d0eaafb1e1
separate header file. This change will help integrate properties into JSBSim. Also, I (David Megginson) removed most of the SimGear include statements from globals.hxx, reducing the amount of recompilation every time SimGear changes. This required making minor changes to a lot of files that were depending on the side-effects of the inclusions in globals.hxx.
443 lines
14 KiB
C++
443 lines
14 KiB
C++
// moonpos.cxx (basically, this is a slightly modified version of the
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// 'sunpos.cxx' file, adapted from XEarth)
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//
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// kirk johnson
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// july 1993
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//
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// code for calculating the position on the earth's surface for which
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// the moon is directly overhead (adapted from _practical astronomy
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// with your calculator, third edition_, peter duffett-smith,
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// cambridge university press, 1988.)
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//
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// Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
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//
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// Parts of the source code (as marked) are:
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// Copyright (C) 1989, 1990, 1991 by Jim Frost
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// Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
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//
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// Permission to use, copy, modify and freely distribute xearth for
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// non-commercial and not-for-profit purposes is hereby granted
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// without fee, provided that both the above copyright notice and this
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// permission notice appear in all copies and in supporting
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// documentation.
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//
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// The author makes no representations about the suitability of this
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// software for any purpose. It is provided "as is" without express or
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// implied warranty.
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//
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// THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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// INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
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// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
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// OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
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// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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//
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// $Id$
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include <simgear/compiler.h>
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#ifdef SG_HAVE_STD_INCLUDES
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# include <cmath>
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# include <cstdio>
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# include <ctime>
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#else
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# include <math.h>
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# include <stdio.h>
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# include <time.h>
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#endif
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#include <simgear/constants.h>
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#include <simgear/debug/logstream.hxx>
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#include <simgear/ephemeris/ephemeris.hxx>
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#include <simgear/math/point3d.hxx>
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#include <simgear/math/polar3d.hxx>
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#include <simgear/math/sg_geodesy.hxx>
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#include <simgear/math/vector.hxx>
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#include <simgear/timing/sg_time.hxx>
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#include <Main/globals.hxx>
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#include <Main/viewer.hxx>
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#include <Scenery/scenery.hxx>
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#include <Time/light.hxx>
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#include "moonpos.hxx"
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#undef E
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/*
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* the epoch upon which these astronomical calculations are based is
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* 1990 january 0.0, 631065600 seconds since the beginning of the
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* "unix epoch" (00:00:00 GMT, Jan. 1, 1970)
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*
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* given a number of seconds since the start of the unix epoch,
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* DaysSinceEpoch() computes the number of days since the start of the
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* astronomical epoch (1990 january 0.0)
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*/
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#define EpochStart (631065600)
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#define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600)))
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/*
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* assuming the apparent orbit of the moon about the earth is circular,
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* the rate at which the orbit progresses is given by RadsPerDay --
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* SG_2PI radians per orbit divided by 365.242191 days per year:
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*/
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#define RadsPerDay (SG_2PI/365.242191)
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/*
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* details of moon's apparent orbit at epoch 1990.0 (after
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* duffett-smith, table 6, section 46)
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*
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* Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees
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* OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees
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* Eccentricity (eccentricity of orbit) 0.016713
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*/
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#define Epsilon_g (279.403303*(SGD_2PI/360))
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#define OmegaBar_g (282.768422*(SGD_2PI/360))
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#define Eccentricity (0.016713)
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/*
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* MeanObliquity gives the mean obliquity of the earth's axis at epoch
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* 1990.0 (computed as 23.440592 degrees according to the method given
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* in duffett-smith, section 27)
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*/
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#define MeanObliquity (23.440592*(SGD_2PI/360))
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/* static double solve_keplers_equation(double); */
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/* static double moon_ecliptic_longitude(time_t); */
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static void ecliptic_to_equatorial(double, double, double *, double *);
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static double julian_date(int, int, int);
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static double GST(time_t);
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/*
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* solve Kepler's equation via Newton's method
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* (after duffett-smith, section 47)
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*/
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/*
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static double solve_keplers_equation(double M) {
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double E;
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double delta;
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E = M;
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while (1) {
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delta = E - Eccentricity*sin(E) - M;
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if (fabs(delta) <= 1e-10) break;
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E -= delta / (1 - Eccentricity*cos(E));
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}
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return E;
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}
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*/
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/* compute ecliptic longitude of moon (in radians) (after
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* duffett-smith, section 47) */
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/*
