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#include <u.h>
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#include <libc.h>
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#include <bio.h>
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#include "sky.h"
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/*
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* dec varies from -89 to 89, inclusive.
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* ra varies depending on dec; each patch is about 1 square degree.
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*
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* Northern hemisphere (0<=dec<=89):
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* from 0<=dec<=59, ra is every 4m, 360 values
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* from 60<=dec<=69, ra is every 8m, 180 values
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* from 70<=dec<=79, ra is every 12m, 120 values
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* from 80<=dec<=84, ra is every 24m, 60 values
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* at dec=85 and 86, ra is every 48m, 30 values
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* at dec=87, ra is every 60m, 24 values
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* at dec=88, ra is every 120m, 12 values
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* at dec=89, ra is 12h, 1 value
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*
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* Total number of patches in northern hemisphere is therefore:
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* 360*60+180*10+120*10+60*5+30*2+24*1+12*1+1 = 24997
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* Total number of patches is therefore
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* 2*24997-360 = 49634 (dec=0 has been counted twice)
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* (cf. 41253 square degrees in the sky)
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*/
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void
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radec(int p, int *rah, int *ram, int *deg)
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{
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*deg = (p&255)-90;
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p >>= 8;
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*rah = p/15;
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*ram = (p%15)*4;
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if(*deg<0)
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(*deg)++;
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}
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long
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patcha(Angle ra, Angle dec)
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{
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ra = DEG(ra);
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dec = DEG(dec);
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if(dec >= 0)
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return patch(floor(ra/15), ((int)floor(ra*4))%60, floor(dec));
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dec = -dec;
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return patch(floor(ra/15), ((int)floor(ra*4))%60, -floor(dec));
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}
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char round[91]={ /* extra 0 is to offset the array */
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/* 0 */ 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 10 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 20 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 30 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 40 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 50 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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/* 60 */ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
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/* 70 */ 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
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/* 80 */ 6, 6, 6, 6, 6, 12, 12, 15, 30, -1,
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/* 90 */
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};
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long
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patch(int rah, int ram, int deg)
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{
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int ra, dec;
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/*
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* patches go from lower limit <= position < upper limit.
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* therefore dec ' " can be ignored; always inc. dec degrees.
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* the computed angle is then the upper limit (ignoring sign).
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* when done, +ve values are shifted down so 90 (0 degrees) is a value;
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*/
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if(rah<0 || rah>=24 || ram<0 || abs(deg)>=90){
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fprint(2, "scat: patch: bad ra or dec %dh%dm %d\n", rah, ram, deg);
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abort();
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}
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if(deg < 0)
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deg--;
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else if(deg < 90)
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deg++;
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dec = deg+90;
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deg = abs(deg);
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if(deg<1 || deg>90){
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fprint(2, "scat: patch: panic %dh%dm %d\n", rah, ram, deg);
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abort();
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}
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if(deg == 90)
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ra = 180;
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else{
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ra = 15*rah+ram/4;
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ra -= ra%round[deg];
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}
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/* close the hole at 0 */
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if(dec > 90)
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--dec;
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if(ra >= 360)
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ra -= 360;
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return (ra<<8)|dec;
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}
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