source: trunk/workshop-routing-foss4g/web/proj4js/lib/projCode/ortho.js @ 76

/*******************************************************************************
NAME                             ORTHOGRAPHIC 

PURPOSE:        Transforms input longitude and latitude to Easting and
                Northing for the Orthographic projection.  The
                longitude and latitude must be in radians.  The Easting
                and Northing values will be returned in meters.

PROGRAMMER              DATE
----------              ----
T. Mittan               Mar, 1993

ALGORITHM REFERENCES

1.  Snyder, John P., "Map Projections--A Working Manual", U.S. Geological
    Survey Professional Paper 1395 (Supersedes USGS Bulletin 1532), United
    State Government Printing Office, Washington D.C., 1987.

2.  Snyder, John P. and Voxland, Philip M., "An Album of Map Projections",
    U.S. Geological Survey Professional Paper 1453 , United State Government
    Printing Office, Washington D.C., 1989.
*******************************************************************************/

Proj4js.Proj.ortho = {

  /* Initialize the Orthographic projection
    -------------------------------------*/
  init: function(def) {
    //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
    ---------------------------------------------------*/
  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;              
    var lon=p.x;
    var lat=p.y;        
    /* Forward equations
      -----------------*/
    dlon = Proj4js.common.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 = 1.0;
    if ((g > 0) || (Math.abs(g) <= Proj4js.common.EPSLN)) {
      var x = this.a * ksp * cosphi * Math.sin(dlon);
      var y = this.y0 + this.a * ksp * (this.cos_p14 * sinphi - this.sin_p14 * cosphi * coslon);
    } else {
      Proj4js.reportError("orthoFwdPointError");
    }
    p.x=x;
    p.y=y;
    return p;
  },


  inverse: function(p) {
    var rh;             /* height above ellipsoid                       */
    var z;              /* angle                                        */
    var sinz,cosz;      /* sin of z and cos of z                        */
    var temp;
    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);
    if (rh > this.a + .0000001) {
      Proj4js.reportError("orthoInvDataError");
    }
    z = Proj4js.common.asinz(rh / this.a);

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

    lon = this.long0;
    if (Math.abs(rh) <= Proj4js.common.EPSLN) {
      lat = this.lat0; 
    }
    lat = Proj4js.common.asinz(cosz * this.sin_p14 + (p.y * sinz * this.cos_p14)/rh);
    con = Math.abs(this.lat0) - Proj4js.common.HALF_PI;
    if (Math.abs(con) <= Proj4js.common.EPSLN) {
       if (this.lat0 >= 0) {
          lon = Proj4js.common.adjust_lon(this.long0 + Math.atan2(p.x, -p.y));
       } else {
          lon = Proj4js.common.adjust_lon(this.long0 -Math.atan2(-p.x, p.y));
       }
    }
    con = cosz - this.sin_p14 * Math.sin(lat);
    p.x=lon;
    p.y=lat;
    return p;
  }
};