blob: 583a7c7dd6bafa659ec4fad09313ecbf200ba776 [file] [log] [blame]
 #include #include #include #include "sky.h" /* * dec varies from -89 to 89, inclusive. * ra varies depending on dec; each patch is about 1 square degree. * * Northern hemisphere (0<=dec<=89): * from 0<=dec<=59, ra is every 4m, 360 values * from 60<=dec<=69, ra is every 8m, 180 values * from 70<=dec<=79, ra is every 12m, 120 values * from 80<=dec<=84, ra is every 24m, 60 values * at dec=85 and 86, ra is every 48m, 30 values * at dec=87, ra is every 60m, 24 values * at dec=88, ra is every 120m, 12 values * at dec=89, ra is 12h, 1 value * * Total number of patches in northern hemisphere is therefore: * 360*60+180*10+120*10+60*5+30*2+24*1+12*1+1 = 24997 * Total number of patches is therefore * 2*24997-360 = 49634 (dec=0 has been counted twice) * (cf. 41253 square degrees in the sky) */ void radec(int p, int *rah, int *ram, int *deg) { *deg = (p&255)-90; p >>= 8; *rah = p/15; *ram = (p%15)*4; if(*deg<0) (*deg)++; } int32 patcha(Angle ra, Angle dec) { ra = DEG(ra); dec = DEG(dec); if(dec >= 0) return patch(floor(ra/15), ((int)floor(ra*4))%60, floor(dec)); dec = -dec; return patch(floor(ra/15), ((int)floor(ra*4))%60, -floor(dec)); } #define round scatround char round[91]={ /* extra 0 is to offset the array */ /* 0 */ 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 10 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 20 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 30 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 40 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 50 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* 60 */ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, /* 70 */ 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, /* 80 */ 6, 6, 6, 6, 6, 12, 12, 15, 30, -1, /* 90 */ }; int32 patch(int rah, int ram, int deg) { int ra, dec; /* * patches go from lower limit <= position < upper limit. * therefore dec ' " can be ignored; always inc. dec degrees. * the computed angle is then the upper limit (ignoring sign). * when done, +ve values are shifted down so 90 (0 degrees) is a value; */ if(rah<0 || rah>=24 || ram<0 || abs(deg)>=90){ fprint(2, "scat: patch: bad ra or dec %dh%dm %d\n", rah, ram, deg); abort(); } if(deg < 0) deg--; else if(deg < 90) deg++; dec = deg+90; deg = abs(deg); if(deg<1 || deg>90){ fprint(2, "scat: patch: panic %dh%dm %d\n", rah, ram, deg); abort(); } if(deg == 90) ra = 180; else{ ra = 15*rah+ram/4; ra -= ra%round[deg]; } /* close the hole at 0 */ if(dec > 90) --dec; if(ra >= 360) ra -= 360; return (ra<<8)|dec; }