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XEphem/GUI/xephem/xe3.c

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/* Fetch the desired region of xe3-formatted catalog stars.
*
* xe3 is a very compact format storing just ra/dec/mag/class for each star.
* Each star occupies 3 bytes and stores RA to a precision of +/- .38 arcsecs,
* Dec to .44 arcsec, Mag in the range 10..20 to .16 and 1 class bit set to 0
* for star or 1 for other. One xe3 file stores all stars in a band of
* declination one degree hi, beginning on an integral dec boundary. Thus 180
* xe3 files are required to cover the entire sky.
*
* The overall file structure is an initial line of ASCII giving file type and
* the base declination, followed by a table of 360 records indexed by RA in
* whole degs giving the file offset and starting RA into the star records
* for that RA, followed by any number of star records sorted by increasing RA.
* Each star record occupies 3 bytes and stores the dec offset from the base
* dec of the band, the RA offset from the RA of the previous record, the mag
* and the class.
*
* The file starts with 8 ASCII chars including a final newline in the format
* "xe3 HDD\n", where H is 'N' for north hemishere else 'S'. DD is the base
* of the dec band, zero filled whole degrees. Dec offsets in the star
* records are added to the base dec if H is 'N' else subtracted from base.
*
* Following the header is a table of 360 records each 8 bytes long. The array
* is indexed by RA in whole degrees. Each index record contains a file offset
* in bytes from the front of the file to the first star record with an RA
* greater than or equal to the index RA value, and the RA of said star. Each
* of these values is 4 bytes stored big-endian.
*
* Following the index table are star records sorted in increasing RA. Each star
* record is 3 bytes. The bits are packed as follows (stored bigendian):
* 0.. 5 rabits
* 6..17 decbits
* 18..22 magbits
* 23 star
* then
* ra = (rasum + rabits+.5)*RAPBIT/cos(decband)
* dec = (north ? decband + (decbits+.5) : decband - (decbits+.5))*DECPBIT
* mag = BRMAG + (magbits + .5)*MAGPBIT
* starlike if star else really a star
* where decband is the integer from the ASCII header line, rasum is an unsigned
* int to accumulate the rabits values (initialized at the start of a sweep
* from the index table entry) and dec and ra are in degrees (so beware if
* your cos() expects rads).
*/
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include "xephem.h"
#define MAXGSC22FOV degrad(5) /* max FOV to fetch */
/* packing in each record */
#define DECBITS 12 /* dec stored in 12 bits */
#define DECHI 1.0 /* height of dec band, degrees */
#define DECPBIT (DECHI/(1<<DECBITS)) /* dec degs per bit */
#define DECMASK ((1<<DECBITS)-1) /* dec mask */
#define RABITS 6 /* delta ra stored in 6 bits */
#define MAXDRA (49.0/3600.0) /* max delta RA from one to next, degs*/
#define RAPBIT (MAXDRA/(1<<RABITS)) /* ra delta degrees per bit */
#define RAMASK ((1<<RABITS)-1) /* ra mask */
#define MAGBITS 5 /* mag stored in 5 bits */
#define BRMAG 10.0 /* brightest mag we encode */
#define DIMMAG 22.0 /* dimmest mag we encode */
#define DELMAG (DIMMAG-BRMAG) /* mag range */
#define MAGPBIT (DELMAG/(1<<MAGBITS)) /* mags per bit within range */
#define MAGMASK ((1<<MAGBITS)-1) /* mag mask */
#define HDRLEN 8 /* bytes in ASCII header line */
#define BPIDX 8 /* bytes per index entry */
/* room for one star packet */
#define XE3PKTSZ 3 /* bytes per packet - DO NOT CHANGE */
typedef unsigned char UC;
typedef unsigned long UL;
typedef UC PKT[XE3PKTSZ];
/* an array of ObjF which can be grown efficiently in multiples of NINC */
typedef struct {
ObjF *mem; /* malloced array */
int max; /* max number of cells in mem[] or -1 to just count */
int used; /* number actually in use */
} ObjFArray;
#define NINC 32 /* grow mem array this many at a time */
static FILE *xe3open (char *dir, int north, int db, char fn[], char msg[]);
static int addDec (ObjFArray *ofap, char *dir, double mag, int dec, double dmin,
double dmax, double rmin, double rmax, char *msg);
static int addOneObjF (ObjFArray *ap, Obj *op);
static void unpack (unsigned *rasump, double cdb, int db, PKT pkt,
Obj *op);
static void mkxe3name (char *dir, Obj *op);
/* return 0 if dir looks like it contains some xe3 files, else -1
*/
int
xe3chkdir (char *dir, char *msg)
{
char fn[1024];
FILE *fp;
fp = xe3open (dir, 1, 0, fn, msg);
if (!fp)
return (-1);
fclose (fp);
return (0);
}
/* add a collection of XE3 stars around the given location at *opp, which already contains
* nop entries. if trouble fill msg[] and return -1, else return count.
* N.B. *opp is only changed if we return > 0.
