tethys-feature-service/node_modules/proj4/lib/projections/aea.js

import msfnz from '../common/msfnz';
import qsfnz from '../common/qsfnz';
import adjust_lon from '../common/adjust_lon';
import asinz from '../common/asinz';
import {EPSLN} from '../constants/values';

export function init() {

  if (Math.abs(this.lat1 + this.lat2) < EPSLN) {
    return;
  }
  this.temp = this.b / this.a;
  this.es = 1 - Math.pow(this.temp, 2);
  this.e3 = Math.sqrt(this.es);

  this.sin_po = Math.sin(this.lat1);
  this.cos_po = Math.cos(this.lat1);
  this.t1 = this.sin_po;
  this.con = this.sin_po;
  this.ms1 = msfnz(this.e3, this.sin_po, this.cos_po);
  this.qs1 = qsfnz(this.e3, this.sin_po);

  this.sin_po = Math.sin(this.lat2);
  this.cos_po = Math.cos(this.lat2);
  this.t2 = this.sin_po;
  this.ms2 = msfnz(this.e3, this.sin_po, this.cos_po);
  this.qs2 = qsfnz(this.e3, this.sin_po);

  this.sin_po = Math.sin(this.lat0);
  this.cos_po = Math.cos(this.lat0);
  this.t3 = this.sin_po;
  this.qs0 = qsfnz(this.e3, this.sin_po);

  if (Math.abs(this.lat1 - this.lat2) > EPSLN) {
    this.ns0 = (this.ms1 * this.ms1 - this.ms2 * this.ms2) / (this.qs2 - this.qs1);
  }
  else {
    this.ns0 = this.con;
  }
  this.c = this.ms1 * this.ms1 + this.ns0 * this.qs1;
  this.rh = this.a * Math.sqrt(this.c - this.ns0 * this.qs0) / this.ns0;
}

/* Albers Conical Equal Area forward equations--mapping lat,long to x,y
  -------------------------------------------------------------------*/
export function forward(p) {

  var lon = p.x;
  var lat = p.y;

  this.sin_phi = Math.sin(lat);
  this.cos_phi = Math.cos(lat);

  var qs = qsfnz(this.e3, this.sin_phi);
  var rh1 = this.a * Math.sqrt(this.c - this.ns0 * qs) / this.ns0;
  var theta = this.ns0 * adjust_lon(lon - this.long0);
  var x = rh1 * Math.sin(theta) + this.x0;
  var y = this.rh - rh1 * Math.cos(theta) + this.y0;

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

export function inverse(p) {
  var rh1, qs, con, theta, lon, lat;

  p.x -= this.x0;
  p.y = this.rh - p.y + this.y0;
  if (this.ns0 >= 0) {
    rh1 = Math.sqrt(p.x * p.x + p.y * p.y);
    con = 1;
  }
  else {
    rh1 = -Math.sqrt(p.x * p.x + p.y * p.y);
    con = -1;
  }
  theta = 0;
  if (rh1 !== 0) {
    theta = Math.atan2(con * p.x, con * p.y);
  }
  con = rh1 * this.ns0 / this.a;
  if (this.sphere) {
    lat = Math.asin((this.c - con * con) / (2 * this.ns0));
  }
  else {
    qs = (this.c - con * con) / this.ns0;
    lat = this.phi1z(this.e3, qs);
  }

  lon = adjust_lon(theta / this.ns0 + this.long0);
  p.x = lon;
  p.y = lat;
  return p;
}

/* Function to compute phi1, the latitude for the inverse of the
   Albers Conical Equal-Area projection.
-------------------------------------------*/
export function phi1z(eccent, qs) {
  var sinphi, cosphi, con, com, dphi;
  var phi = asinz(0.5 * qs);
  if (eccent < EPSLN) {
    return phi;
  }

  var eccnts = eccent * eccent;
  for (var i = 1; i <= 25; i++) {
    sinphi = Math.sin(phi);
    cosphi = Math.cos(phi);
    con = eccent * sinphi;
    com = 1 - con * con;
    dphi = 0.5 * com * com / cosphi * (qs / (1 - eccnts) - sinphi / com + 0.5 / eccent * Math.log((1 - con) / (1 + con)));
    phi = phi + dphi;
    if (Math.abs(dphi) <= 1e-7) {
      return phi;
    }
  }
  return null;
}

export var names = ["Albers_Conic_Equal_Area", "Albers", "aea"];
export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names,
  phi1z: phi1z
};