@id-sdk/geo

@id-sdk/geo

🌐 Geographic (spherical) math functions

Installing

npm install @id-sdk/geo

This library is available in both ES5/CommonJS and ES6 module formats.

const geo = require('@id-sdk/geo');                             // CommonJS import all
const geoLatToMeters = require('@id-sdk/geo').geoLatToMeters;   // CommonJS import named
// or
import * as geo from '@id-sdk/geo';               // ES6 import all
import { geoLatToMeters } from '@id-sdk/geo';     // ES6 import named

Contributing

This project is just getting started! 🌱

We're not able to support external contributors at this time, but check back in a bit when things have matured.

API Reference

Functions

• geoLatToMeters(dLat: number): number
• geoLonToMeters(dLon: number, atLat: number): number
• geoMetersToLat(m: number): number
• geoMetersToLon(m: number, atLat: number): number
• geoMetersToOffset(m: Vec2, tileSize?: number): Vec2
• geoOffsetToMeters(offset: Vec2, tileSize?: number): Vec2
• geoSphericalDistance(a: Vec2, b: Vec2): number
• geoScaleToZoom(k: number, tileSize?: number): number
• geoZoomToScale(z: number, tileSize?: number): number
• geoSphericalClosestPoint(points: Vec2[], a: Vec2): Closest | null

Types

• Vec2: [number, number]
• Closest: { index: number, distance: number, point: Vec2 }

Functions

# geoLatToMeters(dLat: number): number <>

Convert degrees latitude to meters.

geoLatToMeters(1);  // returns ≈111319

# geoLonToMeters(dLon: number, atLat: number): number <>

Convert degrees longitude to meters at a given latitude.

geoLonToMeters(1, 0);  // returns ≈110946 at equator

# geoMetersToLat(m: number): number <>

Convert meters to degrees latitude.

geoMetersToLat(111319);  // returns ≈1°

# geoMetersToLon(m: number, atLat: number): number <>

Convert meters to degrees longitude at a given latitude.

geoMetersToLon(110946, 0);  // returns ≈1° at equator

# geoMetersToOffset(m: Vec2, tileSize?: number): Vec2 <>

Convert offset in meters (for example, imagery offset) to offset in tile pixels. tileSize defaults to 256px.

geoMetersToOffset([100, 100]);  // returns ≈[0.00064, -0.00064] pixels

# geoOffsetToMeters(offset: Vec2, tileSize?: number): Vec2 <>

Convert imagery offset in tile pixels to offset in meters. tileSize defaults to 256px.

geoOffsetToMeters([0.00064, -0.00064]);  // returns ≈[100, 100] meters

# geoSphericalDistance(a: Vec2, b: Vec2): number <>

Equirectangular approximation of spherical distances on Earth.

geoSphericalDistance([0, 0], [1, 0]);  // returns ≈110946 meters

# geoScaleToZoom(k: number, tileSize?: number): number <>

Projection scale factor to tile zoom level. tileSize defaults to 256px.

geoScaleToZoom(5340353.7154);  // returns ≈17

# geoZoomToScale(z: number, tileSize?: number): number <>

Tile zoom to projection scale factor. tileSize defaults to 256px.

geoZoomToScale(17);  // returns ≈5340353.7154

# geoSphericalClosestPoint(points: Vec2[], a: Vec2): Closest | null <>

Returns info about the point from points closest to the given test point a.

Types

# Vec2

An array of two numbers.

[number, number]

# Closest

An Object containing index, distance, and point properties. Used as the return value for geoSphericalClosestPoint().

{ index: number, distance: number, point: Vec2 }