plan9port

fork of plan9port with libvec, libstr and libsdb
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gall.c (512B)

      1 #include <u.h>
      2 #include <libc.h>
      3 #include "map.h"
      4 
      5 static double scale;
      6 
      7 static int
      8 Xgall(struct place *place, double *x, double *y)
      9 {
     10 	/* two ways to compute tan(place->nlat.l/2) */
     11 	if(fabs(place->nlat.s)<.1)
     12 		*y = sin(place->nlat.l/2)/cos(place->nlat.l/2);
     13 	else
     14 		*y = (1-place->nlat.c)/place->nlat.s;
     15 	*x = -scale*place->wlon.l;
     16 	return 1;
     17 }
     18 
     19 proj
     20 gall(double par)
     21 {
     22 	double coshalf;
     23 	if(fabs(par)>80)
     24 		return 0;
     25 	par *= RAD;
     26 	coshalf = cos(par/2);
     27 	scale = cos(par)/(2*coshalf*coshalf);
     28 	return Xgall;
     29 }