Aetheria/docs/aetheria-gravity-map.md

Aetheria gravity: map

Target: aetheria-gravity:target:r2 (rationale in docs/aetheria-gravity-target.md). Rulings in force: aetheria-gravity:ruling:grid-shows-how-you-move; from other campaigns, aetheria-release:ruling:gravity-honest-wells-agreed, aetheria-fauna:ruling:ink-pillars-are-suns, aetheria-fauna:ruling:sim-knows-the-flow, aetheria-release:ruling:liquid-grid-from-sim-brushes. Prior art: docs/research/2026-10-14-gravity-prior-art.md. Orbit measurements: docs/research/2026-10-13-orbit-probe/report.md.

Body facts

All read at c6519383 in the detached worktree C:\aeth-wt\ag2-docs on 2026-10-14 unless marked. Scripts live in the Imagination scratchpad (imagination-ag2-gravity-0b/).

• B1. Sim gravity today. Zone.GetHeight (Zone.cs:631-658) sums the zone bowl -PowerPulse(|p|/(2·Pack.Radius), ZoneDepthExponent)·ZoneDepth, one PowerPulse well per PlanetInstances entry (radius GravityWellRadius, depth GravityWellDepth, exponent BodyData.GravityDepthExponent), and for every GasGiant (suns included) a RadialWaves ripple in zone time. GetNormal (:725-734) differences GetHeight at ±0.1; GetForce (:692-696) and Ship.Update (Ship.cs:133-135) feed the normal's xz to GravityAcceleration (:684-689), S·R·(1/(1-|n|²)-1) gated off at |n|² <= .001. Wells read body.Orbit.Position, which is float2.zero until the first Zone.Update (follow-up zone-orbits-unplaced-before-first-tick).

• B2. The bowl and the ripples are live in code. The operator's ruling says the zone bowl is disabled and stays so, ripples likewise. At c6519383 neither is disabled: Settings.asset (the only asset carrying PlanetSettings) has ZoneDepth: 64, ZoneDepthExponent: 2, WaveDepth 0.5·m^0.3; GetHeight applies both unconditionally; the bowl is felt only in zones with radius under about 3117 (the force gate, probe F3) and the ripples are felt around every gas giant and sun (8 to 32% of peak force, probe wave table). The drawn grid shows both: the scene Boundary object (PowerBrush, layer Displacement, active) is driven each frame by ZoneRenderer (ZoneRenderer.cs:621-622) with ZoneDepth plus ZoneBoundaryFog (0), and the Gravity Waves objects in Gas Giant.prefab and Sun.prefab (layer FineDisplacement, active) carry the ripple. So flatspace-no-bowl-no-ripples is delivered by deletion in a cut, not already true.

• B3. The drawn grid is a second height owner. It is not sampled from Zone.GetHeight. Camera Surface Displacement (ARPG.unity, culling layers 9 Displacement and 10 FineDisplacement) renders additive brush quads into Assets/Resources/Fog Surface Displacement.renderTexture, which VolumeSampling.cs:63 publishes as the global _NebulaSurfaceHeight. Brushes on those layers:

  object (where)	layer	material and shader	sim counterpart
  Gravity Well (Planet, Gas Giant, Sun prefabs)	9	Gravity Well, PowerBrush, _Power 16 fixed in the material, _Depth set from GravityWellDepth, quad scaled by GravityWellRadius (ZoneRenderer.cs:500-503)	the well in GetHeight, but the exponent is the material's 16, not BodyData.GravityDepthExponent, and the shader's envelope adds saturate(abs(x))-.001, min(_Cutoff, …) and a smoothstep(1,.95) rim fade the sim lacks
  Gravity Waves (Gas Giant, Sun)	10	Gravity Waves, RadialWaveBrush, _Power 8, _Cutoff .5	the ripple in GetHeight
  Boundary (ARPG scene)	9	Sector Boundary, PowerBrush, _Power and _Depth driven by ZoneRenderer	the zone bowl
  Waves Small / Medium / Large (ARPG scene)	10	Sector Waves *, SimplexBrush, depths -16.75, 7.58, 2	none: drawn, never felt
  Gravity Well, Gravity Pit, Gravity Waves (Wormhole 1 prefab)	9	Wormhole Gravity 1 (_Depth 54, _Power 4), Wormhole Gravity (_Depth 2000, _Power 64, _Cutoff .15), Wormhole Waves	none: the sim has no wormhole well
  Gravity Well (PlanetOutpost station prefab)	9	Gravity Well	none found; whether this prefab is instantiated in play was not checked

  Other cameras render the same layers into their own textures: Patch Displacement (layers 9, 10, 12), Map Gravity (9, the minimap; MapView.cs), Slime Gravity Renderer (9; Slime.cs binds it as Heightmap).

