security-game/docs/npc-proportion-audit.md

NPC proportion audit

Status: audited 2026-11-02. All eight library variants are inside the stylized proportion guide; no geometry correction was required in this pass. The report is repeatable from the exported GLBs:

python3 tools/npc_proportions.py report
python3 tools/npc_proportions.py report --json

Method

tools/npc_proportions.py reads the GLB meshes and rest-pose joint hierarchy:

• height from the full mesh bounds;
• head height, width and aspect from Head/skin vertices (hair excluded so long hairstyles do not change the head measurement);
• shoulder silhouette from vertices in the upper-chest band around the shoulder joint;
• hip width from HipL/HipR pants vertices;
• torso length from the Spine joint to the shoulder joint;
• leg length from the Spine joint to the lowest vertex;
• arm length from the shoulder joint to the Hand joint;
• foot length from the forward extent of the KneeL/KneeR shoe vertices.

All ratios are divided by total standing height except head_aspect (width / head height).

Guide

These are stylized-but-credible bands for the game's low-poly adults, not photoreal anatomy. The broad build is allowed a larger shoulder/hip silhouette than the slim build.

Ratio	Target	Notes
head_height	0.16–0.22	deliberately larger than a realistic 0.13–0.15
head_aspect	0.70–1.00	width / height; rounded heads are acceptable
shoulder_width	0.28–0.38	silhouette includes sleeves and build scaling
hip_width	0.17–0.23	pants-only width, not skirt/coat flare
torso_length	0.28–0.38	Spine joint to shoulder
leg_length	0.40–0.48	Spine joint to ground
arm_length	0.28–0.38	shoulder to hand
foot_length	0.12–0.18	shoe forward extent

Result

Character	Height	Head	Aspect	Shoulder	Hip	Torso	Leg	Arm	Foot	Result
npc_casual	1.824 m	0.190	0.907	0.320	0.209	0.307	0.449	0.329	0.144	PASS
npc_jacket	1.824 m	0.190	0.907	0.325	0.209	0.307	0.449	0.329	0.144	PASS
npc_coat	1.824 m	0.190	0.907	0.329	0.209	0.307	0.449	0.329	0.144	PASS
npc_vest	1.819 m	0.191	0.907	0.321	0.210	0.308	0.451	0.330	0.144	PASS
npc_dress	1.825 m	0.190	0.907	0.287	0.191	0.307	0.449	0.329	0.144	PASS
npc_hoodie	1.856 m	0.187	0.907	0.320	0.205	0.302	0.442	0.323	0.141	PASS
npc_firefighter	1.819 m	0.191	0.907	0.356	0.225	0.308	0.451	0.330	0.148	PASS
npc_guard	1.819 m	0.191	0.907	0.370	0.219	0.308	0.451	0.330	0.144	PASS

No variant is outside a band, so the body pass does not need a global skeleton or mesh rescale. The values closest to a boundary are:

• head height 0.190 against the 0.22 upper bound, and head aspect 0.907 against 1.00 — the head is deliberately large. Any head-size change must be coordinated with the face/headgear pass and its gear-fit measurements.
• guard shoulder 0.370 and firefighter hip 0.225 against the broad-build upper bounds — these are the intended uniform/turnout silhouettes, not outliers.
• leg length 0.449 and torso 0.307 sit inside the guide for all variants; the earlier short-leg impression came from the hip joint position, not the visible pelvis line.

Follow-up

The proportion audit does not replace the visual criteria in npc-visual-review.md: neck/shoulder/hip transitions, face depth, hand grips, clothing hems and shoes still need the appearance pass. Re-run the audit after any body mesh or skeleton change and record the new ratios here.