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flightgear/Simulator/Time/moonpos.cxx
curt fcfbba74db Changed contributed by Durk Talsma: 
- Converted struct fgTIME to class FGTime
- Don't draw textured moon/sun halos when --disable-textures requested
1999-04-08 19:53:46 +00:00

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// moonpos.cxx (basically, this is a slightly modified version of the 'sunpos.cxx' file, adapted from XEarth)
// kirk johnson
// july 1993
//
// code for calculating the position on the earth's surface for which
// the moon is directly overhead (adapted from _practical astronomy
// with your calculator, third edition_, peter duffett-smith,
// cambridge university press, 1988.)
//
// Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
//
// Parts of the source code (as marked) are:
// Copyright (C) 1989, 1990, 1991 by Jim Frost
// Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
//
// Permission to use, copy, modify and freely distribute xearth for
// non-commercial and not-for-profit purposes is hereby granted
// without fee, provided that both the above copyright notice and this
// permission notice appear in all copies and in supporting
// documentation.
//
// The author makes no representations about the suitability of this
// software for any purpose. It is provided "as is" without express or
// implied warranty.
//
// THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
// INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
// OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
//
// $Id$
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include "Include/compiler.h"
#ifdef FG_HAVE_STD_INCLUDES
# include <cmath>
# include <cstdio>
# include <ctime>
#else
# include <math.h>
# include <stdio.h>
# include <time.h>
#endif
//#include <Astro/orbits.hxx>
#include <Astro/solarsystem.hxx>
#include <Debug/logstream.hxx>
#include <Include/fg_constants.h>
#include <Main/views.hxx>
#include <Math/fg_geodesy.hxx>
#include <Math/mat3.h>
#include <Math/point3d.hxx>
#include <Math/polar3d.hxx>
#include <Math/vector.hxx>
#include <Scenery/scenery.hxx>
#include "fg_time.hxx"
#include "moonpos.hxx"
extern SolarSystem *solarSystem;
#undef E
/*
* the epoch upon which these astronomical calculations are based is
* 1990 january 0.0, 631065600 seconds since the beginning of the
* "unix epoch" (00:00:00 GMT, Jan. 1, 1970)
*
* given a number of seconds since the start of the unix epoch,
* DaysSinceEpoch() computes the number of days since the start of the
* astronomical epoch (1990 january 0.0)
*/
#define EpochStart (631065600)
#define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600)))
/*
* assuming the apparent orbit of the moon about the earth is circular,
* the rate at which the orbit progresses is given by RadsPerDay --
* FG_2PI radians per orbit divided by 365.242191 days per year:
*/
#define RadsPerDay (FG_2PI/365.242191)
/*
* details of moon's apparent orbit at epoch 1990.0 (after
* duffett-smith, table 6, section 46)
*
* Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees
* OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees
* Eccentricity (eccentricity of orbit) 0.016713
*/
#define Epsilon_g (279.403303*(FG_2PI/360))
#define OmegaBar_g (282.768422*(FG_2PI/360))
#define Eccentricity (0.016713)
/*
* MeanObliquity gives the mean obliquity of the earth's axis at epoch
* 1990.0 (computed as 23.440592 degrees according to the method given
* in duffett-smith, section 27)
*/
#define MeanObliquity (23.440592*(FG_2PI/360))
/* static double solve_keplers_equation(double); */
/* static double moon_ecliptic_longitude(time_t); */
static void ecliptic_to_equatorial(double, double, double *, double *);
static double julian_date(int, int, int);
static double GST(time_t);
/*
* solve Kepler's equation via Newton's method
* (after duffett-smith, section 47)
*/
/*
static double solve_keplers_equation(double M) {
double E;
double delta;
E = M;
while (1) {
delta = E - Eccentricity*sin(E) - M;
if (fabs(delta) <= 1e-10) break;
E -= delta / (1 - Eccentricity*cos(E));
}
return E;
}
*/
/* compute ecliptic longitude of moon (in radians) (after
* duffett-smith, section 47) */
/*
static double moon_ecliptic_longitude(time_t ssue) {
// time_t ssue; // seconds since unix epoch
