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, sun_gc_lat, sl_radius;
51 fgSunPositionGST( t.getGst(), &sun_lon, &sun_gd_lat );
53 sgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &sun_gc_lat);
55 p = Point3D( sun_lon, sun_gc_lat, sl_radius );
56 Point3D sunpos = sgPolarToCart3d(p);
58 SG_LOG( SG_EVENT, SG_DEBUG, " t.cur_time = " << t.get_cur_time() );
59 SG_LOG( SG_EVENT, SG_DEBUG,
60 " Sun Geodetic lat = " << sun_gd_lat
61 << " Geocentric lat = " << sun_gc_lat );
63 // calculate the sun's relative angle to local up
64 sgCopyVec3( nup, world_up );
65 sgSetVec3( nsun, sunpos.x(), sunpos.y(), sunpos.z() );
67 sgNormalizeVec3(nsun);
68 // cout << "nup = " << nup[0] << "," << nup[1] << ","
70 // cout << "nsun = " << nsun[0] << "," << nsun[1] << ","
71 // << nsun[2] << endl;
73 double sun_angle = acos( sgScalarProductVec3 ( nup, nsun ) );
74 double sun_angle_deg = sun_angle * SG_RADIANS_TO_DEGREES;
75 while ( sun_angle_deg < -180 ) { sun_angle += 360; }
76 SG_LOG( SG_EVENT, SG_DEBUG, "sun angle relative to current location = "
84 * Given the current unix time in seconds, calculate seconds to noon
86 time_t fgTimeSecondsUntilNoon( time_t cur_time,
90 // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
91 // << lat_rad * SG_RADIANS_TO_DEGREES << endl;
92 Point3D geod( lon_rad, lat_rad, 0 );
93 Point3D tmp = sgGeodToCart( geod );
95 sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
96 SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
98 double best_angle = 180.0;
99 time_t best_time = cur_time;
101 for ( time_t secs = cur_time - half_day_secs;
102 secs < cur_time + half_day_secs;
105 t.update( lon_rad, lat_rad, secs, 0 );
106 double angle = sun_angle( t, world_up, lon_rad, lat_rad );
107 if ( angle < best_angle ) {
108 // cout << "best angle = " << angle << " offset = "
109 // << secs - cur_time << endl;
115 return best_time - cur_time;
120 * Given the current unix time in seconds, calculate seconds to midnight
122 time_t fgTimeSecondsUntilMidnight( time_t cur_time,
126 // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
127 // << lat_rad * SG_RADIANS_TO_DEGREES << endl;
128 Point3D geod( lon_rad, lat_rad, 0 );
129 Point3D tmp = sgGeodToCart( geod );
131 sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
132 SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
134 double best_angle = 0.0;
135 time_t best_time = cur_time;
137 for ( time_t secs = cur_time - half_day_secs;
138 secs < cur_time + half_day_secs;
141 t.update( lon_rad, lat_rad, secs, 0 );
142 double angle = sun_angle( t, world_up, lon_rad, lat_rad );
143 if ( angle > best_angle ) {
144 // cout << "best angle = " << angle << " offset = "
145 // << secs - cur_time << endl;
151 return best_time - cur_time;
156 * Given the current unix time in seconds, calculate seconds to dusk
158 time_t fgTimeSecondsUntilDusk( time_t cur_time,
162 // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
163 // << lat_rad * SG_RADIANS_TO_DEGREES << endl;
164 Point3D geod( lon_rad, lat_rad, 0 );
165 Point3D tmp = sgGeodToCart( geod );
167 sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
168 SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
170 double best_diff = 90.0;
171 double last_angle = -99999.0;
172 time_t best_time = cur_time;
174 for ( time_t secs = cur_time - half_day_secs;
175 secs < cur_time + half_day_secs;
178 t.update( lon_rad, lat_rad, secs, 0 );
179 double angle = sun_angle( t, world_up, lon_rad, lat_rad );
180 double diff = fabs( angle - 90.0 );
181 if ( diff < best_diff ) {
182 if ( last_angle <= 180.0 && ( last_angle < angle ) ) {
183 // cout << "best angle = " << angle << " offset = "
184 // << secs - cur_time << endl;
193 return best_time - cur_time;
198 * Given the current unix time in seconds, calculate seconds to dawn
200 time_t fgTimeSecondsUntilDawn( time_t cur_time,
204 // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
205 // << lat_rad * SG_RADIANS_TO_DEGREES << endl;
206 Point3D geod( lon_rad, lat_rad, 0 );
207 Point3D tmp = sgGeodToCart( geod );
209 sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
210 SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
212 double best_diff = 90.0;
213 double last_angle = -99999.0;
214 time_t best_time = cur_time;
216 for ( time_t secs = cur_time - half_day_secs;
217 secs < cur_time + half_day_secs;
220 t.update( lon_rad, lat_rad, secs, 0 );
221 double angle = sun_angle( t, world_up, lon_rad, lat_rad );
222 double diff = fabs( angle - 90.0 );
223 if ( diff < best_diff ) {
224 if ( last_angle <= 180.0 && ( last_angle > angle ) ) {
225 // cout << "best angle = " << angle << " offset = "
226 // << secs - cur_time << endl;
235 return best_time - cur_time;