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uber / h3-js

h3-js provides a JavaScript version of H3, a hexagon-based geospatial indexing system.
https://uber.github.io/h3
Apache License 2.0
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emscripten geospatial h3 hexagon javascript spatial-indexing uber

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H3 Logo

h3-js

Build Status Coverage Status License npm version H3 Version

The h3-js library provides a pure-JavaScript version of the H3 Core Library, a hexagon-based geographic grid system. It can be used either in Node >= 6 or in the browser. The core library is transpiled from C using emscripten, offering full parity with the C API and highly efficient operations.

For more information on H3 and for the full API documentation, please see the H3 Documentation.

Install

npm install h3-js

Usage

:tada: Note: The following usage docs apply to H3 v4, which was released on August 23, 2022.

The library uses ES6 modules. Bundles for Node and the browser are built to the dist folder.

Import

ES6 usage:

import {latLngToCell} from "h3-js";

CommonJS usage:

const h3 = require("h3-js");

Pre-bundled script (library is available as an h3 global):

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

Core functions

// Convert a lat/lng point to a hexagon index at resolution 7
const h3Index = h3.latLngToCell(37.3615593, -122.0553238, 7);
// -> '87283472bffffff'

// Get the center of the hexagon
const hexCenterCoordinates = h3.cellToLatLng(h3Index);
// -> [37.35171820183272, -122.05032565263946]

// Get the vertices of the hexagon
const hexBoundary = h3.cellToBoundary(h3Index);
// -> [ [37.341099093235684, -122.04156135164334 ], ...]

Useful algorithms

// Get all neighbors within 1 step of the hexagon
const disk = h3.gridDisk(h3Index, 1);
// -> ['87283472bffffff', '87283472affffff', ...]

// Get the set of hexagons within a polygon
const polygon = [
    [37.813318999983238, -122.4089866999972145],
    [37.7198061999978478, -122.3544736999993603],
    [37.8151571999998453, -122.4798767000009008]
];
const hexagons = h3.polygonToCells(polygon, 7);
// -> ['872830828ffffff', '87283082effffff', ...]

// Get the outline of a set of hexagons, as a GeoJSON-style MultiPolygon
const coordinates = h3.cellsToMultiPolygon(hexagons, true);
// -> [[[
//      [-122.37681938644465, 37.76546768434345],
//      [-122.3856345540363,37.776004200673846],
//      ...
//    ]]]

API Reference

h3

h3.UNITS

Length/Area units

Properties

Name Type
m string
m2 string
km string
km2 string
rads string
rads2 string

h3.h3IndexToSplitLong(h3Index) ⇒ SplitLong

Convert an H3 index (64-bit hexidecimal string) into a "split long" - a pair of 32-bit ints

Returns: SplitLong - A two-element array with 32 lower bits and 32 upper bits

Param Type Description
h3Index H3IndexInput H3 index to check

h3.splitLongToH3Index(lower, upper) ⇒ H3Index

Get a H3 index string from a split long (pair of 32-bit ints)

Returns: H3Index - H3 index

Param Type Description
lower number Lower 32 bits
upper number Upper 32 bits

h3.isValidCell(h3Index) ⇒ boolean

Whether a given string represents a valid H3 index

Returns: boolean - Whether the index is valid

Param Type Description
h3Index H3IndexInput H3 index to check

h3.isPentagon(h3Index) ⇒ boolean

Whether the given H3 index is a pentagon

Returns: boolean - isPentagon

Param Type Description
h3Index H3IndexInput H3 index to check

h3.isResClassIII(h3Index) ⇒ boolean

Whether the given H3 index is in a Class III resolution (rotated versus the icosahedron and subject to shape distortion adding extra points on icosahedron edges, making them not true hexagons).

