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Physical Plausibility-aware Trajectory Prediction via Locomotion Embodiment
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Proposes Locomotion Embodiment, which trains a differentiable Locomotion Value (LocoVal) surrogate of a physics-based humanoid locomotion generator (PACER) and uses it as an EmLoco loss to regularize trajectory predictors and as a filter at inference.
Problem
Human trajectory prediction (HTP) from momentary observations often produces physically implausible trajectories, because pose cues are used only implicitly and indifferentiable physics simulators cannot supervise HTP networks directly.
Approach
Distill the plausibility of physics-simulated humanoid locomotion (discounted reward of a trajectory-following policy) into a differentiable MLP (LocoVal), then use it as a regularization loss on all predicted heads of a multi-head HTP network and as an inference-time filter.
Key results
- On JTA with standard 9-frame setting, the method reaches ADE 0.97 / FDE 1.91 vs Social-Trans 1.11 / 2.26.
- With 2-frame momentary observations on JTA (deterministic), ADE 1.33 vs Social-Trans 1.36; with 5 heads minADE 0.87 vs 0.92.
- LocoVal filter on zero-shot ETH/UCY with EqMotion reduces mean ADE from 1.12 to 0.88 and FDE from 2.41 to 1.89.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add the EmLoco loss to Social-Trans | Social-Trans · JTA | ADE: 1.11 -> 0.97 | Helped |
| Add the EmLoco loss to Social-Trans | Social-Trans · JRDB | ADE: 0.40 -> 0.37 | Helped |
| Add the EmLoco loss to multi-head Social-Trans | Social-Trans, JTA, 9 observed frames · JTA | χ2 velocity distance: 0.134/0.169 -> 0.100/0.087 | Helped |
| Add the EmLoco loss to Social-Trans | Social-Trans, 2-frame observations · JTA, deterministic | ADE: 1.36 -> 1.33 | Helped |
| Add the EmLoco loss to Social-Trans | Social-Trans, 2-frame observations · JRDB, deterministic | ADE: 0.50 -> 0.44 | Helped |
| Add the ground-truth trajectory loss LT alongside EmLoco loss (ablation) | Ours · JTA | ADE: 3.52 -> 0.97 | Helped |
| Add the ground-truth trajectory loss LT alongside EmLoco loss (ablation) | Ours · JRDB | ADE: 0.92 -> 0.37 | Helped |
| Include implausible pose-trajectory pairs when training LocoVal (ablation) | Ours · JTA | ADE: 1.01 -> 0.97 | Helped |
| Include the initial pose j0 as a LocoVal input (ablation) | Ours · JTA | ADE: 1.07 -> 0.97 | Helped |
| Include root velocity vroot,0 as a LocoVal input (ablation) | Ours · JTA | ADE: 0.99 -> 0.97 | Helped |
| Apply the LocoVal filter at inference | Social-Trans · JTA, 9 observed frames, 5 heads | ADE: 1.86 -> 1.81 | Helped |
| Apply the LocoVal filter at inference | EqMotion · ETH/UCY Mean | ADE: 1.12 -> 0.88 | Helped |
Surprising findings
- Training with only the EmLoco loss (no ground-truth MSE/minMSE loss) still improves over an randomly initialized network, with JTA ADE going from 5.07 to 3.52.
- Filtering rejects trajectories that are much worse, and the LocoVal function estimates plausibility from root velocity alone well enough to help even without poses on ETH/UCY.
Limitations
- Performance gains are smaller on JRDB, attributed to noisy estimated 3D poses that the method assumes to be accurate.
- Requires accurate 3D poses from AMASS and a physics-based locomotion generator to train the LocoVal function.
- Some JTA trajectories are infeasible for a humanoid and are deprioritized, which may limit coverage.
Experimental setup
Datasets: JTA JRDB AMASS ETH/UCY
Benchmarks: JTA JRDB ETH/UCY
Metrics: ADE FDE minADE minFDE chi-squared distance over velocity, acceleration, angular ve
Baselines: Social-Transmotion Social-GAN Social-LSTM Trajectron++ Autobots EqMotion HST MATRIX
Builds on: Social-Transmotion PACER minMSE multi-head prediction MATRIX
Closest papers by meaning
- Human Motion Prediction Under Unexpected Perturbation (CVPR 2024 · similarity 0.86)
- Universal Humanoid Motion Representations for Physics-Based Control (ICLR 2024 · similarity 0.86)
- SingularTrajectory: Universal Trajectory Predictor Using Diffusion Model (CVPR 2024 · similarity 0.86)
- MoFlow: One-Step Flow Matching for Human Trajectory Forecasting via Implicit Maximum Likelihood Estimation based Distillation (CVPR 2025 · similarity 0.85)
- Multi-modal Knowledge Distillation-based Human Trajectory Forecasting (CVPR 2025 · similarity 0.85)
- HVIS: A Human-like Vision and Inference System for Human Motion Prediction (AAAI 2025 · similarity 0.85)
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