proj4/lib/projections/ortho.js

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

import adjust_lon from '../common/adjust_lon';
import asinz from '../common/asinz';
import { EPSLN, HALF_PI } from '../constants/values';

/**
 * @typedef {Object} LocalThis
 * @property {number} sin_p14
 * @property {number} cos_p14
 */

/** @this {import('../defs.js').ProjectionDefinition & LocalThis} */
export function init() {
  // double temp;      /* temporary variable    */

  /* Place parameters in static storage for common use
      ------------------------------------------------- */
  this.sin_p14 = Math.sin(this.lat0 || 0);
  this.cos_p14 = Math.cos(this.lat0 || 0);
}

/* Orthographic forward equations--mapping lat,long to x,y
    --------------------------------------------------- */
export function forward(p) {
  var sinphi, cosphi; /* sin and cos value        */
  var dlon; /* delta longitude value      */
  var coslon; /* cos of longitude        */
  var ksp; /* scale factor          */
  var g, x, y;
  var lon = p.x;
  var lat = p.y;
  /* Forward equations
      ----------------- */
  dlon = adjust_lon(lon - (this.long0 || 0), this.over);

  sinphi = Math.sin(lat);
  cosphi = Math.cos(lat);

  coslon = Math.cos(dlon);
  g = this.sin_p14 * sinphi + this.cos_p14 * cosphi * coslon;
  ksp = 1;
  if ((g > 0) || (Math.abs(g) <= EPSLN)) {
    x = this.a * ksp * cosphi * Math.sin(dlon);
    y = (this.y0 || 0) + this.a * ksp * (this.cos_p14 * sinphi - this.sin_p14 * cosphi * coslon);
  }
  p.x = x;
  p.y = y;
  return p;
}

export function inverse(p) {
  var rh; /* height above ellipsoid      */
  var z; /* angle          */
  var sinz, cosz; /* sin of z and cos of z      */
  var con;
  var lon, lat;
  var long0, lat0;
  /* Inverse equations
      ----------------- */
  p.x -= this.x0 || 0;
  p.y -= this.y0 || 0;
  rh = Math.sqrt(p.x * p.x + p.y * p.y);
  z = asinz(rh / this.a);

  sinz = Math.sin(z);
  cosz = Math.cos(z);

  long0 = this.long0 || 0;
  lat0 = this.lat0 || 0;
  lon = long0;
  if (Math.abs(rh) <= EPSLN) {
    lat = lat0;
    p.x = lon;
    p.y = lat;
    return p;
  }
  lat = asinz(cosz * this.sin_p14 + (p.y * sinz * this.cos_p14) / rh);
  con = Math.abs(lat0) - HALF_PI;
  if (Math.abs(con) <= EPSLN) {
    if (lat0 >= 0) {
      lon = adjust_lon(long0 + Math.atan2(p.x, -p.y), this.over);
    } else {
      lon = adjust_lon(long0 - Math.atan2(-p.x, p.y), this.over);
    }
    p.x = lon;
    p.y = lat;
    return p;
  }
  lon = adjust_lon(long0 + Math.atan2((p.x * sinz), rh * this.cos_p14 * cosz - p.y * this.sin_p14 * sinz), this.over);
  p.x = lon;
  p.y = lat;
  return p;
}

export var names = ['ortho'];
export default {
  init: init,
  forward: forward,
  inverse: inverse,
  names: names
};