double D, N;
double M_moon, E;
double v;
D = DaysSinceEpoch(ssue);
N = RadsPerDay * D;
N = fmod(N, FG_2PI);
if (N < 0) N += FG_2PI;
M_moon = N + Epsilon_g - OmegaBar_g;
if (M_moon < 0) M_moon += FG_2PI;
E = solve_keplers_equation(M_moon);
v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2));
return (v + OmegaBar_g);
}
*/
/* convert from ecliptic to equatorial coordinates (after
* duffett-smith, section 27) */
static void ecliptic_to_equatorial(double lambda, double beta,
double *alpha, double *delta) {
/* double lambda; ecliptic longitude */
/* double beta; ecliptic latitude */
/* double *alpha; (return) right ascension */
/* double *delta; (return) declination */
double sin_e, cos_e;
double sin_l, cos_l;
sin_e = sin(MeanObliquity);
cos_e = cos(MeanObliquity);
sin_l = sin(lambda);
cos_l = cos(lambda);
*alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l);
*delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l);
}
/* computing julian dates (assuming gregorian calendar, thus this is
* only valid for dates of 1582 oct 15 or later) (after duffett-smith,
* section 4) */
static double julian_date(int y, int m, int d) {
/* int y; year (e.g. 19xx) */
/* int m; month (jan=1, feb=2, ...) */
/* int d; day of month */
int A, B, C, D;
double JD;
/* lazy test to ensure gregorian calendar */
if (y < 1583) {
FG_LOG( FG_EVENT, FG_ALERT,
"WHOOPS! Julian dates only valid for 1582 oct 15 or later" );
}
if ((m == 1) || (m == 2)) {
y -= 1;
m += 12;
}
A = y / 100;
B = 2 - A + (A / 4);
C = (int)(365.25 * y);
D = (int)(30.6001 * (m + 1));
JD = B + C + D + d + 1720994.5;
return JD;
}
/* compute greenwich mean sidereal time (GST) corresponding to a given
* number of seconds since the unix epoch (after duffett-smith,
* section 12) */
static double GST(time_t ssue) {
/* time_t ssue; seconds since unix epoch */
double JD;
double T, T0;
double UT;
struct tm *tm;
tm = gmtime(&ssue);
JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
T = (JD - 2451545) / 36525;
T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
T0 = fmod(T0, 24.0);
if (T0 < 0) T0 += 24;
UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
T0 += UT * 1.002737909;
T0 = fmod(T0, 24.0);
if (T0 < 0) T0 += 24;
return T0;
}
/* given a particular time (expressed in seconds since the unix
* epoch), compute position on the earth (lat, lon) such that moon is
* directly overhead. (lat, lon are reported in radians */
void fgMoonPosition(time_t ssue, double *lon, double *lat) {
/* time_t ssue; seconds since unix epoch */
/* double *lat; (return) latitude */
/* double *lon; (return) longitude */
/* double lambda; */
double alpha, delta;
double tmp;
/* lambda = moon_ecliptic_longitude(ssue); */
/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
//ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
/* **********************************************************************
* NOTE: in the next function, each time the moon's position is updated, the
* the moon's longitude is returned from solarSystem->moon. Note that the
* moon's position is updated at a much higher frequency than the rate at
* which the solar system's rebuilds occur. This is not a problem, however,
* because the fgMoonPosition we're talking about here concerns the changing
* position of the moon due to the daily rotation of the earth.
* The ecliptic longitude, however, represents the position of the moon with
* respect to the stars, and completes just one cycle over the course of a
* year. Its therefore pretty safe to update the moon's longitude only once
* every ten minutes. (Comment added by Durk Talsma).
************************************************************************/
ecliptic_to_equatorial( SolarSystem::theSolarSystem->getMoon()->getLon(),
0.0, &alpha, &delta );
tmp = alpha - (FG_2PI/24)*GST(ssue);
if (tmp < -FG_PI) {
do tmp += FG_2PI;
while (tmp < -FG_PI);
} else if (tmp > FG_PI) {
do tmp -= FG_2PI;
while (tmp < -FG_PI);
}
*lon = tmp;
*lat = delta;
}
/* given a particular time expressed in side real time at prime
* meridian (GST), compute position on the earth (lat, lon) such that
* moon is directly overhead. (lat, lon are reported in radians */
static void fgMoonPositionGST(double gst, double *lon, double *lat) {
/* time_t ssue; seconds since unix epoch */
