tguyou.c - plan9port - [fork] Plan 9 from user space
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       tguyou.c (1754B)
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            1 #include <u.h>
            2 #include <libc.h>
            3 #include "map.h"
            4 
            5 static struct place gywhem, gyehem;
            6 static struct coord gytwist;
            7 static double gyconst, gykc, gyside;
            8 
            9 
           10 static void
           11 dosquare(double z1, double z2, double *x, double *y)
           12 {
           13         double w1,w2;
           14         w1 = z1 -1;
           15         if(fabs(w1*w1+z2*z2)>.000001) {
           16                 cdiv(z1+1,z2,w1,z2,&w1,&w2);
           17                 w1 *= gyconst;
           18                 w2 *= gyconst;
           19                 if(w1<0)
           20                         w1 = 0;
           21                 elco2(w1,w2,gykc,1.,1.,x,y);
           22         } else {
           23                 *x = gyside;
           24                 *y = 0;
           25         }
           26 }
           27 
           28 int
           29 Xguyou(struct place *place, double *x, double *y)
           30 {
           31         int ew;                /*which hemisphere*/
           32         double z1,z2;
           33         struct place pl;
           34         ew = place->wlon.l<0;
           35         copyplace(place,&pl);
           36         norm(&pl,ew?&gyehem:&gywhem,&gytwist);
           37         Xstereographic(&pl,&z1,&z2);
           38         dosquare(z1/2,z2/2,x,y);
           39         if(!ew)
           40                 *x -= gyside;
           41         return(1);
           42 }
           43 
           44 proj
           45 guyou(void)
           46 {
           47         double junk;
           48         gykc = 1/(3+2*sqrt(2.));
           49         gyconst = -(1+sqrt(2.));
           50         elco2(-gyconst,0.,gykc,1.,1.,&gyside,&junk);
           51         gyside *= 2;
           52         latlon(0.,90.,&gywhem);
           53         latlon(0.,-90.,&gyehem);
           54         deg2rad(0.,&gytwist);
           55         return(Xguyou);
           56 }
           57 
           58 int
           59 guycut(struct place *g, struct place *og, double *cutlon)
           60 {
           61         int c;
           62         c = picut(g,og,cutlon);
           63         if(c!=1)
           64                 return(c);
           65         *cutlon = 0.;
           66         if(g->nlat.c<.7071||og->nlat.c<.7071)
           67                 return(ckcut(g,og,0.));
           68         return(1);
           69 }
           70 
           71 static int
           72 Xsquare(struct place *place, double *x, double *y)
           73 {
           74         double z1,z2;
           75         double r, theta;
           76         struct place p;
           77         copyplace(place,&p);
           78         if(place->nlat.l<0) {
           79                 p.nlat.l = -p.nlat.l;
           80                 p.nlat.s = -p.nlat.s;
           81         }
           82         if(p.nlat.l<FUZZ && fabs(p.wlon.l)>PI-FUZZ){
           83                 *y = -gyside/2;
           84                 *x = p.wlon.l>0?0:gyside;
           85                 return(1);
           86         }
           87         Xstereographic(&p,&z1,&z2);
           88         r = sqrt(sqrt(hypot(z1,z2)/2));
           89         theta = atan2(z1,-z2)/4;
           90         dosquare(r*sin(theta),-r*cos(theta),x,y);
           91         if(place->nlat.l<0)
           92                 *y = -gyside - *y;
           93         return(1);
           94 }
           95 
           96 proj
           97 square(void)
           98 {
           99         guyou();
          100         return(Xsquare);
          101 }