From 7e0f021a9aec35fd8e6725e87e3313b101d26f5e Mon Sep 17 00:00:00 2001 From: Tobias Klauser Date: Sun, 27 Jan 2008 11:37:44 +0100 Subject: Initial import (2.0.2-6) --- reference/C/CONTRIB/SNIP/sunriset.c | 507 ++++++++++++++++++++++++++++++++++++ 1 file changed, 507 insertions(+) create mode 100755 reference/C/CONTRIB/SNIP/sunriset.c (limited to 'reference/C/CONTRIB/SNIP/sunriset.c') diff --git a/reference/C/CONTRIB/SNIP/sunriset.c b/reference/C/CONTRIB/SNIP/sunriset.c new file mode 100755 index 0000000..fa67e67 --- /dev/null +++ b/reference/C/CONTRIB/SNIP/sunriset.c @@ -0,0 +1,507 @@ +/* + +SUNRISET.C - computes Sun rise/set times, start/end of twilight, and + the length of the day at any date and latitude + +Written as DAYLEN.C, 1989-08-16 + +Modified to SUNRISET.C, 1992-12-01 + +(c) Paul Schlyter, 1989, 1992 + +Released to the public domain by Paul Schlyter, December 1992 + +*/ + + +#include +#include + + +/* A macro to compute the number of days elapsed since 2000 Jan 0.0 */ +/* (which is equal to 1999 Dec 31, 0h UT) */ + +#define days_since_2000_Jan_0(y,m,d) \ + (367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L) + +/* Some conversion factors between radians and degrees */ + +#ifndef PI + #define PI 3.1415926535897932384 +#endif + +#define RADEG ( 180.0 / PI ) +#define DEGRAD ( PI / 180.0 ) + +/* The trigonometric functions in degrees */ + +#define sind(x) sin((x)*DEGRAD) +#define cosd(x) cos((x)*DEGRAD) +#define tand(x) tan((x)*DEGRAD) + +#define atand(x) (RADEG*atan(x)) +#define asind(x) (RADEG*asin(x)) +#define acosd(x) (RADEG*acos(x)) +#define atan2d(y,x) (RADEG*atan2(y,x)) + + +/* Following are some macros around the "workhorse" function __daylen__ */ +/* They mainly fill in the desired values for the reference altitude */ +/* below the horizon, and also selects whether this altitude should */ +/* refer to the Sun's center or its upper limb. */ + + +/* This macro computes the length of the day, from sunrise to sunset. */ +/* Sunrise/set is considered to occur when the Sun's upper limb is */ +/* 35 arc minutes below the horizon (this accounts for the refraction */ +/* of the Earth's atmosphere). */ +#define day_length(year,month,day,lon,lat) \ + __daylen__( year, month, day, lon, lat, -35.0/60.0, 1 ) + +/* This macro computes the length of the day, including civil twilight. */ +/* Civil twilight starts/ends when the Sun's center is 6 degrees below */ +/* the horizon. */ +#define day_civil_twilight_length(year,month,day,lon,lat) \ + __daylen__( year, month, day, lon, lat, -6.0, 0 ) + +/* This macro computes the length of the day, incl. nautical twilight. */ +/* Nautical twilight starts/ends when the Sun's center is 12 degrees */ +/* below the horizon. */ +#define day_nautical_twilight_length(year,month,day,lon,lat) \ + __daylen__( year, month, day, lon, lat, -12.0, 0 ) + +/* This macro computes the length of the day, incl. astronomical twilight. */ +/* Astronomical twilight starts/ends when the Sun's center is 18 degrees */ +/* below the horizon. */ +#define day_astronomical_twilight_length(year,month,day,lon,lat) \ + __daylen__( year, month, day, lon, lat, -18.0, 0 ) + + +/* This macro computes times for sunrise/sunset. */ +/* Sunrise/set is considered to occur when the Sun's upper limb is */ +/* 35 arc minutes below the horizon (this accounts for the refraction */ +/* of the Earth's atmosphere). */ +#define sun_rise_set(year,month,day,lon,lat,rise,set) \ + __sunriset__( year, month, day, lon, lat, -35.0/60.0, 1, rise, set ) + +/* This