Returns: boolean - isResClassIII

Param Type Description
h3Index H3IndexInput H3 index to check

h3.getBaseCellNumber(h3Index) ⇒ number

Get the number of the base cell for a given H3 index

Returns: number - Index of the base cell (0-121)

Param Type Description
h3Index H3IndexInput H3 index to get the base cell for

h3.getIcosahedronFaces(h3Index) ⇒ Array.<number>

Get the indices of all icosahedron faces intersected by a given H3 index

Returns: Array.<number> - Indices (0-19) of all intersected faces
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get faces for

h3.getResolution(h3Index) ⇒ number

Returns the resolution of an H3 index

Returns: number - The number (0-15) resolution, or -1 if invalid

Param Type Description
h3Index H3IndexInput H3 index to get resolution

h3.latLngToCell(lat, lng, res) ⇒ H3Index

Get the hexagon containing a lat,lon point

Returns: H3Index - H3 index
Throws:

Param Type Description
lat number Latitude of point
lng number Longtitude of point
res number Resolution of hexagons to return

h3.cellToLatLng(h3Index) ⇒ CoordPair

Get the lat,lon center of a given hexagon

Returns: CoordPair - Point as a [lat, lng] pair
Throws:

Param Type Description
h3Index H3IndexInput H3 index

h3.cellToBoundary(h3Index, [formatAsGeoJson]) ⇒ Array.<CoordPair>

Get the vertices of a given hexagon (or pentagon), as an array of [lat, lng] points. For pentagons and hexagons on the edge of an icosahedron face, this function may return up to 10 vertices.

Returns: Array.<CoordPair> - Array of [lat, lng] pairs
Throws:

Param Type Description
h3Index H3IndexInput H3 index
[formatAsGeoJson] boolean Whether to provide GeoJSON output: [lng, lat], closed loops

h3.cellToParent(h3Index, res) ⇒ H3Index

Get the parent of the given hexagon at a particular resolution

Returns: H3Index - H3 index of parent, or null for invalid input
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get parent for
res number Resolution of hexagon to return

h3.cellToChildren(h3Index, res) ⇒ Array.<H3Index>

Get the children/descendents of the given hexagon at a particular resolution

Returns: Array.<H3Index> - H3 indexes of children, or empty array for invalid input
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get children for
res number Resolution of hexagons to return

h3.cellToChildrenSize(h3Index, res) ⇒ number

Get the number of children for a cell at a given resolution

Returns: number - Number of children at res for the given cell
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get child count for
res number Child resolution

h3.cellToCenterChild(h3Index, res) ⇒ H3Index

Get the center child of the given hexagon at a particular resolution

Returns: H3Index - H3 index of child, or null for invalid input
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get center child for
res number Resolution of cell to return

h3.cellToChildPos(h3Index, parentRes) ⇒ number

Get the position of the cell within an ordered list of all children of the cell's parent at the specified resolution.

Returns: number - Position of child within parent at parentRes
Throws:

Param Type Description
h3Index H3IndexInput H3 index to get child pos for
parentRes number Resolution of reference parent

h3.childPosToCell(childPos, h3Index, childRes) ⇒ H3Index

Get the child cell at a given position within an ordered list of all children at the specified resolution

Returns: H3Index - H3 index of child
Throws:

Param Type Description
childPos number Position of the child cell to get
h3Index H3IndexInput H3 index of the parent cell
childRes number Resolution of child cell to return

h3.gridDisk(h3Index, ringSize) ⇒ Array.<H3Index>

Get all hexagons in a k-ring around a given center. The order of the hexagons is undefined.

Returns: Array.<H3Index> - H3 indexes for all hexagons in ring
Throws:

Param Type Description
h3Index H3IndexInput H3 index of center hexagon
ringSize number Radius of k-ring

h3.gridDiskDistances(h3Index, ringSize) ⇒ Array.<Array.<H3Index>>

Get all hexagons in a k-ring around a given center, in an array of arrays ordered by distance from the origin. The order of the hexagons within each ring is undefined.

