MoonGeoKit

MoonGeoKit is a MoonBit-native 2D geometry and observable uniform-grid spatial index for map editors, GIS-style overlays, simulations, and WebAssembly clients. It is a reusable library, not a rendering demo: callers own the map data and use the library for deterministic geometry, incremental index changes, and inspectable query costs.

Production-facing capabilities

• Points, segments, bounds, polylines, polygons, convex hulls, containment, intersections, nearest points, distances, and tolerant predicates.
• Area-weighted polygon centroid with a defined fallback for degenerate rings.
• Fixed-world uniform-grid index with point/range queries, cross-cell deduplication, candidate/bucket diagnostics, and out-of-world protection.
• Editor/simulation mutations: single and batched insert, update, and delete; batch mutations rebuild bucket membership once.
• Bounded nearest-item lookup using grid candidate reduction plus exact point-to-AABB distance.
• Standard GeoJSON Point, LineString, Polygon, bounds, and Feature export for browser/Wasm hand-off without a runtime dependency.

Install

moon add cn-xjr/moongeokit

Minimal example

let index = @geo.GridSpatialIndex::new(@geo.Bounds::new(0.0, 0.0, 100.0, 100.0), 10, 10)
ignore(index.insert(@geo.SpatialItem::new(7, @geo.Bounds::new(10.0, 10.0, 15.0, 15.0))))
match index.query_nearest(@geo.Point::new(18.0, 12.0), 20.0) {
  Some(item) => println(item.to_geojson_feature())
  None => println("no nearby feature")
}

Run the repository demo (including GeoJSON output) with:

moon run cmd/main --target js

Reproducible verification

MoonBit 0.10.4 does not accept --deny-warn for moon fmt or moon info. The commands below are the supported strict equivalents and are exactly the quality gates used by CI:

moon fmt --check
moon check --deny-warn --target all
moon info && git diff --exit-code -- '*.mbti'
moon test --deny-warn --target all
moon run cmd/main --target js
moon run cmd/bench --target js

cmd/bench prints deterministic candidate/bucket counts for 1k, 10k, and roughly 100k indexed records. It deliberately does not publish wall-clock claims because elapsed time depends on the native/JS/Wasm host.

Scope and compatibility

The index is a mutable, fixed-world AABB index. It is appropriate for dynamic editor entities and bounded simulation worlds; it is not a replacement for an R-tree, polygon topology engine, coordinate-reference transformation library, or a GeoJSON parser. GeoJSON output is provided for integration; input parsing and application-specific feature properties remain in the host application.

See README.mbt.md for API notes, docs/ACCEPTANCE.md for verification evidence, and docs/RELATED_WORK.md for scope and prior-art notes.