wgs84

Introduction

A tiny library fully implemented in Typescript to handle WGS84 coordinates in GeoJson and "small" distances between them with very high accuracy (~1 cm), based on a local, flat earth approximation.

• All functions uses degrees for latitude and longitude, and meters for distances.
• Parses and gives output in GeoJson using the Point definition. If you already have imported the typescript definition for Point in the geojson package you can use that (that is what I do in unit testing). Otherwise you can import Point from this package.
• No dependencies to other NPM modules.
• The math is based on Aviation Formulary V1.47 by Ed Williams.
• Functions will throw Error if fed impossible values, e.g. incorrectly formatted GeoJSON or lat >= 90 degrees (math will not work!). Make sure to handle that!

Getting Started

Include in your project as any other NPM package

npm install @ulrik.ek/wgs84

Usage

import * as wgs84 from '@ulrik.ek/wgs84'; // The functions can obviously also be imported separately

// helper function to construct a GeoJSON Point
const lat = 15;
const lon = 25;
const p: wgs84.Point = wgs84.point(lat, lon);

// Getting a new point 100m north and 200m east of the first point
const p1: wgs84.Point = wgs84.pointEastOf(wgs84.pointNorthOf(p, 300), 400);
const newLat = p1.coordinates[1]; // GeoJSON uses [lon, lat] order!
const newLon = p1.coordinates[0];
console.log(`lat=${newLat}, lon=${newLon}`);

// get the distance along north between the 2 points
console.log(`Distance along north=${wgs84.distanceNorth(p, p1)}`);
console.log(`Distance along east=${wgs84.distanceEast(p, p1)}`);
console.log(`Total distance=${wgs84.distance(p, p1)}`);

This will produce the following output

lat=15.002711283642645, lon=25.003719230339353
Distance along north=300.00000000009265
Distance along east=400.00504064747975
Total distance=500.0040325271862

Documention

The following functions are available:

point(lat: number, lon: number, height?: number): Point;
R1(position: Point): number;
R2(position: Point): number;
distanceNorth(origin: Point, target: Point): number;
distanceEast(origin: Point, target: Point): number;
distanceUp(origin: Point, target: Point): number;
distance(origin: Point, target: Point): number;
bearing(origin: Point, target: Point): number;
pointNorthOf(origin: Point, dN: number): Point;
pointEastOf(origin: Point, dE: number): Point;
pointAbove(origin: Point, dH: number): Point;

Full Typedoc documentation

Build and Test

All functions are unit tested.