/* double *lat; (return) latitude */
/* double *lon; (return) longitude */
/* double lambda; */
double alpha, delta;
double tmp;
/* lambda = moon_ecliptic_longitude(ssue); */
/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
//ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
ecliptic_to_equatorial( SolarSystem::theSolarSystem->getMoon()->getLon(),
SolarSystem::theSolarSystem->getMoon()->getLat(),
&alpha, &delta );
// tmp = alpha - (FG_2PI/24)*GST(ssue);
tmp = alpha - (FG_2PI/24)*gst;
if (tmp < -FG_PI) {
do tmp += FG_2PI;
while (tmp < -FG_PI);
} else if (tmp > FG_PI) {
do tmp -= FG_2PI;
while (tmp < -FG_PI);
}
*lon = tmp;
*lat = delta;
}
// update the cur_time_params structure with the current moon position
void fgUpdateMoonPos( void ) {
fgLIGHT *l;
FGTime *t;
FGView *v;
MAT3vec nup, nmoon, v0, surface_to_moon;
Point3D p, rel_moonpos;
double dot, east_dot;
double moon_gd_lat, sl_radius;
double ntmp;
l = &cur_light_params;
t = FGTime::cur_time_params;
v = &current_view;
FG_LOG( FG_EVENT, FG_INFO, " Updating Moon position" );
// (not sure why there was two)
// fgMoonPosition(t->cur_time, &l->moon_lon, &moon_gd_lat);
fgMoonPositionGST(t->getGst(), &l->moon_lon, &moon_gd_lat);
fgGeodToGeoc(moon_gd_lat, 0.0, &sl_radius, &l->moon_gc_lat);
p = Point3D( l->moon_lon, l->moon_gc_lat, sl_radius );
l->fg_moonpos = fgPolarToCart3d(p);
FG_LOG( FG_EVENT, FG_INFO, " t->cur_time = " << t->get_cur_time() );
FG_LOG( FG_EVENT, FG_INFO,
" Moon Geodetic lat = " << moon_gd_lat
<< " Geocentric lat = " << l->moon_gc_lat );
// I think this will work better for generating the moon light vector
l->moon_vec[0] = l->fg_moonpos.x();
l->moon_vec[1] = l->fg_moonpos.y();
l->moon_vec[2] = l->fg_moonpos.z();
MAT3_NORMALIZE_VEC(l->moon_vec, ntmp);
MAT3_SCALE_VEC(l->moon_vec_inv, l->moon_vec, -1.0);
// make sure these are directional light sources only
l->moon_vec[3] = 0.0;
l->moon_vec_inv[3] = 0.0;
// printf(" l->moon_vec = %.2f %.2f %.2f\n", l->moon_vec[0], l->moon_vec[1],
// l->moon_vec[2]);
// calculate the moon's relative angle to local up
MAT3_COPY_VEC(nup, v->get_local_up());
nmoon[0] = l->fg_moonpos.x();
nmoon[1] = l->fg_moonpos.y();
nmoon[2] = l->fg_moonpos.z();
MAT3_NORMALIZE_VEC(nup, ntmp);
MAT3_NORMALIZE_VEC(nmoon, ntmp);
l->moon_angle = acos(MAT3_DOT_PRODUCT(nup, nmoon));
// printf(" MOON ANGLE relative to current location = %.3f rads.\n",
// l->moon_angle);
// calculate vector to moon's position on the earth's surface
rel_moonpos = l->fg_moonpos - (v->get_view_pos() + scenery.center);
v->set_to_moon( rel_moonpos.x(), rel_moonpos.y(), rel_moonpos.z() );
// printf( "Vector to moon = %.2f %.2f %.2f\n",
// v->to_moon[0], v->to_moon[1], v->to_moon[2]);
// make a vector to the current view position
Point3D view_pos = v->get_view_pos();
MAT3_SET_VEC(v0, view_pos.x(), view_pos.y(), view_pos.z());
// Given a vector from the view position to the point on the
// earth's surface the moon is directly over, map into onto the
// local plane representing "horizontal".
map_vec_onto_cur_surface_plane( v->get_local_up(), v0, v->get_to_moon(),
surface_to_moon );
MAT3_NORMALIZE_VEC(surface_to_moon, ntmp);
v->set_surface_to_moon( surface_to_moon[0], surface_to_moon[1],
surface_to_moon[2] );
// printf("Surface direction to moon is %.2f %.2f %.2f\n",
// v->surface_to_moon[0], v->surface_to_moon[1], v->surface_to_moon[2]);
// printf("Should be close to zero = %.2f\n",
// MAT3_DOT_PRODUCT(v->local_up, v->surface_to_moon));
// calculate the angle between v->surface_to_moon and
// v->surface_east. We do this so we can sort out the acos()
// ambiguity. I wish I could think of a more efficient way ... :-(
east_dot = MAT3_DOT_PRODUCT( surface_to_moon, v->get_surface_east() );
// printf(" East dot product = %.2f\n", east_dot);
// calculate the angle between v->surface_to_moon and
// v->surface_south. this is how much we have to rotate the sky
// for it to align with the moon
dot = MAT3_DOT_PRODUCT( surface_to_moon, v->get_surface_south() );
// printf(" Dot product = %.2f\n", dot);
if ( east_dot >= 0 ) {
l->moon_rotation = acos(dot);
} else {
l->moon_rotation = -acos(dot);
}
// printf(" Sky needs to rotate = %.3f rads = %.1f degrees.\n",
// angle, angle * RAD_TO_DEG); */
}
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