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flightgear/Time/sunpos.cxx
curt b5cf8b7323 Changes for new astro code.
1998-09-15 04:27:49 +00:00

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// sunpos.c (taken from XEarth)
// kirk johnson
// july 1993
//
// code for calculating the position on the earth's surface for which
// the sun 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.
//
// $Id$
// (Log is kept at end of this file)
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <math.h>
#include <stdio.h>
#include <time.h>
//#include <Astro/orbits.hxx>
#include <Astro/solarsystem.hxx>
#include <Include/fg_constants.h>
#include <Main/views.hxx>
#include <Math/fg_geodesy.h>
#include <Math/mat3.h>
#include <Math/polar3d.hxx>
#include <Math/vector.hxx>
#include <Scenery/scenery.hxx>
#include "fg_time.hxx"
#include "sunpos.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 sun 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 sun'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 sun_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 sun (in radians) (after
* duffett-smith, section 47) */
/*
static double sun_ecliptic_longitude(time_t ssue) {
// time_t ssue; // seconds since unix epoch
double D, N;
double M_sun, E;
double v;
D = DaysSinceEpoch(ssue);
N = RadsPerDay * D;
N = fmod(N, FG_2PI);
if (N < 0) N += FG_2PI;
M_sun = N + Epsilon_g - OmegaBar_g;
if (M_sun < 0) M_sun += FG_2PI;
E = solve_keplers_equation(M_sun);
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) {
printf("WHOOPS! Julian dates only valid for 1582 oct 15 or later\n");
}
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 sun is
* directly overhead. (lat, lon are reported in radians */
void fgSunPosition(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 = sun_ecliptic_longitude(ssue); */
/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
//ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
/* **********************************************************************
* NOTE: in the next function, each time the sun's position is updated, the
* the sun's longitude is returned from solarSystem->sun. Note that the
* sun'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 fgSunPosition we're talking about here concerns the changing
* position of the sun due to the daily rotation of the earth.
* The ecliptic longitude, however, represents the position of the sun with
* respect to the stars, and completes just one cycle over the course of a
* year. Its therefore pretty safe to update the sun's longitude only once
* every ten minutes. (Comment added by Durk Talsma).
************************************************************************/
ecliptic_to_equatorial( SolarSystem::theSolarSystem->getSun()->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
* sun is directly overhead. (lat, lon are reported in radians */
static void fgSunPositionGST(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 = sun_ecliptic_longitude(ssue); */
/* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
//ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
ecliptic_to_equatorial( SolarSystem::theSolarSystem->getSun()->getLon(),
0.0, &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 sun position
void fgUpdateSunPos( void ) {
fgLIGHT *l;
fgTIME *t;
fgVIEW *v;
MAT3vec nup, nsun, v0;
fgPoint3d p;
double dot, east_dot;
double sun_gd_lat, sl_radius;
double ntmp;
l = &cur_light_params;
t = &cur_time_params;
v = &current_view;
printf(" Updating Sun position\n");
// (not sure why there was two)
// fgSunPosition(t->cur_time, &l->sun_lon, &sun_gd_lat);
fgSunPositionGST(t->gst, &l->sun_lon, &sun_gd_lat);
fgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &l->sun_gc_lat);
p.lon = l->sun_lon;
p.lat = l->sun_gc_lat;
p.radius = sl_radius;
