# axiolid-spatial implementation plan
Status: BVH and uniform point grid implemented; octree remains unimplemented
and is deliberately not claimed in the crate description or docs.
## Established
- Crate boundary and dependency direction are executable in the layering gate.
- [`Bvh`](src/bvh.rs) is a read-only, deterministic median-split broad-phase
provider. It rejects malformed bounds, preserves accepted input pair order,
supports callback AABB/ray traversal, pair candidates, and filtered nearest
queries.
- It is intentionally serial today. The public `SpatialIndex` callback seam
leaves room for parallel CPU and GPU providers without coupling the contract
to either execution strategy.
## Next implementation wave
- Benchmark this BVH against an external reference implementation on
representative sparse, dense, and adversarial distributions before adding
parallel build/query code.
- `PointIndex` (uniform grid) is implemented for point KNN/radius queries.
- Add an octree only where a measured workload justifies it. The BVH covers
object queries and the grid covers point queries; an octree's advantage is
sparse volumetric subdivision, which no consumer needs yet.
## Exit evidence
Targeted differential tests, feature-isolated compile where applicable,
mutation-verified architecture/validation gates, and benchmarks before
performance claims.