Level of detail

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As a Level of Detail ( LOD ; German: level of detail ) is referred to the various levels of detail in the presentation of virtual worlds.

In order to increase the speed of virtual reality applications , one usually relies on the simultaneous use of a high level of detail in the close range and a low level of detail in the far range. This can affect the complexity (number of polygons ) of the 3D objects, the number of graphic operations to be carried out, but also the resolution of the textures. The mip-mapping effect is not relevant for optimizing the file, since the textures are loaded in their full size into the memory of the graphics card.

The appropriate LOD is automatically selected depending on the distance and position of the objects to the observer. If only a few levels of detail are available, the model change may be perceived by the sudden appearance and disappearance of details. To avoid this popping effect , continuous LOD is sometimes used or the models are merged into one another by blending (cross-fading) and morphing . For example, progressive meshes are used for terrain models .

Number of triangles

The example on the right shows the sequence of several levels of detail in a building. The reduction takes place in all three areas:

  • Reducing the number of triangles
  • Minimization of the absolute texture size per LOD level
  • Reduction of the required graphics commands ("draw calls")

LOD concepts are also used in the area of ​​virtual three-dimensional landscape and city models. Depending on the application, different levels of detail are required here. The following levels of detail were worked out for the CityGML specification and are currently based on many German city models:

  • LOD 0: Regional model, 2.5D terrain model with aerial photo texture
  • LOD 1: block model, building block (raised area)
  • LOD 2: 3D model of the outer shell and roof structures and simple textures
  • LOD 3: Architectural model, 3D model of the outer shell with texture
  • LOD 4: Interior model, 3D model of the building with floors, interior spaces etc. and textures

literature

  • David Luebke et al. a .: Level of Detail for 3D Graphics . Morgan Kaufmann Publishers, San Francisco 2003, ISBN 1-55860-838-9 .
  • Dirk Schlender: Requirements for level management in virtual simulation environments . VDI-Verlag, Düsseldorf 1999, ISBN 3-18-359710-1 .

Web links

  • Hugues Hoppe: Progressive Meshes . 1996 ( online [accessed December 8, 2007]). (English)