ref: 75f5332c9dce891845e57b188efad28d7530d8ae
dir: /sys/src/cmd/map/libmap/guyou.c/
#include <u.h> #include <libc.h> #include "map.h" static struct place gywhem, gyehem; static struct coord gytwist; static double gyconst, gykc, gyside; static void dosquare(double z1, double z2, double *x, double *y) { double w1,w2; w1 = z1 -1; if(fabs(w1*w1+z2*z2)>.000001) { cdiv(z1+1,z2,w1,z2,&w1,&w2); w1 *= gyconst; w2 *= gyconst; if(w1<0) w1 = 0; elco2(w1,w2,gykc,1.,1.,x,y); } else { *x = gyside; *y = 0; } } int Xguyou(struct place *place, double *x, double *y) { int ew; /*which hemisphere*/ double z1,z2; struct place pl; ew = place->wlon.l<0; copyplace(place,&pl); norm(&pl,ew?&gyehem:&gywhem,&gytwist); Xstereographic(&pl,&z1,&z2); dosquare(z1/2,z2/2,x,y); if(!ew) *x -= gyside; return(1); } proj guyou(void) { double junk; gykc = 1/(3+2*sqrt(2.)); gyconst = -(1+sqrt(2.)); elco2(-gyconst,0.,gykc,1.,1.,&gyside,&junk); gyside *= 2; latlon(0.,90.,&gywhem); latlon(0.,-90.,&gyehem); deg2rad(0.,&gytwist); return(Xguyou); } int guycut(struct place *g, struct place *og, double *cutlon) { int c; c = picut(g,og,cutlon); if(c!=1) return(c); *cutlon = 0.; if(g->nlat.c<.7071||og->nlat.c<.7071) return(ckcut(g,og,0.)); return(1); } static int Xsquare(struct place *place, double *x, double *y) { double z1,z2; double r, theta; struct place p; copyplace(place,&p); if(place->nlat.l<0) { p.nlat.l = -p.nlat.l; p.nlat.s = -p.nlat.s; } if(p.nlat.l<FUZZ && fabs(p.wlon.l)>PI-FUZZ){ *y = -gyside/2; *x = p.wlon.l>0?0:gyside; return(1); } Xstereographic(&p,&z1,&z2); r = sqrt(sqrt(hypot(z1,z2)/2)); theta = atan2(z1,-z2)/4; dosquare(r*sin(theta),-r*cos(theta),x,y); if(place->nlat.l<0) *y = -gyside - *y; return(1); } proj square(void) { guyou(); return(Xsquare); }