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463 lines
15 KiB
463 lines
15 KiB
/***************************************************************************
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sun.cpp - Sun Rise and Set Calculations
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-------------------
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begin : Friday July 11 2003
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copyright : (C) 2003 by John Ratke
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email : jratke@comcast.net
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history:
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Written as DAYLEN.C, 1989-08-16
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Modified to SUNRISET.C, 1992-12-01
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(c) Paul Schlyter, 1989, 1992
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Released to the public domain by Paul Schlyter, December 1992
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Portions Modified to SUNDOWN.NLM by Cliff Haas 98-05-22
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Converted to C++ and modified by John Ratke
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***************************************************************************/
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/***************************************************************************
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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***************************************************************************/
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#include <kdebug.h>
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#include <math.h>
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#include "sun.h"
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/* A function to compute the number of days elapsed since 2000 Jan 0.0 */
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/* (which is equal to 1999 Dec 31, 0h UT) */
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static inline double days_since_2000_Jan_0(int y, int m, int d)
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{
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return (367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L);
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}
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/* Some conversion factors between radians and degrees */
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static const double PI = 3.14159265358979323846;
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static const double RADEG = ( 180.0 / PI );
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static const double DEGRAD = ( PI / 180.0 );
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/* The trigonometric functions in degrees */
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static inline double sind(double x) { return sin( x * DEGRAD ); }
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static inline double cosd(double x) { return cos( x * DEGRAD ); }
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static inline double tand(double x) { return tan( x * DEGRAD ); }
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static inline double atand(double x) { return RADEG * atan(x); }
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static inline double asind(double x) { return RADEG * asin(x); }
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static inline double acosd(double x) { return RADEG * acos(x); }
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static inline double atan2d(double y, double x) { return RADEG * atan2(y, x); }
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/* Other local functions */
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static double latitudeToDouble( const TQString &latitude );
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static double longitudeToDouble( const TQString &longitude );
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static int __sunriset__( int year, int month, int day, double lon, double lat,
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double altit, int upper_limb, double &trise, double &tset );
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static void sunpos( double d, double &lon, double &r );
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static void sun_RA_dec( double d, double &RA, double &dec, double &r );
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static inline double revolution( const double x );
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static inline double rev180( const double x );
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static inline double GMST0( const double d );
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/*
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* This function computes times for sunrise/sunset.
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* Sunrise/set is considered to occur when the Sun's upper limb is
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* 35 arc minutes below the horizon (this accounts for the refraction
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* of the Earth's atmosphere).
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*/
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static inline int sun_rise_set(int year, int month, int day, double lon, double lat, double &rise, double &set)
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{
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return __sunriset__( year, month, day, lon, lat, -35.0/60.0, 1, rise, set );
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}
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/*
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* This function computes the start and end times of civil twilight.
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* Civil twilight starts/ends when the Sun's center is 6 degrees below
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* the horizon.
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*/
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static inline int civil_twilight(int year, int month, int day, double lon, double lat, double &start, double &end)
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{
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return __sunriset__( year, month, day, lon, lat, -6.0, 0, start, end );
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}
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Sun::Sun(const TQString &latitude, const TQString &longitude, TQDate date, const int localUTCOffset) :
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m_date(date),
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m_lat(latitudeToDouble(latitude)), m_lon(longitudeToDouble(longitude)),
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m_localUTCOffset(localUTCOffset)
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{
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}
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TQTime Sun::computeRiseTime()
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{
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double riseTime;
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double setTime;
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sun_rise_set( m_date.year(), m_date.month(), m_date.day(), m_lon, m_lat, riseTime, setTime );
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TQTime result = convertDoubleToLocalTime( riseTime );
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if ( ! result.isValid() )
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result.setHMS( 6, 0, 0 );
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return result;
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}
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TQTime Sun::computeSetTime()
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{
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double riseTime;
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double setTime;
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sun_rise_set( m_date.year(), m_date.month(), m_date.day(), m_lon, m_lat, riseTime, setTime );
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TQTime result = convertDoubleToLocalTime( setTime );
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if ( ! result.isValid() )
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result.setHMS( 19, 0, 0 );
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return result;
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}
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TQTime Sun::computeCivilTwilightStart()
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{
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double start;
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double end;
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civil_twilight( m_date.year(), m_date.month(), m_date.day(), m_lon, m_lat, start, end );
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TQTime result = convertDoubleToLocalTime( start );
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if ( ! result.isValid() )
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result.setHMS( 6, 0, 0 );
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return result;
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}
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TQTime Sun::computeCivilTwilightEnd()
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{
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double start;
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double end;
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civil_twilight( m_date.year(), m_date.month(), m_date.day(), m_lon, m_lat, start, end );
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TQTime result = convertDoubleToLocalTime( end );
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if ( ! result.isValid() )
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result.setHMS( 19, 0, 0 );
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return result;
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}
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/*
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* Converts latitude in format DD-MMH, where DD is degrees, MM is minutes,
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* and H is Hemisphere (N for North, or S for South) to a floating point number.