l->fg_sunpos = fgPolarToCart3d(p);
printf( " t->cur_time = %ld\n", t->cur_time);
printf( " Sun Geodetic lat = %.5f Geocentric lat = %.5f\n",
sun_gd_lat, l->sun_gc_lat);
// I think this will work better for generating the sun light vector
l->sun_vec[0] = l->fg_sunpos.x;
l->sun_vec[1] = l->fg_sunpos.y;
l->sun_vec[2] = l->fg_sunpos.z;
MAT3_NORMALIZE_VEC(l->sun_vec, ntmp);
MAT3_SCALE_VEC(l->sun_vec_inv, l->sun_vec, -1.0);
// make sure these are directional light sources only
l->sun_vec[3] = 0.0;
l->sun_vec_inv[3] = 0.0;
// printf(" l->sun_vec = %.2f %.2f %.2f\n", l->sun_vec[0], l->sun_vec[1],
// l->sun_vec[2]);
// calculate the sun's relative angle to local up
MAT3_COPY_VEC(nup, v->local_up);
nsun[0] = l->fg_sunpos.x;
nsun[1] = l->fg_sunpos.y;
nsun[2] = l->fg_sunpos.z;
MAT3_NORMALIZE_VEC(nup, ntmp);
MAT3_NORMALIZE_VEC(nsun, ntmp);
l->sun_angle = acos(MAT3_DOT_PRODUCT(nup, nsun));
// printf(" SUN ANGLE relative to current location = %.3f rads.\n",
// l->sun_angle);
// calculate vector to sun's position on the earth's surface
v->to_sun[0] = l->fg_sunpos.x - (v->view_pos.x + scenery.center.x);
v->to_sun[1] = l->fg_sunpos.y - (v->view_pos.y + scenery.center.y);
v->to_sun[2] = l->fg_sunpos.z - (v->view_pos.z + scenery.center.z);
// printf( "Vector to sun = %.2f %.2f %.2f\n",
// v->to_sun[0], v->to_sun[1], v->to_sun[2]);
// make a vector to the current view position
MAT3_SET_VEC(v0, v->view_pos.x, v->view_pos.y, v->view_pos.z);
// Given a vector from the view position to the point on the
// earth's surface the sun is directly over, map into onto the
// local plane representing "horizontal".
map_vec_onto_cur_surface_plane(v->local_up, v0, v->to_sun,
v->surface_to_sun);
MAT3_NORMALIZE_VEC(v->surface_to_sun, ntmp);
// printf("Surface direction to sun is %.2f %.2f %.2f\n",
// v->surface_to_sun[0], v->surface_to_sun[1], v->surface_to_sun[2]);
// printf("Should be close to zero = %.2f\n",
// MAT3_DOT_PRODUCT(v->local_up, v->surface_to_sun));
// calculate the angle between v->surface_to_sun 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(v->surface_to_sun, v->surface_east);
// printf(" East dot product = %.2f\n", east_dot);
// calculate the angle between v->surface_to_sun and
// v->surface_south. this is how much we have to rotate the sky
// for it to align with the sun
dot = MAT3_DOT_PRODUCT(v->surface_to_sun, v->surface_south);
// printf(" Dot product = %.2f\n", dot);
if ( east_dot >= 0 ) {
l->sun_rotation = acos(dot);
} else {
l->sun_rotation = -acos(dot);
}
// printf(" Sky needs to rotate = %.3f rads = %.1f degrees.\n",
// angle, angle * RAD_TO_DEG); */
}
// $Log$
// Revision 1.12 1998/09/15 04:27:50 curt
// Changes for new astro code.
//
// Revision 1.11 1998/08/12 21:13:22 curt
// Optimizations by Norman Vine.
//
// Revision 1.10 1998/07/22 21:45:39 curt
// fg_time.cxx: Removed call to ctime() in a printf() which should be harmless
// but seems to be triggering a bug.
// light.cxx: Added code to adjust fog color based on sunrise/sunset effects
// and view orientation. This is an attempt to match the fog color to the
// sky color in the center of the screen. You see discrepancies at the
// edges, but what else can be done?
// sunpos.cxx: Caculate local direction to sun here. (what compass direction
// do we need to face to point directly at sun)
//
// Revision 1.9 1998/07/08 14:48:39 curt
// polar3d.h renamed to polar3d.hxx
//
// Revision 1.8 1998/05/02 01:53:18 curt
// Fine tuning mktime() support because of varying behavior on different
// platforms.
//
// Revision 1.7 1998/04/30 12:36:05 curt
// C++-ifying a couple source files.
//
// Revision 1.6 1998/04/28 01:22:18 curt
// Type-ified fgTIME and fgVIEW.
//
// Revision 1.5 1998/04/26 05:10:05 curt
// "struct fgLIGHT" -> "fgLIGHT" because fgLIGHT is typedef'd.