Returns: Array.<Array.<H3Index>> - Array of arrays with H3 indexes for all hexagons each ring
Throws:

Param Type Description
h3Index H3IndexInput H3 index of center hexagon
ringSize number Radius of k-ring

h3.gridRingUnsafe(h3Index, ringSize) ⇒ Array.<H3Index>

Get all hexagons in a hollow hexagonal ring centered at origin with sides of a given length. Unlike gridDisk, this function will throw an error if there is a pentagon anywhere in the ring.

Returns: Array.<H3Index> - H3 indexes for all hexagons in ring
Throws:

Param Type Description
h3Index H3IndexInput H3 index of center hexagon
ringSize number Radius of ring

h3.polygonToCells(coordinates, res, [isGeoJson]) ⇒ Array.<H3Index>

Get all hexagons with centers contained in a given polygon. The polygon is specified with GeoJson semantics as an array of loops. Each loop is an array of [lat, lng] pairs (or [lng, lat] if isGeoJson is specified). The first loop is the perimeter of the polygon, and subsequent loops are expected to be holes.

Returns: Array.<H3Index> - H3 indexes for all hexagons in polygon
Throws:

Param Type Description
coordinates Array.<Array.<number>> | Array.<Array.<Array.<number>>> Array of loops, or a single loop
res number Resolution of hexagons to return
[isGeoJson] boolean Whether to expect GeoJson-style [lng, lat] pairs instead of [lat, lng]

h3.cellsToMultiPolygon(h3Indexes, [formatAsGeoJson]) ⇒ Array.<Array.<Array.<CoordPair>>>

Get the outlines of a set of H3 hexagons, returned in GeoJSON MultiPolygon format (an array of polygons, each with an array of loops, each an array of coordinates). Coordinates are returned as [lat, lng] pairs unless GeoJSON is requested.

It is the responsibility of the caller to ensure that all hexagons in the set have the same resolution and that the set contains no duplicates. Behavior is undefined if duplicates or multiple resolutions are present, and the algorithm may produce unexpected or invalid polygons.

Returns: Array.<Array.<Array.<CoordPair>>> - MultiPolygon-style output.
Throws:

Param Type Description
h3Indexes Array.<H3IndexInput> H3 indexes to get outlines for
[formatAsGeoJson] boolean Whether to provide GeoJSON output: [lng, lat], closed loops

h3.compactCells(h3Set) ⇒ Array.<H3Index>

Compact a set of hexagons of the same resolution into a set of hexagons across multiple levels that represents the same area.

Returns: Array.<H3Index> - Compacted H3 indexes
Throws:

Param Type Description
h3Set Array.<H3IndexInput> H3 indexes to compact

h3.uncompactCells(compactedSet, res) ⇒ Array.<H3Index>

Uncompact a compacted set of hexagons to hexagons of the same resolution

Returns: Array.<H3Index> - The uncompacted H3 indexes
Throws:

Param Type Description
compactedSet Array.<H3IndexInput> H3 indexes to uncompact
res number The resolution to uncompact to

h3.areNeighborCells(origin, destination) ⇒ boolean

Whether two H3 indexes are neighbors (share an edge)

Returns: boolean - Whether the hexagons share an edge
Throws:

Param Type Description
origin H3IndexInput Origin hexagon index
destination H3IndexInput Destination hexagon index

h3.cellsToDirectedEdge(origin, destination) ⇒ H3Index

Get an H3 index representing a unidirectional edge for a given origin and destination

Returns: H3Index - H3 index of the edge, or null if no edge is shared
Throws:

Param Type Description
origin H3IndexInput Origin hexagon index
destination H3IndexInput Destination hexagon index

h3.getDirectedEdgeOrigin(edgeIndex) ⇒ H3Index

Get the origin hexagon from an H3 index representing a unidirectional edge

Returns: H3Index - H3 index of the edge origin
Throws:

Param Type Description
edgeIndex H3IndexInput H3 index of the edge

h3.getDirectedEdgeDestination(edgeIndex) ⇒ H3Index

Get the destination hexagon from an H3 index representing a unidirectional edge

Returns: H3Index - H3 index of the edge destination
Throws:

Param Type Description
edgeIndex H3IndexInput H3 index of the edge

h3.isValidDirectedEdge(edgeIndex) ⇒ boolean

Whether the input is a valid unidirectional edge

Returns: boolean - Whether the index is valid

Param Type Description
edgeIndex H3IndexInput H3 index of the edge

h3.directedEdgeToCells(edgeIndex) ⇒ Array.<H3Index>

Get the [origin, destination] pair represented by a unidirectional edge

Returns: Array.<H3Index> - [origin, destination] pair as H3 indexes
Throws:

Param Type Description
edgeIndex H3IndexInput H3 index of the edge

h3.originToDirectedEdges(h3Index) ⇒ Array.<H3Index>

Get all of the unidirectional edges with the given H3 index as the origin (i.e. an edge to every neighbor)

Returns: Array.<H3Index> - List of unidirectional edges
Throws:

Param Type Description
h3Index H3IndexInput H3 index of the origin hexagon

h3.directedEdgeToBoundary(edgeIndex, [formatAsGeoJson]) ⇒ Array.<CoordPair>

Get the vertices of a given edge as an array of [lat, lng] points. Note that for edges that cross the edge of an icosahedron face, this may return 3 coordinates.

Returns: Array.<CoordPair> - Array of geo coordinate pairs
Throws:

Param Type Description
edgeIndex H3IndexInput H3 index of the edge
[formatAsGeoJson] boolean Whether to provide GeoJSON output: [lng, lat]

h3.gridDistance(origin, destination) ⇒ number

Get the grid distance between two hex indexes. This function may fail to find the distance between two indexes if they are very far apart or on opposite sides of a pentagon.

Returns: number - Distance between hexagons
Throws:

Param Type Description
origin H3IndexInput Origin hexagon index
destination H3IndexInput Destination hexagon index

h3.gridPathCells(origin, destination) ⇒ Array.<H3Index>

Given two H3 indexes, return the line of indexes between them (inclusive).

This function may fail to find the line between two indexes, for example if they are very far apart. It may also fail when finding distances for indexes on opposite sides of a pentagon.

Notes:

Returns: Array.<H3Index> - H3 indexes connecting origin and destination
Throws:

Param Type Description
origin H3IndexInput Origin hexagon index
destination H3IndexInput Destination hexagon index

h3.cellToLocalIj(origin, destination) ⇒ CoordIJ

Produces IJ coordinates for an H3 index anchored by an origin.

Returns: CoordIJ - Coordinates as an {i, j} pair
Throws:

Param Type Description
origin H3IndexInput Origin H3 index
destination H3IndexInput H3 index for which to find relative coordinates

h3.localIjToCell(origin, coords) ⇒ H3Index

Produces an H3 index for IJ coordinates anchored by an origin.

Returns: H3Index - H3 index at the relative coordinates
Throws:

Param Type Description
origin H3IndexInput Origin H3 index
coords CoordIJ Coordinates as an {i, j} pair

h3.greatCircleDistance(latLng1, latLng2, unit) ⇒ number

Great circle distance between two geo points. This is not specific to H3, but is implemented in the library and provided here as a convenience.

Returns: number - Great circle distance
Throws:

Param Type Description
latLng1 Array.<number> Origin coordinate as [lat, lng]
latLng2 Array.<number> Destination coordinate as [lat, lng]
unit string Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

h3.cellArea(h3Index, unit) ⇒ number

Exact area of a given cell

Returns: number - Cell area
Throws:

Param Type Description
h3Index H3IndexInput H3 index of the hexagon to measure
unit string Distance unit (either UNITS.m2, UNITS.km2, or UNITS.rads2)

h3.edgeLength(edge, unit) ⇒ number

Calculate length of a given unidirectional edge

Returns: number - Cell area
Throws:

Param Type Description
edge H3IndexInput H3 index of the edge to measure
unit string Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

h3.getHexagonAreaAvg(res, unit) ⇒ number

Average hexagon area at a given resolution

Returns: number - Average area
Throws:

Param Type Description
res number Hexagon resolution
unit string Area unit (either UNITS.m2, UNITS.km2, or UNITS.rads2)

h3.getHexagonEdgeLengthAvg(res, unit) ⇒ number

Average hexagon edge length at a given resolution

Returns: number - Average edge length
Throws:

Param Type Description
res number Hexagon resolution
unit string Distance unit (either UNITS.m, UNITS.km, or UNITS.rads)

h3.cellToVertex(h3Index, vertexNum) ⇒ H3Index

Find the index for a vertex of a cell.

Returns: H3Index - Vertex index
Throws:

Param Type Description
h3Index H3IndexInput Cell to find the vertex for
vertexNum number Number (index) of the vertex to calculate

h3.cellToVertexes(h3Index) ⇒ Array.<H3Index>

Find the indexes for all vertexes of a cell.

Returns: Array.<H3Index> - All vertex indexes of this cell
Throws:

Param Type Description
h3Index H3IndexInput Cell to find all vertexes for

h3.vertexToLatLng(h3Index) ⇒ CoordPair

Get the lat, lng of a given vertex

Returns: CoordPair - Latitude, longitude coordinates of the vertex
Throws:

Param Type Description
h3Index H3IndexInput A vertex index

h3.isValidVertex(h3Index) ⇒ boolean

Returns true if the input is a valid vertex index.

Returns: boolean - True if the index represents a vertex

Param Type Description
h3Index H3IndexInput An index to test for being a vertex index

h3.getNumCells(res) ⇒ number

The total count of hexagons in the world at a given resolution. Note that above resolution 8 the exact count cannot be represented in a JavaScript 32-bit number, so consumers should use caution when applying further operations to the output.

Returns: number - Count
Throws:

Param Type Description
res number Hexagon resolution

h3.getRes0Cells() ⇒ Array.<H3Index>

Get all H3 indexes at resolution 0. As every index at every resolution > 0 is the descendant of a res 0 index, this can be used with h3ToChildren to iterate over H3 indexes at any resolution.

Returns: Array.<H3Index> - All H3 indexes at res 0

h3.getPentagons(res) ⇒ Array.<H3Index>

Get the twelve pentagon indexes at a given resolution.

Returns: Array.<H3Index> - All H3 pentagon indexes at res
Throws:

Param Type Description
res number Hexagon resolution

h3.degsToRads(deg) ⇒ number

Convert degrees to radians

Returns: number - Value in radians

Param Type Description
deg number Value in degrees

h3.radsToDegs(rad) ⇒ number

Convert radians to degrees

Returns: number - Value in degrees

Param Type Description
rad number Value in radians

h3.H3Index : string

64-bit hexidecimal string representation of an H3 index

h3.H3IndexInput : string | Array.<number>

64-bit hexidecimal string representation of an H3 index, or two 32-bit integers in little endian order in an array.

h3.CoordIJ

Coordinates as an {i, j} pair

Properties

Name Type
i number
j number

h3.H3Error

Custom JS Error instance with an attached error code. Error codes come from the core H3 library and can be found in the H3 docs.

Properties

Name Type
message string
code number

h3.CoordPair : Array.<number>

Pair of lat,lng coordinates (or lng,lat if GeoJSON output is specified)

h3.SplitLong : Array.<number>

Pair of lower,upper 32-bit ints representing a 64-bit value

Legacy API

H3 v4 renamed the majority of the functions in the library. To help ease migration from H3 v3 to H3 v4, we offer a legacy API wrapper at h3-js/legacy, which exports the v4 functions with the v3 names. Users are welcome to use the legacy API wrapper as a transitional support, but are encouraged to upgrade to the H3 v4 API as soon as possible.

