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flightgear/src/Time/bodysolver.cxx
Edward d'Auvergne 6e62228c1d Time: The sun solver has been generalised to to handle any solar system body.
The functions fgSunPositionGST() and fgTimeSecondsUntilSunAngle() have been
renamed to fgBodyPositionGST() and fgBodyPositionGST() respectively, and both
require a new char argument specifying the body of interest.  This allows the
position of all solar system bodies to be calculated from the aircraft frame of
reference.
2016-11-08 11:16:24 +01:00

160 lines
5.6 KiB
C++

/*
* bodysolver.cxx - given a location on earth and a time of day/date,
* find the number of seconds to various solar system body
* positions.
*
* Written by Curtis Olson, started September 2003.
*
* Copyright (C) 2003 Curtis L. Olson - http://www.flightgear.org/~curt
*
* 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.
*
* $Id$
*/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <cmath>
#include <ctime>
#include <cassert>
#include <simgear/math/SGMath.hxx>
#include <simgear/timing/sg_time.hxx>
#include <Main/globals.hxx>
#include <Main/fg_props.hxx>
#include "bodysolver.hxx"
static const time_t day_secs = 86400;
static const time_t half_day_secs = day_secs / 2;
static const time_t step_secs = 60;
/* given a particular time expressed in side real time at prime
* meridian (GST), compute position on the earth (lat, lon) such that
* solar system body is directly overhead. (lat, lon are reported in
* radians) */
void fgBodyPositionGST(double gst, double *lon, double *lat, const char *body) {
/* time_t ssue; seconds since unix epoch */
/* double *lat; (return) latitude */
/* double *lon; (return) longitude */
double tmp;
SGPropertyNode* body_node = fgGetNode("/ephemeris/" + std::string(body));
assert(body_node);
double xs = body_node->getDoubleValue("xs");
//double ys = body_node->getDoubleValue("ys");
double ye = body_node->getDoubleValue("ye");
double ze = body_node->getDoubleValue("ze");
double ra = atan2(ye, xs);
double dec = atan2(ze, sqrt(xs * xs + ye * ye));
tmp = ra - (SGD_2PI/24)*gst;
double signedPI = (tmp < 0.0) ? -SGD_PI : SGD_PI;
tmp = fmod(tmp+signedPI, SGD_2PI) - signedPI;
*lon = tmp;
*lat = dec;
}
static double body_angle( const SGTime &t, const SGVec3d& world_up, const char* body) {
SG_LOG( SG_EVENT, SG_DEBUG, " Updating " << body << " position" );
SG_LOG( SG_EVENT, SG_DEBUG, " Gst = " << t.getGst() );
double lon, gc_lat;
fgBodyPositionGST( t.getGst(), &lon, &gc_lat, body );
SGVec3d bodypos = SGVec3d::fromGeoc(SGGeoc::fromRadM(lon, gc_lat,
SGGeodesy::EQURAD));
SG_LOG( SG_EVENT, SG_DEBUG, " t.cur_time = " << t.get_cur_time() );
SG_LOG( SG_EVENT, SG_DEBUG,
" " << body << " geocentric lat = " << gc_lat );
// calculate the body's relative angle to local up
SGVec3d nup = normalize(world_up);
SGVec3d nbody = normalize(bodypos);
// cout << "nup = " << nup[0] << "," << nup[1] << ","
// << nup[2] << endl;
// cout << "nbody = " << nbody[0] << "," << nbody[1] << ","
// << nbody[2] << endl;
double body_angle = acos( dot( nup, nbody ) );
double signedPI = (body_angle < 0.0) ? -SGD_PI : SGD_PI;
body_angle = fmod(body_angle+signedPI, SGD_2PI) - signedPI;
double body_angle_deg = body_angle * SG_RADIANS_TO_DEGREES;
SG_LOG( SG_EVENT, SG_DEBUG, body << " angle relative to current location = "
<< body_angle_deg );
return body_angle_deg;
}
/**
* Given the current unix time in seconds, calculate seconds to the
* specified body angle (relative to straight up.) Also specify if we
* want the angle while the body is ascending or descending. For
* instance noon is when the sun angle is 0 (or the closest it can
* get.) Dusk is when the sun angle is 90 and descending. Dawn is
* when the sun angle is 90 and ascending.
*/
time_t fgTimeSecondsUntilBodyAngle( time_t cur_time,
const SGGeod& loc,
double target_angle_deg,
bool ascending,
const char *body )
{
SGVec3d world_up = SGVec3d::fromGeod(loc);
SGTime t = SGTime( loc, SGPath(), 0 );
double best_diff = 180.0;
double last_angle = -99999.0;
time_t best_time = cur_time;
for ( time_t secs = cur_time - half_day_secs;
secs < cur_time + half_day_secs;
secs += step_secs )
{
t.update( loc, secs, 0 );
double angle_deg = body_angle( t, world_up, body );
double diff = fabs( angle_deg - target_angle_deg );
if ( diff < best_diff ) {
if ( last_angle <= 180.0 && ascending
&& ( last_angle > angle_deg ) ) {
// cout << "best angle = " << angle << " offset = "
// << secs - cur_time << endl;
best_diff = diff;
best_time = secs;
} else if ( last_angle <= 180.0 && !ascending
&& ( last_angle < angle_deg ) ) {
// cout << "best angle = " << angle << " offset = "
// << secs - cur_time << endl;
best_diff = diff;
best_time = secs;
}
}
last_angle = angle_deg;
}
return best_time - cur_time;
}