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static double moon_ecliptic_longitude(time_t ssue) {
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// time_t ssue; // seconds since unix epoch
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double D, N;
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double M_moon, E;
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double v;
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D = DaysSinceEpoch(ssue);
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N = RadsPerDay * D;
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N = fmod(N, SG_2PI);
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if (N < 0) N += SG_2PI;
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M_moon = N + Epsilon_g - OmegaBar_g;
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if (M_moon < 0) M_moon += SG_2PI;
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E = solve_keplers_equation(M_moon);
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v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2));
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return (v + OmegaBar_g);
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}
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*/
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/* convert from ecliptic to equatorial coordinates (after
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* duffett-smith, section 27) */
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static void ecliptic_to_equatorial(double lambda, double beta,
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double *alpha, double *delta) {
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/* double lambda; ecliptic longitude */
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/* double beta; ecliptic latitude */
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/* double *alpha; (return) right ascension */
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/* double *delta; (return) declination */
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double sin_e, cos_e;
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double sin_l, cos_l;
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sin_e = sin(MeanObliquity);
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cos_e = cos(MeanObliquity);
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sin_l = sin(lambda);
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cos_l = cos(lambda);
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*alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l);
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*delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l);
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}
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/* computing julian dates (assuming gregorian calendar, thus this is
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* only valid for dates of 1582 oct 15 or later) (after duffett-smith,
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* section 4) */
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static double julian_date(int y, int m, int d) {
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/* int y; year (e.g. 19xx) */
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/* int m; month (jan=1, feb=2, ...) */
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/* int d; day of month */
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int A, B, C, D;
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double JD;
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/* lazy test to ensure gregorian calendar */
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if (y < 1583) {
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SG_LOG( SG_EVENT, SG_ALERT,
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"WHOOPS! Julian dates only valid for 1582 oct 15 or later" );
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}
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if ((m == 1) || (m == 2)) {
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y -= 1;
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m += 12;
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}
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A = y / 100;
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B = 2 - A + (A / 4);
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C = (int)(365.25 * y);
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D = (int)(30.6001 * (m + 1));
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JD = B + C + D + d + 1720994.5;
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return JD;
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}
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/* compute greenwich mean sidereal time (GST) corresponding to a given
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* number of seconds since the unix epoch (after duffett-smith,
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* section 12) */
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static double GST(time_t ssue) {
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/* time_t ssue; seconds since unix epoch */
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double JD;
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double T, T0;
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double UT;
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struct tm *tm;
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tm = gmtime(&ssue);
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JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
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T = (JD - 2451545) / 36525;
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T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
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T0 = fmod(T0, 24.0);
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if (T0 < 0) T0 += 24;
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UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
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T0 += UT * 1.002737909;
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T0 = fmod(T0, 24.0);
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if (T0 < 0) T0 += 24;
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return T0;
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}
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/* given a particular time (expressed in seconds since the unix
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* epoch), compute position on the earth (lat, lon) such that moon is
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* directly overhead. (lat, lon are reported in radians */
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void fgMoonPosition(time_t ssue, double *lon, double *lat) {
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/* time_t ssue; seconds since unix epoch */
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/* double *lat; (return) latitude */
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/* double *lon; (return) longitude */
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/* double lambda; */
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double alpha, delta;
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double tmp;
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/* lambda = moon_ecliptic_longitude(ssue); */
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/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
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//ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
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/* **********************************************************************
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* NOTE: in the next function, each time the moon's position is updated, the
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* the moon's longitude is returned from solarSystem->moon. Note that the
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* moon's position is updated at a much higher frequency than the rate at
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* which the solar system's rebuilds occur. This is not a problem, however,
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* because the fgMoonPosition we're talking about here concerns the changing
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* position of the moon due to the daily rotation of the earth.
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* The ecliptic longitude, however, represents the position of the moon with
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* respect to the stars, and completes just one cycle over the course of a
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* year. Its therefore pretty safe to update the moon's longitude only once
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* every ten minutes. (Comment added by Durk Talsma).
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************************************************************************/
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ecliptic_to_equatorial( globals->get_ephem()->get_moon()->getLon(),
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0.0, &alpha, &delta );
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tmp = alpha - (SGD_2PI/24)*GST(ssue);
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if (tmp < -SGD_PI) {
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do tmp += SGD_2PI;
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while (tmp < -SGD_PI);
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} else if (tmp > SGD_PI) {
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do tmp -= SGD_2PI;
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while (tmp < -SGD_PI);
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}
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*lon = tmp;
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*lat = delta;
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}
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/* given a particular time expressed in side real time at prime
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* meridian (GST), compute position on the earth (lat, lon) such that
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* moon is directly overhead. (lat, lon are reported in radians */
