net.grelf.astro
Class StarChartLoader

java.lang.Object
  net.grelf.astro.StarChartLoader

Direct Known Subclasses:

AstroGridGateway, Hipparcos, SimbadGateway, StarChart, Tycho

public abstract class StarChartLoader
extends java.lang.Object

Base for classes loading data for StarChart. Particularly for calculating cartesian equatorial coordinates most efficiently for each star.

 Method of plotting:

 (RA, Dec):

 Star S at (as, ds)
 Plot centre P at (ap, dp)

 Rotate all coordinates so that (ap, dp) becomes (90, 0) degrees
 ie, the plot area is out along the y axis

 1. Represent (as, ds) as cartesian coordinates:

 ( x ) = ( cos(as).cos(ds) )
 ( y )   ( sin(as).cos(ds) )
 ( z )   ( sin(ds)         )

 2. Rotate about 0z through 90 - ap:

 ( x' ) = ( cos(90-ap)  -sin(90-ap)   0 ) ( x )
 ( y' )   ( sin(90-ap)   cos(90-ap)   0 ) ( y )
 ( z' )   (     0             0       1 ) ( z )

 3. Then rotate about 0x through -dp:

 ( x" ) = (     1         0        0       ) ( x' )
 ( y" )   (     0      cos(-dp)  -sin(-dp) ) ( y' )
 ( z" )   (     0      sin(-dp)   cos(-dp) ) ( z' )

 so the combined rotation is

 ( x" ) = (     cos(90-ap)           -sin(90-ap)           0     ) ( x )
 ( y" )   ( cos(-dp).sin(90-ap)   cos(-dp).cos(90-ap)  -sin(-dp) ) ( y )
 ( z" )   ( sin(-dp).sin(90-ap)   sin(-dp).cos(90-ap)   cos(-dp) ) ( z )

 4. Then check that y" > 0 and that x" and z" are within range for the plot.

Field Summary

protected double	cos90ap
protected double	cosdp
protected JulianDate	epoch
protected Epoch	equinox
protected double	sin90ap
protected double	sindp
protected double	sinFieldRadius

Constructor Summary

StarChartLoader()

Method Summary

protected void	calculateChartCoordinates(Star star) This version is fine if the Star is already known to be within the required cone.
JulianDate	getEpoch()
Epoch	getEquinox()
protected void	initialiseChartCoordinates(SkyPoint plotCentre, double fieldRadius) Calculate certain fields just once so they do not have to be calculated for every star.

Methods inherited from class java.lang.Object

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

Field Detail

equinox

protected Epoch equinox

epoch

protected JulianDate epoch

cos90ap

protected double cos90ap

sin90ap

protected double sin90ap

cosdp

protected double cosdp

sindp

protected double sindp

sinFieldRadius

protected double sinFieldRadius

Constructor Detail

StarChartLoader

public StarChartLoader()

Method Detail

getEquinox

public Epoch getEquinox()

getEpoch

public JulianDate getEpoch()

initialiseChartCoordinates

protected void initialiseChartCoordinates(SkyPoint plotCentre,
                                          double fieldRadius)

Calculate certain fields just once so they do not have to be calculated for every star. This needs to be called once a data set for a star chart has been obtained successfully but before retrieving the stars from it.

calculateChartCoordinates

protected void calculateChartCoordinates(Star star)

This version is fine if the Star is already known to be within the required cone. Loading from data files needs a different version, to do cone selection using lines shown in this source as commented out. This needs to be done after retrieving each star from the data set for the chart.