In the rendering of landscapes, radiosity has so far rarely been used. The enormous amount of geometric information causes extreme computing times and needs a huge amount of memory. Soler and Sillion [204] decreased this by integrating hierarchical instancing in radiosity procedures (see Sect. 8.5).
hierarchical radiosity ^ With the hierarchical version of the algorithms, Eqn. (9.7) is not solved in one
step, but rather this is accomplished through a recursive mechanism that first calculates directly the energy exchange between the larger part of the scene, and only then includes the smaller units when a given error threshold is crossed [202]. The hierarchical instancing is integrated into the hierarchical structuring of the scene using so called clusters, for which the energy exchange with the environment is managed through a simplified and geometry-independent representation.
However, the computing time still is extremely high. For example, a scene with 1 million triangles still needs approximately 2 hours on an efficient workstation (SGI Origin 2000). Here it should be noted, however, that the computed solution is independent of the viewing location, and an animation can later be produced relatively quickly.
applications ^ The correct calculation of the light exchange between plants, and especially the
backscattering of vegetation, is of interest for satellite-based earth observation. Here the reflection behavior is used for determining the type and the condition of the vegetation. Various rendering methods were applied in the past to adjust satellite data using computer models [145]. However, also here the procedures fail often because of the complexity of the geometric data.
Max et al. [133] reduce this complexity, in that they compute the illumination only relative to the height above the ground and not for the individual locations on the plane. Thus for homogeneous vegetation the originally threedimensional problem of the light exchange can be reduced to one dimension.
