xref: /plan9-contrib/sys/src/cmd/map/libmap/trapezoidal.c (revision 219b2ee8daee37f4aad58d63f21287faa8e4ffdc)
1 #include "map.h"
2 
3 static struct coord stdpar0, stdpar1;
4 static double k;
5 static double yeq;
6 
7 static int
8 Xtrapezoidal(struct place *place, double *x, double *y)
9 {
10 	*y = yeq + place->nlat.l;
11 	*x = *y*k*place->wlon.l;
12 	return 1;
13 }
14 
15 proj
16 trapezoidal(double par0, double par1)
17 {
18 	if(fabs(fabs(par0)-fabs(par1))<.1)
19 		return rectangular(par0);
20 	deg2rad(par0,&stdpar0);
21 	deg2rad(par1,&stdpar1);
22 	if(fabs(par1-par0) < .1)
23 		k = stdpar1.s;
24 	else
25 		k = (stdpar1.c-stdpar0.c)/(stdpar0.l-stdpar1.l);
26 	yeq = -stdpar1.l - stdpar1.c/k;
27 	return Xtrapezoidal;
28 }
29