stella.util

Class ExposureTime

java.lang.Object

util.PropertyContainer

math.ExpressionCalculator

stella.util.ExposureTime

All Implemented Interfaces:

Serializable, Cloneable, Initializable, PropertySupplying

public class ExposureTime
extends ExpressionCalculator
implements Serializable

A class to calculate an exposure time out of an aim S/N and vice verse. This calculation will heavenly depend on instrument characteristics and therefore extends the ExpressionCalculator. Formula used:

• V 1.0:28.07.03:
  

         S/N = tge/sqrt(s+gte),
   

  where t is the exposure time, g the gain, KEY_GAIN, s is the source term, KEY_SOURCE, and e is the intensity in R magnitude of the star compared to a 10th mag star, i.e.

         e = 10-0.4(R-10)
   

  If the R magnitude is not given, the approximation R = V - 0.5(B-V) may be used.

The unit of the time is arbitrary, as long as the gain is scaled appropriatedly. The default value for the gain assumes an exposure time in seconds.

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Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private static double	DEFGAIN The default gain.
private static String	DEFINITEXPRESSION The default forward expression to get exposure time.
private static String	DEFREVERSEEXPRESSION The default backward expression.
private static double	DEFSOURCE The default source.
static String	KEY_GAIN The key to the gain value of the S/N calculator.
static String	KEY_REVERSEEXPRESSION The key to the gain value of the S/N calculator.
static String	KEY_SOURCE The key to the source value of the S/N calculator.

Fields inherited from class math.ExpressionCalculator

KEY_INITEXPRESSION

Fields inherited from class util.PropertyContainer

KEY_LISTSEPARATOR, KEY_MAPKEYVALUECHAR, KEY_MAPSEPARATOR

Fields inherited from interface util.PropertySupplying

CONFIG, KEY_CLASS

Constructor Summary

Constructors

Constructor and Description
ExposureTime(Map info) Constructs a new exposure time calculator.

Method Summary

Modifier and Type	Method and Description
Double	getTimeFromSN(GlobalGrouping set, TargetDefinition td, Number sn) Calculates the exposure time required to yield a target S/N.

Methods inherited from class math.ExpressionCalculator

evaluate, getExpression, init, initCalculator

Methods inherited from class util.PropertyContainer

augment, augment, augment, augment, augment, clone, defaultBoolean, defaultChar, defaultDouble, defaultFloat, defaultInt, defaultLong, defaultObject, defaultObject, defaultProperties, defaultProperty, getAsBoolean, getAsChar, getAsDouble, getAsEnums, getAsFloat, getAsInt, getAsList, getAsLong, getAsMap, getAsMap, getAsObject, getAsObject, getProperties, getProperty, has, initProperties, isNew, parseObject, parseObject, reload, reload, removeProperty, requires, rescanned, setObject, setProperties, setProperty, stringProperties, toString

Methods inherited from class java.lang.Object

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

Field Detail

KEY_GAIN

public static final String KEY_GAIN

The key to the gain value of the S/N calculator.

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Constant Field Values

KEY_SOURCE

public static final String KEY_SOURCE

The key to the source value of the S/N calculator.

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Constant Field Values

KEY_REVERSEEXPRESSION

public static final String KEY_REVERSEEXPRESSION

The key to the gain value of the S/N calculator.

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Constant Field Values

DEFGAIN

private static final double DEFGAIN

The default gain.

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Constant Field Values

DEFSOURCE

private static final double DEFSOURCE

The default source.

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Constant Field Values

DEFINITEXPRESSION

private static final String DEFINITEXPRESSION

The default forward expression to get exposure time.

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Constant Field Values

DEFREVERSEEXPRESSION

private static final String DEFREVERSEEXPRESSION

The default backward expression.

See Also:

Constant Field Values

Constructor Detail

ExposureTime

public ExposureTime(Map info)

Constructs a new exposure time calculator. The main purpose of using a constructer here is to allow overriding of the default parameters.

Method Detail

getTimeFromSN

public Double getTimeFromSN(GlobalGrouping set,
                            TargetDefinition td,
                            Number sn)

Calculates the exposure time required to yield a target S/N. The weather conditions and some target-depending variables are accessible through the parameter set handed over.

Returns:

Zero if the exposure time cannot be derived.