From 9bb782ce720071100e995b017f7a0051a2530568 Mon Sep 17 00:00:00 2001
From: curt <curt>
Date: Mon, 15 Sep 2003 22:55:39 +0000
Subject: [PATCH] Added a command line option to specify a starting time of day
 in the sense of:

  --timeofday=dawn
  --timeofday=dusk
  --timeofday=noon
  --timeofday=midnight
---
 src/Main/fg_init.cxx   | 107 ++++++++++++------
 src/Main/fg_init.hxx   |   4 +
 src/Main/main.cxx      |  18 ++--
 src/Main/options.cxx   |   1 +
 src/Model/acmodel.cxx  |   2 +-
 src/Time/Makefile.am   |   1 +
 src/Time/moonpos.hxx   |   2 +-
 src/Time/sunpos.cxx    |   4 +-
 src/Time/sunpos.hxx    |   7 +-
 src/Time/sunsolver.cxx | 238 +++++++++++++++++++++++++++++++++++++++++
 src/Time/sunsolver.hxx |  77 +++++++++++++
 11 files changed, 417 insertions(+), 44 deletions(-)
 create mode 100644 src/Time/sunsolver.cxx
 create mode 100644 src/Time/sunsolver.hxx

diff --git a/src/Main/fg_init.cxx b/src/Main/fg_init.cxx
index 38370e9f5..08a20044f 100644
--- a/src/Main/fg_init.cxx
+++ b/src/Main/fg_init.cxx
@@ -108,8 +108,9 @@
 #include <Systems/system_mgr.hxx>
 #include <Time/FGEventMgr.hxx>
 #include <Time/light.hxx>
-#include <Time/sunpos.hxx>
 #include <Time/moonpos.hxx>
+#include <Time/sunpos.hxx>
+#include <Time/sunsolver.hxx>
 #include <Time/tmp.hxx>
 
 #ifdef FG_MPLAYER_AS
@@ -1255,38 +1256,6 @@ SGTime *fgInitTime() {
                             zone.str(),
                             cur_time_override->getLongValue() );
 
-    // Handle potential user specified time offsets
-    time_t cur_time = t->get_cur_time();
-    time_t currGMT = sgTimeGetGMT( gmtime(&cur_time) );
-    time_t systemLocalTime = sgTimeGetGMT( localtime(&cur_time) );
-    time_t aircraftLocalTime = 
-        sgTimeGetGMT( fgLocaltime(&cur_time, t->get_zonename() ) );
-
-    // Okay, we now have six possible scenarios
-    int offset = fgGetInt("/sim/startup/time-offset");
-    const string &offset_type = fgGetString("/sim/startup/time-offset-type");
-    if (offset_type == "system-offset") {
-        globals->set_warp( offset );
-    } else if (offset_type == "gmt-offset") {
-        globals->set_warp( offset - (currGMT - systemLocalTime) );
-    } else if (offset_type == "latitude-offset") {
-        globals->set_warp( offset - (aircraftLocalTime - systemLocalTime) );
-    } else if (offset_type == "system") {
-        globals->set_warp( offset - cur_time );
-    } else if (offset_type == "gmt") {
-        globals->set_warp( offset - currGMT );
-    } else if (offset_type == "latitude") {
-        globals->set_warp( offset - (aircraftLocalTime - systemLocalTime) - 
-                           cur_time ); 
-    } else {
-        SG_LOG( SG_GENERAL, SG_ALERT,
-                "FG_TIME::Unsupported offset type " << offset_type );
-        exit( -1 );
-    }
-
-    SG_LOG( SG_GENERAL, SG_INFO, "After time init, warp = " 
-            << globals->get_warp() );
-
     globals->set_warp_delta( 0 );
 