• B4. Readers of the drawn height (GPU). Volumetric.cginc:121-130 (gradient of _NebulaSurfaceHeight, the shader's slopeFlow and surface normal; :174 surface displacement), Asteroid.shader:31 (displacement), Stardust.compute:134 (gravHeight), VolumeRenderCustom.shader (property), Slime.compute (Heightmap), the minimap gravity materials (ZoneRenderer.MapGravityMaterials, _StartDepth/_DepthRange at :623-628), and the editor verifier FlowFieldParityVerify.cs:162,261. Follow-up aetheria-fauna:follow_up:flow-slope-gradient-parity already names the slopeFlow mismatch.

• B5. Readers of the sim height and force (CPU). Force: Ship.Update (Ship.cs:133-135, through GetNormal and GravityAcceleration directly, not GetForce), Zone floating bodies, clouds and mines (Zone.cs:411, 437, 451 via GetForce). Gradient for flow: Zone.Flow (:700-704). Height for placement: Entity.cs:1849 (Position.y of non-ship entities), Agents/States/Combat.cs:114 and Behaviors/TurretController.cs:73 (predicted target height), Gameplay/ItemPickup.cs:44, Gameplay/MineInstance.cs:59, ZoneRenderer.cs:545 (belt bounds) and :581 (planet body height, minimap depth range). Ship tilt: Ship.Update builds Rotation from the same normal. Tests: FloatingBodyTests.cs:187-209, 254 (pin the gate and the legacy law), LootTests.cs:299-308, MineTests.cs:623-628, FlowFieldTests.cs (zone with bowl as the slope source), FireControlTests.cs:380. Editor smoke: FloatingItemsDrawnSmoke.cs:159. No AI reader predicts gravity.

• B6. Rails. Orbit.Period = OrbitPeriod.Evaluate(Distance) (Zone.cs:910), with OrbitPeriod = 1·d^1 + 0 in Settings.asset: period is a function of distance only, never of the parent. Other readers of the same curve: Zone.cs:599 (an orbit added at run time, phase back-solved), Zone.cs:822 (each asteroid of a belt), Targeting/BeltTargets.cs:63 (belt target periods). GetOrbitPosition (:465-500) is the closed-form rail; the root orbit has no parent and sits at FixedPosition. Two commented-out period writers remain in ZoneGenerator.cs:589, 650.

• B7. Body well parameters. Planet.CalculateProperties (Zone.cs:755-760): BodyRadius, GravityWellRadius, GravityWellDepth from PlanetSettings curves times per-body multipliers; GasGiant adds wave depth, radius, speed. The generator never writes any multiplier or GravityDepthExponent (no writer in ServerShared). GasGiantData's wave fields reuse the JSON names gravRadiusMul, depthMul and depthExp (twice: WaveDepthExponent and WaveSpeedMultiplier) that BodyData already uses for its gravity fields; MessagePack keys differ (14-17 against 6-8), so the binary store is unambiguous and the JSON names are not. WaveDepthExponent is read by nothing (the sim hard-codes 8).

• B8. Ship scale, measured headless from GameData/Aetheria.cc (CultCache Python runtime, hulls.py, mass.py). Hull Drag: Longinus 0.1/s, Smoke Test Hull 0.1, Djinni 0.2, stations and turret 0. Drag is linear: Velocity = normalize(v)·v·exp(-Drag·dt) (Ship.cs:128-129; CultMath.decay). Thrust ranges: Small Drive 60-90k, Medium 100-300k, Large 200-300k, Rugged 75-250k, Burn and High-Thrust 250k-1M, Racing 200k-1.5M. Entity.Mass starts at hull mass and changes as items are added and removed (Entity.cs:1251, 1407). Items weigh about 40-50 per schematic cell (median over gear, weapons, cargo bays); the Longinus schematic has 66 cells, the Djinni 166. So a Longinus with one Small Drive accelerates at 24-36 u/s² empty and about 11-16 u/s² fully packed (2500 + ~3000); a Djinni 6-9 empty, about 3.4-5 packed. "Fully packed" is an estimate from cell count times median density, not a generated loadout (LoadoutGenerator was not run). Agent TopSpeed defaults to 100 (VelocityLimit).

• B9. What drag means for orbits. Holding a circular orbit at speed v costs a tangential thrust of Drag·v against drag, plus whatever radial thrust the field mismatch needs. At v = 6.3 (today's rail speed) that is 0.63 u/s² for a Longinus (2-6% of its range), 1.26 for a Djinni (14-37%); at v = 17.5 it is 1.75 (5-16%) and 3.5 (39-100%). No free orbit exists for any hull with Drag > 0; with honest wells a ship in orbit needs only the drag term, where today it also fights a radial mismatch of 17-30% of thrust (probe F2).

