NAME

Astro::FITS::Header::Item - A card image from a FITS header

SYNOPSIS

  $item = new Astro::FITS::Header::Item( Card => $card );

  $item = new Astro::FITS::Header::Item( Keyword => $keyword,
                                         Value => $value,
                                         Comment => $comment,
                                         Type => 'int'
                                       );

  $value = $item->value();
  $comment = $item->comment();

  $card = $item->card();

  $card = "$item";

DESCRIPTION

Stores information about a FITS header item (in the FITS standard these are called Card Images). FITS Card Images can be parsed and broken into their component keyword, values and comments. Card Images can also be created from its components keyword, value and comment.

METHODS

Constructor

new

Create a new instance. Optionally can be given a hash containing information from a header item or the card image itself.

  $item = new Astro::FITS::Header::Item( Card => $card );

  $item = new Astro::FITS::Header::Item( Keyword => $keyword,
                                         Value => $value );

The list of allowed hash keys is documented in the configure method.

Returns undef if the information supplied was insufficient to generate a valid header item.

copy

Make a copy of an Astro::FITS::Header::Item object.

  $newitem = $item->copy;

Accessor Methods

keyword

Return (or set) the value of the keyword associated with the FITS card.

  $keyword = $item->keyword();
  $item->keyword( $key );

When a new value is supplied any card in the cache is invalidated.

Supplied value is always upper-cased.

value

Return (or set) the value of the value associated with the FITS card.

  $value = $item->value();
  $item->value( $val );

When a new value is supplied any card in the cache is invalidated.

If the value is an Astro::FITS::Header object, the type is automatically set to "HEADER".

comment

Return (or set) the value of the comment associated with the FITS card.

  $comment = $item->comment();
  $item->comment( $comment );

When a new value is supplied any card in the cache is invalidated.

type

Return (or set) the value of the variable type associated with the FITS card.

  $type = $item->type();
  $item->type( "INT" );

Allowed types are "LOGICAL", "INT", "FLOAT", "STRING", "COMMENT", "HEADER" and "UNDEF".

The special type, "HEADER", is used to specify that this item refers to a subsidiary header (eg a header in an MEFITS file or a header in an NDF in an HDS container). See also the subhdrs method in Astro::FITS::Header for an alternative way of specifying a sub-header.

The type is case-insensitive, but will always be returned up-cased.

card

Return (or set) the 80 character header card associated with this object. It is created if there is no cached version.

  $card = $item->card();

If a new card is supplied it will only be accepted if it is 80 characters long or fewer. The string is padded with spaces if it is too short. No attempt (yet) )is made to shorten the string if it is too long since that may require a check to see if the value is a string that must be shortened with a closing single quote. Returns undef on assignment failure (else returns the supplied string).

  $status = $item->card( $card );

undef is returned if there is insufficient information in the object to create a new card. Can assign undef to clear the cache.

This method is called automatically when attempting to stringify the object.

 $card = "$item";

General Methods

configure

Configures the object from multiple pieces of information.

  $item->configure( %options );

Takes a hash as argument with the following keywords:

Card

If supplied, the value is assumed to be a standard 80 character FITS header card. This is sent to the parse_card method directly. Takes priority over any other key.

If it is an Astro::FITS::Header::Item it will be copied rather than parsed.

Keyword

Used to specify the keyword associated with this object.

Value

Used to specify the value associated with this FITS item.

Comment

Used to specify the comment associated with this FITS item.

Type

Used to specify the variable type. See the type method for more details. A type will be guessed if one is not supplied. The guess may well be wrong.

Does nothing if these keys are not supplied.

freeze

Method to return a blessed reference to the object so that we can store ths object on disk using Data::Dumper module.

parse_card

Parse a FITS card image and store the keyword, value and comment into the object.

  ($key, $val, $com) = $item->parse_card( $card );

Returns an empty list on error.

equals

Compares this Item with another and returns true if the keyword, value, type and comment are all equal.

  $isident = $item->equals( $item2 );

SEE ALSO

Astro::FITS::Header

COPYRIGHT

Copyright (C) 2008-2009 Science and Technology Facilities Council. Copyright (C) 2001-2007 Particle Physics and Astronomy Research Council. All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHORS

Tim Jenness <t.jenness@jach.hawaii.edu>, Alasdair Allan <aa@astro.ex.ac.uk>