macro computes the start and end times of civil twilight. */ +/* Civil twilight starts/ends when the Sun's center is 6 degrees below */ +/* the horizon. */ +#define civil_twilight(year,month,day,lon,lat,start,end) \ + __sunriset__( year, month, day, lon, lat, -6.0, 0, start, end ) + +/* This macro computes the start and end times of nautical twilight. */ +/* Nautical twilight starts/ends when the Sun's center is 12 degrees */ +/* below the horizon. */ +#define nautical_twilight(year,month,day,lon,lat,start,end) \ + __sunriset__( year, month, day, lon, lat, -12.0, 0, start, end ) + +/* This macro computes the start and end times of astronomical twilight. */ +/* Astronomical twilight starts/ends when the Sun's center is 18 degrees */ +/* below the horizon. */ +#define astronomical_twilight(year,month,day,lon,lat,start,end) \ + __sunriset__( year, month, day, lon, lat, -18.0, 0, start, end ) + + +/* Function prototypes */ + +double __daylen__( int year, int month, int day, double lon, double lat, + double altit, int upper_limb ); + +int __sunriset__( int year, int month, int day, double lon, double lat, + double altit, int upper_limb, double *rise, double *set ); + +void sunpos( double d, double *lon, double *r ); + +void sun_RA_dec( double d, double *RA, double *dec, double *r ); + +double revolution( double x ); + +double rev180( double x ); + +double GMST0( double d ); + + + +/* A small test program */ + +void main(void) +{ + int year,month,day; + double lon, lat; + double daylen, civlen, nautlen, astrlen; + double rise, set, civ_start, civ_end, naut_start, naut_end, + astr_start, astr_end; + int rs, civ, naut, astr; + + printf( "Longitude (+ is east) and latitude (+ is north) : " ); + scanf( "%lf %lf", &lon, &lat ); + + for(;;) + { + printf( "Input date ( yyyy mm dd ) (ctrl-C exits): " ); + scanf( "%d %d %d", &year, &month, &day ); + + daylen = day_length(year,month,day,lon,lat); + civlen = day_civil_twilight_length(year,month,day,lon,lat); + nautlen = day_nautical_twilight_length(year,month,day,lon,lat); + astrlen = day_astronomical_twilight_length(year,month,day, + lon,lat); + + printf( "Day length: %5.2f hours\n", daylen ); + printf( "With civil twilight %5.2f hours\n", civlen ); + printf( "With nautical twilight %5.2f hours\n", nautlen ); + printf( "With astronomical twilight %5.2f hours\n", astrlen ); + printf( "Length of twilight: civil %5.2f hours\n", + (civlen-daylen)/2.0); + printf( " nautical %5.2f hours\n", + (nautlen-daylen)/2.0); + printf( " astronomical %5.2f hours\n", + (astrlen-daylen)/2.0); + + rs = sun_rise_set ( year, month, day, lon, lat, + &rise, &set ); + civ = civil_twilight ( year, month, day, lon, lat, + &civ_start, &civ_end ); + naut = nautical_twilight ( year, month, day, lon, lat, + &naut_start, &naut_end ); + astr = astronomical_twilight( year, month, day, lon, lat, + &astr_start, &astr_end ); + + printf( "Sun at south %5.2fh UT\n", (rise+set)/2.0 ); + + switch( rs ) + { + case 0: + printf( "Sun rises %5.2fh UT, sets %5.2fh UT\n", + rise, set ); + break; + case +1: + printf( "Sun above horizon\n" ); + break; + case -1: + printf( "Sun below horizon\n" ); + break; + } + + switch( civ ) + { + case 0: + printf( "Civil twilight starts %5.2fh, " + "ends %5.2fh UT\n", civ_start, civ_end ); + break; + case +1: + printf( "Never darker than civil twilight\n" ); + break; + case -1: + printf( "Never as bright as civil twilight\n" ); + break; + } + + switch( naut ) + { + case 0: + printf( "Nautical twilight starts %5.2fh, " + "ends %5.2fh