Terrain LOD: Runtime Regular-Grid Approaches

Implementations with Source

• seamless
  • An implementation by Tim Moore of the paper Seamless Patches for GPU-Based Terrain Rendering, which guarantees that there won’t be seams — either gaps or skirts — between adjacent patches of terrain.
  • See his blog posts a terrain engine for osgEarth and The Seamless Engine Goes Global
  • Uses an unusual cubic mapping which is similar to a quadrilateralized spherical cube
  • Built on / integrates with the osgEarth library
• CDLOD by Filip Strugar
  • a very clear, easy to follow paper with demos and complete source code, implemented on DirectX
• libMini by Stefan Röttger
  • implements his paper Real-Time Generation of Continuous Levels of Detail for Height Fields
  • LGPL source, highly optimized, 5 bytes/heixel, very fast
  • Encapsulated in the VTP Terrain Library (vtlib) by the class SRTerrain
• Chunked LOD by Thatcher Ulrich
  • ChunkLOD is a hybrid approach which takes a grid as input, and generates a file containing "chunks" which are sections of the terrain as RTIN LODs
  • a runtime engine then loads the "chunk file" and very efficiently swaps as needed, for very high polygonal throughput, approaching the limits of the graphics card
  • includes full public-domain source, using OpenGL and SDL: tu-testbed page at Sourceforge, the paper (pdf) describes the general algorithm, and the readme contains implementation details
  • it can read BT and works very well with the VTP distribution data files
  • an adaptation of chunkLOD to OSG by Vladimir Vukicevic is on the page osg tools and hacks
• ROAM by Mark Duchaineau
  • a full implementation is now available of this classic academic algorithm
  • source compiles on SGI boxes and on recent Linux distributions
• SoTerrain
  • a terrain visualization library for Coin (GPL implementation of OpenInventor)
  • includes a finite dual queue ROAM implementation, and a Geo Mip-Mapping implementation
• SOAR by Peter Lindstrom and Valerio Pascucci
  • implements Visualization of large terrains made easy
  • the preprocessing stage requires "8/3 × 20", or around 53 bytes per heixel
  • at runtime it requires "from 20 to 33" bytes/heixel
  • does geomorphing, reads data from PNG
  • full source, but a restrictive license, only free for limited noncommercial use
• Demeter by Clay Fowler (site was terrainengine.com, now only at SourceForge : Demeter)
  • cross-platform C++ library, license is LGPL
  • the core library is dependent only on OpenGL; useful additional functionality is built on GDAL, SDL, OSG
  • supports detail textures using splatting
• Seumas Young's Terrain Tutorial
  • A ten-part series of articles with a simple description of modeling and rendering a basic artificial terrain.  The LOD is derived from Lindstrom's Terrain Simplification Simplified.  There is lots of good advice with illustrated examples (bake the lighting into the terrain, don't recompute detail every frame, limit camera motion, etc.)
  • Includes source (for Windows and OpenGL)
• Bryan Turner's article describing the TreadMarks algorithm (split-only ROAM bintrees)
• Ranger Mk II by Andras Balogh
  • implements an improved version of Lindstrom's SOAR algorithm; Andras refers to his algorithm as SOARX
  • the improvements, detailed in his thesis (pdf), include optimization of the triangle striping process, and additional of procedural detail to the lowest level of detail
  • makes heavy use of cutting-edge graphics card features, so it runs only on recent NVidia cards
• lScape by Adrian Welbourn
  • implements geomipmapping based on a paper by Willem H. de Boer
  • implements hierarchical visibility based on a paper by A. James Stewart
  • implements texture splatting based on a paper by Charles Bloom
  • beautiful cast shadows
  • includes source under GPL!
  • uses advanced OpenGL features: accelerated rendering with NV Var Fence and texture_env_combine, where supported by ICD
• Danny Chapman's gliding flight sim
  • primarily a glider simulation, with several precalculated "wind field" data files for realistic wind modelling
  • provides a open-source implementation of Lindstrom's Visualization of large terrains made easy, including geomorphing and view-frustum culling
  • binary for Windows, source for Linux; uses OpenGL & GLUT
  • nice cast shadow of the glider onto the ground
• XTerra by Ofer Hoberman
  • open source implementation of Röttger's approach, demo built on GLUT
  • reads supplied .RAW files for height and texture
• Crystal Space / DDG (Digital Dawn Graphics Toolkit)
  • Alex Pfaffe's project DDG developed a CLOD implementation which has been merged with the Crystal Space cross-platform 3D toolkit
  • classes: ddgTBinTree is used for CLOD of 32x32 sample blocks and ddgTBinMesh sews a collection of bintrees together to form a continuous larger mesh
  • implements frame coherency like ROAM
  • basic structure requires 3 bytes plus height field values (2 bytes), total 5 bytes/heightmap sample, plus 12 bytes per drawn vertex

Old / Historical

• awu - terrify
  • 2003 (?) seems to be no longer online.
  • based on Lindstrom and Pascucci's work in "Visualization of Large Terrains Made Easy", but the algorithm has been made even easier
  • clean, simple source and executable for Windows, but should be easily portable
  • efficient memory usage per heixel (1 byte Z, 1 byte error, 1 byte radii lookup)
  
• engine1 by David Dufke (2006)
  • an OpenGL-based engine, full source
  • ROAM-derived CLOD terrain
  • reads BT, handles 4k*4k easily
• Continuous LOD Terrain Renderer, 1997
  • implementation of the Lindstrom-Koller algorithm
  • by Torgeir Lilleskog of the Norwegian University of Science and Technology, packaged and presented by Bjørn Stensrud
  • a very detailed descriptions and analysis of other algorithms is contain in the paper Textured Terrain Rendering on Low-End 3D Hardware
  • their sample terrain is a small nonstandard DEM of Nordoeyane on the coast of Norway, 542*532 points
  • since the data points are so far apart, the LOD algorithm rarely has an opportunity to cull vertices, making this a non-ideal showcase for terrain LOD

See Also: some commercial Game Engines (Middleware) provide impressive Terrain LOD capabilities