1 #include <u.h>
2 #include <libc.h>
3 #include <bio.h>
4 #include "sky.h"
5
6 /*
7 * dec varies from -89 to 89, inclusive.
8 * ra varies depending on dec; each patch is about 1 square degree.
9 *
10 * Northern hemisphere (0<=dec<=89):
11 * from 0<=dec<=59, ra is every 4m, 360 values
12 * from 60<=dec<=69, ra is every 8m, 180 values
13 * from 70<=dec<=79, ra is every 12m, 120 values
14 * from 80<=dec<=84, ra is every 24m, 60 values
15 * at dec=85 and 86, ra is every 48m, 30 values
16 * at dec=87, ra is every 60m, 24 values
17 * at dec=88, ra is every 120m, 12 values
18 * at dec=89, ra is 12h, 1 value
19 *
20 * Total number of patches in northern hemisphere is therefore:
21 * 360*60+180*10+120*10+60*5+30*2+24*1+12*1+1 = 24997
22 * Total number of patches is therefore
23 * 2*24997-360 = 49634 (dec=0 has been counted twice)
24 * (cf. 41253 square degrees in the sky)
25 */
26
27 void
radec(int p,int * rah,int * ram,int * deg)28 radec(int p, int *rah, int *ram, int *deg)
29 {
30 *deg = (p&255)-90;
31 p >>= 8;
32 *rah = p/15;
33 *ram = (p%15)*4;
34 if(*deg<0)
35 (*deg)++;
36 }
37
38 int32
patcha(Angle ra,Angle dec)39 patcha(Angle ra, Angle dec)
40 {
41 ra = DEG(ra);
42 dec = DEG(dec);
43 if(dec >= 0)
44 return patch(floor(ra/15), ((int)floor(ra*4))%60, floor(dec));
45 dec = -dec;
46 return patch(floor(ra/15), ((int)floor(ra*4))%60, -floor(dec));
47 }
48
49 #define round scatround
50
51 char round[91]={ /* extra 0 is to offset the array */
52 /* 0 */ 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
53 /* 10 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
54 /* 20 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
55 /* 30 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
56 /* 40 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
57 /* 50 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
58 /* 60 */ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
59 /* 70 */ 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
60 /* 80 */ 6, 6, 6, 6, 6, 12, 12, 15, 30, -1,
61 /* 90 */
62 };
63
64 int32
patch(int rah,int ram,int deg)65 patch(int rah, int ram, int deg)
66 {
67 int ra, dec;
68
69 /*
70 * patches go from lower limit <= position < upper limit.
71 * therefore dec ' " can be ignored; always inc. dec degrees.
72 * the computed angle is then the upper limit (ignoring sign).
73 * when done, +ve values are shifted down so 90 (0 degrees) is a value;
74 */
75 if(rah<0 || rah>=24 || ram<0 || abs(deg)>=90){
76 fprint(2, "scat: patch: bad ra or dec %dh%dm %d\n", rah, ram, deg);
77 abort();
78 }
79 if(deg < 0)
80 deg--;
81 else if(deg < 90)
82 deg++;
83 dec = deg+90;
84 deg = abs(deg);
85 if(deg<1 || deg>90){
86 fprint(2, "scat: patch: panic %dh%dm %d\n", rah, ram, deg);
87 abort();
88 }
89 if(deg == 90)
90 ra = 180;
91 else{
92 ra = 15*rah+ram/4;
93 ra -= ra%round[deg];
94 }
95 /* close the hole at 0 */
96 if(dec > 90)
97 --dec;
98 if(ra >= 360)
99 ra -= 360;
100 return (ra<<8)|dec;
101 }
102