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*
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* For example: 27-00S to -27.0
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*
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* Does not currently handle seconds.
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*/
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static double latitudeToDouble( const TQString &latitude )
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{
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double result;
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double dd = latitude.left(2).toDouble();
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double mm = latitude.mid(3, 2).toDouble();
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result = dd + (mm / 60);
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if (latitude.tqcontains("S"))
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result *= -1;
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return result;
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}
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static double longitudeToDouble( const TQString &longitude )
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{
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double result;
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double ddd = longitude.left(3).toDouble();
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double mm = longitude.mid(4, 2).toDouble();
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result = ddd + (mm / 60);
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if (longitude.tqcontains("W"))
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result *= -1;
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return result;
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}
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TQTime Sun::convertDoubleToLocalTime( const double time )
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{
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TQTime result;
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// Example: say time is 17.7543 Then hours = 17 and minutes = 0.7543 * 60 = 45.258
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// We need to convert the time to CORRECT local hours
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int hours = (int)floor(time);
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int localhours = hours + (m_localUTCOffset / 60);
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// We need to convert the time to CORRECT local minutes
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int minutes = (int)floor((time - hours) * 60);
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int localminutes = minutes + (m_localUTCOffset % 60);
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// We now have to adjust the time to be within the 60m boundary
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if (localminutes < 0)
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{
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//As minutes is less than 0, we need to
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//reduce a hour and add 60m to minutes.
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localminutes += 60;
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localhours--;
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}
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if (localminutes >= 60)
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{
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//As minutes are more than 60, we need to
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//add one more hour and reduce the minutes to
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//a value between 0 and 59.
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localminutes -= 60;
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localhours++;
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}
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// Round up or down to nearest second.
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// Use rint instead of nearbyint because rint is in FreeBSD
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int seconds = (int)rint( fabs( minutes - ((time - hours) * 60) ) * 60 );
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// We now have to adjust the time to be within the 24h boundary
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if (localhours < 0) { localhours += 24; }
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if (localhours >= 24) { localhours -= 24; }
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// Try to set the hours, minutes and seconds for the local time.
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// If this doesn't work, then we will return the invalid time.
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result.setHMS( localhours, localminutes, seconds );
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return result;
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}
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/*
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* Note: year,month,date = calendar date, 1801-2099 only.
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* Eastern longitude positive, Western longitude negative
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* Northern latitude positive, Southern latitude negative
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* The longitude value IS critical in this function!
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* altit = the altitude which the Sun should cross
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* Set to -35/60 degrees for rise/set, -6 degrees
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* for civil, -12 degrees for nautical and -18
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* degrees for astronomical twilight.
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* upper_limb: non-zero -> upper limb, zero -> center
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* Set to non-zero (e.g. 1) when computing rise/set
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* times, and to zero when computing start/end of
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* twilight.
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* trise = the rise time gets stored here
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* tset = the set time gets stored here
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* Both times are relative to the specified altitude,
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* and thus this function can be used to comupte
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* various twilight times, as well as rise/set times
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*
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* Return value: 0 = sun rises/sets this day, times stored in
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* trise and tset.
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* +1 = sun above the specified "horizon" 24 hours.
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* trise set to time when the sun is at south,
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* minus 12 hours while tset is set to the south
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* time plus 12 hours. "Day" length = 24 hours
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* -1 = sun is below the specified "horizon" 24 hours
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* "Day" length = 0 hours, trise and tset are
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* both set to the time when the sun is at south.
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*
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*/
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static int __sunriset__( int year, int month, int day, double lon, double lat,
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double altit, int upper_limb, double &trise, double &tset )
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{
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double d; /* Days since 2000 Jan 0.0 (negative before) */
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double sr; /* Solar distance, astronomical units */
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double sRA; /* Sun's Right Ascension */
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double sdec; /* Sun's declination */
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double sradius; /* Sun's aptqparent radius */
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double t; /* Diurnal arc */
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double tsouth; /* Time when Sun is at south */
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double sidtime; /* Local sidereal time */
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int rc = 0; /* Return code from function - usually 0 */
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/* Compute d of 12h local mean solar time */
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d = days_since_2000_Jan_0(year, month, day);
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d = days_since_2000_Jan_0(year, month, day) + 0.5 - lon / 360.0;
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/* Compute local sideral time of this moment */
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sidtime = revolution( GMST0(d) + 180.0 + lon );
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/* Compute Sun's RA + Decl at this moment */
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sun_RA_dec( d, sRA, sdec, sr );
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/* Compute time when Sun is at south - in hours UT */
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tsouth = 12.0 - rev180(sidtime - sRA) / 15.0;
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/* Compute the Sun's aptqparent radius, degrees */
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sradius = 0.2666 / sr;
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/* Do correction to upper limb, if necessary */
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if ( upper_limb )
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altit -= sradius;
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/* Compute the diurnal arc that the Sun traverses to reach */
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/* the specified altitide altit: */
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double cost;
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cost = ( sind(altit) - sind(lat) * sind(sdec) ) /
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( cosd(lat) * cosd(sdec) );
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if ( cost >= 1.0 )
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{
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rc = -1;
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t = 0.0; /* Sun always below altit */
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}
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else if ( cost <= -1.0 )
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{
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rc = +1;
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t = 12.0; /* Sun always above altit */
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}
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else
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t = acosd(cost) / 15.0; /* The diurnal arc, hours */
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/* Store rise and set times - in hours UT */
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trise = tsouth - t;
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tset = tsouth + t;
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return rc;
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}
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/* This function computes the Sun's position at any instant
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*
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* Computes the Sun's ecliptic longitude and distance
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* at an instant given in d, number of days since
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* 2000 Jan 0.0. The Sun's ecliptic latitude is not
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* computed, since it's always very near 0.
