Work-In-Progress

transverseMercator

Ellipsoidal Transverse Mercator Projection (Javascript)

Welcome to the Wonderful World of geospatial visualisation

The nicest about this projection is that Antarctica is correct in proportions. And unlike UTM, it is has no zones.

This project also contains a javascript port of TransverseMercatorProj from the geographiclib (https://geographiclib.sourceforge.io) project. Originally created by Charles Karney.

Installation

  npm install transverseMercator

Example

  const nodeTM = require("transverseMercator");
  const tm = new nodeTM.TransverseMercator();

  const retXY = tm.toXY(42, 42);
  console.log(JSON.stringify(retXY));

  const retLatLon = tm.toLatLon(retXY.x, retXY.y);
  console.log(JSON.stringify(retLatLon));

API

See geographiclib’s manpage for a detailed description.

The default range of N/E coordinates are [-10e6,+10e6] and roughly [-26e6,+26e6] meters.

Constructor

  new TransverseMercator([k0], [extend], [a], [f]) => instance

Returns a transverseMercator instance. Parameters:

• k0 (optional) - the scale k0 on the central meridian (default 0.9996)

• extend (optional) - use the extended domain

• a (optional) - the ellipsoid via the equatorial radius (default 6378137)

• f (optional) - the ellipsoid via the equatorial flattening. (default 1/298.257223563)

toXY

Convert lat/lon in degrees to E/N coordinates in meters.

  TransverseMercator.toXY(lat, lon, [lon0], [withGammaK]) => xy

parameters:

• lat - latitude

• lon - longitude

• lon0 (optional) - central meridian (default 0)

• withGammaK (optional) - non-zero to include gamma/k0 in return. Makes performance slow with about 10%.

returns:

{
	x: [Easting in meters],
	y: [Northing in meters],
	gamma: [meridian convergence in degrees],
	k0: [scale]
}

toLatLon

Convert E/N coordinates in meters to lat/lon in degrees

  TransverseMercator.toLatLon(x, y, [lon0]) => latLon

parameters:

• lat - Easting in meters

• lon - Northing in meters

• lon0 (optional) - central meridian (default 0)

returns:

{
	lat: [Latitude in degrees],
	y: [Longitude in degrees],
	gamma: [meridian convergence in degrees],
	k0: [scale]
}

Performance

This javascript version serves about 95k conversions per second on an AMD FX-8320E. A non-zero withGammaK will slow toXY() with about 10%.

The original TransverseMercatorProj can serve about 240k conversions per second.

Requirements

Plenty, but all way within your level.

Source code

Grab one of the tarballs at https://github.com/RockingShip/transverseMercator/releases or checkout the latest code:

  git clone https://github.com/RockingShip/transverseMercator.git

Versioning

Using SemVer for versioning. For the versions available, see the tags on this repository.

License

This project is licensed under the ISC - see the LICENSE-ISC.txt file for details.

The GeographicLib library is MIT/X11 and compatible with this project.

Acknowledgments

• Charles Karney and his amazing work on his GeographicLib library.