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static void fgMoonPositionGST(double gst, double *lon, double *lat) {
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/* time_t ssue; seconds since unix epoch */
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/* double *lat; (return) latitude */
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/* double *lon; (return) longitude */
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/* double lambda; */
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double alpha, delta;
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double tmp;
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/* lambda = moon_ecliptic_longitude(ssue); */
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/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
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//ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
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ecliptic_to_equatorial( globals->get_ephem()->get_moon()->getLon(),
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globals->get_ephem()->get_moon()->getLat(),
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&alpha, &delta );
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// tmp = alpha - (SG_2PI/24)*GST(ssue);
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tmp = alpha - (SGD_2PI/24)*gst;
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if (tmp < -SGD_PI) {
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do tmp += SGD_2PI;
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while (tmp < -SGD_PI);
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} else if (tmp > SGD_PI) {
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do tmp -= SGD_2PI;
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while (tmp < -SGD_PI);
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}
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*lon = tmp;
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*lat = delta;
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}
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// update the cur_time_params structure with the current moon position
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void fgUpdateMoonPos( void ) {
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fgLIGHT *l;
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FGViewer *v;
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sgVec3 nup, nmoon;
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Point3D p, rel_moonpos;
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double dot, east_dot;
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double moon_gd_lat, sl_radius;
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// vector in cartesian coordinates from current position to the
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// postion on the earth's surface the moon is directly over
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sgVec3 to_moon;
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// surface direction to go to head towards moon
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sgVec3 surface_to_moon;
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l = &cur_light_params;
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SGTime *t = globals->get_time_params();
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v = globals->get_current_view();
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SG_LOG( SG_EVENT, SG_INFO, " Updating Moon position" );
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// (not sure why there was two)
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// fgMoonPosition(t->cur_time, &l->moon_lon, &moon_gd_lat);
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fgMoonPositionGST(t->getGst(), &l->moon_lon, &moon_gd_lat);
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sgGeodToGeoc(moon_gd_lat, 0.0, &sl_radius, &l->moon_gc_lat);
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p = Point3D( l->moon_lon, l->moon_gc_lat, sl_radius );
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l->fg_moonpos = sgPolarToCart3d(p);
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SG_LOG( SG_EVENT, SG_INFO, " t->cur_time = " << t->get_cur_time() );
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SG_LOG( SG_EVENT, SG_INFO,
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" Moon Geodetic lat = " << moon_gd_lat
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<< " Geocentric lat = " << l->moon_gc_lat );
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// update the sun light vector
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sgSetVec4( l->moon_vec,
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l->fg_moonpos.x(), l->fg_moonpos.y(), l->fg_moonpos.z(), 0.0 );
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sgNormalizeVec4( l->moon_vec );
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sgCopyVec4( l->moon_vec_inv, l->moon_vec );
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sgNegateVec4( l->moon_vec_inv );
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// make sure these are directional light sources only
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l->moon_vec[3] = l->moon_vec_inv[3] = 0.0;
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// cout << " l->moon_vec = " << l->moon_vec[0] << "," << l->moon_vec[1]
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// << ","<< l->moon_vec[2] << endl;
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// calculate the moon's relative angle to local up
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sgCopyVec3( nup, v->get_world_up() );
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sgSetVec3( nmoon, l->fg_moonpos.x(), l->fg_moonpos.y(), l->fg_moonpos.z() );
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sgNormalizeVec3(nup);
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sgNormalizeVec3(nmoon);
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// cout << "nup = " << nup[0] << "," << nup[1] << ","
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// << nup[2] << endl;
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// cout << "nmoon = " << nmoon[0] << "," << nmoon[1] << ","
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// << nmoon[2] << endl;
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l->moon_angle = acos( sgScalarProductVec3( nup, nmoon ) );
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SG_LOG( SG_EVENT, SG_INFO, "moon angle relative to current location = "
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<< l->moon_angle );
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// calculate vector to moon's position on the earth's surface
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Point3D vp( v->get_view_pos()[0],
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v->get_view_pos()[1],
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v->get_view_pos()[2] );
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rel_moonpos = l->fg_moonpos - ( vp + scenery.get_center() );
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sgSetVec3( to_moon, rel_moonpos.x(), rel_moonpos.y(), rel_moonpos.z() );
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// printf( "Vector to moon = %.2f %.2f %.2f\n",
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// to_moon[0], to_moon[1], to_moon[2]);
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// Given a vector from the view position to the point on the
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// earth's surface the moon is directly over, map into onto the
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// local plane representing "horizontal".
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sgmap_vec_onto_cur_surface_plane( v->get_world_up(), v->get_view_pos(),
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to_moon, surface_to_moon );
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sgNormalizeVec3(surface_to_moon);
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// cout << "(sg) Surface direction to moon is "
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// << surface_to_moon[0] << ","
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// << surface_to_moon[1] << ","
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// << surface_to_moon[2] << endl;
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// cout << "Should be close to zero = "
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// << sgScalarProductVec3(nup, surface_to_moon) << endl;
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// calculate the angle between v->surface_to_moon and
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// v->surface_east. We do this so we can sort out the acos()
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// ambiguity. I wish I could think of a more efficient way ... :-(
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east_dot = sgScalarProductVec3( surface_to_moon, v->get_surface_east() );
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// cout << " East dot product = " << east_dot << endl;
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// calculate the angle between v->surface_to_moon and
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// v->surface_south. this is how much we have to rotate the sky
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// for it to align with the moon
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dot = sgScalarProductVec3( surface_to_moon, v->get_surface_south() );
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// cout << " Dot product = " << dot << endl;
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if ( east_dot >= 0 ) {
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l->moon_rotation = acos(dot);
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} else {
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l->moon_rotation = -acos(dot);
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}
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// cout << " Sky needs to rotate = " << angle << " rads = "
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// << angle * SGD_RADIANS_TO_DEGREES << " degrees." << endl;
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}
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