edu.wisc.ssec.mcidasv.util

Class SunRelativePosition

java.lang.Object

edu.wisc.ssec.mcidasv.util.SunRelativePosition

public class SunRelativePosition
extends java.lang.Object

Calcule la position du soleil relativement à la position de l'observateur. Cette classe reçoit en entrés les coordonnées spatio-temporelles de l'observateur, soit:

La longitude (en degrées) de l'observateur; La latitude (en degrées) de l'observateur; La date et heure en heure universelle (GMT). La position du soleil calculée en sortie comprend les valeurs suivantes: L'azimuth du soleil (en degrés dans le sens des aiguilles d'une montre depuis le nord); L'élévation du soleil (en degrés par rapport a l'horizon).

Les algorithmes utilisés dans cette classe sont des adaptations des algorithmes en javascript écrit par le "National Oceanic and Atmospheric Administration, Surface Radiation Research Branch". L'application original est le Solar Position Calculator.

The approximations used in these programs are very good for years between 1800 and 2100. Results should still be sufficiently accurate for the range from -1000 to 3000. Outside of this range, results will be given, but the potential for error is higher.

Since:

2.1

Version:

$Id$

Author:

Remi Eve, Martin Desruisseaux (IRD)

Field Summary

Fields

Modifier and Type	Field and Description
static double	ASTRONOMICAL_TWILIGHT Elevation angle of astronomical twilight, in degrees.
private double	azimuth Azimuth du soleil, en degrés dans le sens des aiguilles d'une montre depuis le nord.
static double	CIVIL_TWILIGHT Elevation angle of civil twilight, in degrees.
private static double	DARK Valeur affectée lorsque un resultat n'est pas calculable du fait de la nuit.
private static int	DAY_MILLIS Number of milliseconds in a day.
private double	elevation Elévation du soleil, en degrés par rapport a l'horizon.
(package private) double	eqTime
private double	jddate
private double	julianDay
private double	latitude Geographic coordinate where current elevation and azimuth were computed.
private double	longitude Geographic coordinate where current elevation and azimuth were computed.
static double	NAUTICAL_TWILIGHT Elevation angle of nautical twilight, in degrees.
private long	noonTime Heure à laquelle le soleil est au plus haut dans la journée en millisecondes écoulées depuis le 1er janvier 1970.
(package private) double	solarDec
private long	time Date and time when the current elevation and azimuth were computed.
private boolean	timeUpdated
private double	twilight Sun's elevation angle at twilight, in degrees.
private boolean	updated true is the elevation and azimuth are computed, or false if they need to be computed.

Constructor Summary

Constructors

Constructor and Description
SunRelativePosition() Constructs a sun relative position calculator.
SunRelativePosition(double twilight) Constructs a sun relative position calculator with the specified value for the sun elevation at twilight.

