Despite the incredible leaps digital effects artists have made in the field of modeling for computer animation, many of their methods are often tedious. One of these time-consuming, difficult tasks is the realistic reproduction of weathered rocks. However, with the supervision of Michael Jones, a faculty member in the Department of Computer Science, students Matthew Beardall, Mckay Farley and Joseph Butler have created an algorithm that simplifies the creation of weathered rock surfaces.
“The algorithm is based on estimating the curvature of the rock,” Jones said. “It’s pretty clever.”
Using Utah’s Goblin Valley as the model for their project, the students and Jones studied the curvature of real rock surfaces both in nature and in the geology literature.
One explanation for the weathering observed in Goblin Valley is that the weathering rate depends on ratio of exposed surface area to volume.
“Our algorithm estimates this ratio and computes the weathering rate by estimating surface curvature,” Jones explained.
The rocks’ mean surface curvature can be positive, zero or negative. High positive curvature indicates that the surface has a jutting edge, while zero curvature identifies a flat surface and negative curvature describes a hole in the rock. Using computers to study these findings, Jones and his group confirmed that high positive curvatures weather very quickly while negative ones erode more slowly when modeling spheroidal weathering. Cavernous weathering, on the other hand, happens more quickly in areas with negative curvature.
Understanding these natural processes has allowed Jones to develop a computational program that simplifies the work of animation. Instead of “moving the points of the surface around by hand,” as was done with the previous method, animators may now tell a computer what they want their rocks to look like and it will produce them, Jones explained.
Artists sketch a curve that describes the durability of the rock. Using this information, the computer mimics what might realistically happen in nature. Less durable, high curvature areas weather more than the rest of the virtual surfaces. On the other hand, durable rock that has zero curvature experiences very little alteration in its appearance. The final weathered shape is a plausibly weathered copy of the curve sketched by the artist.
The work of Jones and Beardall demonstrates that surface curvature is a potentially productive approach to the long-standing problem of weathering rock in 3D. Their algorithm may relieve much of the modeling effort required to produce natural scenes in the quality entertainment that we all enjoy.