Mean per-joint position error (MPJPE)

One-line meaning

The average Euclidean distance between corresponding predicted and reference joint positions.

Technical meaning

For $J$ joints in one pose:

$$\mathrm{MPJPE}=\frac{1}{J}\sum _{j=1}^J{\Vert {\hat{\mathbf{p}}}_j-{\mathbf{p}}_j\Vert }_2$$

Here ${\hat{\mathbf{p}}}_j$ and ${\mathbf{p}}_j$ are estimated and reference Cartesian joint positions. For $T$ equally weighted frames, average these errors across all $TJ$ joint–frame pairs. State how episodes are weighted.

Units

A length unit, usually millimetres or metres, matching the joint-position coordinates. Lower is better.

Example

Compare reconstructed 3D joint locations with reference 3D joint locations in the same coordinate frame.

Nuance / common confusion

MPJPE measures Cartesian joint position, not joint-angle error in radians. Root alignment, scale alignment, joint selection, and coordinate frame can change the result. A low MPJPE alone does not establish balance or successful manipulation.

Evaluation caveat

A whole-body average can hide large errors in the few joints actively performing a task. Report per-joint or body-region errors alongside the aggregate, and define any active-joint subset before comparing methods. Check the paper’s actual metric formula: robotics software sometimes uses “joint position” for an angular joint coordinate.

Related concepts

• Motion retargeting
• Benchmark

Sources

Primary source to be added. This entry is a working explanation awaiting source review.

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