• B10. Tide under superposed 1/r tails (computed, hill.py, over the probe's bodies). 2D tidal radius of a parent at R from its own parent: d_H = R·sqrt(c_p/(2c_g)). Fraction of the 17,864 children of non-root parents that orbit inside 0.5·d_H: 11% if c ∝ mass, 35% for m^0.5, 59% for m^0.25, 66% for m^0.175; children of planets 1%, 10%, 30%, 38%. Speeds: if a median sun's field is 0.5 u/s² at 610 u, v_circ = 17.5 u/s around it and 12.4 around a median planet (m^0.175).

• B11. The flow has curl. FlowField.Slope (FlowField.cs:53-59) adds a swirl term, the downhill direction rotated 90 degrees, and Global is a noise field: neither is a gradient, so no height can show them as slopes. No ship reads Zone.Flow; it drives stardust and nebula (shader) and, by ruling, fauna.

• B12. A ruling in force contradicts the target. aetheria-release:ruling:one-gravity-law (Defaulted, 2026-10-07) fixes the slope-squared law and "the feel ships have today". The target replaces both. Self supersedes it; this map does not.

Model page

One row per kind this campaign touches. "Today" is c6519383; "target" is the shape under r2 with the recommended answers, marked where a question is open.

kind	identity	lifecycle	authority (one owner per decision; forbidden writers)
Zone potential φ(p, t)	One per Zone instance, unnamed (a method, not a record). Not persisted: derived from the pack's bodies, orbits and PlanetSettings at zone time. Today it does not exist as such; GetHeight is a shaped heightfield (mass-neutral wells, probe Reading B).	Built when the zone is constructed; must be valid before the first Update (zone-valid-before-tick). Varies with body positions over zone time. No ripple term in flatspace (flatspace-no-bowl-no-ripples). Reference constant: zero at the root body's zone radius (proposal; log tails have no natural zero).	Owner: one ServerShared function (Zone's potential, likely a small pure module beside FlowField so shaders can lower it). Forbidden writers: GravityAcceleration's slope-squared law and its gate, GetNormal as a force source, the zone bowl term, RadialWaves, any brush or shader that composes gravity on its own.
Force a = -∇φ	Derived, never stored.	Per query. Analytic gradient (sum of per-well closed forms), not finite differences of the height.	Owner: the potential module. Every CPU force reader (B5) calls it: ships, floating bodies, clouds, mines. Forbidden: Ship.Update's private normal-to-force path; the per-second GravityReferenceRate restatement (dies with the old law).
Body well parameters (gravitational parameter c, softening radius R)	Derived per body from BodyData.Mass through PlanetSettings curves (today: GravityDepth, GravityRadius, BodyRadius × per-body multipliers). Names: per-body record key (CultRecordRef<BodyData>), injective. The JSON names of GasGiantData's wave fields collide with BodyData's (B7).	Computed once at Planet construction (CalculateProperties); never revised in play. Today's GravityDepthExponent, GravityDepthMultiplier, GravityRadiusMultiplier have no writer; the exponent dies under the target (no PowerPulse well); wave fields die in flatspace.	Owner of the curve: PlanetSettings in Settings.asset (open: well-strength-from-mass, softening-radius). Owner of the per-body value: Planet (or its successor) at construction. Forbidden writers: the brush material's _Power 16 and _Cutoff, ZoneRenderer copying depth into materials, any shader constant. Cell not filled: whether per-body multipliers stay (no writer today; a pillar or authored body may want one).
Pillar (Ink zones)	The zone's central body in a sun's role (ink-pillars-are-suns). Cell not filled: no record names a pillar today (no Pillar or Adrasteia anywhere under Assets/Scripts at c6519383); whether it becomes a BodyData kind is the Ink-zone work's decision.	Built with the zone like any body.	Owner: same law as a sun (pillars-are-suns); its strength comes from the same curve or an authored c. Pseudospace shenanigans are not in scope.
Orbit rail (OrbitData: Distance, Phase, Parent, FixedPosition; runtime Orbit: Period, Position, PreviousPosition, Velocity)	OrbitData is a catalog/pack record keyed by CultRecordKey, parent by CultRecordRef<OrbitData>; root has no parent. Period is derived, not stored.	OrbitData created by ZoneGenerator or Zone (:596-611 back-solves phase); Period computed at Orbit construction; Position written by GetOrbitPosition each Update and float2.zero before the first (follow-up). Asteroids and belt targets recompute periods from the same curve (B6).	Today: OrbitPeriod curve owns period and ignores the field. Target (open: rails-vs-field, recommended field-owns-rails): period derived from the parent's c, T = 2πd/sqrt(c_parent), the same derivation for the four readers in B6. Forbidden writers then: OrbitPeriod as an independent authority, any per-reader period formula. Position placement moves to construction (zone-valid-before-tick).
Orbit placement (child distances)	Generated OrbitData.Distance per body, authored ZoneGenerationSettings ranges.	Written once at generation; persisted in the zone pack.	Owner: ZoneGenerator. Open: moons-beyond-tidal-reach (whether the generator must keep children within their parent's tidal reach, which makes the generator read the strength curve).
Zone bowl	PlanetSettings ZoneDepth, ZoneDepthExponent, ZoneBoundaryFog; scene Boundary brush.	Live today (B2). Target: gone from flatspace gravity.	Ruled (grid-shows-how-you-move, flatspace-no-bowl-no-ripples). Forbidden: the GetHeight term, ZoneRenderer's driving of the Boundary brush on a gravity layer, FlowFieldTests' use of the bowl as a slope source (tests need a well instead). Cell not filled: whether the zone needs a non-gravitational edge (nothing asked for one).
Ripples (gas giant and sun waves)	PlanetSettings WaveDepth, WaveRadius, WaveFrequency, WaveSpeed; GasGiantData wave multipliers; Gravity Waves brush objects.	Live today (B2). Target: gone from flatspace.	Ruled. Forbidden: RadialWaves in the potential, the Gravity Waves objects on displacement layers. Pseudospace pulses (follow-up pseudospace-flavours-campaign) are a different kind, under the same grid invariant.
Exaggeration factor K	Not present today (height is the only quantity). Target: one number, φ = K·h.	Authored; constant in play.	Open: exaggeration-scope (recommended one global value in PlanetSettings). Owner: PlanetSettings. Forbidden: per-class or per-material depth scales, ZoneRenderer's _StartDepth/_DepthRange as an independent mapping of depth (it may normalise the minimap, but from h, not from brush depths).
Drawn grid height (_NebulaSurfaceHeight and the other displacement targets)	Render textures named in B3; global shader names.	Rendered every frame from brush quads.	Today: the brushes own it, independently of the sim (B3), which is the defect this campaign kills. Target: lowered from the sim's potential (h = φ/K), whether by an analytic shader function fed body parameters (as FlowField is lowered) or by brushes whose shapes are generated from the same law; the one owner is the ServerShared potential and the shader is a lowering with a parity check (as FlowFieldParityVerify does for flow). Forbidden: material constants (_Power, _Cutoff, _Depth), smoothstep rim fades, the wormhole and station gravity wells, and any brush on a gravity layer with no sim term. Open: grid-presentation-noise (what becomes of the Sector Waves noise and the liquid-grid detail).
Readers that place things at the height (B5)	Call sites.	Every frame.	Readers only. They read h = φ/K + GridOffset. No change of owner; listed so a cut finds them all.
Flow (FlowField)	PlanetSettings Flow; Zone.Flow; shader globalFlow/slopeFlow.	Zone time.	Owner: FlowField in ServerShared (sim-knows-the-flow). Its slope term must read the potential's gradient, not GetNormal of a separate heightfield. Open: flow-moves-ships (B11).
Ship motion under gravity	Ship.Update.	Per tick: drag, then position, then gravity.	Reader of the force. Hull Drag owns damping (B8, B9). Forbidden: any gravity computation local to Ship.

