Visualization and Interactive Systems Group, University of Stuttgart Page 1

Terrain Rendering

Dirk Ringe (phenomic), Stefan Roettger (VIS)

Visualization and Interactive Systems Group, University of Stuttgart Page 2

Overview

• C-LOD algorithm published at WSCG ‘98• T-SLICE algorithm to be published at VMV ‘01

Visualization and Interactive Systems Group, University of Stuttgart Page 3

Triangulation (C-LOD)

• Quadtree based triangulation• Top-down subdivision based on surface roughness

and distance to the point of view

Visualization and Interactive Systems Group, University of Stuttgart Page 4

Rendering (C-LOD)

• Display of terrain by means of a single or more triangle fans per node

• Obtain conforming mesh by simply skipping the blue vertices

Visualization and Interactive Systems Group, University of Stuttgart Page 5

Subdivision Criterion (C-LOD)

• Whether a subdivision is performed or not depends on the size d of the node, its distance l to the point of view, and the local surface roughness

Visualization and Interactive Systems Group, University of Stuttgart Page 6

Surface Roughness (C-LOD)

• Surface roughness (d2-values) is computed from the elevation differences dh between two consecutive levels of detail

• To propagate the triangulation up the quadtree the d2-values are adjusted where necessary

• Red vertices must be geomorphed

Visualization and Interactive Systems Group, University of Stuttgart Page 7

Results (C-LOD)

• The visible range can be extended to the horizon by using C-LOD algorithms

Visualization and Interactive Systems Group, University of Stuttgart Page 8

Results (C-LOD)

• The popping effect must be suppressed by geomorphing

Visualization and Interactive Systems Group, University of Stuttgart Page 9

Rasterization (T-SLICE)

• NVIDIA white paper (Sim Dietrich)

• Store elevation in alpha channel of texture map

• Use color subtraction extension and alpha test to rasterize only the solid part of a terrain slice

Visualization and Interactive Systems Group, University of Stuttgart Page 10

Hybrid Approach (T-SLICE)

• Calculate the necessary number of terrain slices to achieve subpixel accuracy

• Use a hierarchical bounding box representation of the terrain to adapt the number of drawn terrain slices to the viewing distance

• Calculate for each node whether terrain slicing or polygon rendering is faster and choose the appropriate method

Visualization and Interactive Systems Group, University of Stuttgart Page 11

Results (T-SLICE)

• Approximately 30 fps on a PC with GeForce2 MX (640x480)• Rendering performance does not depend on the size of the

height field• Best suited for displacement maps or radar views

Visualization and Interactive Systems Group, University of Stuttgart Page 12

Fin

Questions?

http://wwwvis.informatik.uni-stuttgart.de/~roettger