Nature in computer graphics
a survey
by Shaun Kichenbrand

Contents   Introduction   Trees   Water   Clouds   Atmospheric phenomena   Conclusion   Printable version   Discuss this article

Clouds

Another integral part of any natural scene is the presence of clouds. In Horng-Shyang et al.^[13] a method is proposed using cellular automata as in Dobashi et al.^[14] which has been modified to allow simulation at run-time.

Modeling

Clouds can be modeled using particle systems^[9], metaball volumes^[14] or image-based modeling^[15]. The metaball approach is used in [13].

Rendering

The two common techniques of rendering clouds are ray-tracing (Kayija et al.^[16]) and procedural texturing (Ebert et al.^[17]) but both are time consuming methods. Most rendering methods use two-pass rendering schemes in which illumination and light-dynamics are taken into account on the first render and the final image is created on the second pass. In [13] a preprocessing scheme is utilized to compute shadow relation tables (STR) and metaball lighting texture databases (MLTDB). The clouds are finally rendered in a back-to-front order by traversing the octree. The texture for each voxel is obtained by multiplying the correct entry from the MLTDB and the voxel density.

Animation

Clouds in [13] implement algorithms for calculating cloud-to-vapor and extinction probabilities. The main facet of the simulation of the cloud relies on the rules as defined in the cellular automata.

Atmospheric phenomena