@flumens/bigu/src/CILatLng.js

British Isles GridRef Utils

import OSCIRef from 'OSCIRef';
import OSGB36LatLng from 'OSGB36LatLng';
import { deg2rad } from 'constants';

/**
 * represents lat lng as INT24 (CI grid projection)
 *
 * @constructor
 * @param {number} lat
 * @param {number} lng
 */
let CILatLng = function(lat, lng) {
  this.lat = lat;
  this.lng = lng;
};

/**
 * converts lat and lon to CI northings and eastings
 *
 * @returns OSCIRef
 */
CILatLng.prototype.to_os_coords = function() {
  //var deg2rad = Math.PI / 180;
  //var rad2deg = 180.0 / Math.PI;

  var phi = this.lat * deg2rad; // convert latitude to radians
  var lam = this.lng * deg2rad; // convert longitude to radians
  var a = 6378388.000;      // OSI semi-major
  var b = 6356911.946;      // OSI semi-minor
  var e0 = 500000;          // OSI easting of false origin
  var n0 = 0;          // OSI northing of false origin
  var f0 = 0.9996;        // OSI scale factor on central meridian
  var e2 = 0.0067226700223333;   // OSI eccentricity squared
  var lam0 = -0.0523598775598;   // OSI false east
  var phi0 = 0;    // OSI false north
  var af0 = a * f0;
  var bf0 = b * f0;

  // easting
  var slat2 = Math.sin(phi) * Math.sin(phi);
  var nu = af0 / (Math.sqrt(1 - (e2 * (slat2))));
  var rho = (nu * (1 - e2)) / (1 - (e2 * slat2));
  var eta2 = (nu / rho) - 1;
  var p = lam - lam0;
  var IV = nu * Math.cos(phi);
  var clat3 = Math.pow(Math.cos(phi), 3);
  var tlat2 = Math.tan(phi) * Math.tan(phi);
  var V = (nu / 6) * clat3 * ((nu / rho) - tlat2);
  var clat5 = Math.pow(Math.cos(phi), 5);
  var tlat4 = Math.pow(Math.tan(phi), 4);
  var VI = (nu / 120) * clat5 * ((5 - (18 * tlat2)) + tlat4 + (14 * eta2) - (58 * tlat2 * eta2));
  var east = e0 + (p * IV) + (Math.pow(p, 3) * V) + (Math.pow(p, 5) * VI);

  // northing
  var n = (af0 - bf0) / (af0 + bf0);
  var M = OSGB36LatLng._Marc(bf0, n, phi0, phi);
  var I = M + (n0);
  var II = (nu / 2) * Math.sin(phi) * Math.cos(phi);
  var III = ((nu / 24) * Math.sin(phi) * Math.pow(Math.cos(phi), 3)) * (5 - Math.pow(Math.tan(phi), 2) + (9 * eta2));
  var IIIA = ((nu / 720) * Math.sin(phi) * clat5) * (61 - (58 * tlat2) + tlat4);
  var north = I + ((p * p) * II) + (Math.pow(p, 4) * III) + (Math.pow(p, 6) * IIIA);

  //return {x: Math.round(east), y: Math.round(north)};
  return new OSCIRef(Math.round(east), Math.round(north));
};

export default CILatLng;