Chapter 1: Metrics

Created by Sarah Choi (prompt writer using ChatGPT)

Metrics (Hitboxes, Clearances, Approach/Departure Angles)

Partnering with Gameplay, Physics, Animation, VFX & Audio

Vehicle metrics translate design intent into numbers the engine can enforce. When hitboxes, clearances, and approach/departure angles are defined early, concept art stays truthful, physics behaves, animation rigs avoid interpenetration, VFX lands exactly where systems expect, and audio occlusion feels believable. This article gives vehicle concept artists—on both the concepting and production sides—a practical methodology for defining, visualizing, and handing off metrics that govern motion and interaction.

1) What metrics are and why they matter across teams

Metrics are quantifiable boundaries and thresholds that constrain how a vehicle moves and interacts. For gameplay, they gate where the vehicle fits, what it can climb, and what it can damage. For physics, they determine collision proxies, mass distribution, and suspension travel. For animation, they set joint limits and safe ranges for doors, gear, and turrets. For VFX, they provide spawn sockets and keep‑out zones. For audio, they define occlusion paths, exhaust cones, and surface contact types. When metrics are missing, every team invents its own “truth,” and bugs multiply.

2) The master metric sentence

Before drawing, write a one‑paragraph metric sentence that captures role and constraints. Example: “Two‑seat recon buggy fits alleyways ≥ 2.3 m, clears 0.35 m obstacles at 20 km/h, climbs 30% slopes, fords to hub height, turns within 9.5 m curb‑to‑curb, and survives a 0.6 m drop without belly contact.” This becomes the north star for proportion passes and packaging.

3) Hitboxes: classes, purposes, and honesty

Use layered proxies rather than a single shape. A physics hull (lowest detail) keeps simulation cheap. A damage hull defines where hits register for gameplay. A raycast hull captures visibility, camera, and cursor targeting. A soft volume marks proximity triggers (enter vehicle, repair reach, docking funnels). Keep these nested and labeled. Resist the urge to wrap every nook; broad, slightly generous hulls perform better and prevent frustrating snags. Ensure symmetry where the asset is symmetric and document any intentional asymmetry (e.g., offset turret basket).

4) Governing clearances and angles

Ground clearance (lowest rigid point to ground plane), approach angle (tangent from tire contact to the foremost rigid point), departure angle (same at the rear), and breakover angle (angle between tires tangent points and belly low point) govern traversal. For tracked, wheeled, and skid vehicles, also define scrub radius envelopes and suspension bump/droop. For aircraft, define flare clearance (tail/engine to ground at max pitch), rotation distance for takeoff, and gear splay. Publish these as numbers and diagrams, not just notes; every pixel of art should agree with them.

5) Stance metrics: wheelbase, track, rake, and CG hints

Wheelbase and track decide stability; rake and ride height decide attitude. Lock nominal ride height and show bump and droop extremes. Place a provisional center of gravity marker based on mass proxies (engine, battery/tank, crew) to anticipate pitch and roll behavior. These marks drive animation posing and VFX (dust, splash) because contact and skid read depend on stance.

6) Articulation and keep‑outs

Create transparent cones, arcs, and boxes for all moving parts: wheel steer sweeps, suspension travel, gear retract envelopes, ramp swings, canopy hinges, turret yaw/pitch/recoil, gimbal spheres, and weapon muzzle blast cones. Mark no‑stand or no‑mount zones for gameplay. These envelopes prevent concept drift and let animation validate collisions before rigs exist. If a keep‑out obliterates a hero read, change the design, not the envelope.

7) Surface interaction metrics

Label the maximum curb height, step height, gap width, and ramp slope the vehicle must handle. Define water fording depth and splash behavior. For aerial/VTOL, define permitted crosswind, downwash hazard radius, and landing pad grid dimensions. Provide contact patches for wheels, skids, and feet so physics knows where friction lives and audio knows which surface to sample (gravel, metal grate, mud).

8) Camera, visibility, and cover reads

For player‑driven vehicles, camera position and lens dictate how big reads need to be. Place camera cones and line‑of‑sight rays from likely viewpoints (cockpit, chase cam, gunner). Ensure faction insignia, brake lights, and silhouette identifiers remain legible at camera distance. Mark cover heights relative to infantry metrics so designers know what the vehicle provides or denies in combat spaces.

9) VFX sockets and volumes

Standardize socket names and positions for exhausts, intakes, muzzle flash, ejection ports, vent steam, radiator heat shimmer, and landing dust. Provide volume primitives for particle bounds (e.g., intake ingestion cones, exhaust plumes) and trail anchors for tires or tracks. VFX needs consistent names and axes or their setups won’t port across variants. Keep these sockets on rigid parts with stable pivots to avoid jitter.