UT\n", naut_start, naut_end ); + break; + case +1: + printf( "Never darker than nautical twilight\n" ); + break; + case -1: + printf( "Never as bright as nautical twilight\n" ); + break; + } + + switch( astr ) + { + case 0: + printf( "Astronomical twilight starts %5.2fh, " + "ends %5.2fh UT\n", astr_start, astr_end ); + break; + case +1: + printf( "Never darker than astronomical twilight\n" ); + break; + case -1: + printf( "Never as bright as astronomical twilight\n" ); + break; + } + + } +} + + +/* The "workhorse" function for sun rise/set times */ + +int __sunriset__( int year, int month, int day, double lon, double lat, + double altit, int upper_limb, double *trise, double *tset ) +/***************************************************************************/ +/* Note: year,month,date = calendar date, 1801-2099 only. */ +/* Eastern longitude positive, Western longitude negative */ +/* Northern latitude positive, Southern latitude negative */ +/* The longitude value IS critical in this function! */ +/* altit = the altitude which the Sun should cross */ +/* Set to -35/60 degrees for rise/set, -6 degrees */ +/* for civil, -12 degrees for nautical and -18 */ +/* degrees for astronomical twilight. */ +/* upper_limb: non-zero -> upper limb, zero -> center */ +/* Set to non-zero (e.g. 1) when computing rise/set */ +/* times, and to zero when computing start/end of */ +/* twilight. */ +/* *rise = where to store the rise time */ +/* *set = where to store the set time */ +/* Both times are relative to the specified altitude, */ +/* and thus this function can be used to comupte */ +/* various twilight times, as well as rise/set times */ +/* Return value: 0 = sun rises/sets this day, times stored at */ +/* *trise and *tset. */ +/* +1 = sun above the specified "horizon" 24 hours. */ +/* *trise set to time when the sun is at south, */ +/* minus 12 hours while *tset is set to the south */ +/* time plus 12 hours. "Day" length = 24 hours */ +/* -1 = sun is below the specified "horizon" 24 hours */ +/* "Day" length = 0 hours, *trise and *tset are */ +/* both set to the time when the sun is at south. */ +/* */ +/**********************************************************************/ +{ + double d, /* Days since 2000 Jan 0.0 (negative before) */ + sr, /* Solar distance, astronomical units */ + sRA, /* Sun's Right Ascension */ + sdec, /* Sun's declination */ + sradius, /* Sun's apparent radius */ + t, /* Diurnal arc */ + tsouth, /* Time when Sun is at south */ + sidtime; /* Local sidereal time */ + + int rc = 0; /* Return cde from function - usually 0 */ + + /* Compute d of 12h local mean solar time */ + d = days_since_2000_Jan_0(year,month,day) + 0.5 - lon/360.0; + + /* Compute local sideral time of this moment */ + sidtime = revolution( GMST0(d) + 180.0 + lon ); + + /* Compute Sun's RA + Decl at this moment */ + sun_RA_dec( d, &sRA, &sdec, &sr ); + + /* Compute time when Sun is at south - in hours UT */ + tsouth = 12.0 - rev180(sidtime - sRA)/15.0; + + /* Compute the Sun's apparent radius, degrees */ + sradius = 0.2666 / sr; + + /* Do correction to upper limb, if necessary */ + if ( upper_limb ) + altit -= sradius; + + /* Compute the diurnal arc that the Sun traverses to reach */ + /* the specified altitide altit: */ + { + double cost; + cost = ( sind(altit) - sind(lat) * sind(sdec) ) / + ( cosd(lat) * cosd(sdec) ); + if ( cost >= 1.0 ) + rc = -1, t = 0.0; /* Sun always below altit */ + else if ( cost <= -1.0 ) + rc = +1, t = 12.0; /* Sun always above altit */ + else + t = acosd(cost)/15.0; /* The diurnal arc, hours */ + } + + /* Store rise and set times - in hours UT */ + *trise = tsouth - t; + *tset = tsouth + t; + + return rc; +} /* __sunriset__ */ + + + +/* The "workhorse" function */ + + +double __daylen__( int year, int month, int day, double lon, double lat, + double altit, int upper_limb ) +/**********************************************************************/ +/* Note: year,month,date = calendar date, 1801-2099 only. */ +/* Eastern longitude positive, Western longitude negative */ +/* Northern latitude positive, Southern latitude negative */ +/* The longitude value is not critical. Set it to the correct */ +/* longitude if you're picky, otherwise set to to, say, 0.0 */ +/* The latitude however IS critical - be sure to get it correct */ +/* altit = the altitude which the Sun should cross */ +/* Set to -35/60 degrees for rise/set, -6 degrees */ +/* for civil, -12 degrees for nautical and -18 */ +/* degrees for astronomical twilight. */ +/* upper_limb: non-zero -> upper limb, zero -> center */ +/* Set to non-zero (e.g. 1) when computing day length */ +/* and to zero when computing day+twilight length. */ +/**********************************************************************/ +{ + double d, /* Days since 2000 Jan 0.0 (negative before) */ + obl_ecl, /* Obliquity (inclination) of Earth's axis */ + sr, /* Solar distance, astronomical units */ + slon, /* True solar longitude */ + sin_sdecl, /* Sine of Sun's declination */ + cos_sdecl, /* Cosine of Sun's declination */ + sradius, /* Sun's apparent radius */ + t; /* Diurnal arc */ + + /* Compute d of 12h local mean solar time */ + d = days_since_2000_Jan_0(year,month,day) + 0.5 - lon/360.0; + + /* Compute obliquity of ecliptic (inclination of Earth's axis) */ + obl_ecl = 23.4393 - 3.563E-7 * d; + + /* Compute Sun's position */ + sunpos( d, &slon, &sr ); + + /* Compute sine and cosine of Sun's declination */ + sin_sdecl = sind(obl_ecl) * sind(slon); + cos_sdecl = sqrt( 1.0 - sin_sdecl * sin_sdecl ); + + /* Compute the Sun's apparent radius, degrees */ + sradius = 0.2666 / sr; + + /* Do correction to upper limb, if necessary */ + if ( upper_limb ) + altit -= sradius; + + /* Compute the diurnal arc that the Sun traverses to reach */ + /* the specified altitide altit: */ + { + double cost; + cost = ( sind(altit) - sind(lat) * sin_sdecl ) / + ( cosd(lat) * cos_sdecl ); + if ( cost >= 1.0 ) + t = 0.0; /* Sun always below altit */ + else if ( cost <= -1.0 ) + t = 24.0; /* Sun always above altit */ + else t = (2.0/15.0) * acosd(cost); /* The diurnal arc, hours */ + } + return t; +} /* __daylen__ */ + + +/* This function computes the Sun's position at any instant */ + +void sunpos( double d, double *lon, double *r ) +/******************************************************/ +/* Computes the Sun's ecliptic longitude and distance */ +/* at an instant given in d, number of days since */ +/* 2000 Jan 0.0. The Sun's ecliptic latitude is not */ +/* computed, since it's always very near 0. */ +/******************************************************/ +{ + double M, /* Mean anomaly of the Sun */ + w, /* Mean longitude of perihelion */ + /* Note: Sun's mean longitude = M + w */ + e, /* Eccentricity of Earth's orbit */ + E, /* Eccentric anomaly */ + x, y, /* x, y coordinates in orbit */ + v; /* True anomaly */ + + /* Compute mean elements */ + M = revolution( 356.0470 + 0.9856002585 * d ); + w = 282.9404 + 4.70935E-5 * d; + e = 0.016709 - 1.151E-9 * d; + + /* Compute true longitude