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*/
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static void sunpos( double d, double &lon, double &r )
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{
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double M; /* Mean anomaly of the Sun */
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double w; /* Mean longitude of perihelion */
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/* Note: Sun's mean longitude = M + w */
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double e; /* Eccentricity of Earth's orbit */
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double E; /* Eccentric anomaly */
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double x;
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double y; /* x, y coordinates in orbit */
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double v; /* True anomaly */
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/* Compute mean elements */
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M = revolution( 356.0470 + 0.9856002585 * d );
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w = 282.9404 + 4.70935E-5 * d;
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e = 0.016709 - 1.151E-9 * d;
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/* Compute true longitude and radius vector */
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E = M + e * RADEG * sind(M) * ( 1.0 + e * cosd(M) );
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x = cosd(E) - e;
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y = sqrt( 1.0 - e*e ) * sind(E);
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r = sqrt( x*x + y*y ); /* Solar distance */
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v = atan2d( y, x ); /* True anomaly */
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lon = v + w; /* True solar longitude */
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if ( lon >= 360.0 )
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lon -= 360.0; /* Make it 0..360 degrees */
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}
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static void sun_RA_dec( double d, double &RA, double &dec, double &r )
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{
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double lon;
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double obl_ecl;
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double x;
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double y;
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double z;
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/* Compute Sun's ecliptical coordinates */
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sunpos( d, lon, r );
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/* Compute ecliptic rectangular coordinates (z=0) */
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x = r * cosd(lon);
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y = r * sind(lon);
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/* Compute obliquity of ecliptic (inclination of Earth's axis) */
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obl_ecl = 23.4393 - 3.563E-7 * d;
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/* Convert to equatorial rectangular coordinates - x is unchanged */
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z = y * sind(obl_ecl);
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y = y * cosd(obl_ecl);
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/* Convert to spherical coordinates */
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RA = atan2d( y, x );
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dec = atan2d( z, sqrt(x*x + y*y) );
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}
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static const double INV360 = 1.0 / 360.0;
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/*
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* This function reduces any angle to within the first revolution
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* by subtracting or adding even multiples of 360.0 until the
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* result is >= 0.0 and < 360.0
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*/
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static inline double revolution( const double x )
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{
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return ( x - 360.0 * floor( x * INV360 ) );
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}
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/*
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* Reduce angle to within +180..+180 degrees
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*/
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static inline double rev180( const double x )
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{
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return ( x - 360.0 * floor( x * INV360 + 0.5 ) );
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}
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/*
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* This function computes GMST0, the Greenwhich Mean Sidereal Time
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* at 0h UT (i.e. the sidereal time at the Greenwhich meridian at
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* 0h UT). GMST is then the sidereal time at Greenwich at any
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* time of the day. I've generelized GMST0 as well, and define it
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* as: GMST0 = GMST - UT -- this allows GMST0 to be computed at
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* other times than 0h UT as well. While this sounds somewhat
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* contradictory, it is very practical: instead of computing
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* GMST like:
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*
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* GMST = (GMST0) + UT * (366.2422/365.2422)
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*
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* where (GMST0) is the GMST last time UT was 0 hours, one simply
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* computes:
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*
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* GMST = GMST0 + UT
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*
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* where GMST0 is the GMST "at 0h UT" but at the current moment!
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* Defined in this way, GMST0 will increase with about 4 min a
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* day. It also happens that GMST0 (in degrees, 1 hr = 15 degr)
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* is equal to the Sun's mean longitude plus/minus 180 degrees!
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* (if we neglect aberration, which amounts to 20 seconds of arc
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* or 1.33 seconds of time)
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*
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*/
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static inline double GMST0( const double d )
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{
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double sidtim0;
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/* Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr */
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/* L = M + w, as defined in sunpos(). Since I'm too lazy to */
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/* add these numbers, I'll let the C compiler do it for me. */
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/* Any decent C compiler will add the constants at compile */
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/* time, imposing no runtime or code overhead. */
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sidtim0 = revolution( ( 180.0 + 356.0470 + 282.9404 ) +
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( 0.9856002585 + 4.70935E-5 ) * d );
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return sidtim0;
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}
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