     t->update( 0.0, 0.0,
@@ -1297,6 +1266,78 @@ SGTime *fgInitTime() {
 }
 
 
+// set up a time offset (aka warp) if one is specified
+void fgInitTimeOffset() {
+    static const SGPropertyNode *longitude
+        = fgGetNode("/position/longitude-deg");
+    static const SGPropertyNode *latitude
+        = fgGetNode("/position/latitude-deg");
+    static const SGPropertyNode *cur_time_override
+        = fgGetNode("/sim/time/cur-time-override", true);
+
+    // Handle potential user specified time offsets
+    SGTime *t = globals->get_time_params();
+    time_t cur_time = t->get_cur_time();
+    time_t currGMT = sgTimeGetGMT( gmtime(&cur_time) );
+    time_t systemLocalTime = sgTimeGetGMT( localtime(&cur_time) );
+    time_t aircraftLocalTime = 
+        sgTimeGetGMT( fgLocaltime(&cur_time, t->get_zonename() ) );
+
+    // Okay, we now have several possible scenarios
+    int offset = fgGetInt("/sim/startup/time-offset");
+    int warp = 0;
+    const string &offset_type = fgGetString("/sim/startup/time-offset-type");
+    if ( offset_type == "noon" ) {
+        warp = fgTimeSecondsUntilNoon( cur_time,
+                                       longitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS,
+                                       latitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS ); 
+    } else if ( offset_type == "midnight" ) {
+        warp = fgTimeSecondsUntilMidnight( cur_time,
+                                           longitude->getDoubleValue()
+                                             * SGD_DEGREES_TO_RADIANS,
+                                           latitude->getDoubleValue()
+                                             * SGD_DEGREES_TO_RADIANS ); 
+    } else if ( offset_type == "dawn" ) {
+        warp = fgTimeSecondsUntilDawn( cur_time,
+                                       longitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS,
+                                       latitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS ); 
+     } else if ( offset_type == "dusk" ) {
+        warp = fgTimeSecondsUntilDusk( cur_time,
+                                       longitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS,
+                                       latitude->getDoubleValue()
+                                         * SGD_DEGREES_TO_RADIANS ); 
+    } else if ( offset_type == "system-offset" ) {
+        warp = offset;
+    } else if ( offset_type == "gmt-offset" ) {
+        warp = offset - (currGMT - systemLocalTime);
+    } else if ( offset_type == "latitude-offset" ) {
+        warp = offset - (aircraftLocalTime - systemLocalTime);
+    } else if ( offset_type == "system" ) {
+        warp = offset - cur_time;
+    } else if ( offset_type == "gmt" ) {
+        warp = offset - currGMT;
+    } else if ( offset_type == "latitude" ) {
+        warp = offset - (aircraftLocalTime - systemLocalTime) - cur_time; 
+    } else {
+        SG_LOG( SG_GENERAL, SG_ALERT,
+                "FG_TIME::Unsupported offset type " << offset_type );
+        exit( -1 );
+    }
+    globals->set_warp( warp );
+    t->update( 0.0, 0.0, cur_time_override->getLongValue(),
+               globals->get_warp() );
+
+    SG_LOG( SG_GENERAL, SG_INFO, "After fgInitTimeOffset(): warp = " 
+            << globals->get_warp() );
+
+    fgUpdateSkyAndLightingParams();
+}
+
 // This is the top level init routine which calls all the other
 // initialization routines.  If you are adding a subsystem to flight
 // gear, its initialization call should located in this routine.
diff --git a/src/Main/fg_init.hxx b/src/Main/fg_init.hxx
index 56325fca1..adfc4cc3c 100644
--- a/src/Main/fg_init.hxx
+++ b/src/Main/fg_init.hxx
@@ -90,6 +90,10 @@ bool fgInitPosition();
 // returns a new instance of the SGTime class
 SGTime *fgInitTime();
 
+// set up a time offset (aka warp) if one is specified
+void fgInitTimeOffset();
+
+
 #endif // _FG_INIT_HXX
 
 
diff --git a/src/Main/main.cxx b/src/Main/main.cxx
index 4f2947fbd..0a6a53f91 100644
--- a/src/Main/main.cxx
+++ b/src/Main/main.cxx
@@ -954,8 +954,8 @@ void fgUpdateTimeDepCalcs() {
 
