# How do primary motion-generation papers define foot skating, penetration, floating and jitter, with what thresholds and units?

- id: art_01M5MV072S7J1WSBKZEKHPJ69X
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T07, T20 · tags: none
- updated: 2026-10-23T16:55:11.676Z
- url: https://veyrul.com/articles/art_01M5MV072S7J1WSBKZEKHPJ69X

Definitions differ by paper. PhysDiff (v3): Penetrate and Float are distances from the ground to the lowest body mesh vertex with 5 mm tolerance, Skate is mean horizontal displacement of foot joints in contact in two adjacent frames, Phys-Err is their sum, all in mm. GMD (v3) and Yi et al. (v1) use a skating ratio: fraction of frames where a foot slides more than 2.5 cm while foot height is under 5 cm. Body-momentum (v1) measures jitter as the derivative of acceleration in world coordinates (10 m/s^3) and foot sliding in mm during contact. MDM v2 uses a foot-contact loss in training, not an evaluation metric.

Definitions differ by paper. PhysDiff (v3): Penetrate and Float are distances from the ground to the lowest body mesh vertex with 5 mm tolerance, Skate is mean horizontal displacement of foot joints in contact in two adjacent frames, Phys-Err is their sum, all in mm. GMD (v3) and Yi et al. (v1) use a skating ratio: fraction of frames where a foot slides more than 2.5 cm while foot height is under 5 cm. Body-momentum (v1) measures jitter as the derivative of acceleration in world coordinates (10 m/s^3) and foot sliding in mm during contact. MDM v2 uses a foot-contact loss in training, not an evaluation metric.

Curator qualifications: Excerpted evidence located (one excerpt-less row); foot-skating/penetration/floating/jitter definitions with thresholds per paper.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://arxiv.org/abs/2212.02500v3",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://arxiv.org/abs/2305.12577v3",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://arxiv.org/abs/2404.10685v1",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://arxiv.org/abs/2509.09496v1",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://arxiv.org/abs/2209.14916v2",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://arxiv.org/abs/2507.05419v1",
      "note": "candidate evidence excerpts"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Definitions differ by paper. PhysDiff (v3): Penetrate and Float are distances from the ground to the lowest body mesh vertex with 5 mm tolerance, Skate is mean horizontal displacement of foot joints in contact in two adjacent frames, Phys-Err is their sum, all in mm. GMD (v3) and Yi et al. (v1) use a skating ratio: fraction of frames where a foot slides more than 2.5 cm while foot height is under 5 cm. Body-momentum (v1) measures jitter as the derivative of acceleration in world coordinates (10 m/s^3) and foot sliding in mm during contact. MDM v2 uses a foot-contact loss in training, not an evaluation metric. · locator: candidate evidence excerpts · source: https://arxiv.org/abs/2212.02500v3

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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