UNL Core Library

This library can be used to convert a UNL locationId to/from a latitude/longitude point. It also contains helper functions like retrieving the bounds of a UNL cell or the UNL grid lines for a given boundingbox (these can be used to draw a UNL cell or a UNL grid).

Install

npm install unl-core
yarn add unl-core

TypeScript

npm install @types/unl-core --save-dev
yarn add @types/unl-core --dev

Usage

You can either import certain functions from the package directly:

import { encode } from "unl-core";

or load the whole library:

import UnlCore from "unl-core";

Usage in browser

UnlCore can be used in the browser by taking a local copy, or loading it from jsDelivr: for example,

<!DOCTYPE html><title>locationId example</title><meta charset="utf-8" />
<script type="module">
import UnlCore from "https://cdn.jsdelivr.net/npm/unl-core@2.0.2";
const locationId = UnlCore.encode(52.2, 0.12, 6);
console.assert(locationId == "u120fw");
const latlon = UnlCore.decode("u120fw");
console.assert(JSON.stringify(latlon) == '{"lat":52.1988,"lon":0.115}');
</script>

Usage in Node.js

UnlCore can be used in a Node.js app from npm (currently the esm package is required to load ES-modules):

$ npm install unl-core esm
$ node -r esm
> import UnlCore from 'unl-core';
> const locationId = UnlCore.encode(52.20, 0.12, 6);
> console.assert(locationId == 'u120fw');
> const latlon = UnlCore.decode('u120fw');
> console.assert(JSON.stringify(latlon) == '{"lat":52.1988,"lon":0.115}');

Interfaces

Direction

type Direction = "N" | "S" | "E" | "W";

ElevationType

type ElevationType = "floor" | "heightincm";

Neighbours

interface Neighbours {
n: string;
ne: string;
e: string;
se: string;
s: string;
sw: string;
w: string;
nw: string;
}

Point

interface Point {
lat: number;
lon: number;
}

Bounds

interface Bounds {
sw: Point;
ne: Point;
}

BoundsWithElevation

interface BoundsWithElevation extends Bounds {
elevation: number;
elevationType: ElevationType;
}

PointWithElevation

interface PointWithElevation extends Point {
elevation: number;
elevationType: ElevationType;
bounds: BoundsWithElevation;
}

EncodeOptions

interface EncodeOptions {
elevation: number;
elevationType: ElevationType;
}

LocationIdWithElevation

interface LocationIdWithElevation {
elevation: number;
elevationType: ElevationType;
locationId: string;
}

Functions

encode(lat: number, lon: number, precision?: number, options?: EncodeOptions): string

Encodes latitude/longitude coordinates to locationId, either to specified precision or to default precision. Elevation information can be optionally specified in options parameter.

UnlCore.encode(52.37686, 4.90065);

Returns a string:

"u173zwbt3"

decode(locationId: string): PointWithElevation

Decodes a locationId to latitude/longitude (location is approximate centre of locationId cell, to reasonable precision).

UnlCore.decode("u173zwbt3");

Returns a Point object:

{
lat: centerLat,
lon: centerLon,
bounds: {
sw: {
lat: minLat,
lon: minLon
},
ne: {
lat: maxLat,
lon: maxLon
}
}
}

bounds(locationId: string): BoundsWithElevation

Returns SW/NE latitude/longitude bounds of specified locationId cell.

UnlCore.bounds("u173zwbt3");

Returns a Bounds object:

{
sw: {
lat: minLat,
lon: minLon
},
ne: {
lat: maxLat,
lon: maxLon
},
elevation: 0,
elevationType: "floor"
}

function gridLines(bounds: Bounds, precision?: number): Array<[[number, number], [number, number]]>

Returns the vertical and horizontal lines that can be used to draw a UNL grid in the specified SW/NE latitude/longitude bounds and precision. Each line is represented by an array of two coordinates in the format: [[startLon, startLat], [endLon, endLat]].

UnlCore.gridLines({
sw: {
lat: 52.369915397800824,
lon: 4.88533463041897,
},
ne: {
lat: 52.38788170348322,
lon: 4.91476651006799,
},
});

Returns an array of lines:

[
[[startLon, startLat], [endLon, endLat]]
...
]

adjacent(locationId: string, direction: Direction): string

Determines adjacent cell in given direction.

UnlCore.adjacent("ezzz@5", "N");

Returns a string:

"gbpb@5"

neighbours(locationId: string): Neighbours

Returns all 8 adjacent cells to specified locationId.

UnlCore.neighbours("ezzz");

Returns a Neighbours object :

{
n: "gbpb",
ne: "u000",
e: "spbp",
se: "spbn",
s: "ezzy",
sw: "ezzw",
w: "ezzx",
nw: "gbp8",
}

excludeElevation(locationIdWithElevation: string): LocationIdWithElevation

Returns locationId and elevation properties. It is mainly used by internal functions.

UnlCore.excludeElevation("6gkzwgjz@5");

Returns a LocationIdWithElevation object:

{
locationId: "6gkzwgjz",
elevation: 5,
elevationType: "floor",
}

appendElevation(locationIdWithoutElevation: string, elevation: number, elevationType: ElevationType): string

Adds elevation chars and elevation. It is mainly used by internal functions.

UnlCore.appendElevation("6gkzwgjz", 5);

Returns a string:

"6gkzwgjz@5"

Note

To obtain neighbours as an array, you can use

const neighboursObj = UnlCore.neighbours(locationId);
const neighboursArr = Object.keys(neighboursObj).map(n => neighboursObj[n]);

The parent of a locationId is simply locationId.slice(0, -1).

If you want the locationId converted from Base32 to Base4, you can e.g.:

parseInt(UnlCore.encode(52.20, 0.12, 6), 32).toString(4);