proj4/lib/projections/merc.js

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

import msfnz from '../common/msfnz';

import adjust_lon from '../common/adjust_lon';
import tsfnz from '../common/tsfnz';
import phi2z from '../common/phi2z';
import { FORTPI, R2D, EPSLN, HALF_PI } from '../constants/values';

/**
 * @typedef {Object} LocalThis
 * @property {number} es
 * @property {number} e
 * @property {number} k
 */

/** @this {import('../defs.js').ProjectionDefinition & LocalThis} */
export function init() {
  var con = this.b / this.a;
  this.es = 1 - con * con;
  if (!('x0' in this)) {
    this.x0 = 0;
  }
  if (!('y0' in this)) {
    this.y0 = 0;
  }
  this.e = Math.sqrt(this.es);
  if (this.lat_ts) {
    if (this.sphere) {
      this.k0 = Math.cos(this.lat_ts);
    } else {
      this.k0 = msfnz(this.e, Math.sin(this.lat_ts), Math.cos(this.lat_ts));
    }
  } else {
    if (!this.k0) {
      if (this.k) {
        this.k0 = this.k;
      } else {
        this.k0 = 1;
      }
    }
  }
}

/* Mercator forward equations--mapping lat,long to x,y
  -------------------------------------------------- */

export function forward(p) {
  var lon = p.x;
  var lat = p.y;
  // convert to radians
  if (lat * R2D > 90 && lat * R2D < -90 && lon * R2D > 180 && lon * R2D < -180) {
    return null;
  }

  var x, y;
  if (Math.abs(Math.abs(lat) - HALF_PI) <= EPSLN) {
    return null;
  } else {
    if (this.sphere) {
      x = this.x0 + this.a * this.k0 * adjust_lon(lon - this.long0, this.over);
      y = this.y0 + this.a * this.k0 * Math.log(Math.tan(FORTPI + 0.5 * lat));
    } else {
      var sinphi = Math.sin(lat);
      var ts = tsfnz(this.e, lat, sinphi);
      x = this.x0 + this.a * this.k0 * adjust_lon(lon - this.long0, this.over);
      y = this.y0 - this.a * this.k0 * Math.log(ts);
    }
    p.x = x;
    p.y = y;
    return p;
  }
}

/* Mercator inverse equations--mapping x,y to lat/long
  -------------------------------------------------- */
export function inverse(p) {
  var x = p.x - this.x0;
  var y = p.y - this.y0;
  var lon, lat;

  if (this.sphere) {
    lat = HALF_PI - 2 * Math.atan(Math.exp(-y / (this.a * this.k0)));
  } else {
    var ts = Math.exp(-y / (this.a * this.k0));
    lat = phi2z(this.e, ts);
    if (lat === -9999) {
      return null;
    }
  }
  lon = adjust_lon(this.long0 + x / (this.a * this.k0), this.over);

  p.x = lon;
  p.y = lat;
  return p;
}

export var names = ['Mercator', 'Popular Visualisation Pseudo Mercator', 'Mercator_1SP', 'Mercator_Auxiliary_Sphere', 'Mercator_Variant_A', 'merc'];
export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names
};