get_lat_lon.c

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#include "prototypes.h"
 
void get_lat_lon(int newx,int newy,float *lat,float *lon)
 
{
 
extern struct dval dval;
double conv=.0174,c,lonf;
double t1,t2,t3,t4,t5,lat1,lat2;
 
t1=.0001;
 
lonf= atan(((double)newy-dval.yo)/(t1))/conv-90.;
 
t1=(double)newx-dval.xo;
 
*lon= atan(((double)newy-dval.yo)/(t1))/conv;
 
if(*lon > 0)
          *lon=-180+*lon-2*lonf;
 
*lon=*lon+90+dval.lo;
 
c=dval.a*cos((*lon-dval.lo-90)*conv)/((double)newx-dval.xo);
c=pow(c,2);
 
t1=1/(1+c);
t2=1-c;
t3=pow(2*t1,2);
t4=4*t2*t1;
t5=pow(t3-t4,.5)/2;
 
if(fabs(-t1+t5) > 1.0)
          lat1=-9999;
else
          lat1=asin(-t1+t5)/conv;
 
if(fabs(-t1-t5) > 1.0)
          lat2=-9999;
else
          lat2=asin(-t1-t5)/conv;
 
if(lat1 > 0 && lat1 < 90)
                 *lat=lat1;
 
else
                 *lat=lat2;
 
return;
 
}