     // Update solar system
     globals->get_ephem()->update( globals->get_time_params()->getMjd(),
-                              globals->get_time_params()->getLst(),
-                              cur_fdm_state->get_Latitude() );
+                                  globals->get_time_params()->getLst(),
+                                  cur_fdm_state->get_Latitude() );
 
     // Update radio stack model
     current_radiostack->update(delta_time_sec);
@@ -1369,6 +1369,10 @@ static void fgIdleFunction ( void ) {
 
         idle_state++;
     } else if ( idle_state == 4 ) {
+        // Initialize the time offset (warp) after fgInitSubsystem
+        // (which initializes the lighting interpolation tables.)
+        fgInitTimeOffset();
+
         // setup OpenGL view parameters
         fgInitVisuals();
 
@@ -1381,6 +1385,9 @@ static void fgIdleFunction ( void ) {
         idle_state++;
     } else if ( idle_state == 6 ) {
         // sleep(1);
+
+        fgUpdateSkyAndLightingParams();
+
         idle_state = 1000;
 
         SG_LOG( SG_GENERAL, SG_INFO, "Panel visible = " << fgPanelVisible() );
@@ -1725,11 +1732,11 @@ bool fgMainInit( int argc, char **argv ) {
     ephem_data_path.append( "Astro" );
     SGEphemeris *ephem = new SGEphemeris( ephem_data_path.c_str() );
     ephem->update( globals->get_time_params()->getMjd(),
-               globals->get_time_params()->getLst(),
-               0.0 );
+                   globals->get_time_params()->getLst(),
+                   0.0 );
     globals->set_ephem( ephem );
 
-                            // TODO: move to environment mgr
+    // TODO: move to environment mgr
     thesky = new SGSky;
     SGPath texture_path(globals->get_fg_root());
     texture_path.append("Textures");
@@ -1739,7 +1746,6 @@ bool fgMainInit( int argc, char **argv ) {
         thesky->add_cloud_layer(layer);
     }
 
-
     SGPath sky_tex_path( globals->get_fg_root() );
     sky_tex_path.append( "Textures" );
     sky_tex_path.append( "Sky" );
diff --git a/src/Main/options.cxx b/src/Main/options.cxx
index 0d178669f..006fea4e4 100644
--- a/src/Main/options.cxx
+++ b/src/Main/options.cxx
@@ -1311,6 +1311,7 @@ struct OptionDesc {
     {"bpp",                          true,  OPTION_FUNC,   "", false, "", fgOptBpp },
     {"units-feet",                   false, OPTION_STRING, "/sim/startup/units", false, "feet", 0 },
     {"units-meters",                 false, OPTION_STRING, "/sim/startup/units", false, "meters", 0 },
+    {"timeofday",                    true,  OPTION_STRING, "/sim/startup/time-offset-type", false, "noon", 0 },
     {"time-offset",                  true,  OPTION_FUNC,   "", false, "", fgOptTimeOffset },
     {"time-match-real",              false, OPTION_STRING, "/sim/startup/time-offset-type", false, "system-offset", 0 },
     {"time-match-local",             false, OPTION_STRING, "/sim/startup/time-offset-type", false, "latitude-offset", 0 },
diff --git a/src/Model/acmodel.cxx b/src/Model/acmodel.cxx
index 90a70f8f6..7096473e8 100644
--- a/src/Model/acmodel.cxx
+++ b/src/Model/acmodel.cxx
@@ -38,7 +38,7 @@ FGAircraftModel::FGAircraftModel ()
     _selector(new ssgSelector),
     _scene(new ssgRoot),
     _nearplane(0.01f),
-    _farplane(100.0f)
+    _farplane(1000.0f)
 {
 }
 
diff --git a/src/Time/Makefile.am b/src/Time/Makefile.am
index 9a0be35ec..02e4ef5d3 100644
--- a/src/Time/Makefile.am
+++ b/src/Time/Makefile.am
@@ -6,6 +6,7 @@ libTime_a_SOURCES = \
 	light.cxx light.hxx \
 	moonpos.cxx moonpos.hxx \
 	sunpos.cxx sunpos.hxx \
+	sunsolver.cxx sunsolver.hxx \
 	tmp.cxx tmp.hxx
 