and radius vector */ + E = M + e * RADEG * sind(M) * ( 1.0 + e * cosd(M) ); + x = cosd(E) - e; + y = sqrt( 1.0 - e*e ) * sind(E); + *r = sqrt( x*x + y*y ); /* Solar distance */ + v = atan2d( y, x ); /* True anomaly */ + *lon = v + w; /* True solar longitude */ + if ( *lon >= 360.0 ) + *lon -= 360.0; /* Make it 0..360 degrees */ +} + +void sun_RA_dec( double d, double *RA, double *dec, double *r ) +{ + double lon, obl_ecl, x, y, z; + + /* Compute Sun's ecliptical coordinates */ + sunpos( d, &lon, r ); + + /* Compute ecliptic rectangular coordinates (z=0) */ + x = *r * cosd(lon); + y = *r * sind(lon); + + /* Compute obliquity of ecliptic (inclination of Earth's axis) */ + obl_ecl = 23.4393 - 3.563E-7 * d; + + /* Convert to equatorial rectangular coordinates - x is uchanged */ + z = y * sind(obl_ecl); + y = y * cosd(obl_ecl); + + /* Convert to spherical coordinates */ + *RA = atan2d( y, x ); + *dec = atan2d( z, sqrt(x*x + y*y) ); + +} /* sun_RA_dec */ + + +/******************************************************************/ +/* This function reduces any angle to within the first revolution */ +/* by subtracting or adding even multiples of 360.0 until the */ +/* result is >= 0.0 and < 360.0 */ +/******************************************************************/ + +#define INV360 ( 1.0 / 360.0 ) + +double revolution( double x ) +/*****************************************/ +/* Reduce angle to within 0..360 degrees */ +/*****************************************/ +{ + return( x - 360.0 * floor( x * INV360 ) ); +} /* revolution */ + +double rev180( double x ) +/*********************************************/ +/* Reduce angle to within +180..+180 degrees */ +/*********************************************/ +{ + return( x - 360.0 * floor( x * INV360 + 0.5 ) ); +} /* revolution */ + + +/*******************************************************************/ +/* This function computes GMST0, the Greenwhich Mean Sidereal Time */ +/* at 0h UT (i.e. the sidereal time at the Greenwhich meridian at */ +/* 0h UT). GMST is then the sidereal time at Greenwich at any */ +/* time of the day. I've generelized GMST0 as well, and define it */ +/* as: GMST0 = GMST - UT -- this allows GMST0 to be computed at */ +/* other times than 0h UT as well. While this sounds somewhat */ +/* contradictory, it is very practical: instead of computing */ +/* GMST like: */ +/* */ +/* GMST = (GMST0) + UT * (366.2422/365.2422) */ +/* */ +/* where (GMST0) is the GMST last time UT was 0 hours, one simply */ +/* computes: */ +/* */ +/* GMST = GMST0 + UT */ +/* */ +/* where GMST0 is the GMST "at 0h UT" but at the current moment! */ +/* Defined in this way, GMST0 will increase with about 4 min a */ +/* day. It also happens that GMST0 (in degrees, 1 hr = 15 degr) */ +/* is equal to the Sun's mean longitude plus/minus 180 degrees! */ +/* (if we neglect aberration, which amounts to 20 seconds of arc */ +/* or 1.33 seconds of time) */ +/* */ +/*******************************************************************/ + +double GMST0( double d ) +{ + double sidtim0; + /* Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr */ + /* L = M + w, as defined in sunpos(). Since I'm too lazy to */ + /* add these numbers, I'll let the C compiler do it for me. */ + /* Any decent C compiler will add the constants at compile */ + /* time, imposing no runtime or code overhead. */ + sidtim0 = revolution( ( 180.0 + 356.0470 + 282.9404 ) + + ( 0.9856002585 + 4.70935E-5 ) * d ); + return sidtim0; +} /* GMST0 */ -- cgit v1.2.3-54-g00ecf