Chapter 1: Placement Metrics & Pick‑Up Radii

Created by Sarah Choi (prompt writer using ChatGPT)

Placement metrics & pick‑up radii for prop concept artists

Why placement metrics belong in the prop pipeline

A prop is more than form and material—it is a spatial promise. Where it sits, how close players must be to notice or use it, and which systems light up when they approach are design questions you can influence from day one. When concept and production artists model with placement metrics and pick‑up radii in mind, level design (LD), systems, UI, VFX, and audio gain predictable hooks. That predictability removes iteration drag and prevents late “make it bigger/add an outline” requests that break styling.

Shared glossary (keep this near your brief)

  • World scale: studio unit convention (m/cm) and player metrics (eye height, capsule size, stride).
  • Pickup radius: spherical or capsule volume where the interaction prompt fires.
  • Interaction cone: angular gate aligned to camera or actor forward for affordance.
  • Snap grid: world/grid increments LD uses for layout (e.g., 10 cm floor, 5 cm props).
  • Nav exclusion/allow: surface tags that permit AI/player traversal.
  • Sockets/anchors: named placement transforms on props for LD/system spawners.
  • Diegetic vs HUD: in‑world indicators vs screen‑space prompts.

Baseline metrics to design around

Anchor your prop reads to three distances:

  • Long read (15–30 m): class/silhouette; use bold negative space and high‑contrast accents.
  • Mid read (5–10 m): affordance and value; status lights, decals, unique color blocks.
  • Close read (0–2 m): interaction hardware; buttons, handles, slots, labels. Match these to the project’s eye height (e.g., ~1.6–1.8 m) and FOV (60–90°) so your panels and icons land within comfortable view angles.

Placement logic from blockout

During blockout, encode placement assumptions:

  • Flat‑on‑flat contact: add planar pads and small chamfers so props settle without z‑fight.
  • Footprint & clearance: show the ground contact patch and a 360° clearance ring; LD will use this to keep navmesh clean.
  • Pivot & origin: set the pivot at the dominant placement surface center; zero transforms; align local axes to world standards.
  • Sockets: define named child empties (e.g., SOCK_TOP_M8, SOCK_WALL_1913RAIL) where LD can snap cables, FX, or attachments.

Pick‑up radii & interaction cones: visualized

Model a gizmo ring in your DCC that matches the intended pickup radius (e.g., 100 cm for auto‑pickup ammo, 60 cm for interactables requiring aim, 30 cm for “hold to pick up”). Sketch the interaction cone (e.g., 40–60°) as a wedge in orthos and present it on the callout sheet. This pre‑aligns expectations with systems/UI about when prompts appear.

Designing affordances for metrics

Tie visual cues to measurable gates:

  • Auto‑pickup items: stronger mid‑read color blocks, subtle hover VFX at radius edge; no fiddly buttons.
  • Interact‑to‑use items: clear handle/button geometry facing typical approach vectors; rim lighting zones for the cone.
  • Hold‑to‑loot items: progress‑bar friendly flat zones; space for UI to sit diegetically (e‑ink labels, small screens). Keep these choices consistent across a prop family so players build intuition.

Partnering with Level Design (LD)

Provide LD with:

  • Placement variants: floor, wall, ceiling, crate‑top; each with correct pivots.
  • Slope tolerance: acceptable tilt degrees before readability breaks.
  • Cover metrics: heights (low 0.9 m / tall 1.2 m) if the prop doubles as cover; bevels at player thigh/shoulder contact.
  • Traversal tags: which faces are standable, vaultable, or off‑limits; show in orthos.
  • Spawn bounds: a simple bounding box asset for LD’s procedural tools.

Systems hooks (gameplay)

Anticipate rules:

  • Stacking/physics: set mass and friction expectations; suggest physics/material layers (METAL, RUBBER, GLASS) for interactions.
  • Rarity/loot tables: space on the prop for rarity glints or color chips; avoid conflict with faction colorways.
  • State machines: ready your prop for S0→S3 damage or ON→OFF→LOCKED; reserve emissive and decal areas per state.
  • Interaction cadence: fast pickups need clean silhouettes; puzzle props justify smaller radii but stronger icons.

UI collaboration

Design UI in 3D:

  • Reserve screen real estate on the model (angled 10–20° toward camera) for prompts or progress rings.
  • Add fiducials (small brackets/dots) around intended prompt zones; UI can align diegetic graphics here.
  • Define color/contrast budgets for status elements so prompts remain legible under different lighting.
  • Supply Material IDs for UI surfaces so shaders can isolate glow/bloom without touching the rest.

