SolTrack.c File Reference

(SolTrack version 2.2, revision 13, hash 9f77eee, 2017-09-09)

#include "SolTrack.h"

Include dependency graph for SolTrack.c:

Functions
void	SolTrack (struct Time time, struct Location location, struct Position *position, int useDegrees, int useNorthEqualsZero, int computeRefrEquatorial, int computeDistance)
	Main function to compute the position of the Sun. More...
double	computeJulianDay (int year, int month, int day, int hour, int minute, double second)
	Compute the Julian Day from the date and time. More...
void	computeLongitude (int computeDistance, struct Position *position)
	Compute the ecliptic longitude of the Sun for a given Julian Day. More...
void	convertEclipticToEquatorial (double longitude, double cosObliquity, double *rightAscension, double *declination)
	Convert ecliptic coordinates to equatorial coordinates. More...
void	convertEquatorialToHorizontal (struct Location location, struct Position *position)
	Convert equatorial to horizontal coordinates. More...
void	eq2horiz (double sinLat, double cosLat, double longitude, double rightAscension, double declination, double agst, double *azimuth, double *sinAlt)
	Convert equatorial coordinates to horizontal coordinates. More...
void	convertHorizontalToEquatorial (double sinLat, double cosLat, double azimuth, double altitude, double *hourAngle, double *declination)
	Convert (refraction-corrected) horizontal coordinates to equatorial coordinates. More...
void	setNorthToZero (double *azimuth, double *hourAngle, int computeRefrEquatorial)
	Convert the South=0 convention to North=0 convention for azimuth and hour angle. More...
void	convertRadiansToDegrees (double *longitude, double *rightAscension, double *declination, double *altitude, double *azimuthRefract, double *altitudeRefract, double *hourAngle, double *declinationRefract, int computeRefrEquatorial)
	Convert final results from radians to degrees. More...
double	STatan2 (double y, double x)
	My version of the atan2() function - ~39% faster than built-in (in terms of number of instructions) More...

Function Documentation

SolTrack()

void SolTrack	(	struct Time	time,
		struct Location	location,
		struct Position *	position,
		int	useDegrees,
		int	useNorthEqualsZero,
		int	computeRefrEquatorial,
		int	computeDistance
	)

Main function to compute the position of the Sun.

Parameters

[in]	time	Struct containing date and time to compute the position for, in UT
[in,out]	location	Struct containing the geographic location to compute the position for
[out]	position	Struct containing the position of the Sun in horizontal (and equatorial if desired) coordinates
[in]	useDegrees	Use degrees for input and output angular variables, rather than radians
[in]	useNorthEqualsZero	Use the definition where azimuth=0 denotes north, rather than south
[in]	computeRefrEquatorial	Compute refraction correction for equatorial coordinates: 0-no, 1-yes
[in]	computeDistance	Compute distance to the Sun (in AU): 0-no, 1-yes

Example Usage:

SolTrack(time, location, &position, 1); 

References Position::altitude, Position::altitudeRefract, Position::azimuthRefract, computeJulianDay(), computeLongitude(), convertEclipticToEquatorial(), convertEquatorialToHorizontal(), convertHorizontalToEquatorial(), convertRadiansToDegrees(), Location::cosLat, Position::cosObliquity, Time::day, Position::declination, Position::declinationRefract, Time::hour, Position::hourAngleRefract, Position::julianDay, Location::latitude, Location::longitude, Position::longitude, Time::minute, Time::month, R2D, Position::rightAscension, Time::second, setNorthToZero(), Location::sinLat, Position::tJC, Position::tJC2, Position::tJD, and Time::year.

Referenced by SolTrack_RiseSet().

computeJulianDay()

double computeJulianDay	(	int	year,
		int	month,
		int	day,
		int	hour,
		int	minute,
		double	second
	)

Compute the Julian Day from the date and time.

Gregorian calendar only (>~1582).

Parameters

[in]	year	Year of date
[in]	month	Month of date
[in]	day	Day of date
[in]	hour	Hour of time
[in]	minute	Minute of time
[in]	second	Second of time

Return values

JulianDay

Julian day for the given date and time

Referenced by SolTrack().

computeLongitude()

void computeLongitude	(	int	computeDistance,
		struct Position *	position
	)

Compute the ecliptic longitude of the Sun for a given Julian Day.

Also computes the obliquity of the ecliptic and nutation.

Parameters

[in]	computeDistance	Compute distance to the Sun (in AU): 0-no, 1-yes
[in,out]	position	Position of the Sun

References Position::cosObliquity, Position::distance, Position::longitude, Position::nutationLon, Position::obliquity, Position::tJC, Position::tJC2, and TWO_PI.

Referenced by SolTrack().

convertEclipticToEquatorial()

void convertEclipticToEquatorial	(	double	longitude,
		double	cosObliquity,
		double *	rightAscension,
		double *	declination
	)

Convert ecliptic coordinates to equatorial coordinates.

This function assumes that the ecliptic latitude = 0.

