h3_core

Dart/Flutter bindings for the H3 geospatial indexing library, originally developed at Uber.

Wraps H3 v4.4.1 via dart:ffi on native platforms and h3-js via dart:js_interop on web. Same API on all platforms.

Features

Full H3 v4.4.1 API (~80 functions)
Native: zero-overhead FFI calls via Build Hooks (compiles C natively — no pre-built binaries)
Web: h3-js interop via dart:js_interop
Single package, identical API on all platforms
Type-safe Dart API with extension types (H3Index, LatLng, CellBoundary)
Async wrappers for heavy operations

Platform Support

Platform	Backend	CI Tested
Android	dart:ffi (C)	via macOS build
iOS	dart:ffi (C)	via macOS build
macOS	dart:ffi (C)	macOS stable
Linux	dart:ffi (C)	Ubuntu stable + beta
Windows	dart:ffi (C)	Windows stable
Web	h3-js (JS)	Chrome stable

Installation

dependencies:
  h3_core: ^1.0.4

Quick Start

import 'package:h3_core/h3_core.dart';

// Convert coordinates to H3 cell
final cell = latLngToCell(LatLng(37.7749, -122.4194), 9);
print(cell.toHex()); // 89283082803ffff

// Get cell center
final center = cellToLatLng(cell);
print('${center.lat}, ${center.lng}');

// Get neighbors
final neighbors = gridDisk(cell, 1); // 7 cells (origin + 6 neighbors)

// Check cell properties
print(getResolution(cell)); // 9
print(isValidCell(cell));   // true
print(isPentagon(cell));    // false

API Overview

Indexing

latLngToCell — Convert coordinates to H3 cell
cellToLatLng — Get cell center point
cellToBoundary — Get cell boundary vertices

Inspection

getResolution, getBaseCellNumber, isValidCell, isPentagon, isResClassIII
getIcosahedronFaces, isValidIndex, isValidDirectedEdge, isValidVertex

Traversal

gridDisk, gridDiskDistances — Get cells within k distance
gridRing — Get hollow ring at distance k
gridDistance — Distance between two cells
gridPathCells — Line of cells between two cells

Hierarchy

cellToParent, cellToChildren, cellToCenterChild
cellToChildPos, childPosToCell
compactCells, uncompactCells

Directed Edges

areNeighborCells, cellsToDirectedEdge
getDirectedEdgeOrigin, getDirectedEdgeDestination
originToDirectedEdges, directedEdgeToBoundary

Vertices

cellToVertex, cellToVertexes, vertexToLatLng

Measurements

greatCircleDistanceKm, greatCircleDistanceM
cellAreaKm2, cellAreaM2
edgeLengthKm, edgeLengthM
getHexagonAreaAvgKm2, getHexagonEdgeLengthAvgKm
getNumCells

Regions

polygonToCells — Fill polygon with cells
cellsToMultiPolygon — Convert cells to polygon boundaries

Coordinates

cellToLocalIj, localIjToCell

Async

polygonToCellsAsync, gridDiskAsync, compactCellsAsync, uncompactCellsAsync

Web Setup

Add the h3-js script tag to your web/index.html before the Flutter bootstrap:

<script src="https://unpkg.com/h3-js"></script>
<script src="flutter_bootstrap.js" async></script>

Versioning

Package version uses its own semver. Wraps H3 C library v4.4.1.

License

Apache 2.0 (matching H3)