ref: 5030157da9e89da53739b13c36942a5355de669f
dir: /sys/src/cmd/scat/patch.c/
#include <u.h>
#include <libc.h>
#include <bio.h>
#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)++;
}
long
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));
}
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 */
};
long
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;
}