 INCLUDES = -I$(top_srcdir) -I$(top_srcdir)/src
diff --git a/src/Time/moonpos.hxx b/src/Time/moonpos.hxx
index 8551afebd..ab22d26d8 100644
--- a/src/Time/moonpos.hxx
+++ b/src/Time/moonpos.hxx
@@ -61,4 +61,4 @@ void fgUpdateMoonPos( void );
 void fgMoonPosition(time_t ssue, double *lon, double *lat);
 
 
-#endif /* _MOONPOS_H */
+#endif /* _MOONPOS_HXX */
diff --git a/src/Time/sunpos.cxx b/src/Time/sunpos.cxx
index ebc45f9d5..3cd794c15 100644
--- a/src/Time/sunpos.cxx
+++ b/src/Time/sunpos.cxx
@@ -211,7 +211,7 @@ void fgSunPosition(time_t ssue, double *lon, double *lat) {
  * 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) {
+void fgSunPositionGST(double gst, double *lon, double *lat) {
     /* time_t  ssue;           seconds since unix epoch */
     /* double *lat;            (return) latitude        */
     /* double *lon;            (return) longitude       */
@@ -227,7 +227,7 @@ static void fgSunPositionGST(double gst, double *lon, double *lat) {
 			    globals->get_ephem()->get_sun()->getLat(),
 			    &alpha, &delta );
 
-//    tmp = alpha - (SGD_2PI/24)*GST(ssue);
+    // tmp = alpha - (SGD_2PI/24)*GST(ssue);
     tmp = alpha - (SGD_2PI/24)*gst;	
     if (tmp < -SGD_PI) {
 	do tmp += SGD_2PI;
diff --git a/src/Time/sunpos.hxx b/src/Time/sunpos.hxx
index 7d38a9abf..b2919f044 100644
--- a/src/Time/sunpos.hxx
+++ b/src/Time/sunpos.hxx
@@ -60,5 +60,10 @@ void fgUpdateMoonPos( void );
 
 void fgSunPosition(time_t ssue, double *lon, double *lat);
 
+/* 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 */
+void fgSunPositionGST(double gst, double *lon, double *lat);
 
