proj4/lib/projections/sterea.js

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

import gauss from './gauss';
import adjust_lon from '../common/adjust_lon';
import hypot from '../common/hypot';

/**
 * @typedef {Object} LocalThis
 * @property {number} sinc0
 * @property {number} cosc0
 * @property {number} R2
 * @property {number} rc
 * @property {number} phic0
 */

/** @this {import('../defs.js').ProjectionDefinition & LocalThis} */
export function init() {
  gauss.init.apply(this);
  if (!this.rc) {
    return;
  }
  this.sinc0 = Math.sin(this.phic0);
  this.cosc0 = Math.cos(this.phic0);
  this.R2 = 2 * this.rc;
  if (!this.title) {
    this.title = 'Oblique Stereographic Alternative';
  }
}

export function forward(p) {
  var sinc, cosc, cosl, k;
  p.x = adjust_lon(p.x - this.long0, this.over);
  gauss.forward.apply(this, [p]);
  sinc = Math.sin(p.y);
  cosc = Math.cos(p.y);
  cosl = Math.cos(p.x);
  k = this.k0 * this.R2 / (1 + this.sinc0 * sinc + this.cosc0 * cosc * cosl);
  p.x = k * cosc * Math.sin(p.x);
  p.y = k * (this.cosc0 * sinc - this.sinc0 * cosc * cosl);
  p.x = this.a * p.x + this.x0;
  p.y = this.a * p.y + this.y0;
  return p;
}

export function inverse(p) {
  var sinc, cosc, lon, lat, rho;
  p.x = (p.x - this.x0) / this.a;
  p.y = (p.y - this.y0) / this.a;

  p.x /= this.k0;
  p.y /= this.k0;
  if ((rho = hypot(p.x, p.y))) {
    var c = 2 * Math.atan2(rho, this.R2);
    sinc = Math.sin(c);
    cosc = Math.cos(c);
    lat = Math.asin(cosc * this.sinc0 + p.y * sinc * this.cosc0 / rho);
    lon = Math.atan2(p.x * sinc, rho * this.cosc0 * cosc - p.y * this.sinc0 * sinc);
  } else {
    lat = this.phic0;
    lon = 0;
  }

  p.x = lon;
  p.y = lat;
  gauss.inverse.apply(this, [p]);
  p.x = adjust_lon(p.x + this.long0, this.over);
  return p;
}

export var names = ['Stereographic_North_Pole', 'Oblique_Stereographic', 'sterea', 'Oblique Stereographic Alternative', 'Double_Stereographic'];
export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names
};