Parameters

[in]	longitude	Ecliptic longitude of the Sun (rad)
[in]	cosObliquity	Cosine of the obliquity of the ecliptic
[out]	rightAscension	Right ascension of the Sun (rad)
[out]	declination	Declination of the Sun (rad)

References STatan2().

Referenced by SolTrack().

convertEquatorialToHorizontal()

void convertEquatorialToHorizontal	(	struct Location	location,
		struct Position *	position
	)

Convert equatorial to horizontal coordinates.

Also corrects for parallax and atmospheric refraction.

Parameters

[in]	location	Geographic location of the observer (rad)
[in,out]	position	Position of the Sun (rad)

References Position::agst, Position::altitude, Position::altitudeRefract, Position::azimuthRefract, Location::cosLat, Position::cosObliquity, Position::declination, eq2horiz(), Location::longitude, Position::nutationLon, Location::pressure, Position::rightAscension, Location::sinLat, Location::temperature, Position::tJC2, and Position::tJD.

Referenced by SolTrack().

eq2horiz()

void eq2horiz	(	double	sinLat,
		double	cosLat,
		double	longitude,
		double	rightAscension,
		double	declination,
		double	agst,
		double *	azimuth,
		double *	sinAlt
	)

Convert equatorial coordinates to horizontal coordinates.

Parameters

[in]	sinLat	Sine of the geographic latitude of the observer
[in]	cosLat	Cosine of the geographic latitude of the observer
[in]	longitude	Geographic longitude of the observer (rad)
[in]	rightAscension	Right ascension of the Sun (rad)
[in]	declination	Declination of the Sun (rad)
[in]	agst	Apparent Greenwich sidereal time (Greenwich mean sidereal time, corrected for the equation of the equinoxes)
[out]	azimuth	Azimuth ("wind direction") of the Sun (rad; 0=South)
[out]	sinAlt	Sine of the altitude of the Sun above the horizon

References STatan2().

Referenced by convertEquatorialToHorizontal().

convertHorizontalToEquatorial()

void convertHorizontalToEquatorial	(	double	sinLat,
		double	cosLat,
		double	azimuth,
		double	altitude,
		double *	hourAngle,
		double *	declination
	)

Convert (refraction-corrected) horizontal coordinates to equatorial coordinates.

Parameters

[in]	sinLat	Sine of the geographic latitude of the observer
[in]	cosLat	Cosine of the geographic latitude of the observer
[in]	azimuth	Azimuth ("wind direction") of the Sun (rad; 0=South)
[in]	altitude	Altitude of the Sun above the horizon (rad)
[out]	hourAngle	Hour angle of the Sun (rad; 0=South)
[out]	declination	Declination of the Sun (rad)

References STatan2().

Referenced by SolTrack().

setNorthToZero()

void setNorthToZero	(	double *	azimuth,
		double *	hourAngle,
		int	computeRefrEquatorial
	)

Convert the South=0 convention to North=0 convention for azimuth and hour angle.

South=0 is the default in celestial astronomy. This makes the angles compatible with the compass/wind directions.

Parameters

[in,out]	azimuth	Azimuth ("wind direction") of the Sun (rad)
[in,out]	hourAngle	Hour angle of the Sun (rad)
[in]	computeRefrEquatorial	Compute refraction correction for equatorial coordinates

References PI, and TWO_PI.

Referenced by SolTrack().

convertRadiansToDegrees()

void convertRadiansToDegrees	(	double *	longitude,
		double *	rightAscension,
		double *	declination,
		double *	altitude,
		double *	azimuthRefract,
		double *	altitudeRefract,
		double *	hourAngle,
		double *	declinationRefract,
		int	computeRefrEquatorial
	)

Convert final results from radians to degrees.

Not touching intermediate results.

Parameters

[in,out]	longitude	Ecliptical longitude of the Sun (rad->deg)
[in,out]	rightAscension	Right ascension of the Sun (rad->deg)
[in,out]	declination	Declination of the Sun (rad->deg)
[in,out]	altitude	Altitude of the Sun above the horizon (rad->deg)
[in,out]	azimuthRefract	Azimuth ("wind direction") of the Sun (rad->deg), corrected for refraction
[in,out]	altitudeRefract	Altitude of the Sun above the horizon (rad->deg), corrected for refraction
[in,out]	hourAngle	Hour angle of the Sun (rad->deg)
[in,out]	declinationRefract	Declination of the Sun (rad->deg), corrected for refraction
[in]	computeRefrEquatorial	Compute refraction correction for equatorial coordinates

References R2D.

Referenced by SolTrack().

STatan2()

double STatan2	(	double	y,
		double	x
	)

My version of the atan2() function - ~39% faster than built-in (in terms of number of instructions)

Parameters

[in]	y	Numerator of the fraction to compute the arctangent for
[in]	x	Denominator of the fraction to compute the arctangent for

atan2(y,x) = atan(y/x), where the result will be put in the correct quadrant

See also

https://en.wikipedia.org/wiki/Atan2#Definition_and_computation

References PI.

Referenced by convertEclipticToEquatorial(), convertHorizontalToEquatorial(), and eq2horiz().