Method Summary

Modifier and Type	Method and Description
private void	compute() Calculates solar position for the current date, time and location.
private static double	eccentricityEarthOrbit(double t) Calculate the eccentricity of earth's orbit.
private static double	equationOfTime(double t) Calculate the difference between true solar time and mean.
double	getAzimuth() Retourne l'azimuth en degrés.
java.awt.geom.Point2D	getCoordinate() Returns the coordinate used for elevation and azimuth computation.
static void	getCosSolarZenith(float[] longitudes, float[] latitudes, java.util.Date dateTime, visad.FlatField output)
java.util.Date	getDate() Returns the date used for elevation and azimuth computation.
double	getElevation() Retourne l'élévation en degrés.
java.util.Date	getNoonDate() Retourne la date à laquelle le soleil est au plus haut dans la journée.
long	getNoonTime() Retourne l'heure à laquelle le soleil est au plus haut.
double	getSolarZenith()
static void	getSolarZenith(float[] longitudes, float[] latitudes, java.util.Date dateTime, visad.FlatField output)
static float[]	getSolarZenith(float[] longitudes, float[] latitudes, java.util.Date dateTime, float[] solzen)
double	getTwilight() Returns the sun's elevation angle at twilight, in degrees.
static void	main(java.lang.String[] args) Affiche la position du soleil à la date et coordonnées spécifiée.
private static double	meanObliquityOfEcliptic(double t) Calculate the mean obliquity of the ecliptic.
private static double	obliquityCorrected(double t) Calculate the corrected obliquity of the ecliptic.
private static double	refractionCorrection(double zenith) Computes the refraction correction angle.
void	setCoordinate(double longitude, double latitude) Set the geographic coordinate where to compute the elevation and azimuth.
void	setCoordinate(java.awt.geom.Point2D point) Set the geographic coordinate where to compute the elevation and azimuth.
void	setDate(java.util.Date date) Set the date and time when to compute the elevation and azimuth.
void	setTwilight(double twilight) Set the sun's elevation angle at twilight, in degrees.
private static double	solarNoonTime(double lon, double eqTime) Calculate the Universal Coordinated Time (UTC) of solar noon for the given day at the given location on earth.
private static double	sunApparentLongitude(double t) Calculate the apparent longitude of the sun.
private static double	sunDeclination(double t) Calculate the declination of the sun.
private static double	sunEquationOfCenter(double t) Calculate the equation of center for the sun.
private static double	sunGeometricMeanAnomaly(double t) Calculate the Geometric Mean Anomaly of the Sun.
private static double	sunGeometricMeanLongitude(double t) Calculate the Geometric Mean Longitude of the Sun.
private static double	sunRadiusVector(double t) Calculate the distance to the sun in Astronomical Units (AU).
private static double	sunRightAscension(double t) Calculate the right ascension of the sun.
private static double	sunTrueAnomaly(double t) Calculate the true anamoly of the sun.
private static double	sunTrueLongitude(double t) Calculate the true longitude of the sun.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DAY_MILLIS

private static final int DAY_MILLIS

Number of milliseconds in a day.

See Also:

Constant Field Values

DARK

private static final double DARK

Valeur affectée lorsque un resultat n'est pas calculable du fait de la nuit. Cette valeur concerne les valeurs de sorties elevation et azimuth.

See Also:

Constant Field Values

ASTRONOMICAL_TWILIGHT

public static final double ASTRONOMICAL_TWILIGHT

Elevation angle of astronomical twilight, in degrees. Astronomical twilight is the time of morning or evening when the sun is 18° below the horizon (solar elevation angle of -18°).

See Also:

Constant Field Values

NAUTICAL_TWILIGHT

public static final double NAUTICAL_TWILIGHT

Elevation angle of nautical twilight, in degrees. Nautical twilight is the time of morning or evening when the sun is 12° below the horizon (solar elevation angle of -12°).

See Also:

Constant Field Values

CIVIL_TWILIGHT

public static final double CIVIL_TWILIGHT

Elevation angle of civil twilight, in degrees. Civil twilight is the time of morning or evening when the sun is 6° below the horizon (solar elevation angle of -6°).

See Also:

Constant Field Values

twilight

private double twilight

Sun's elevation angle at twilight, in degrees. Common values are defined for the astronomical twilight (-18°), nautical twilight (-12°) and civil twilight (-6°). If no twilight are defined, then this value is NaN. The elevation and azimuth are set to NaN when the sun elevation is below the twilight value (i.e. during night). The default value is CIVIL_TWILIGHT.

noonTime

private long noonTime

Heure à laquelle le soleil est au plus haut dans la journée en millisecondes écoulées depuis le 1er janvier 1970.

azimuth

private double azimuth

Azimuth du soleil, en degrés dans le sens des aiguilles d'une montre depuis le nord.

elevation

private double elevation

Elévation du soleil, en degrés par rapport a l'horizon.

latitude

private double latitude

Geographic coordinate where current elevation and azimuth were computed. Value are in degrees of longitude or latitude.

longitude

private double longitude

Geographic coordinate where current elevation and azimuth were computed. Value are in degrees of longitude or latitude.

time

private long time

Date and time when the current elevation and azimuth were computed. Value is in milliseconds ellapsed since midnight UTC, January 1st, 1970.

julianDay

private double julianDay

jddate

private double jddate

solarDec

double solarDec

eqTime

double eqTime

timeUpdated

private boolean timeUpdated

updated

private boolean updated

true is the elevation and azimuth are computed, or false if they need to be computed. This flag is set to false when the date and/or the coordinate change.

Constructor Detail

SunRelativePosition

public SunRelativePosition()

Constructs a sun relative position calculator.