*/
int
xe3fetch (char *dir, double ra, double dec, double fov, double mag,
ObjF **opp, int nop, char *msg)
{
int topd, botd, d;
double dmin, dmax;
double rov;
ObjFArray ofa;
int s = 0;
/* bug if not given a place to save new stars */
if (!opp) {
printf ("xe3fetch with opp == NULL\n");
abort();
}
/* enforce limit */
if (fov > MAXGSC22FOV) {
static int fovwarned;
if (!fovwarned) {
xe_msg (1, "All XE3 catalog requests will be limited to %.2f degree FOV", raddeg(MAXGSC22FOV));
fovwarned = 1;
}
fov = MAXGSC22FOV;
}
/* switch everything to degrees */
ra = raddeg(ra);
dec = raddeg(dec);
rov = raddeg(fov/2);
/* find top and bottom dec limits, in degrees */
dmin = dec - rov;
dmax = dec + rov;
botd = (int)floor(dmin);
topd = (int)floor(dmax);
/* init ofa */
ofa.mem = *opp;
ofa.max = nop;
ofa.used = nop;
/* read across ra range for each dec band, beware 360 wrap */
for (d = botd; d <= topd; d++) {
double rovdec = d==90||d==-90 ? 180 : rov/cos(degrad(d));
double rmin = ra - rovdec, rmax = ra + rovdec;
int db = d;
if (d < -90) {
db = -181-d;
rmin = 0;
rmax = 360;
} else if (d > 89) {
db = 179-d;
rmin = 0;
rmax = 360;
} else if (rmin < 0) {
s = addDec (&ofa, dir, mag, db, dmin, dmax, rmin+360, 360, msg);
if (s < 0)
break;
rmin = 0;
} else if (rmax > 360) {
s = addDec (&ofa, dir, mag, db, dmin, dmax, 0.0, rmax-360, msg);
if (s < 0)
break;
rmax = 360;
}
s = addDec (&ofa, dir, mag, db, dmin, dmax, rmin, rmax, msg);
if (s < 0)
break;
}
/* finished */
if (s < 0) {
if (ofa.mem)
free (ofa.mem);
return (-1);
}
if (ofa.mem)
*opp = ofa.mem;
return (ofa.used);
}
/* add stars for dec band [-90..89] from dmin..dmax rmin..rmax to ofap.
* all units in degrees.
* if ok return 0 else -1 with reason in msg[].
* dec is floor of band, ie, -90 .. 89.
*/
static int
addDec (ObjFArray *ofap, char *dir, double mag, int dec, double dmin,
double dmax, double rmin, double rmax, char *msg)
{
int north = dec >= 0;
int db = north ? dec : dec+1;
double cdb = cos(degrad(db));
int rabase = (int)floor(rmin);
char fn[1024];
unsigned rasum, offset;
UC idx[BPIDX];
PKT pkt;
FILE *fp;
Obj o;
/*
fprintf (stderr, "addDec %g .. %g %g .. %g\n", rmin, rmax, dmin, dmax);
*/
/* open file */
fp = xe3open (dir, north, db, fn, msg);
if (!fp)
return (-1);
/* read index */
if (fseek (fp, HDRLEN + rabase*BPIDX, SEEK_SET) < 0) {
sprintf (msg, "%s:\nindex is short", fn);
fclose (fp);
return (-1);
}
if (fread (idx, BPIDX, 1, fp) != 1) {
sprintf (msg, "%s:\nindex entry is short", fn);
fclose (fp);
return (-1);
}
offset = (idx[0] << 24) | (idx[1] << 16) | (idx[2] << 8) | idx[3];
rasum = (idx[4] << 24) | (idx[5] << 16) | (idx[6] << 8) | idx[7];
/* move to first ra packet */
if (fseek (fp, offset, SEEK_SET) < 0) {
sprintf (msg, "%s:\npacket list is short", fn);
fclose (fp);
return (-1);
}
/* scan to rmax, work in rads */
dmin = degrad(dmin);
dmax = degrad(dmax);
rmin = degrad(rmin);
rmax = degrad(rmax);
while (1) {
if (fread (pkt, sizeof(pkt), 1, fp) != 1) {
if (feof(fp))
break;
sprintf (msg, "%s:\n%s", fn, syserrstr());
fclose (fp);
return (-1);
}
unpack (&rasum, cdb, dec, pkt, &o);
if (o.f_RA > rmax)
break;
if (get_fmag(&o) <= mag && o.f_RA >= rmin && dmin <= o.f_dec &&
o.f_dec <= dmax) {
mkxe3name (dir, &o);
if (addOneObjF (ofap, &o) < 0) {
sprintf (msg, "not enough memory after %d objects",
ofap->used);
fclose (fp);
return (-1);
}
}
}
/* ok */
fclose(fp);
return (0);
}
/* unpack the raw PKT into Obj *op.
