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/* lunar2.cpp: functions for modest-precision lunar coords
Copyright (C) 2010, Project Pluto
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA. */
/* Implements a simplified lunar ephemeris via the method described
in Meeus' _Astronomical Algorithms_. The actual series coefficients
are stored in 'vsop.bin', which must be read into a buffer before
you call these functions. At the time I wrote all this -- early
1990s -- memory was a scarce resource, so I packed bytes as much
as possible. I suppose all this would still be a good idea on some
embedded systems. It's probably not the way I would do things now.
The code is not easy to follow. But it _does_ all work, and runs
fast and has a small footprint.
NOTE that this will fail on big-Endian machines, and on some
little-Endians that require byte alignment. Let me know if you have
such a machine. The fix is simple, but I'm reluctant to try it
without a means of verifying that it works. */
#include <math.h>
#include <stdlib.h>
#include <stdint.h>
#include "watdefs.h"
#include "lunar.h"
#include "get_bin.h"
#define Lp fund[0]
#define D fund[1]
#define M fund[2]
#define Mp fund[3]
#define F fund[4]
#define A1 fund[5]
#define A2 fund[6]
#define A3 fund[7]
#define T fund[8]
#define N_TERM1 60
#define TERM1 struct term1
/* 28 Jul 2011: modified these structures so they're packed (they
are read from disk files) and that 32-bit ints are specified.
Obviously, they'll still break on non-Intel order hardware. */
#pragma pack( 1)
TERM1
{
char d, m, mp, f;
int32_t sl, sr;
};
#pragma pack( )
#define N_TERM2 60
#define TERM2 struct term2
#pragma pack( 1)
TERM2
{
char d, m, mp, f;
int32_t sb;
};
#pragma pack( )
#define PI 3.1415926535897932384626433832795028841971693993751058209749445923
#define CVT (PI / 180.)
int DLL_FUNC lunar_fundamentals( const void FAR *data, const double t,
double DLLPTR *fund)
{
int i, j;
const double FAR *tptr = (const double FAR *)((const char FAR *)data + 60554U);
double tpow;
for( i = 0; i < 5; i++)
{
fund[i] = get_double( tptr);
tptr++;
tpow = t;
for( j = 4; j; j--, tpow *= t, tptr++)
fund[i] += tpow * get_double( tptr);
}
A1 = 119.75 + 131.849 * t;
A2 = 53.09 + 479264.290 * t;
A3 = 313.45 + 481266.484 * t;
T = t;
for( i = 0; i < N_FUND - 1; i++) /* convert to radians */
{
fund[i] = fmod( fund[i], 360.);
if( fund[i] < 0.) fund[i] += 360.;
fund[i] *= CVT;
}
return( 0);
}
int DLL_FUNC lunar_lon_and_dist( const void FAR *data, const double DLLPTR *fund,
double DLLPTR *lon, double DLLPTR *r, const long precision)
{
int i, j;
const TERM1 FAR *tptr = (const TERM1 FAR *)((const char FAR *)data + 59354U);
double sl = 0., sr = 0., e;
e = 1. - .002516 * T - .0000074 * T * T;
for( i = N_TERM1; i; i--, tptr++)
if( labs( tptr->sl) > precision || labs( tptr->sr) > precision)
{
double arg, term;
switch( tptr->d)
{
case 1: arg = D; break;
case -1: arg =-D; break;
case 2: arg = D+D; break;
case -2: arg =-D-D; break;
case 0: arg = 0.; break;
default: arg = (double)tptr->d * D; break;
}
switch( tptr->m)
{
case 1: arg += M; break;
case -1: arg -= M; break;
case 2: arg += M+M; break;
case -2: arg -= M+M; break;
case 0: ; break;
default: arg += (double)tptr->m * M; break;
}
switch( tptr->mp)
{
case 1: arg += Mp; break;
case -1: arg -= Mp; break;
case 2: arg += Mp+Mp; break;
case -2: arg -= Mp+Mp; break;
case 0: ; break;
default: arg += (double)tptr->mp * Mp; break;
}
switch( tptr->f)
{
case 1: arg += F; break;
case -1: arg -= F; break;
case 2: arg += F+F; break;
case -2: arg -= F+F; break;
case 0: ; break;
default: arg += (double)tptr->f * F; break;
}
if( tptr->sl)
{
term = (double)tptr->sl * sin( arg);
for( j = abs( tptr->m); j; j--)
term *= e;
sl += term;
}
if( tptr->sr)
{
term = (double)tptr->sr * cos( arg);
for( j = abs( tptr->m); j; j--)
term *= e;
sr += term;
}
}
if( precision < 3959L)
sl += 3958. * sin( A1) + 1962. * sin( Lp - F) + 318. * sin( A2);
*lon = (Lp * 180. / PI) + sl * 1.e-6;
while( *lon < 0.)
*lon += 360.;
while( *lon > 360.)
*lon -= 360.;
*r = 385000.56 + sr / 1000.;
return( 0);
}
double DLL_FUNC lunar_lat( const void FAR *data, const double DLLPTR *fund,
const long precision)
{
int i, j;
const TERM2 FAR *tptr;
const TERM2 FAR *term2 = (const TERM2 FAR *)((const char FAR *)data + 60074U);
double rval = 0., e;
tptr = term2;
e = 1. - .002516 * T - .0000074 * T * T;
for( i = N_TERM2; i; i--, tptr++)
if( labs( tptr->sb) > precision)
{
double arg, term;
switch( tptr->d)
{
case 1: arg = D; break;
case -1: arg =-D; break;
case 2: arg = D+D; break;
case -2: arg =-D-D; break;
case 0: arg = 0.; break;
default: arg = (double)tptr->d * D; break;
}
switch( tptr->m)
{
case 1: arg += M; break;
case -1: arg -= M; break;
case 2: arg += M+M; break;
case -2: arg -= M+M; break;
case 0: ; break;
default: arg += (double)tptr->m * M; break;
}
switch( tptr->mp)
{
case 1: arg += Mp; break;
case -1: arg -= Mp; break;
case 2: arg += Mp+Mp; break;
case -2: arg -= Mp+Mp; break;
case 0: ; break;
default: arg += (double)tptr->mp * Mp; break;
}
switch( tptr->f)
{
case 1: arg += F; break;
case -1: arg -= F; break;
case 2: arg += F+F; break;
case -2: arg -= F+F; break;
case 0: ; break;
default: arg += (double)tptr->f * F; break;
}
term = (double)tptr->sb * sin( arg);
for( j = abs( tptr->m); j; j--)
term *= e;
rval += term;
}
if( precision < 2236L)
rval += -2235. * sin( Lp) + 382. * sin( A3) + 175. * sin( A1 - F) +
175. * sin( A1 + F) + 127. * sin(Lp - Mp) - 115. * sin(Lp+Mp);
return( rval * 1.e-6);
}
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