SunRelativePosition

public SunRelativePosition(double twilight)
                    throws java.lang.IllegalArgumentException

Constructs a sun relative position calculator with the specified value for the sun elevation at twilight.

Parameters:

twilight - The new sun elevation at twilight, or Double.NaN if no twilight value should be taken in account.

Throws:

java.lang.IllegalArgumentException - if the twilight value is illegal.

Method Detail

sunEquationOfCenter

private static double sunEquationOfCenter(double t)

Calculate the equation of center for the sun. This value is a correction to add to the geometric mean longitude in order to get the "true" longitude of the sun.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Equation of center in degrees.

sunGeometricMeanLongitude

private static double sunGeometricMeanLongitude(double t)

Calculate the Geometric Mean Longitude of the Sun. This value is close to 0° at the spring equinox, 90° at the summer solstice, 180° at the automne equinox and 270° at the winter solstice.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Geometric Mean Longitude of the Sun in degrees, in the range 0° (inclusive) to 360° (exclusive).

sunTrueLongitude

private static double sunTrueLongitude(double t)

Calculate the true longitude of the sun. This the geometric mean longitude plus a correction factor ("equation of center" for the sun).

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun's true longitude in degrees.

sunApparentLongitude

private static double sunApparentLongitude(double t)

Calculate the apparent longitude of the sun.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun's apparent longitude in degrees.

sunGeometricMeanAnomaly

private static double sunGeometricMeanAnomaly(double t)

Calculate the Geometric Mean Anomaly of the Sun.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Geometric Mean Anomaly of the Sun in degrees.

sunTrueAnomaly

private static double sunTrueAnomaly(double t)

Calculate the true anamoly of the sun.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun's true anamoly in degrees.

eccentricityEarthOrbit

private static double eccentricityEarthOrbit(double t)

Calculate the eccentricity of earth's orbit. This is the ratio (a-b)/a where a is the semi-major axis length and b is the semi-minor axis length. Value is 0 for a circular orbit.

Parameters:

t - number of Julian centuries since J2000.

Returns:

The unitless eccentricity.

sunRadiusVector

private static double sunRadiusVector(double t)

Calculate the distance to the sun in Astronomical Units (AU).

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun radius vector in AUs.

meanObliquityOfEcliptic

private static double meanObliquityOfEcliptic(double t)

Calculate the mean obliquity of the ecliptic.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Mean obliquity in degrees.

obliquityCorrected

private static double obliquityCorrected(double t)

Calculate the corrected obliquity of the ecliptic.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Corrected obliquity in degrees.

sunRightAscension

private static double sunRightAscension(double t)

Calculate the right ascension of the sun. Similar to the angular system used to define latitude and longitude on Earth's surface, right ascension is roughly analogous to longitude, and defines an angular offset from the meridian of the vernal equinox.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun's right ascension in degrees.

sunDeclination

private static double sunDeclination(double t)

Calculate the declination of the sun. Declination is analogous to latitude on Earth's surface, and measures an angular displacement north or south from the projection of Earth's equator on the celestial sphere to the location of a celestial body.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Sun's declination in degrees.

solarNoonTime

private static double solarNoonTime(double lon,
                                    double eqTime)

Calculate the Universal Coordinated Time (UTC) of solar noon for the given day at the given location on earth.

Parameters:

lon - longitude of observer in degrees.

eqTime - Equation of time.

Returns:

Time in minutes from beginnning of day in UTC.

equationOfTime

private static double equationOfTime(double t)

Calculate the difference between true solar time and mean. The "equation of time" is a term accounting for changes in the time of solar noon for a given location over the course of a year. Earth's elliptical orbit and Kepler's law of equal areas in equal times are the culprits behind this phenomenon. See the Analemma page. Below is a plot of the equation of time versus the day of the year.

Parameters:

t - number of Julian centuries since J2000.

Returns:

Equation of time in minutes of time.

refractionCorrection

private static double refractionCorrection(double zenith)

Computes the refraction correction angle. The effects of the atmosphere vary with atmospheric pressure, humidity and other variables. Therefore the calculation is approximate. Errors can be expected to increase the further away you are from the equator, because the sun rises and sets at a very shallow angle. Small variations in the atmosphere can have a larger effect.

Parameters:

zenith - The sun zenith angle in degrees.

