Astro::Coords::Fixed - Manipulate coordinates that are fixed on the sky
$c = new Astro::Coords::Fixed( az => 180, el => 45, units => 'degrees'); $c = new Astro::Coords::Fixed( ha => '02:30:00.0', dec => '45:30:03', units => 'sexagesimal', tel => $telescope, );
This subclass of
Astro::Coords allows for the manipulation of coordinates that are fixed on the sky. Sometimes a telescope should be commanded to go to a fixed location (eg for a calibration) and this class puts those coordinates (Azimuth and elevation for telescopes such as JCMT and Gemini and Hour Angle and Declination for equatorial telescopes such as UKIRT) on the same footing as astronomical coordinates.
Note that Azimuth and elevation do not require the telescope latitude whereas Hour Angle and declination does.
Constructor. Recognizes hash keys "ha", "dec" and "az", "el".
$c = new Astro::Coords::Fixed( az => 35, el => 30 ); $c = new Astro::Coords::Fixed( ha => $ha, dec => $dec, tel => $tel);
Usually called via
Astro::Coords rather than directly.
Note that the declination is equivalent to "Apparent Dec" used elsewhere in these classes.
Azimuth and Elevation is the internal format. Currently there is no caching (so there is always overhead converting to apparent RA and Dec) since there is no cache flushing when the telescope is changed.
A telescope is required (in the form of an
Astro::Telescope object) if the position is specified as HA/Dec.
A name can be associated with this position.
Return azimuth and elevation (as two
($az, $el) = $c->azel;
Can also be used to store the azimuth and elevation (as
$c->_azel( $az, $el);
Returns the generic type associated with the coordinate system. For this class the answer is always "FIXED".
This is used to aid construction of summary tables when using mixed coordinates.
Returns a string representation of the object. Returns Azimth and Elevation in degrees.
Return a one line summary of the coordinates. In the future will accept arguments to control output.
$summary = $c->summary();
Array summarizing the object. Retuns Return back 11 element array with first 3 elements being the coordinate type (FIXED) and the az/el coordinates (radians).
This method returns a standardised set of elements across all types of coordinates.
Get the hour angle for the currently stored LST. By default returns format as for other angular methods.
$ha = $c->ha; $ha = $c->ha( format => "deg" );
Return the apparent RA and Dec (as two
Astro::Coords::Angle objects) for the current time [note that the apparent declination is fixed and the apparent RA changes].
If no telescope is present the equator is used.
Return the Hour angle and apparent declination (as two
Astro::Coords::Angle objects). If no telescope is present the equator is used.
($ha, $dec) = $c->hadec;
For a fixed source, the setting Hour Angle has no meaning.
Meridian time is not defined for a fixed source.
Transit elevation is not defined for a fixed source. Always returns undef.
Overrided method to prevent
Astro::Coords::apply_offset being called on this subclass.
Usually called via
Astro::PAL is used for all internal astrometric calculations.
Tim Jenness <firstname.lastname@example.org>
Copyright (C) 2001-2005 Particle Physics and Astronomy Research Council. All Rights Reserved.
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