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Libraries of geodesy functions implemented in JavaScript

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geodesy

Libraries of geodesy functions implemented in JavaScript – intended to serve as examples or starting-points for people wanting to develop geodesy applications (in JavaScript or other languages), though they can also be used as-is.

latlon.js

This is a library of geodesy functions for working with points and paths on (a spherical model of) the earth’s surface, including (orthodromic) great-circle geodesics and (loxodromic) rhumb lines. All calculations are done using spherical trigonometry.

The library includes the following functions:

  • distanceTo destination point (using haversine formulation)
  • bearingTo destination point
  • finalBearingTo destination point
  • midpointTo destination point
  • destinationPoint following initial bearing for given distance
  • intersection of two paths
  • rhumbDistanceTo destination point
  • rhumbBearingTo destination point
  • rhumbDestinationPoint following given bearing for given distance
  • rhumbMidpointTo destination point

Full details are available at www.movable-type.co.uk/scripts/latlong.html.

latlon-vincenty.js

Vincenty’s formulae for ‘direct and inverse solutions of geodesics on the ellipsoid’; these give distances and bearings on an ellipsoidal earth model accurate to within 0.5mm distance, 0.000015″ bearing.

The library includes the following wrapper functions:

  • distanceTo destination point
  • initialBearingTo destination point
  • finalBearingTo destination point
  • destinationPoint following initial bearing for given distance
  • finalBearingOn initial bearing for given distance

The heaving lifting is done in two routines:

  • direct (implementing the direct solution of geodesics on the ellipsoid)
  • inverse (implementing the inverse solution of geodesics on the ellipsoid)

Full details are available at www.movable-type.co.uk/scripts/latlong-vincenty.html.

latlon-ellipsoid.js

Geodesy tools for an ellipsoidal earth model.

The LatLonE object incorporates not just latitude & longitude coordinates, but also the datum the lat/lon point is defined on.

LatLonE also holds ellipsoid parameters and Helmert transform parameters for translating between different datums (e.g. between OSGB36 & WGS-84).

The convertDatum function performs such translations between datums.

The library includes:

  • ellipsoid parameters
  • datum parameters (reference ellipsoid & Helmert transform parameters)
  • convertDatum: convert lat/lon point to new datum
  • toCartesian: convert lat/lon point to ECEF 3-d vector
  • toLatLon: convert ECEF 3-d vector to lat/lon point

More information at www.movable-type.co.uk/scripts/latlong-convert-coords.html.

latlon-vectors.js

This is a library of functions for working with points and paths on (a spherical model of) the earth’s surface using a vector-based approach using ‘n-vectors’ (rather than the more common spherical trigonometry; a vector-based approach makes most calculations much simpler, and easier to follow, compared with trigonometric equivalents).

The library includes:

  • distanceTo destination point
  • bearingTo destination point
  • midpointTo destination point
  • destinationPoint following initial bearing for given distance
  • intersection of two paths
  • crossTrackDistanceTo great circle path
  • enclosedBy polygon
  • meanOf set of points

More information at www.movable-type.co.uk/scripts/latlong-vectors.html.

osgridref.js

Routines for converting between Ordnance Survey grid references and (OSGB-36) latitude/longitude coordinates, based on Ordnance Survey formulae.

The library includes:

  • latLonToOsGrid: convert (OSGB) latitude/longitude to (numeric) OS grid reference
  • osGridToLatLon: convert (numeric) OS grid reference to (OSGB) latitude/longitude
  • parse standard format grid reference to numeric grid reference
  • toString: convert numeric grid reference to standard format

More information at www.movable-type.co.uk/scripts/latlong-gridref.html.

geohash.js

Functions to convert geohash to/from latitude/longitude points, also to determine bounds of a geohash cell and find neighbours of a geohash.

The library includes:

  • encode: latitude/longitude point to geohash
  • decode: geohash to latitude/longitude
  • bounds of a geohash cell
  • neighbours: of a geohash

More information at www.movable-type.co.uk/scripts/geohash.html.

geo.js

Tools for converting between numeric degrees and degrees / minutes / seconds.

The library includes the following functions:

  • parseDMS: parse string representing degrees/minutes/seconds into numeric degrees
  • toLat: convert decimal degrees to latitude
  • toLon: convert decimal degrees to longitude
  • toBrng: convert decimal degrees to bearing

Documentation

Documentation for all these methods is available at www.movable-type.co.uk/scripts/js/geodesy/docs.

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