-#endif /* _SUNPOS_H */
+
+#endif /* _SUNPOS_HXX */
diff --git a/src/Time/sunsolver.cxx b/src/Time/sunsolver.cxx
new file mode 100644
index 000000000..c04e366dd
--- /dev/null
+++ b/src/Time/sunsolver.cxx
@@ -0,0 +1,238 @@
+/*
+ * sunsolver.cxx - given a location on earth and a time of day/date,
+ *                 find the number of seconds to various sun positions.
+ *
+ * Written by Curtis Olson, started September 2003.
+ *
+ * Copyright (C) 2003  Curtis L. Olson  - curt@flightgear.org
+ *
+ * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id$
+ */
+
+
+#include <simgear/math/point3d.hxx>
+#include <simgear/math/sg_geodesy.hxx>
+#include <simgear/timing/sg_time.hxx>
+
+#include <Main/globals.hxx>
+
+#include "sunpos.hxx"
+
+#include "sunsolver.hxx"
+
+
+const time_t day_secs = 86400;
+
+static double sun_angle( const SGTime &t, sgVec3 world_up,
+                         double lon_rad, double lat_rad ) {
+    sgVec3 nup, nsun;
+    Point3D p, rel_sunpos;
+
+    SG_LOG( SG_EVENT, SG_DEBUG, "  Updating Sun position" );
+    SG_LOG( SG_EVENT, SG_DEBUG, "  Gst = " << t.getGst() );
+
+    double sun_lon, sun_gd_lat, sun_gc_lat, sl_radius;
+    fgSunPositionGST( t.getGst(), &sun_lon, &sun_gd_lat );
+
+    sgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &sun_gc_lat);
+
+    p = Point3D( sun_lon, sun_gc_lat, sl_radius );
+    Point3D sunpos = sgPolarToCart3d(p);
+
+    SG_LOG( SG_EVENT, SG_DEBUG, "    t.cur_time = " << t.get_cur_time() );
+    SG_LOG( SG_EVENT, SG_DEBUG, 
+	    "    Sun Geodetic lat = " << sun_gd_lat
+	    << " Geocentric lat = " << sun_gc_lat );
+
+    // calculate the sun's relative angle to local up
+    sgCopyVec3( nup, world_up );
+    sgSetVec3( nsun, sunpos.x(), sunpos.y(), sunpos.z() );
+    sgNormalizeVec3(nup);
+    sgNormalizeVec3(nsun);
+    // cout << "nup = " << nup[0] << "," << nup[1] << "," 
+    //      << nup[2] << endl;
+    // cout << "nsun = " << nsun[0] << "," << nsun[1] << "," 
+    //      << nsun[2] << endl;
+
+    double sun_angle = acos( sgScalarProductVec3 ( nup, nsun ) );
+    double sun_angle_deg = sun_angle * SG_RADIANS_TO_DEGREES;
+    while ( sun_angle_deg < -180 ) { sun_angle += 360; }
+    SG_LOG( SG_EVENT, SG_DEBUG, "sun angle relative to current location = "
+	    << sun_angle_deg );
+
+    return sun_angle_deg;
+}
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to noon
+ */
+time_t fgTimeSecondsUntilNoon( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad )
+{
+    // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
+    //      << lat_rad * SG_RADIANS_TO_DEGREES << endl;
+    Point3D geod( lon_rad, lat_rad, 0 );
+    Point3D tmp = sgGeodToCart( geod );
+    sgVec3 world_up;
+    sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
+    SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
+
+    double best_angle = 180.0;
+    time_t best_time = cur_time;
+
+    for ( time_t secs = cur_time; secs < cur_time + day_secs; secs += 300 ) {
+        t.update( lon_rad, lat_rad, secs, 0 );
+        double angle = sun_angle( t, world_up, lon_rad, lat_rad );
+        if ( angle < best_angle ) {
+            // cout << "best angle = " << angle << " offset = "
+            // << secs - cur_time << endl;
+            best_angle = angle;
+            best_time = secs;
+        }
+    }
+
+    if ( best_time > day_secs / 2 ) {
+        best_time -= day_secs;
+    }
+
+    return best_time - cur_time;
+}
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to midnight
+ */
+time_t fgTimeSecondsUntilMidnight( time_t cur_time,
+                                   double lon_rad,
+                                   double lat_rad )
+{
+    // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
+    //      << lat_rad * SG_RADIANS_TO_DEGREES << endl;
+    Point3D geod( lon_rad, lat_rad, 0 );
+    Point3D tmp = sgGeodToCart( geod );
+    sgVec3 world_up;
+    sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
+    SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
+
+    double best_angle = 0.0;
+    time_t best_time = cur_time;
+
+    for ( time_t secs = cur_time; secs < cur_time + day_secs; secs += 300 ) {
+        t.update( lon_rad, lat_rad, secs, 0 );
+        double angle = sun_angle( t, world_up, lon_rad, lat_rad );
+        if ( angle > best_angle ) {
+            // cout << "best angle = " << angle << " offset = "
+            //      << secs - cur_time << endl;
+            best_angle = angle;
+            best_time = secs;