Note that the legacy API is not 100% backwards compatible - it's a thin wrapper on top of the v4 functions, so in cases where behavior has changed, the v4 behavior will be used. In particular, many of the v4 functions will throw errors for invalid input, where v3 functions would return null.

Installation:

npm install h3-js

Usage:

import {geoToH3} from 'h3-js/legacy';

const h3Index = geoToH3(37.3615593, -122.0553238, 7);

Development

The h3-js library uses yarn as the preferred package manager. To install the dev dependencies, just run:

yarn

To lint the code:

yarn lint

To run the tests:

yarn test

Code must be formatted with prettier; unformatted code will fail the build. To format all files:

yarn prettier

Benchmarks

The h3-js library includes a basic benchmark suite using Benchmark.js. Because many of the functions may be called over thousands of hexagons in a "hot loop", performance is an important concern. Benchmarks are run against the transpiled ES5 code by default.

To run the benchmarks in Node:

yarn benchmark-node

To run the benchmarks in a browser:

yarn benchmark-browser

Sample Node output (Macbook Pro running Node 12):

isValidCell x 3,650,995 ops/sec ±1.67% (87 runs sampled)
latLngToCell x 429,982 ops/sec ±1.39% (86 runs sampled)
cellToLatLng x 1,161,867 ops/sec ±1.11% (84 runs sampled)
cellToLatLng - integers x 1,555,791 ops/sec ±1.29% (86 runs sampled)
cellToBoundary x 375,938 ops/sec ±1.25% (87 runs sampled)
cellToBoundary - integers x 377,181 ops/sec ±1.18% (85 runs sampled)
getIcosahedronFaces x 992,946 ops/sec ±1.13% (85 runs sampled)
gridDisk x 194,400 ops/sec ±1.16% (85 runs sampled)
polygonToCells_9 x 4,919 ops/sec ±0.79% (87 runs sampled)
polygonToCells_11 x 368 ops/sec ±0.76% (86 runs sampled)
polygonToCells_10ring x 76.88 ops/sec ±0.57% (68 runs sampled)
cellsToMultiPolygon x 760 ops/sec ±1.06% (86 runs sampled)
compactCells x 2,466 ops/sec ±0.75% (86 runs sampled)
uncompactCells x 715 ops/sec ±1.15% (85 runs sampled)
areNeighborCells x 1,073,086 ops/sec ±1.56% (89 runs sampled)
cellsToDirectedEdge x 692,172 ops/sec ±1.06% (86 runs sampled)
getDirectedEdgeOrigin x 995,390 ops/sec ±1.60% (85 runs sampled)
getDirectedEdgeDestination x 930,473 ops/sec ±1.11% (86 runs sampled)
isValidDirectedEdge x 3,505,407 ops/sec ±1.05% (87 runs sampled)

When making code changes that may affect performance, please run benchmarks against master and then against your branch to identify any regressions.

Transpiling the C Source

The core library is transpiled using emscripten. The easiest way to build from source locally is by using Docker. Make sure Docker is installed, then:

yarn docker-boot
yarn build-emscripten

The build script uses the H3_VERSION file to determine the version of the core library to build. To use a different version of the library (e.g. to test local changes), clone the desired H3 repo to ./h3c and then run yarn docker-emscripten.

Contributing

Pull requests and Github issues are welcome. Please include tests for new work, and keep the library test coverage at 100%. Please note that the purpose of this module is to expose the API of the H3 Core library, so we will rarely accept new features that are not part of that API. New proposed feature work is more appropriate in the core C library or in a new JS library that depends on h3-js.

Before we can merge your changes, you must agree to the Uber Contributor License Agreement.

Versioning

The H3 core library adheres to Semantic Versioning. The h3-js library has a major.minor.patch version scheme. The major and minor version numbers of h3-js are the major and minor version of the bound core library, respectively. The patch version is incremented independently of the core library.

Legal and Licensing

The h3-js library is licensed under the Apache 2.0 License.

DGGRID Copyright (c) 2015 Southern Oregon University