* dec is -90..89
*/
static void
unpack (unsigned *rasump, double cdb, int dec, PKT pkt, Obj *op)
{
unsigned v = (pkt[0] << 16) | (pkt[1] << 8) | pkt[2];
unsigned radelta = (v&RAMASK);
double decoffset = (((v>>RABITS)&DECMASK) + 0.5)*DECPBIT;
double mag = (((v>>(RABITS+DECBITS))&MAGMASK) + 0.5)*MAGPBIT + BRMAG;
int isother = (v >> (RABITS+DECBITS+MAGBITS));
double ra = (*rasump + radelta + 0.5)*RAPBIT/cdb;
double dc = dec<0 ? dec+1-decoffset : dec+decoffset;
*rasump += radelta;
zero_mem ((void *)op, sizeof(ObjF));
op->o_type = FIXED;
op->f_class = isother ? 'T' : 'S';
op->f_RA = (float)degrad(ra);
op->f_dec = (float)degrad(dc);
op->f_epoch = (float)J2000;
set_fmag (op, mag);
}
/* make up a name from the f_RA/dec fields of the given object */
static void
mkxe3name (char *dir, Obj *op)
{
char rstr[32], dstr[32];
char *cat;
/* get RA and dec as fixed-length strings */
fs_sexa (rstr, radhr(op->f_RA), 2, 36000);
if (rstr[0] == ' ') rstr[0] = '0';
rstr[2] = rstr[3];
rstr[3] = rstr[4];
rstr[4] = rstr[6];
rstr[5] = rstr[7];
rstr[6] = rstr[9];
rstr[7] = '\0';
fs_sexa (dstr, raddeg(op->f_dec), 3, 3600);
if (dstr[1] == ' ') { dstr[0] = '+'; dstr[1] = '0'; }
if (dstr[1] == '-') { dstr[0] = '-'; dstr[1] = '0'; }
if (dstr[0] == ' ') dstr[0] = '+';
dstr[3] = dstr[4];
dstr[4] = dstr[5];
dstr[5] = dstr[7];
dstr[6] = dstr[8];
dstr[7] = '\0';
/* use as much as possible of basename as catalog name */
if ((cat = strrchr(dir,'/')) || (cat = strrchr(dir,'\\')))
cat++; /* skip the / */
else
cat = dir;
sprintf (op->o_name, "%.*s %s%s", MAXNM-(7+7+2), cat, rstr, dstr);
}
/* add one ObjF entry to ap[], growing if necessary.
* return 0 if ok else return -1
*/
static int
addOneObjF (ObjFArray *ap, Obj *op)
{
ObjF *newf;
if (ap->used >= ap->max) {
/* add room for NINC more */
char *newmem = ap->mem ? realloc ((void *)ap->mem,
(ap->max+NINC)*sizeof(ObjF))
: malloc (NINC*sizeof(ObjF));
if (!newmem)
return (-1);
ap->mem = (ObjF *)newmem;
ap->max += NINC;
}
newf = &ap->mem[ap->used++];
(void) memcpy ((void *)newf, (void *)op, sizeof(ObjF));
return (0);
}
/* open the given xe3 file.
* if ok return name and FILE * else return NULL with reason in msg[]
* north is 1 for dec floors 0..89, 0 for dec floors -90..-1.
* db is dec band as used in xe3 file, ie, rounded towards 0, ie, -89..89.
*/
static FILE *
xe3open (char *dir, int north, int db, char fn[], char msg[])
{
char nschar = north ? 'N' : 'S';
char header[HDRLEN+1];
FILE *fp;
char myns;
int mydb;
/* want abs band in file name and header */
db = abs(db);
/* open and check header */
sprintf (fn, "%s/%c%02d.xe3", dir, nschar, db);
fp = fopenh (fn, "rb");
if (!fp) {
(void) sprintf (msg, "%s:\n%s", fn, syserrstr());
return (NULL);
}
if (fread (header, HDRLEN, 1, fp) != 1) {
sprintf (msg, "%s:\nno header: %s", fn, syserrstr());
fclose (fp);
return(NULL);
}
header[HDRLEN-1] = '\0';
if (sscanf (header, "xe3 %c%2d", &myns, &mydb) != 2
|| myns != nschar || mydb != db) {
sprintf (msg, "%s:\nnot an XE3 file", fn);
fclose (fp);
return(NULL);
}
/* ok */
return (fp);
}
#ifdef MAIN_TEST
/* stand alone dump a region of xe3 to stdout.
* cc -o xe3 -DMAIN_TEST -Ilibastro -Ilibip -Llibastro xe3.c -lastro -lm
*/
#include <errno.h>
int
main (int ac, char *av[])
{
ObjF *ofp = NULL;
char msg[1024];
double ra, dec, fov;
char *dir;
int n;
if (ac != 5) {
fprintf (stderr, "usage: %s xe3dir ra dec fov (all degs)\n", av[0]);
return(1);
}
dir = av[1];
ra = degrad(atof(av[2]));
dec = degrad(atof(av[3]));
fov = degrad(atof(av[4]));
n = xe3fetch (dir, ra, dec, fov, 100.0, &ofp, msg);
if (n < 0) {
fprintf (stderr, "%s\n", msg);
exit(1);
}
while (n) {
db_write_line ((Obj *)&ofp[--n], msg);
printf ("%s\n", msg);
}
return (0);
}
char *
syserrstr ()
{
return (strerror(errno));
}
FILE *
fopenh (char *name, char *how)
{
return (fopen (name, how));
}
#endif
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