+        }
+    }
+
+    if ( best_time > day_secs / 2 ) {
+        best_time -= day_secs;
+    }
+
+    return best_time - cur_time;
+}
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to dusk
+ */
+time_t fgTimeSecondsUntilDusk( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad )
+{
+    // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
+    //      << lat_rad * SG_RADIANS_TO_DEGREES << endl;
+    Point3D geod( lon_rad, lat_rad, 0 );
+    Point3D tmp = sgGeodToCart( geod );
+    sgVec3 world_up;
+    sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
+    SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
+
+    double best_diff = 90.0;
+    double last_angle = -99999.0;
+    time_t best_time = cur_time;
+
+    for ( time_t secs = cur_time; secs < cur_time + day_secs; secs += 300 ) {
+        t.update( lon_rad, lat_rad, secs, 0 );
+        double angle = sun_angle( t, world_up, lon_rad, lat_rad );
+        double diff = fabs( angle - 90.0 );
+        if ( diff < best_diff ) {
+            if ( last_angle <= 180.0 && ( last_angle < angle ) ) {
+                // cout << "best angle = " << angle << " offset = "
+                //      << secs - cur_time << endl;
+                best_diff = diff;
+                best_time = secs;
+            }
+        }
+
+        last_angle = angle;
+    }
+
+    if ( best_time > day_secs / 2 ) {
+        best_time -= day_secs;
+    }
+
+    return best_time - cur_time;
+}
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to dawn
+ */
+time_t fgTimeSecondsUntilDawn( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad )
+{
+    // cout << "location = " << lon_rad * SG_RADIANS_TO_DEGREES << ", "
+    //      << lat_rad * SG_RADIANS_TO_DEGREES << endl;
+    Point3D geod( lon_rad, lat_rad, 0 );
+    Point3D tmp = sgGeodToCart( geod );
+    sgVec3 world_up;
+    sgSetVec3( world_up, tmp.x(), tmp.y(), tmp.z() );
+    SGTime t = SGTime( lon_rad, lat_rad, "", 0 );
+
+    double best_diff = 90.0;
+    double last_angle = -99999.0;
+    time_t best_time = cur_time;
+
+    for ( time_t secs = cur_time; secs < cur_time + day_secs; secs += 300 ) {
+        t.update( lon_rad, lat_rad, secs, 0 );
+        double angle = sun_angle( t, world_up, lon_rad, lat_rad );
+        double diff = fabs( angle - 90.0 );
+        if ( diff < best_diff ) {
+            if ( last_angle <= 180.0 && ( last_angle > angle ) ) {
+                // cout << "best angle = " << angle << " offset = "
+                //      << secs - cur_time << endl;
+                best_diff = diff;
+                best_time = secs;
+            }
+        }
+
+        last_angle = angle;
+    }
+
+    if ( best_time > day_secs / 2 ) {
+        best_time -= day_secs;
+    }
+
+    return best_time - cur_time;
+}
diff --git a/src/Time/sunsolver.hxx b/src/Time/sunsolver.hxx
new file mode 100644
index 000000000..6ba4c4208
--- /dev/null
+++ b/src/Time/sunsolver.hxx
@@ -0,0 +1,77 @@
+/*
+ * sunsolver.hxx - given a location on earth and a time of day/date,
+ *                 find the number of seconds to various sun positions.
+ *
+ * Written by Curtis Olson, started September 2003.
+ *
+ * Copyright (C) 2003  Curtis L. Olson  - curt@flightgear.org
+ *
+ * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id$
+ */
+
+
+#ifndef _SUNSOLVER_HXX
+#define _SUNSOLVER_HXX
+
+
+#ifndef __cplusplus                                                          
+# error This library requires C++
+#endif                                   
+
+#include <simgear/compiler.h>
+
+#ifdef SG_HAVE_STD_INCLUDES
+#  include <ctime>
+#else
+#  include <time.h>
+#endif
+
+/**
+ * Given the current unix time in seconds, calculate seconds to
+ * highest sun angle.
+ */
+time_t fgTimeSecondsUntilNoon( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad );
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to lowest
+ * sun angle.
+ */
+time_t fgTimeSecondsUntilMidnight( time_t cur_time,
+                                   double lon_rad,
+                                   double lat_rad );
+
+/**
+ * Given the current unix time in seconds, calculate seconds to dusk
+ */
+time_t fgTimeSecondsUntilDusk( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad );
+
+
+/**
+ * Given the current unix time in seconds, calculate seconds to dawn
+ */
+time_t fgTimeSecondsUntilDawn( time_t cur_time,
+                               double lon_rad,
+                               double lat_rad );
+
+
+
+#endif /* _SUNSOLVER_HXX */