plan9port

fork of plan9port with libvec, libstr and libsdb
Log | Files | Refs | README | LICENSE

elliptic.c (627B)

      1 #include <u.h>
      2 #include <libc.h>
      3 #include "map.h"
      4 
      5 struct coord center;
      6 
      7 static int
      8 Xelliptic(struct place *place, double *x, double *y)
      9 {
     10 	double r1,r2;
     11 	r1 = acos(place->nlat.c*(place->wlon.c*center.c
     12 		- place->wlon.s*center.s));
     13 	r2 = acos(place->nlat.c*(place->wlon.c*center.c
     14 		+ place->wlon.s*center.s));
     15 	*x = -(r1*r1 - r2*r2)/(4*center.l);
     16 	*y = (r1*r1+r2*r2)/2 - (center.l*center.l+*x**x);
     17 	if(*y < 0)
     18 		*y = 0;
     19 	*y = sqrt(*y);
     20 	if(place->nlat.l<0)
     21 		*y = -*y;
     22 	return(1);
     23 }
     24 
     25 proj
     26 elliptic(double l)
     27 {
     28 	l = fabs(l);
     29 	if(l>89)
     30 		return(0);
     31 	if(l<1)
     32 		return(Xazequidistant);
     33 	deg2rad(l,&center);
     34 	return(Xelliptic);
     35 }