Geotypical Imagery

• geotypical means that the image is typical of a kind of surface, like grass or snow, but is not any specific place

Sources of Imagery

• CG Textures is a great source of  grass, soil, pavement, etc.
• Paul Bourke's textures page is not really oriented toward textures at a geotypical scale, but a few of them might be useful (grass, dirt, rock)

Textures are also sold by a number of commercial texture vendors:

• Terrain Textures from How in the World? provides 237 geotypical textures
  • forests, rangeland, urban, sand, barren, farmland, etc. at 15 m/pixel, all tileable
  • well-suited for being viewed from a good distance above, e.g. flight simulation
  • only $20 for the whole set, for personal/non-commercial use (or at higher cost for commercial use)
• CGSD Corporation RealTexture Library ($2395, or $25 per texture)
• Marlin Studios has some ground textures in their CD libraries ($100-$200 each)
• 3DCafe emporium has a section on Textures, though most are not applicable for geotypical usage
• RealEyz Textures

Texture Synthesis

• parametric texture generation has a long history, but tends to produce textures that aren't too useful for real-world scenes
• DACHSBACHER, C., AND STAMMINGER, M. Cached Procedural Textures for Terrain Rendering. In Shader X4 (2005)
  • paper isn't online, but is included as section 8.2 of Dachsbacher's giant paper Interactive Terrain Rendering: Towards Realism with Procedural Models and Graphics Hardware (2006)
  • Reportedly, there's a DirectX implementation of the terrain texture cache in the book Shader X4 (pp. 457) along with source code.
• Texture Synthesis by Non-parametric Sampling
  • Alexei A. Efros and Thomas K. Leung, UC Berkeley / CMU
  • they take an input sample, and use it to synthesize textures which don't have the limitations of traditional stochastic synthesis approaches
• Geospecific Rendering of Alpine Terrain
  • Simon Premoze, William B. Thompson, Peter Shirley, Visual Simulation Lab at the University of Utah
  • their approach is to analyze a panchromatic geospecific input image, use image techniques to "normalize" them (remove shading and shadowing effects) and classify the image into categories
  • they can then reconstruct, with geotypical textures, an image which is flexible in regards to time of day and 3D vegetation, which can look far better than just doing a simple drape of the source image

    traditional drape of panchromatic aerial imagery

    rendering using the techniques from the paper

• numerous programs generate procedural textures from a variety of parameters
  • e.g. Texture Editor (freeware for Windows) which includes a callable library (header/dll)
  • Genetica is another option ($135 for Windows)

Tiling of Geotypical Textures

• one approach, used by many games, is to generate a large number of tiles, consisting of each type of ground cover, and transitions between each possible combination of adjacent types
• a good description of this approach is found in Procedural Landscapes (PPT presentation) by Glenn Corpes, particularly the system used for Magic Carpet

Detail texture / Blending Multiple Ground Textures

Placement of Snow

• The Synthesis of Snowcovered Terrains, Sinyan Law, Byong Mok Oh, Jonathan Zalesky, MIT 1996 [no longer online]

• satellite data tends to be of very poor quality, and makes it difficult to do smooth transitions to high-detail ground texture based on known cultural (GIS data) features
• a possible solution: generate the macroscopic ground texture by "rendering" the full-detail, small-area information such as land use, vegetation coverage, roads etc. using geospecific textures only, repeatedly downsampled as needed
• that way you save the considerable cost of the geospecific data, and are likely to get a smoother transition as well