Computer Animation: Algorithms and Techniques (nonfiction)

Computer Animation: Algorithms and Techniques is a book by Rick Parent.

Excerpts

Simulation cirrus, stratus, and mackerel clouds

Cirrus clouds differ greatly from cumulus clouds in their density, thickness, and falloff. In general, cirrus clouds are thinner, less dense, and wispier. These effects can be created by altering the parameters of the cumulus cloud procedure and also by changing the implicit primitives. The density value parameter for a cirrus cloud is normally chosen as a smaller value and the chosen exponent is larger, producing larger areas of no clouds and a greater number of individual clouds. To create cirrus clouds, the user can simply specify the global shape (envelope) of the clouds with a few implicit primitives, or he or she can specify implicit primitives to determine the location and shape of each cloud. In the former case, the shape of each cloud is controlled mainly by the volumetric procedural function and turbulence simulation, unlike with cumulus clouds, for which the implicit functions are the main shape control. In is also useful to modulate the densities along the direction of the jet stream to produce more natural wisps. This can be created by the user specifying a predominant direction of wind flow and using a turbulent version of this vector in controlling the densities as follows ... [CODE]

Stratus clouds can also be modeled by using a few implicits to create the global shape or extent of the stratus layer while using volumetric procedural functions to define the detailed structure of all clouds within this layer. Stratus cloud layers are normally thicker and less wispy than cirrus clouds. This effect can be created by adjusting the size of the turbulent space (smaller/fewer wisps), using a smaller exponent value (created more of a cloud layer effect), and increasing the density of the cloud. Some of the more interesting stratus effects, such as a mackerel sky, can be created by using simple mathematical functions to shape the densities.

• Pages 306 - 308

Fiction cross-reference

• Gnomon algorithm
• Gnomon Chronicles

External links

• Computer Animation: Algorithms and Techniques @ books. google.com
• Rick Parent's website