Rod constraints for simplified ragdolls

Programmers sometimes love rag dolls. This study is the fruit of one such love:

Rod constraints for simplified ragdolls,” Chris Lewin, Matt Thorman, Tom Waterson, Chris Williams, and Phil Willis, Proceedings of the 12th ACM SIGGRAPH/Eurographics Symposium on Computer Animation, pp. 79-84. ACM, 2013. The authors, at the University of Bath, UK, and Electronic Arts, explain:

“Physics-based animation has become a standard feature in modern games. Typically, the bones in a character’s animation rig are each associated with a simulated rigid body, leading to a jointed assembly commonly called a ragdoll. The high density of animation bones in the spine area can cause instability and performance issues, so we are motivated to find a simplified physical representation for this region. We approximate the spine region of a ragdoll as an inextensible elastic curve, building a circular arc constraint based on the Kirchhoff rod model. Our simplified spine shows improved performance and stability over the standard group of socket joints, and proves to be more controllable.”

Here’s more detail from the study: