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Diffstat (limited to 'reference/C/CONTRIB/SNIP/sunriset.c')
| -rwxr-xr-x | reference/C/CONTRIB/SNIP/sunriset.c | 507 |
1 files changed, 507 insertions, 0 deletions
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 <stdio.h>
+#include <math.h>
+
+
+/* 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 */
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