Cells not filled, plainly: whether per-body well multipliers survive (no writer today, no consumer asked); what record names an Ink pillar; whether the PlanetOutpost prefab's drawn well is ever instantiated; whether the zone needs a non-gravitational edge once the bowl is gone; real generated loadout masses (B8 is a bound, not a measurement).

Rationale

• Why the drawn grid is a lowering, not an owner: grid-shows-how-you-move makes the slope a promise about motion. Six brush kinds on the gravity layers have no sim term or a different envelope (B3), so today the grid shows motion that does not happen (sector noise, wormholes, rim fades) and hides motion that does (the bowl in small zones is drawn at the same depth everywhere while felt only under the gate).
• Why rails follow the field: every shipped game where ships feel gravity derives the rails from the same parameter (KSP) or simulates bodies (Outer Wilds); authored rails coexist only with no felt gravity (Elite, Starsector). See the prior-art doc, section 3.
• Why strength, softening and tide are separate questions: a·r = v² ties felt strength to body speed (field-strength); c(mass) sets both readability and how many moons a ship can follow (well-strength-from-mass, B10); R sets the peak (softening-radius). Any two can be ruled without the third.
• A constraint for pseudospace, not solved here: a push with curl (B11) has no height, so under grid-shows-how-you-move it either never moves ships, or is drawn by another channel, or is restricted to its gradient part.

Cut sequence

Not yet written. Waits on the step-0b questions.