Returns:

The refraction correction in degrees.

compute

private void compute()

Calculates solar position for the current date, time and location. Results are reported in azimuth and elevation in degrees.

setCoordinate

public void setCoordinate(double longitude,
                          double latitude)

Set the geographic coordinate where to compute the elevation and azimuth.

Parameters:

longitude - The longitude in degrees. Positive values are East; negative values are West.

latitude - The latitude in degrees. Positive values are North, negative values are South.

setCoordinate

public void setCoordinate(java.awt.geom.Point2D point)

Set the geographic coordinate where to compute the elevation and azimuth.

Parameters:

point - The geographic coordinates in degrees of longitude and latitude.

getCoordinate

public java.awt.geom.Point2D getCoordinate()

Returns the coordinate used for elevation and azimuth computation. This is the coordinate specified during the last call to a setCoordinate(...) method.

setDate

public void setDate(java.util.Date date)

Set the date and time when to compute the elevation and azimuth.

Parameters:

date - The date and time.

getDate

public java.util.Date getDate()

Returns the date used for elevation and azimuth computation. This is the date specified during the last call to setDate(java.util.Date).

setTwilight

public void setTwilight(double twilight)
                 throws java.lang.IllegalArgumentException

Set the sun's elevation angle at twilight, in degrees. Common values are defined for the astronomical twilight (-18°), nautical twilight (-12°) and civil twilight (-6°). The elevation and azimuth are set to NaN when the sun elevation is below the twilight value (i.e. during night). The default value is CIVIL_TWILIGHT.

Parameters:

twilight - The new sun elevation at twilight, or Double.NaN if no twilight value should be taken in account.

Throws:

java.lang.IllegalArgumentException - if the twilight value is illegal.

getTwilight

public double getTwilight()

Returns the sun's elevation angle at twilight, in degrees. This is the value set during the last call to setTwilight(double).

getAzimuth

public double getAzimuth()

Retourne l'azimuth en degrés.

Returns:

L'azimuth en degrés.

getElevation

public double getElevation()

Retourne l'élévation en degrés.

Returns:

L'élévation en degrés.

getSolarZenith

public double getSolarZenith()

Returns:

solar zenith angle in degrees

getNoonTime

public long getNoonTime()

Retourne l'heure à laquelle le soleil est au plus haut. L'heure est retournée en nombre de millisecondes écoulées depuis le debut de la journée (minuit) en heure UTC.

getNoonDate

public java.util.Date getNoonDate()

Retourne la date à laquelle le soleil est au plus haut dans la journée. Cette méthode est équivalente à getNoonTime() mais inclue le jour de la date qui avait été spécifiée à la méthode compute().

getCosSolarZenith

public static void getCosSolarZenith(float[] longitudes,
                                     float[] latitudes,
                                     java.util.Date dateTime,
                                     visad.FlatField output)
                              throws java.lang.Exception

Parameters:

longitudes - float[] of degrees

latitudes - float[] of degrees

dateTime - java.util.Date

output - FlatField of which computed angles (degrees) will be written into the range

Throws:

java.lang.Exception

getSolarZenith

public static void getSolarZenith(float[] longitudes,
                                  float[] latitudes,
                                  java.util.Date dateTime,
                                  visad.FlatField output)
                           throws java.lang.Exception

Parameters:

longitudes - float[] of degrees

latitudes - float[] of degrees

dateTime - java.util.Date

output - FlatField of which computed angles (degrees) will be written into the range

Throws:

java.lang.Exception

getSolarZenith

public static float[] getSolarZenith(float[] longitudes,
                                     float[] latitudes,
                                     java.util.Date dateTime,
                                     float[] solzen)
                              throws java.lang.Exception

Parameters:

longitudes - float[] of degrees

latitudes - float[] of degrees

dateTime - java.util.Date

solzen - float[] of computed solar zenith angle (degrees). If null, array will be allocated.

Returns:

the compute values

Throws:

java.lang.Exception

main

public static void main(java.lang.String[] args)
                 throws java.text.ParseException

Affiche la position du soleil à la date et coordonnées spécifiée. Cette application peut être lancée avec la syntaxe suivante:

SunRelativePosition [longitude] [latitude] [date]

où date est un argument optionel spécifiant la date et l'heure. Si cet argument est omis, la date et heure actuelles seront utilisées.

Throws:

java.text.ParseException