1 #include <u.h>
2 #include <libc.h>
3 #include "map.h"
4 
5 #define ORTHRAD 1000
6 static double viewpt;
7 
8 static int
9 Xperspective(struct place *place, double *x, double *y)
10 {
11 	double r;
12 	if(viewpt<=1+FUZZ && fabs(place->nlat.s)<=viewpt+.01)
13 		return(-1);
14 	r = place->nlat.c*(viewpt - 1.)/(viewpt - place->nlat.s);
15 	*x = - r*place->wlon.s;
16 	*y = - r*place->wlon.c;
17 	if(r>4.)
18 		return(-1);
19 	if(fabs(viewpt)>1 && place->nlat.s<1/viewpt ||
20 	   fabs(viewpt)<=1 && place->nlat.s<viewpt)
21 			return 0;
22 	return(1);
23 }
24 
25 proj
26 perspective(double radius)
27 {
28 	viewpt = radius;
29 	if(viewpt >= ORTHRAD)
30 		return(Xorthographic);
31 	if(fabs(viewpt-1.)<.0001)
32 		return(0);
33 	return(Xperspective);
34 }
35 
36 	/* called from various conformal projections,
37            but not from stereographic itself */
38 int
39 Xstereographic(struct place *place, double *x, double *y)
40 {
41 	double v = viewpt;
42 	int retval;
43 	viewpt = -1;
44 	retval = Xperspective(place, x, y);
45 	viewpt = v;
46 	return retval;
47 }
48 
49 proj
50 stereographic(void)
51 {
52 	viewpt = -1.;
53 	return(Xperspective);
54 }
55 
56 proj
57 gnomonic(void)
58 {
59 	viewpt = 0.;
60 	return(Xperspective);
61 }
62 
63 int
64 plimb(double *lat, double *lon, double res)
65 {
66 	static int first = 1;
67 	if(viewpt >= ORTHRAD)
68 		return olimb(lat, lon, res);
69 	if(first) {
70 		first = 0;
71 		*lon = -180;
72 		if(fabs(viewpt) < .01)
73 			*lat = 0;
74 		else if(fabs(viewpt)<=1)
75 			*lat = asin(viewpt)/RAD;
76 		else
77 			*lat = asin(1/viewpt)/RAD;
78 	} else
79 		*lon += res;
80 	if(*lon <= 180)
81 		return 1;
82 	first = 1;
83 	return -1;
84 }