proj4/lib/common/invlatiso.js

Proj4js is a JavaScript library to transform point coordinates from one coordinate system to another, including datum transformations.

var fL = require('./fL');

module.exports = function(eccent, ts) {
  var phi = fL(1, ts);
  var Iphi = 0;
  var con = 0;
  do {
    Iphi = phi;
    con = eccent * Math.sin(Iphi);
    phi = fL(Math.exp(eccent * Math.log((1 + con) / (1 - con)) / 2), ts);
  } while (Math.abs(phi - Iphi) > 1.0e-12);
  return phi;
};