Terrain Modeling Prasanna 8162002

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Terrain Modeling-Prasanna 8/16/2002

• Terrain Information
• Terrain Generation- Algorithm/Data Struc.
• Terrain Traversal
• V-Lab Terrain Model

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Terrain Information

• Terrain Information can be modeled using the
  following Terrain Attributes
• Surface Area
• Obstacles

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Surface Area

• The entire dimension of the environment where
  obstacles and other sources of information for
  simulation are provided. Divided into Grid.
• Inputs
• Total Dimension of the area.
• Elevation of Surface from 0 Level.
• Position of elevation (x,y,z).
• Height of Elevation (/-)

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Surface Area...

• Area of Elevation
• Surface Information(Rough/Slippery)
• Position of surface information(x,y,z).
• Dimension of this surface information.
• Color Information.
• (Blue water, Green Grass)

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Obstacles

• Obstacles may be placed at any (x,y,z) position
  on the surface. User would specify type, width,
  height, and/or other related information of the
  object (like radius,mass).

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obstacles

• Input Position of the obstacle.
• Type of Obstacle (Rectangular, Spherical,
  Random )
• Length, Breadth, Height, Mass (if reactangular)
• Radius and Mass (If Spherical)
• Surface of Obstacle (Hard, Soft, Rough)
• Output Generate a Category depending on 'type
  of obstacle'. (Large, Medium, Small). Would help
  the agent to either move over it or execute an
  algorithm for avoiding it.

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Terrain Generation

• DATA STRUCTURES
• Triangular Irregular Networks(TIN)
• Square Grid (Raster)
• Choosing
• To describe every shape? - Triangular N/w
• Memory Requirements? - Square grid N/w

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Data Struc.

• TIN
• Don't Create regular geometric pattern.
• Points are distributed more dense where bigger
  accuracy is needed.
• Any terrain feature can be described.
• Modifications are not simple

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Data Struc.

• Square Grid
• - Store data Efficiently in 2D Array.
• - Modification is very trivial.
• - Memory used is less.
• - Not possible to define all terrain features.
• - Good for Collision detection, when No
  Accuracy is needed application like image
  synthesis.

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ALGORITHMS

• Based on HEIGHT-FIELDS
• Height Fields
• Two Dimensional Array holding Height Values(Z) at
  each (X,Y) poistion.

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Algorithms

• Hill Algorithm
• 1) Choose a random point X1,Y1 and radius R
• 2) Formula generates a parabola at X1 Y1. More
  the R, greater is height.
• 3) Generate the height(Z) using equation
• Z2 R2 - ((X2-X1)2 (Y2-Y1)2).
• 4) Repeat for several iteration to obtain
  multiple hills.

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Algorithms

• Fault Algorithm
• Divide the Surface into two parts by randomly
  drwaing a line.
• Elevate one side of the line by height H.
• And decrease the height of the other side of line
  by -H.
• Repeat this until we get valleys and mountians.

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Algorithms

• Subdivision Algorithms
• Diamond Square Algorithm (Mid Point
  Displacement/Plasma Algorithm)
• Consists of Two steps Diamond Step and Square
  Step.
• Very inexpensive compared to Fault Algorithm.
• 10 Iterations yeilds 1024 x 1024 grid points.

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Diamond-Square Algo.

• E (ABCD) / 4 RAND(d)

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• Can have roughness parameter for this.
• How much do we perturb(choose rand(d)) the grid?
  The answer is that we start out with a roughness
  coefficient 0.0 lt roughness lt 1.0
• At iteration n of our Diamond-Square algorithm we
  add a random perturbation to the grid
  -roughnessn lt perturbation lt roughnessn.

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Terrain Traversal

• The Terrain traversal for an agent would be using
  some techniques such as Fuzzy-Logic.(Proposed by
  Ed Tunstel)

steep
Flat
slopped
Rocky
smooth
Rough
Roughness parameter
Slope parameter
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VLAB Terrain Model

• Users are allowed to create thier own Terrain
  depending on type of application
  (Robotics,BioMedical,Etc.). - Set of APIs. -
  createTerrain( area, ..), placeObstacle(
  x,y,z.)
• The terrain is then modelled using Java 3D or
  similar graphics package(rendering).
• Given a Position (X,Y,Z) sent from SimMan, a
  Terrain Model should return back
• - Height (elevation/Descent) from ground (0)
  level.
• - Obstacle Yes/NO Boolean Value
• - If YES, Large/Medium/Small ?
• - Roughness parameter of the surface at that
  position.