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)
• Blender Textures has free (Creative Commons licenses) textures of grass, pavement, concrete, etc.

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

• Terrain Textures from How in the World? provides 237 geotypical textures [offline as of 2011?]
  • 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)

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 (2001 GDCE 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]

a radical idea (1998)

• 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
• something like this was actually implemented a decade later in an academic paper (2008):
• Real-time rendering and editing of vector-based terrains, Eric Bruneton and Fabrice Neyret, EUROGRAPHICS 2008
  • Uses vector descriptions of linear and areal features, with associated shaders to specify their appearance (terrain color and material), their footprint (effect on terrain shape), and their associated objects, rasterized as needed and cached on the GPU
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