3D GRID placement needs two separate answers:
- Where is the supporting surface?
- Is this footprint supported well enough to place?
Grid Placement keeps those questions separate from collision overlap and from the GRID targeting coordinates.
Default behavior
GridMap remains the normal/default 3D GRID workflow. The plugin can scan GridMap columns to resolve surface height and validate the footprint without requiring every existing project to add physics-based terrain sampling.
Projects that need real sloped-mesh support can opt into physics-backed sampling. A physics-required mode should be used only when missing physics evidence must reject placement.
Surface support modes
The 6.0 slope implementation defines three policy levels:
| Mode | Behavior |
|---|---|
GRIDMAP_ONLY |
Use GridMap surface/footprint evidence. Best compatibility with grid-authored worlds. |
PHYSICS_WITH_GRIDMAP_FALLBACK |
Prefer physics support when available; retain the GridMap path when physics support is absent. |
PHYSICS_REQUIRED |
Require usable physics support evidence and reject when it cannot be evaluated. |
Use the least strict mode that matches your project. Do not select PHYSICS_REQUIRED just because it sounds more accurate; it intentionally fails closed if the physics world/mask is not configured.
GridMap scan range
GridMap surface resolution scans each footprint column through a configurable Y range.
| Setting | Purpose |
|---|---|
surface_scan_min_y |
Lowest GridMap Y layer considered. |
surface_scan_max_y |
Highest GridMap Y layer considered. |
surface_offset |
Optional vertical offset added to the resolved support position. |
If every GRID placement reports missing ground, confirm that the terrain actually falls inside this scan range before changing placement rules.
Slope and support policy
A structure can be valid on uneven ground when the support stays inside its configured policy. The important controls are:
- Maximum slope — reject support steeper than the configured angle.
- Support coverage — require enough sampled footprint support.
- Center/edge requirements — optionally require support at important parts of the footprint.
- Height/planarity tolerance — reject support that is too uneven for the entry.
- Per-entry overrides — let different placeables use different tolerances.
A foundation can therefore be strict while a small decorative prop can permit some overhang.
Partial support
Partial support is configurable, not universally allowed or blocked.
For example, if a 2×2 footprint has support under three corners and one unsupported corner:
- a strict foundation policy can reject it;
- a prop policy can allow it when its minimum support/center/edge requirements are satisfied.
The preview, per-cell indicators, final commit, diagnostics, and restored placement must agree on the same support decision.
Structures stay world-up
GRID structures remain world-up by default. Slope controls whether a structure may sit on the terrain; it does not automatically tilt walls/foundations to match the terrain normal.
Optional surface alignment is appropriate for selected props, not the default modular-building contract.
Physics-backed support
Physics sampling is useful when the visible/supporting terrain is not represented accurately by GridMap column tops—for example, a sloped mesh.
Check these when physics-backed placement unexpectedly rejects:
- The supporting body has collision.
- The support collision mask includes that body.
- The placement service has a usable
World3D. - The footprint samples actually reach the support surface.
- The entry's slope/support thresholds allow the sampled result.
PHYSICS_REQUIRED must reject rather than silently falling back when physics support cannot be evaluated.
Support evidence and placement height
The support evidence used to validate a placement must also be the evidence used to resolve its final height/transform. Do not display GridMap-only metadata while committing from a different physics support anchor.
This parity matters for:
- preview vs commit;
- placement reports/diagnostics;
- save/restore;
- debugging a structure that appears to float or sink.
Common failures
| Symptom | Check |
|---|---|
| All placements report no ground | GridMap scan range, ground cells, or selected support mode. |
| Valid GridMap cell but physics-required placement rejects | Physics world/mask/support collider configuration. |
| Structure rejected on a gentle hill | Maximum slope, support coverage, height/planarity settings. |
| One corner hangs over empty space | Entry-specific partial-support/center/edge policy. |
| Preview and final object use different Y | Support-evidence parity; preview and commit must share the same resolved result. |
| Building leans with the hill | Structural GRID entries should remain world-up; disable prop-style support-plane alignment. |
What this is not
Slope/support validation does not add 3D terrain editing. Grid Placement 6.0 does not paint/deform GridMap terrain or generate foundations to reshape terrain under a building.