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119 lines
4.8 KiB
119 lines
4.8 KiB
3 years ago
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/*
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SUNRISET.H - computes Sun rise/set times, start/end of twilight, and
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the length of the day at any date and latitude
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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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Split to a header file, 2017-12-10, by Joachim Nilsson
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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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*/
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/* A macro 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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#define days_since_2000_Jan_0(y,m,d) \
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(367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L)
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/* Some conversion factors between radians and degrees */
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#ifndef PI
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#define PI 3.1415926535897932384
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#endif
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#define RADEG ( 180.0 / PI )
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#define DEGRAD ( PI / 180.0 )
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/* The trigonometric functions in degrees */
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#define sind(x) sin((x)*DEGRAD)
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#define cosd(x) cos((x)*DEGRAD)
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#define tand(x) tan((x)*DEGRAD)
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#define atand(x) (RADEG*atan(x))
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#define asind(x) (RADEG*asin(x))
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#define acosd(x) (RADEG*acos(x))
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#define atan2d(y,x) (RADEG*atan2(y,x))
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/* Following are some macros around the "workhorse" function __daylen__ */
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/* They mainly fill in the desired values for the reference altitude */
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/* below the horizon, and also selects whether this altitude should */
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/* refer to the Sun's center or its upper limb. */
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/* This macro computes the length of the day, from sunrise to 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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#define day_length(year,month,day,lon,lat) \
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__daylen__( year, month, day, lon, lat, -35.0/60.0, 1 )
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/* This macro computes the length of the day, including 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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#define day_civil_twilight_length(year,month,day,lon,lat) \
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__daylen__( year, month, day, lon, lat, -6.0, 0 )
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/* This macro computes the length of the day, incl. nautical twilight. */
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/* Nautical twilight starts/ends when the Sun's center is 12 degrees */
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/* below the horizon. */
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#define day_nautical_twilight_length(year,month,day,lon,lat) \
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__daylen__( year, month, day, lon, lat, -12.0, 0 )
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/* This macro computes the length of the day, incl. astronomical twilight. */
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/* Astronomical twilight starts/ends when the Sun's center is 18 degrees */
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/* below the horizon. */
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#define day_astronomical_twilight_length(year,month,day,lon,lat) \
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__daylen__( year, month, day, lon, lat, -18.0, 0 )
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/* This macro 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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#define sun_rise_set(year,month,day,lon,lat,rise,set) \
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__sunriset__( year, month, day, lon, lat, -35.0/60.0, 1, rise, set )
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/* This macro 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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#define civil_twilight(year,month,day,lon,lat,start,end) \
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__sunriset__( year, month, day, lon, lat, -6.0, 0, start, end )
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/* This macro computes the start and end times of nautical twilight. */
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/* Nautical twilight starts/ends when the Sun's center is 12 degrees */
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/* below the horizon. */
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#define nautical_twilight(year,month,day,lon,lat,start,end) \
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__sunriset__( year, month, day, lon, lat, -12.0, 0, start, end )
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/* This macro computes the start and end times of astronomical twilight. */
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/* Astronomical twilight starts/ends when the Sun's center is 18 degrees */
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/* below the horizon. */
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#define astronomical_twilight(year,month,day,lon,lat,start,end) \
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__sunriset__( year, month, day, lon, lat, -18.0, 0, start, end )
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/* Function prototypes */
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double __daylen__( int year, int month, int day, double lon, double lat,
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double altit, int upper_limb );
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int __sunriset__( int year, int month, int day, double lon, double lat,
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double altit, int upper_limb, double *rise, double *set );
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void sunpos( double d, double *lon, double *r );
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void sun_RA_dec( double d, double *RA, double *dec, double *r );
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double revolution( double x );
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double rev180( double x );
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double GMST0( double d );
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