x3 pixel window or 5x5 to check flatness

12
Particle Deposition
13
Caldera
14
Continuous Navigation Around the World
Atlanta, GA area
World
Grand Canyon
Rwanda
15
Hierarchical Urban Data Cities Everywhere
16
Global Data Model Forest of Quadtrees

• 32 zones
• 8 levels per quadtree
• Separate coodinate system at each leaf node
  (256x256 total nested systems)
• 1 mm worst case resolution

17
General Zonal Quadtree

tree structure
Data-dependent, detailed, low-level representation
18
Terrain Zonal Quadtree

22 levels
Regular Triangularization (128 x 128 grid points)
19
Level of Detail

• Key Idea
• Screen-space level of detail
• Evaluate a model based on projected size
• Continuous terrain
• Projected distance from old edge to new vertex