2 * sunsolver.cxx - given a location on earth and a time of day/date,
3 * find the number of seconds to various sun positions.
5 * Written by Curtis Olson, started September 2003.
7 * Copyright (C) 2003 Curtis L. Olson - curt@flightgear.org
9 * This program is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU General Public License as
11 * published by the Free Software Foundation; either version 2 of the
12 * License, or (at your option) any later version.
14 * This program is distributed in the hope that it will be useful, but
15 * WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * General Public License for more details.
19 * You should have received a copy of the GNU General Public License
20 * along with this program; if not, write to the Free Software
21 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
27 #include <simgear/math/point3d.hxx>
28 #include <simgear/math/sg_geodesy.hxx>
29 #include <simgear/timing/sg_time.hxx>
31 #include <Main/globals.hxx>
35 #include "sunsolver.hxx"
38 static const time_t day_secs = 86400;
39 static const time_t half_day_secs = day_secs / 2;
40 static const time_t step_secs = 60;
42 static double sun_angle( const SGTime &t, sgVec3 world_up,
43 double lon_rad, double lat_rad ) {
45 Point3D p, rel_sunpos;
47 SG_LOG( SG_EVENT, SG_DEBUG, " Updating Sun position" );
48 SG_LOG( SG_EVENT, SG_DEBUG, " Gst = " << t.getGst() );
50 double sun_lon, sun_gd_lat;
51 fgSunPositionGST( t.getGst(), &sun_lon, &sun_gd_lat );
52 Point3D sunpos = sgGeodToCart(Point3D(sun_lon, sun_gd_lat, 0));
54 SG_LOG( SG_EVENT, SG_DEBUG, " t.cur_time = " << t.get_cur_time() );
55 SG_LOG( SG_EVENT, SG_DEBUG,
56 " Sun Geodetic lat = " << sun_gd_lat );
58 // calculate the sun's relative angle to local up
59 sgCopyVec3( nup, world_up );
60 sgSetVec3( nsun, sunpos.x(), sunpos.y(), sunpos.z() );
62 sgNormalizeVec3(nsun);
63 // cout << "nup = " << nup[0] << "," << nup[1] << ","
65 // cout << "nsun = " << nsun[0] << "," << nsun[1] << ","
66 // << nsun[2] << endl;
68 double sun_angle = acos( sgScalarProductVec3 ( nup, nsun ) );
69 double sun_angle_deg = sun_angle * SG_RADIANS_TO_DEGREES;
70 while ( sun_angle_deg < -180 ) { sun_angle += 360; }
71 SG_LOG( SG_EVENT, SG_DEBUG, "sun angle relative to current location = "
79 * Given the current unix time in seconds, calculate seconds to the
80 * specified sun angle (relative to straight up.) Also specify if we
81 * want the angle while the sun is ascending or descending. For
82 * instance noon is when the sun angle is 0 (or the closest it can
83 * get.) Dusk is when the sun angle is 90 and descending. Dawn is
84 * when the sun angle is 90 and ascending.
86 time_t fgTimeSecondsUntilSunAngle( time_t cur_time,
89 double target_angle_deg,
92 // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
93 // << lat_rad * SG_RADIANS_TO_DEGREES << endl;
94 Point3D geod( lon_rad, lat_rad, 0 );
95 Point3D tmp = sgGeodToCart( geod );
97 sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
98 SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
100 double best_diff = 180.0;
101 double last_angle = -99999.0;
102 time_t best_time = cur_time;
104 for ( time_t secs = cur_time - half_day_secs;
105 secs < cur_time + half_day_secs;
108 t.update( lon_rad, lat_rad, secs, 0 );
109 double angle_deg = sun_angle( t, world_up, lon_rad, lat_rad );
110 double diff = fabs( angle_deg - target_angle_deg );
111 if ( diff < best_diff ) {
112 if ( last_angle <= 180.0 && ascending
113 && ( last_angle > angle_deg ) ) {
114 // cout << "best angle = " << angle << " offset = "
115 // << secs - cur_time << endl;
118 } else if ( last_angle <= 180.0 && !ascending
119 && ( last_angle < angle_deg ) ) {
120 // cout << "best angle = " << angle << " offset = "
121 // << secs - cur_time << endl;
127 last_angle = angle_deg;
130 return best_time - cur_time;