dbrockman / earth-radius-at-geodetic-latitude

Estimate the Earth radius at given latitude

earth-radius-at-geodetic-latitude

Estimate the Earth radius at given latitude

Install

$ npm install --save earth-radius-at-geodetic-latitude

Usage

const earthRadiusAtGeodeticLatitude = require('earth-radius-at-geodetic-latitude');

const latitudeNewYork = 40.730610;
earthRadiusAtGeodeticLatitude(latitudeNewYork);
//=> 6377880.978308504

const latitudeNewOrleans = 30.0154753;
earthRadiusAtGeodeticLatitude(latitudeNewOrleans);
//=> 6357371.8965936005

This function is based on the equation discussed on this GIS Stack Exchange thread and this wikipedia entry on Geocentric Earth radius:

The equation:

R = ( (a^2 cos(f))^2 + (b^2 sin(f))^2 ) / ( (a cos(f))^2 + (b sin(f))^2 )

where f is the latitude and a and b are the equatorial radius and the polar radius, respectively.

API

earthRadiusAtGeodeticLatitude(latitude)

Takes latitude (number) and returns an estimate of the Earth radius at that given latitude.

The radius is in meters.