Layered character models for fast physics-based simulation
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Date
2022
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Abstract
This thesis presents two different layered character models that are ready to be used
in physics-based simulations, in particular they enable convincing character animations
in real-time. We start by introducing a two-layered model consisting of rigid bones and
an elastic soft tissue layer that is efficiently constructed from a surface mesh of the
character and its underlying skeleton. Building on this model, we introduce Fast Projective
Skinning, a novel approach for physics-based character skinning. While maintaining
real-time performance it overcomes the well-known artifacts of commonly used geometric
skinning approaches. It further enables dynamic effects and resolves local and global self-collisions.
In particular, our method neither requires skinning weights, which are often
expensive to compute or tedious to hand-tune, nor a complex volumetric tessellation,
which fails for many real-world input meshes due to self-intersections. By developing a
custom-tailored GPU implementation and a high-quality upsampling method, our ap-
proach is the first skinning method capable of detecting and handling arbitrary global
collisions in real-time.
In the second part of the thesis, we extend the idea of a simplified two-layered volumetric
model by developing an anatomically plausible three-layered representation of
human virtual characters. Starting with an anatomy model of the male and female body,
we show how to generate a layered body template for both sexes. It is composed of three
surfaces for bones, muscles and skin enclosing the volumetric skeleton, muscles and fat
tissues. Utilizing the simple structure of these templates, we show how to fit them to
the surface scan of a person in just a few seconds. Our approach includes a data-driven
method for estimating the amount of muscle mass and fat mass from a surface scan,
which provides more accurate fits to the variety of human body shapes compared to
previous approaches. Additionally, we demonstrate how to efficiently embed fine-scale
anatomical details, such as high resolution skeleton and muscle models, into the layered
fit of a person. Our second model can be used for physical simulation, statistical analysis
and anatomical visualization in computer animation or in medical applications, which
we demonstrate on several examples.
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Keywords
Animation, Virtual character, Skinning, Physics-based simulation, GPU computing