VFX & Audio

  • VFX: Provide spawn sockets (FX_SPARK_A, FX_GLOW_RING) and occluder shells for correct compositing; define LOD rules so glows don’t overdraw off‑screen.
  • Audio: List contact materials and interaction types; add cavity space where a pickup “clink” could originate; offer an audio radius suggestion aligned to pickup range.

Photobash and scan ethics at placement scale

At placement distances, bashing brand marks, certification labels, or cultural symbols has legal/story weight. Keep a source sheet for decals and avoid implying endorsements without clearance. For scans, strip baked AO/shadows; at mid‑read distances double lighting is obvious.

Accessibility & comfort

  • Keep prompts within 15–25° of screen center at intended approach.
  • Avoid flicker or high‑frequency VFX on auto‑pickup items.
  • Provide color‑agnostic cues (shape changes, motion) for color‑vision deficiency.
  • Allow controller magnetism: design approach faces broad enough for soft snap without clipping.

Multiplayer & networking implications

If pickups replicate, silhouette and prompt zones must be authoritative and identical across clients. Avoid thin greebles at the contact edge; network jitter makes them buzz. Use bold, low‑frequency reads for shared objects and keep the pickup radius slightly larger than the visual cue to mask latency.

Performance and LOD strategy

  • Keep pickup cues shader‑driven at distance (outline/bloom), swapping to mesh detail only near.
  • Author mask atlases so VFX/UI can reference a single texture set across a family.
  • For dense prop scatters, enable deferred prompts (only the nearest N items show UI) and plan icon placement so overlap doesn’t occur.

Callout sheet essentials (what to include)

  • Orthos with pickup radius ring and interaction cone overlay.
  • Approach vectors and preferred facing.
  • Sockets & pivots labeled with names and units.
  • Clearance volumes (navmesh safe ring, vault blockers).
  • UI/VFX planes and emissive masks.
  • Audio notes: materials, suggested SFX hooks.
  • State ladder reference if the prop changes interaction by damage.

Example defaults you can start from (tune per project)

  • Auto‑pickup loot: R=1.0 m sphere, no cone, trigger once per 0.25 s.
  • Interact pickup: R=0.6 m sphere + 60° cone; facing tolerance ±20°.
  • Heavy object grab: R=0.9 m, 40° cone; requires ground contact.
  • Puzzle console: R=1.2 m, 70° cone; prompt anchors to screen plane.
  • Diegetic outlines: width 1.5–2.5 px at 1080p equivalent at mid‑read. Document these in the style guide and keep them consistent across families.

Testing loop for artists (fast and honest)

  1. Render a neutral studio plate and a hostile contrast plate of the blockout.
  2. Paint the prompt UI atop the plate using your reserved planes.
  3. Downscale to gameplay resolution and apply a motion‑blur mock.
  4. If the prompt/UI overlaps the silhouette or becomes unreadable, adjust mesh surfaces—not just the paint.
  5. Export an ID legend and socket list; share with LD/Systems for a 5‑minute gut check.

Handoff package

Include: layered PSD with orthos and metric overlays; neutral Beauty PNG; EXR pack (Normal, Curvature, Z, IDs); a text file with radius/cone values, socket names, pivot positions, slope tolerance, cover heights; simple LOD notes; and a preview GIF showing prompt behavior from approach.

Common pitfalls checklist

  • Props beautiful in isolation, unreadable at 10 m.
  • Pickup prompt sits on a curved surface—UI warps or floats.
  • Pivot off‑center; placement spawns half inside geometry.
  • Radius tuned to cinematic camera; breaks at gameplay FOV.
  • Icon color conflicts with faction palette; fails in red‑green deficiency.
  • VFX bloom hides prop silhouette at distance.
  • Scanned decals imply real‑world brands without permission.

A 45‑minute drill

  • 0–10 min: Block out a small loot crate with flat contact pads, set pivot/origin.
  • 10–20 min: Add sockets and define pickup radius (1.0 m) + 60° cone; overlay them on orthos.
  • 20–30 min: Reserve UI plane and emissive strip; pick contrasting but style‑safe colors.
  • 30–40 min: Render plates; quick paintover with prompt; downscale + blur check.
  • 40–45 min: Assemble a one‑page callout with metrics and a short handoff note.

Closing

Placement and pickup are part of the design, not an afterthought. By encoding pivots, sockets, radii, and cones during blockout—and by coordinating UI/VFX/Audio surfaces—you’ll hand off props that drop into levels cleanly, communicate intent at the right distance, and feel great to interact with. Align early, document clearly, and your art will ship with fewer surprises.