ref: 88ccea37f65b87312292b2b1a107c39927c6a2c3
dir: /sys/src/cmd/map/libmap/gall.c/
#include <u.h> #include <libc.h> #include "map.h" static double scale; static int Xgall(struct place *place, double *x, double *y) { /* two ways to compute tan(place->nlat.l/2) */ if(fabs(place->nlat.s)<.1) *y = sin(place->nlat.l/2)/cos(place->nlat.l/2); else *y = (1-place->nlat.c)/place->nlat.s; *x = -scale*place->wlon.l; return 1; } proj gall(double par) { double coshalf; if(fabs(par)>80) return 0; par *= RAD; coshalf = cos(par/2); scale = cos(par)/(2*coshalf*coshalf); return Xgall; }