source: issm/trunk/src/c/modules/Xy2llx/Xy2llx.cpp@ 8698

/*!\file Xy2llx.cpp
 */

#include "./Xy2llx.h"
#include "../../include/include.h"
#include "../../shared/shared.h"
#include <math.h>

int Xy2llx(double* lat, double* lon, double* x, double* y, int ncoord, int sgn){
/*  This is a cpp conversion of the following:
%XY2LL - converts xy to lat long
%
%   Converts Polar  Stereographic (X,Y) coordinates for the polar regions to
%   latitude and longitude Stereographic (X,Y) coordinates for the polar
%   regions.
%   Author: Michael P. Schodlok, December 2003 (map2xy.m)
%
%   Usage:
%      [lat,lon] = xy2ll(x,y,sgn);
%      [lat,lon] = xy2ll(x,y,sgn,central_meridian,standard_parallel);
%
%      - sgn = Sign of latitude +1 : north latitude (default is mer=45 lat=70)
%                               -1 : south latitude (default is mer=0  lat=71)
*/

        double  delta,slat;
        bool    flag=true;

        /*  Get central_meridian and standard_parallel depending on hemisphere  */
        if (sgn == 1) {
                delta= 45;
                slat = 70;
                _printf_(flag,"Warning: expecting coordinates in polar stereographic (Std Latitude: 70N Meridian: 45).\n");
        }
        else if (sgn == -1) {
                delta= 0;
                slat = 71;
                _printf_(flag,"Warning: expecting coordinates in polar stereographic (Std Latitude: 71S Meridian: 0).\n");
        }
        else _error_("Sign should be either +1 or -1.\n");

        return(Xy2llx(lat,lon,x,y,ncoord,sgn,delta,slat));
}

int Xy2llx(double* lat, double* lon, double* x, double* y, int ncoord, int sgn, double central_meridian, double standard_parallel){
/*  This is a cpp conversion of the following:
%XY2LL - converts xy to lat long
%
%   Converts Polar  Stereographic (X,Y) coordinates for the polar regions to
%   latitude and longitude Stereographic (X,Y) coordinates for the polar
%   regions.
%   Author: Michael P. Schodlok, December 2003 (map2xy.m)
%
%   Usage:
%      [lat,lon] = xy2ll(x,y,sgn);
%      [lat,lon] = xy2ll(x,y,sgn,central_meridian,standard_parallel);
%
%      - sgn = Sign of latitude +1 : north latitude (default is mer=45 lat=70)
%                               -1 : south latitude (default is mer=0  lat=71)
*/

        int     i,iret=0;
        double  delta,slat;
        double  cde,re,ex2,ex,pi;
        double  sl,rho,cm,T,chi;

        if((sgn!=1) && (sgn!=-1)) _error_("Sign should be either +1 or -1.\n");

        delta = central_meridian;
        slat  = standard_parallel;

        /*  Conversion constant from degrees to radians  */
        cde  = 57.29577951;
        /*  Radius of the earth in meters  */
        re   = 6378.273*pow(10.,3.);
        /*  Eccentricity of the Hughes ellipsoid squared  */
        ex2  = 0.006693883;
        /*  Eccentricity of the Hughes ellipsoid  */
        ex   =  sqrt(ex2);

        /*  loop over all the coordinate pairs  */
        for(i=0; i<ncoord; i++){
                sl = slat*PI/180.;
                cm = cos(sl)/sqrt(1.0-ex2*(pow(sin(sl),2.)));
                rho= sqrt(pow(x[i],2.) + pow(y[i],2.));
                T  = tan((PI/4.0) - (sl/2.0))/pow(((1.0-ex*sin(sl))/(1.0+ex*sin(sl))),(ex/2.0));

                if(fabs(slat-90.) < 1.e-5)
                        T =rho*sqrt(pow((1.+ex),(1.+ex))*pow((1.-ex),(1.-ex)))/2./re;
                else
                        T =rho*T/(re*cm);

                chi = (PI / 2.0) - 2.0 * atan(T);
                lat[i] = chi + ((ex2 / 2.0) + (5.0 * pow(ex2,2.0) / 24.0) + (pow(ex2,3.0) / 12.0)) *
                           sin(2.0 * chi) + ((7.0 * pow(ex2,2.0) / 48.0) + (29.0 * pow(ex2,3.0) / 240.0)) *
                           sin(4.0 * chi) + (7.0 * pow(ex2,3.0) / 120.0) * sin(6.0 * chi) ;

                lat[i] = (double)sgn * lat[i];
                lon[i] = atan2((double)sgn * x[i],-(double)sgn * y[i]);
                lon[i] = (double)sgn * lon[i];

                if(rho <= 0.1){
                        lat[i] = 90. * (double)sgn;
                        lon[i] = 0.0;
                        iret=1;
                }

                lon[i] = lon[i] * 180. / pi;
                lat[i] = lat[i] * 180. / pi;
                lon[i] = lon[i] - delta; 
        }

        return(iret);
}