1 cd5bae78 2004-04-21 devnull #include "astro.h"
8 cd5bae78 2004-04-21 devnull * uses alpha, delta, rp
12 cd5bae78 2004-04-21 devnull * sets ra, decl, lha, decl2, az, el
16 cd5bae78 2004-04-21 devnull * geo converts geocentric equatorial coordinates
17 cd5bae78 2004-04-21 devnull * to topocentric equatorial and topocentric horizon
18 cd5bae78 2004-04-21 devnull * coordinates.
19 cd5bae78 2004-04-21 devnull * All are (usually) referred to the true equator.
22 cd5bae78 2004-04-21 devnull double sel, saz, caz;
23 cd5bae78 2004-04-21 devnull double f;
24 cd5bae78 2004-04-21 devnull double sa, ca, sd;
27 cd5bae78 2004-04-21 devnull * convert to local hour angle and declination
30 cd5bae78 2004-04-21 devnull lha = gst - alpha - wlong;
31 cd5bae78 2004-04-21 devnull decl = delta;
34 cd5bae78 2004-04-21 devnull * compute diurnal parallax (requires geocentric latitude)
37 cd5bae78 2004-04-21 devnull sa = cos(decl)*sin(lha);
38 cd5bae78 2004-04-21 devnull ca = cos(decl)*cos(lha) - erad*cos(glat)*sin(hp);
39 cd5bae78 2004-04-21 devnull sd = sin(decl) - erad*sin(glat)*sin(hp);
41 cd5bae78 2004-04-21 devnull lha = atan2(sa, ca);
42 cd5bae78 2004-04-21 devnull decl2 = atan2(sd, sqrt(sa*sa+ca*ca));
43 cd5bae78 2004-04-21 devnull f = sqrt(sa*sa+ca*ca+sd*sd);
44 cd5bae78 2004-04-21 devnull semi2 = semi/f;
45 cd5bae78 2004-04-21 devnull ra = gst - lha - wlong;
46 cd5bae78 2004-04-21 devnull ra = pinorm(ra);
49 cd5bae78 2004-04-21 devnull * convert to horizon coordinates
52 cd5bae78 2004-04-21 devnull sel = sin(nlat)*sin(decl2) + cos(nlat)*cos(decl2)*cos(lha);
53 cd5bae78 2004-04-21 devnull el = atan2(sel, pyth(sel));
54 cd5bae78 2004-04-21 devnull saz = sin(lha)*cos(decl2);
55 cd5bae78 2004-04-21 devnull caz = cos(nlat)*sin(decl2) - sin(nlat)*cos(decl2)*cos(lha);
56 cd5bae78 2004-04-21 devnull az = pi + atan2(saz, -caz);
58 cd5bae78 2004-04-21 devnull az /= radian;
59 cd5bae78 2004-04-21 devnull el /= radian;