proj4/lib/projections/lcc.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 tsfnz from '../common/tsfnz';
import sign from '../common/sign';
import adjust_lon from '../common/adjust_lon';
import phi2z from '../common/phi2z';
import { HALF_PI, EPSLN } from '../constants/values';

/**
 * @typedef {Object} LocalThis
 * @property {number} e
 * @property {number} ns
 * @property {number} f0
 * @property {number} rh
 */

/** @this {import('../defs.js').ProjectionDefinition & LocalThis} */
export function init() {
  // double lat0;                    /* the reference latitude               */
  // double long0;                   /* the reference longitude              */
  // double lat1;                    /* first standard parallel              */
  // double lat2;                    /* second standard parallel             */
  // double r_maj;                   /* major axis                           */
  // double r_min;                   /* minor axis                           */
  // double false_east;              /* x offset in meters                   */
  // double false_north;             /* y offset in meters                   */

  // the above value can be set with proj4.defs
  // example: proj4.defs("EPSG:2154","+proj=lcc +lat_1=49 +lat_2=44 +lat_0=46.5 +lon_0=3 +x_0=700000 +y_0=6600000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs");

  if (!this.lat2) {
    this.lat2 = this.lat1;
  } // if lat2 is not defined
  if (!this.k0) {
    this.k0 = 1;
  }
  this.x0 = this.x0 || 0;
  this.y0 = this.y0 || 0;
  // Standard Parallels cannot be equal and on opposite sides of the equator
  if (Math.abs(this.lat1 + this.lat2) < EPSLN) {
    return;
  }

  var temp = this.b / this.a;
  this.e = Math.sqrt(1 - temp * temp);

  var sin1 = Math.sin(this.lat1);
  var cos1 = Math.cos(this.lat1);
  var ms1 = msfnz(this.e, sin1, cos1);
  var ts1 = tsfnz(this.e, this.lat1, sin1);

  var sin2 = Math.sin(this.lat2);
  var cos2 = Math.cos(this.lat2);
  var ms2 = msfnz(this.e, sin2, cos2);
  var ts2 = tsfnz(this.e, this.lat2, sin2);

  var ts0 = Math.abs(Math.abs(this.lat0) - HALF_PI) < EPSLN
    ? 0 // Handle poles by setting ts0 to 0
    : tsfnz(this.e, this.lat0, Math.sin(this.lat0));

  if (Math.abs(this.lat1 - this.lat2) > EPSLN) {
    this.ns = Math.log(ms1 / ms2) / Math.log(ts1 / ts2);
  } else {
    this.ns = sin1;
  }
  if (isNaN(this.ns)) {
    this.ns = sin1;
  }
  this.f0 = ms1 / (this.ns * Math.pow(ts1, this.ns));
  this.rh = this.a * this.f0 * Math.pow(ts0, this.ns);
  if (!this.title) {
    this.title = 'Lambert Conformal Conic';
  }
}

// Lambert Conformal conic forward equations--mapping lat,long to x,y
// -----------------------------------------------------------------
export function forward(p) {
  var lon = p.x;
  var lat = p.y;

  // singular cases :
  if (Math.abs(2 * Math.abs(lat) - Math.PI) <= EPSLN) {
    lat = sign(lat) * (HALF_PI - 2 * EPSLN);
  }

  var con = Math.abs(Math.abs(lat) - HALF_PI);
  var ts, rh1;
  if (con > EPSLN) {
    ts = tsfnz(this.e, lat, Math.sin(lat));
    rh1 = this.a * this.f0 * Math.pow(ts, this.ns);
  } else {
    con = lat * this.ns;
    if (con <= 0) {
      return null;
    }
    rh1 = 0;
  }
  var theta = this.ns * adjust_lon(lon - this.long0, this.over);
  p.x = this.k0 * (rh1 * Math.sin(theta)) + this.x0;
  p.y = this.k0 * (this.rh - rh1 * Math.cos(theta)) + this.y0;

  return p;
}

// Lambert Conformal Conic inverse equations--mapping x,y to lat/long
// -----------------------------------------------------------------
export function inverse(p) {
  var rh1, con, ts;
  var lat, lon;
  var x = (p.x - this.x0) / this.k0;
  var y = (this.rh - (p.y - this.y0) / this.k0);
  if (this.ns > 0) {
    rh1 = Math.sqrt(x * x + y * y);
    con = 1;
  } else {
    rh1 = -Math.sqrt(x * x + y * y);
    con = -1;
  }
  var theta = 0;
  if (rh1 !== 0) {
    theta = Math.atan2((con * x), (con * y));
  }
  if ((rh1 !== 0) || (this.ns > 0)) {
    con = 1 / this.ns;
    ts = Math.pow((rh1 / (this.a * this.f0)), con);
    lat = phi2z(this.e, ts);
    if (lat === -9999) {
      return null;
    }
  } else {
    lat = -HALF_PI;
  }
  lon = adjust_lon(theta / this.ns + this.long0, this.over);

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

export var names = [
  'Lambert Tangential Conformal Conic Projection',
  'Lambert_Conformal_Conic',
  'Lambert_Conformal_Conic_1SP',
  'Lambert_Conformal_Conic_2SP',
  'lcc',
  'Lambert Conic Conformal (1SP)',
  'Lambert Conic Conformal (2SP)'
];

export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names
};