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C: Unrolled the truncated IAU2000B formula.

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Don Cross committed 2022-12-04 20:56:15 -05:00
1 parent b8c0a1f0cc
commit b9738d9661
3 files changed
+68 -70
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generate/template/astronomy.c
+32 -26
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@@ -1292,39 +1292,45 @@ astro_observer_t Astronomy_MakeObserver(double latitude, double longitude, doubl
static void iau2000b(astro_time_t *time)
{
/* Adapted from the NOVAS C 3.1 function of the same name. */
struct row_t
{
int nals[5];
double cls[6];
};
static const struct row_t row[] =
{
$ASTRO_IAU_DATA()
};
double t, elp, f, d, om, arg, dp, de, sarg, carg;
int i;
/* Truncated and hand-optimized nutation model. */
if (isnan(time->psi))
{
t = time->tt / 36525;
double t, elp, f, d, om, arg, dp, de, sarg, carg;
t = time->tt / 36525.0;
elp = fmod(1287104.79305 + t * 129596581.0481, ASEC360) * ASEC2RAD;
f = fmod(335779.526232 + t * 1739527262.8478, ASEC360) * ASEC2RAD;
d = fmod(1072260.70369 + t * 1602961601.2090, ASEC360) * ASEC2RAD;
om = fmod(450160.398036 - t * 6962890.5431, ASEC360) * ASEC2RAD;
dp = 0;
de = 0;
for (i=sizeof(row)/sizeof(row[0]) - 1; i >= 0; --i)
{
arg = fmod((row[i].nals[1]*elp + row[i].nals[2]*f + row[i].nals[3]*d + row[i].nals[4]*om), PI2);
sarg = sin(arg);
carg = cos(arg);
dp += (row[i].cls[0] + row[i].cls[1]*t) * sarg + row[i].cls[2]*carg;
de += (row[i].cls[3] + row[i].cls[4]*t) * carg + row[i].cls[5]*sarg;
}
sarg = sin(om);
carg = cos(om);
dp = (-172064161.0 - 174666.0*t)*sarg + 33386.0*carg;
de = (92052331.0 + 9086.0*t)*carg + 15377.0*sarg;
arg = 2.0*(f - d + om);
sarg = sin(arg);
carg = cos(arg);
dp += (-13170906.0 - 1675.0*t)*sarg - 13696.0*carg;
de += (5730336.0 - 3015.0*t)*carg - 4587.0*sarg;
arg = 2.0*(f + om);
sarg = sin(arg);
carg = cos(arg);
dp += (-2276413.0 - 234.0*t)*sarg + 2796.0*carg;
de += (978459.0 - 485.0*t)*carg + 1374.0*sarg;
arg = 2.0*om;
sarg = sin(arg);
carg = cos(arg);
dp += (2074554.0 + 207.0*t)*sarg - 698.0*carg;
de += (-897492.0 + 470.0*t)*carg - 291.0*sarg;
sarg = sin(elp);
carg = cos(elp);
dp += (1475877.0 - 3633.0*t)*sarg + 11817.0*carg;
de += (73871.0 - 184.0*t)*carg - 1924.0*sarg;
time->psi = -0.000135 + (dp * 1.0e-7);
time->eps = +0.000388 + (de * 1.0e-7);