10) Audio hooks and occlusion

Audio relies on simple geometry and metadata. Mark engine/exhaust origin, intake hiss, gear/clunk contact points, wind shear positions on leading edges, and interior occlusion thickness for doors and hatches. Provide a material map (rubber, steel, composite, glass, fabric) so footfalls, impacts, and scrapes pick the right sound. Define occlusion logic: which panels block engine noise, where vents leak, and how open states modulate volume.

11) Naming, axes, and units

Set axis (+X forward, +Y right, +Z up or studio standard) and units (1u = 1 cm or 1 m) once and repeat them on every plate. Name proxies by function: col.chassis, col.turret, col.wheel.FL, soft.entry, vfx.exhaust.R, audio.exhaust, keepout.turret.recoil. Consistent names are the backbone of automation for rigging, VFX, and damage states.

12) Visualization plates

Deliver metrics as clear plates: a side view for approach/departure/breakover, a plan for turn radius and turret arcs, a front for track and tip danger, and a section for crew packaging. Keep dashed lines for hidden geometry minimal; when they multiply, switch to a cutaway. Place a scale bar, projection symbol, and unit declaration. Annotate with short, declarative sentences and numbers near the geometry they govern.

13) Collaboration rhythm with Gameplay, Physics, Animation, VFX & Audio

Run short, regular checkpoints. With Gameplay, validate alley widths, ramps, door apertures, and class grids. With Physics, test collision sweeps and center‑of‑mass assumptions. With Animation, dry‑run hinge, gear, and turret envelopes. With VFX, verify sockets and plume cones in the engine. With Audio, place sources and check occlusion toggles for open/closed states. Capture decisions on the metric plates and bump version numbers.

14) Testing rituals and quick proofs

Use a graybox level with ramps, curbs, stairs, narrow gates, and water basins sized to your metrics. Drive a proxy rig with only the collision hulls to validate traversal. If the proxy snags where the concept looks clear, adjust the hull or the art; do not accept “it will be fine.” For aircraft/VTOL, test pad sizes, approach corridors, and downwash hazard rings in the same graybox. Export simple FBX/GLTF proxies so design can test while concept refines.

15) Common failure modes and fixes

Pretty over truth: beautified art hides approach angle violations. Fix by returning to line plates with angles drawn and numbers printed. Too many tiny colliders: simulation churn and snaggy gameplay. Fix by merging into a few convex hulls. Asymmetric drift: one side different “by accident.” Fix with mirrored metric checks or a reflection overlay. Unowned camera: reads fail at gameplay lens. Fix by locking camera presets in the lighting rig. Socket drift: VFX anchors move between versions. Fix by parenting sockets to named rigid parts and tracking changes on the plate.

16) Case study: light recon buggy

Brief requires alley fit, curb hop, and quick turnarounds. The metric sentence calls for 2.3 m width clearance, 0.35 m curb, 30% slope, and 9.5 m curb‑to‑curb. Side plate draws 27° approach, 25° departure, 14° breakover with a 0.32 m belly clearance at nominal ride, bump/droop ±80 mm. Plan plate shows a 9.5 m circle with inside tire path. Front plate marks track 1.68 m, scrub radius envelope, and tip angles to 40% slope before rollover risk. Keep‑outs for a 60°/±180° remote weapon station are drawn. VFX sockets define twin exhaust plumes and dust emitters at wheel contact patches; audio hooks sit at exhaust tips and intake snorkel. In graybox, the physics hull clears the curb and hits the alley gate with 5 cm to spare—designers adjust gates globally to the agreed metric. The team locks the angles and the hull; later surfacing does not change them.

17) Hand‑off checklist

A complete metric package includes: the metric sentence; orthos with governing dimensions; approach/departure/breakover diagrams; articulation envelopes; collision hulls (physics/damage/raycast/soft) with names; camera presets; VFX socket list and plume volumes; audio source list and occlusion notes; graybox test results; unit/axis declaration; version history; and a short risks/open‑items note. With these in place, every partner discipline can build with confidence.

18) Closing thoughts

Metrics are design promises written as geometry and numbers. When concept declares them early and production treats them as sacred, vehicles feel capable and fair, collisions look intentional, and the whole studio saves time. Tie your silhouettes to real angles and clearances, publish hitboxes that match the art, and speak the same metric language with Gameplay, Physics, Animation, VFX, and Audio. The result is a vehicle that not only looks right but also plays right, sounds right, and ships without surprises.