Viper

Abstract

a) (b) (c) (d) Fig. 1. (a) We compactly model muscles as a collection of generalized rods, where volume conservation is expressed by a radius function defined on curve's vertices -vis sphere's radii. (b) The rods create a subspace on which physics is solved, and its effects later propagated to the muscle mesh via linear blend skinning; please see the animation in our supplemental video. The anatomical model is courtesy of Ziva Dynamics. (c) We show how rods and/or bundles can be skinned to a surface mesh to drive its deformation (d), resulting in an alternative to cages for real-time volumetric deformation.We extend the formulation of position-based rods to include elastic volumetric deformations. We achieve this by introducing an additional degree of freedom per vertex -isotropic scale (and its velocity). Including scale enriches the space of possible deformations, allowing the simulation of volumetric effects, such as a reduction in cross-sectional area when a rod is stretched. We rigorously derive the continuous formulation of its elastic energy potentials, and hence its associated position-based dynamics (PBD) updates to realize this model, enabling the simulation of up to 26000 DOFs at 140 Hz in our GPU implementation. We further show how rods can provide a compact alternative to tetrahedral meshes for the representation of complex muscle deformations, as well as providing a convenient representation for collision detection. This is achieved by modeling a muscle as a bundle of rods, for which we also introduce a technique to automatically convert a muscle surface mesh into a rods-bundle. Finally, we show how rods and/or bundles can be skinned to a surface mesh to drive its deformation, resulting in an alternative to cages for real-time volumetric deformation. The source code of our physics engine will be openly available 1 .

A novel radial basis function description of a smooth implicit surface for musculoskeletal modelling

“…In 2019, Angles et al [19] introduced an XPBD-based method for muscle modelling, virtually decomposing the muscle into flexible "rods" approximating muscle fibres. These rods adjust their diameter to maintain volume, enabling real-time simulation.…”

State‐of‐the‐art improvements and applications of position based dynamics

“…The work by Lee et al 66 proposed and integrated an internal shape preserving constraint (ISPC) generation algorithm into the position based dynamics, which reduces the number of nodes filling the interior of 3D models and computation time of tetrahedral models while achieving similar volume maintenance and physical properties of tetrahedral models. In the work by Angles et al 71 , a bundle of cosserat rods was used as an alternative to tetrahedral meshes for modelling muscles and PBD simulation of volume invariant rods was coupled to a surface mesh to simulate soft-body deformation with high efficiency. Without using tetrahedral meshes, triangle meshes were deformed via a Verlet integration framework of PBD simulation to reduce the computational cost, which provides the simulation of deformable surfaces on the selected area of the 3D mesh with a desired range 72 .…”

MARF: The Medial Atom Ray Field object representation

“…The MAT has various downstream uses, including 3D shape retrieval [73,74], segmentation [75], and manipulation [76]. MAT-inspired sphere representations have further applications in constructing simplified static [77] and dynamic [78] shapes, closest point computations [79], and volumetric physics simulation [80].…”