proj4/lib/projections/ortho.js

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

var adjust_lon = require('../common/adjust_lon');
var EPSLN = 1.0e-10;
var asinz = require('../common/asinz');
var HALF_PI = Math.PI/2;
exports.init = function() {
  //double temp;      /* temporary variable    */

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


/* Orthographic forward equations--mapping lat,long to x,y
    ---------------------------------------------------*/
exports.forward = function(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);

  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 + this.a * ksp * (this.cos_p14 * sinphi - this.sin_p14 * cosphi * coslon);
  }
  p.x = x;
  p.y = y;
  return p;
};


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

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

  lon = this.long0;
  if (Math.abs(rh) <= EPSLN) {
    lat = this.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(this.lat0) - HALF_PI;
  if (Math.abs(con) <= EPSLN) {
    if (this.lat0 >= 0) {
      lon = adjust_lon(this.long0 + Math.atan2(p.x, - p.y));
    }
    else {
      lon = adjust_lon(this.long0 - Math.atan2(-p.x, p.y));
    }
    p.x = lon;
    p.y = lat;
    return p;
  }
  lon = adjust_lon(this.long0 + Math.atan2((p.x * sinz), rh * this.cos_p14 * cosz - p.y * this.sin_p14 * sinz));
  p.x = lon;
  p.y = lat;
  return p;
};
exports.names = ["ortho"];