//
// Revision 1.4 1998/04/25 22:06:34 curt
// Edited cvs log messages in source files ... bad bad bad!
//
// Revision 1.3 1998/04/25 20:24:03 curt
// Cleaned up initialization sequence to eliminate interdependencies
// between sun position, lighting, and view position. This creates a
// valid single pass initialization path.
//
// Revision 1.2 1998/04/24 00:52:31 curt
// Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
// Fog color fixes.
// Separated out lighting calcs into their own file.
//
// Revision 1.1 1998/04/22 13:24:07 curt
// C++ - ifiing the code a bit.
// Starting to reorginize some of the lighting calcs to use a table lookup.
//
// Revision 1.27 1998/04/03 22:12:57 curt
// Converting to Gnu autoconf system.
// Centralized time handling differences.
//
// Revision 1.26 1998/02/23 19:08:00 curt
// Incorporated Durk's Astro/ tweaks. Includes unifying the sun position
// calculation code between sun display, and other FG sections that use this
// for things like lighting.
//
// Revision 1.25 1998/02/09 15:07:53 curt
// Minor tweaks.
//
// Revision 1.24 1998/01/27 00:48:07 curt
// Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
// system and commandline/config file processing code.
//
// Revision 1.23 1998/01/19 19:27:21 curt
// Merged in make system changes from Bob Kuehne <rpk@sgi.com>
// This should simplify things tremendously.
//
// Revision 1.22 1998/01/19 18:40:40 curt
// Tons of little changes to clean up the code and to remove fatal errors
// when building with the c++ compiler.
//
// Revision 1.21 1997/12/30 23:10:19 curt
// Calculate lighting parameters here.
//
// Revision 1.20 1997/12/30 22:22:43 curt
// Further integration of event manager.
//
// Revision 1.19 1997/12/30 20:47:59 curt
// Integrated new event manager with subsystem initializations.
//
// Revision 1.18 1997/12/23 04:58:40 curt
// Tweaked the sky coloring a bit to build in structures to allow finer rgb
// control.
//
// Revision 1.17 1997/12/15 23:55:08 curt
// Add xgl wrappers for debugging.
// Generate terrain normals on the fly.
//
// Revision 1.16 1997/12/11 04:43:57 curt
// Fixed sun vector and lighting problems. I thing the moon is now lit
// correctly.
//
// Revision 1.15 1997/12/10 22:37:55 curt
// Prepended "fg" on the name of all global structures that didn't have it yet.
// i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
//
// Revision 1.14 1997/12/09 04:25:39 curt
// Working on adding a global lighting params structure.
//
// Revision 1.13 1997/11/25 19:25:42 curt
// Changes to integrate Durk's moon/sun code updates + clean up.
//
// Revision 1.12 1997/11/15 18:15:39 curt
// Reverse direction of sun vector, so object normals can be more normal.
//
// Revision 1.11 1997/10/28 21:07:21 curt
// Changed GLUT/ -> Main/
//
// Revision 1.10 1997/09/13 02:00:09 curt
// Mostly working on stars and generating sidereal time for accurate star
// placement.
//
// Revision 1.9 1997/09/05 14:17:31 curt
// More tweaking with stars.
//
// Revision 1.8 1997/09/05 01:36:04 curt
// Working on getting stars right.
//
// Revision 1.7 1997/09/04 02:17:40 curt
// Shufflin' stuff.
//
// Revision 1.6 1997/08/27 03:30:37 curt
// Changed naming scheme of basic shared structures.
//
// Revision 1.5 1997/08/22 21:34:41 curt
// Doing a bit of reorganizing and house cleaning.
//
// Revision 1.4 1997/08/19 23:55:09 curt
// Worked on better simulating real lighting.
//
// Revision 1.3 1997/08/13 20:23:49 curt
// The interface to sunpos now updates a global structure rather than returning
// current sun position.
//
// Revision 1.2 1997/08/06 00:24:32 curt
// Working on correct real time sun lighting.
//
// Revision 1.1 1997/08/01 15:27:56 curt
// Initial revision.
//
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