NDF(F)         User Contributed Perl Documentation         NDF(F)



NAME
       PDL::IO::NDF - PDL Module for reading and writing Starlink
       N-dimensional data structures as PDLs.

SYNOPSIS
        use PDL::IO::NDF;

        $a = PDL->rndf($file);

        $a = rndf('test_image');
        $a = rndf('test_image', 1);

        $a->wndf($file);
        wndf($a, 'out_image');

        propndfx($a, 'template', 'out_image');


DESCRIPTION
       This module adds the ability to read and write Starlink
       N-dimensional data files as N-dimensional PDLs.

FUNCTIONS
       rndf()

       Reads a piddle from a NDF format data file.

        $pdl = rndf('file.sdf');
        $pdl = rndf('file.sdf',1);

       The '.sdf' suffix is optional. The optional second argu-
       ment turns off automatic quality masking and returns a
       quality array as well.

       BUG? "rndf('bob.sdf',1)" calls ndf_sqmf(1,...), which
       means that the quality array is turned into bad pixels -
       ie the opposite of above. Or am I confused?

       Header information and NDF Extensions are stored in the
       piddle as a hash which can be retreived with the
       "$pdl->gethdr" command.  Array extensions are stored in
       the header as follows:

        $a - the base DATA_ARRAY

       If "$hdr = $a->gethdr";

       then:

        %{$hdr}        contains all the FITS headers plus:
        $$hdr{Error}   contains the Error/Variance PDL
        $$hdr{Quality} The quality byte array (if reqeusted)
        @{$$hdr{Axis}} Is an array of piddles containing the information
                       for axis 0, 1, etc.
        $$hdr{NDF_EXT} Contains all the NDF extensions
        $$hdr{Hist}    Contains the history information
        $$hdr{NDF_EXT}{_TYPES}
                       Data types for non-PDL NDF extensions so that
                       wndf can reconstruct a NDF.

       All extension information is stored in the header hash
       array.  Extension structures are preserved in hashes, so
       that the PROJ_PARS component of the IRAS.ASTROMETRY exten-
       sion is stored in $$hdr{NDF_EXT}{IRAS}{ASTROME-
       TRY}{'PROJ_PARS'}. All array structures are stored as
       arrays in the Hdr: numeric arrays are stored as PDLs, log-
       ical and character arrays are stored as plain Perl arrays.
       FITS arrays are a special case and are expanded as scalars
       into the header.

       PDL does not have a signed byte datatype, so any '_BYTE'
       data is read into a "byte" (unsigned) piddle and a warning
       is printed to "STDOUT".

       wndf()

       Writes a piddle to a NDF format file:

          $pdl->wndf($file);
          wndf($pdl,$file);

       wndf can be used for writing PDLs to NDF files.  The
       '.sdf' suffix is optional. All the extensions created by
       rndf are supported by wndf.  This means that error, axis
       and quality arrays will be written if they exist. Exten-
       sions are also reconstructed by using their name (ie
       FIGARO.TEST would be expanded as a FIGARO extension and a
       TEST component). Hdr keywords Label, Title and Units are
       treated as special cases and are written to the label,
       title and units fields of the NDF.

       Header information is written to corresponding NDF exten-
       sions.  NDF extensions can also be created in the {NDF}
       hash by using a key containing '.', ie {NDF}{'IRAS.DATA'}
       would write the information to an IRAS.DATA extension in
       the NDF. rndf stores this as $$hdr{NDF}{IRAS}{DATA} and
       the two systems are interchangeable.

       rndf stores type information in {NDF}{'_TYPES'} and below
       so that wndf can reconstruct the data type of non-PDL
       extensions. If no entry exists in _TYPES, wndf chooses
       between characters, integer and double on a best guess
       basis.  Any perl arrays are written as CHAR array exten-
       sions (on the assumption that numeric arrays will exist as
       PDLs).

       propndfx()

       Routine to write a PDL to an NDF by copying the extension
       information from an existing NDF and writing DATA,VARI-
       ANCE, QUALITY and AXIS info from a PDL (if they exist).

       Extensions, labels and history are propogated from the old
       NDF.  No new extension information is written.

       This command has been superseded by wndf().

NOTES
       The perl NDF module must be available. This is available
       from the author or from Starlink (http://www.star-
       link.rl.ac.uk).

       If an NDF is read which contains AST World Coordinate
       information (a .WCS component) this information is cur-
       rently ignored. Currently WCS information can only be
       written and stored using standard FITS headers.  See
       http://rlspc5.bnsc.rl.ac.uk/star/docs/sun211.htx/sun211.html#xref_
       for more information on AST.

AUTHOR
       This module was written by Tim Jenness <t.jen-
       ness@jach.hawaii.edu>.  Copyright (C) Tim Jenness
       1997-2000. All Rights Reserved.

SEE ALSO
       PDL::FAQ for general information on the Perl Data lan-
       guage, NDF for information on the NDF module.



perl v5.6.1                 2002-04-08                     NDF(F)