/*******************************************************************************
NAME                            MOLLWEIDE

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

PROGRAMMER              DATE
----------              ----
D. Steinwand, EROS      May, 1991;  Updated Sept, 1992; Updated Feb, 1993
S. Nelson, EROS		Nov, 1993;  fixed infinite loop at poles

ALGORITHM REFERENCES

1.  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.

2.  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.
*******************************************************************************/
#include "gctpc/cproj.h"
#include "gctpc/report.h"

/* Variables common to all subroutines in this code file
  -----------------------------------------------------*/
static double lon_center;	/* Center longitude (projection center) */
static double R;		/* Radius of the earth (sphere) */
static double false_easting;	/* x offset in meters			*/
static double false_northing;	/* y offset in meters			*/

/* Initialize the Mollweide projection
  ------------------------------------*/
long
molwinvint(double r, double center_long, double false_east, double false_north) 
          			/* (I) Radius of the earth (sphere) */
                   		/* (I) Center longitude */
                  		/* x offset in meters			*/
                   		/* y offset in meters			*/
{
/* Place parameters in static storage for common use
  -------------------------------------------------*/
false_easting = false_east;
false_northing = false_north;
R = r;
lon_center = center_long;

/* Report parameters to the user
  -----------------------------*/
ptitle("MOLLWEIDE"); 
radius(r);
cenlon(center_long);
offsetp(false_easting,false_northing);
return(OK);
}

/* Mollweide inverse equations--mapping x,y to lat,long 
  ----------------------------------------------------*/
long
molwinv(double x, double y, double *lon, double *lat)
         		/* (I) X projection coordinate */
         		/* (I) Y projection coordinate */
            		/* (O) Longitude */
            		/* (O) Latitude */
{
double adjust_lon(double x);    /* Function to adjust longitude to -180 - 180 */
double theta;
double arg;

/* Inverse equations
  -----------------*/
x -= false_easting;
y -= false_northing;
arg = y /  (1.4142135623731 * R);

/* Because of division by zero problems, 'arg' can not be 1.0.  Therefore
   a number very close to one is used instead.
   -------------------------------------------------------------------*/
if(fabs(arg) > 0.999999999999) arg=0.999999999999;
theta = asin(arg);
*lon = adjust_lon(lon_center + (x / (0.900316316158 * R * cos(theta))));
if(*lon < (-PI)) *lon= -PI;
if(*lon > PI) *lon= PI;
arg = (2.0 * theta + sin(2.0 * theta)) / PI;
if(fabs(arg) > 1.0)arg=1.0;
*lat = asin(arg);
return(OK);
}
