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SuperTrack: Motion Tracking for Physically Simulated Characters Using Supervisory Signals

Levi Fussell, Kevin Bergamin, Daniel Holden

SIGGRAPH AsiaUbisoft47 cites2 descendantsMotion Synthesis

Supervisory signal method for physics-based motion tracking that enables simulated characters to closely follow diverse motion reference clips.

Abstract

In this paper we show how the task of motion tracking for physically simulated characters can be solved using supervised learning and optimizing a policy directly via back-propagation. To achieve this we make use of a world model trained to approximate a specific subset of the environment's transition function, effectively acting as a differentiable physics simulator through which the policy can be optimized to minimize the tracking error. Compared to popular model-free methods of physically simulated character control which primarily make use of Proximal Policy Optimization (PPO) we find direct optimization of the policy via our approach consistently achieves a higher quality of control in a shorter training time, with a reduced sensitivity to the rate of experience gathering, dataset size, and distribution.

How to read this

Category
Method: learning-based motion tracking for physics-based characters
Contributions
  • Frames physics-based motion tracking as supervised learning, optimizing the control policy directly via back-propagation
  • Trains a world model that approximates the environment's transition function, acting as a differentiable physics simulator
  • Reports higher control quality in shorter training time with reduced sensitivity to dataset size and experience-gathering rate versus PPO-based methods
Context
Positioned against model-free PPO controllers for simulated characters and builds on data-driven responsive control (Bergamin et al.'s DReCon).Builds on: DReCon: Data-Driven Responsive Control of Physics-Based Characters
Correctness
Key assumption is that a learned world model is an accurate-enough differentiable proxy of physics for policy gradients; comparisons are made primarily to PPO on motion tracking, so the world-model approximation error and behavior outside the trained motion distribution are the limitations to watch.
Clarity
The supervised-versus-model-free framing is clear; the world-model training and differentiable-optimization mechanics need a second pass.
How to read it
First pass for the world-model-as-differentiable-simulator idea and why it beats PPO here; second pass on the training loop and loss if you want to reproduce the control quality.

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