NAME

       PDL::IO::IDL -- I/O of IDL Save Files

DESCRIPTION

       PDL::IO::IDL allows you to read and write IDL(tm) data files.

       Currently, only reading is implemented.  Scalars, arrays, and structures are all supported.  Heap
       pointers, compiled code, and objects are not supported.  Of those three, only heap pointers are likely to
       be supported in the future.

       This code was not developed by RSI, makers of IDL.

NOTES

       These things seem to work:

       BYTE, SHORT, LONG, FLOAT, and DOUBLE numeric types and arrays
          All of these types seem to work fine.  The corresponding variable is stored as a PDL in the hash
          element with the same name as the original variable in the file.  Arrays are byteswapped as needed and
          are read in so that the dim list has the same indexing order within PDL as it did within IDL.

       STRINGs and arrays of STRINGs
          String types are stored as Perl list refs, in the hash element with the same name as the original
          variable in the file.

       Structures
          Structures are stored as hash refs.  The elements of the hash may be accessed as values within the
          hash.

       Common blocks
          Variables that are notated as being in a common block are read as normal.  Common-block names are
          collected in the special hash value '+common', which contains a hash each keyword of which is the name
          of a common block and each value of which is an array of variable names.

       These things are known to be not working and may one day be fixed:

       COMPLEX numbers
          These could be implemented as 2-arrays or as PDL::Complex values, but aren't yet.

       PTR types
          These could be implemented as perl refs but currently aren't.

       writing
          Maybe one day -- but why bother writing a broken file format?  NetCDF is better.

       These things are known to be not working and will probably never be fixed

       Compiled code
          Decompiling IDL code is a violation of the IDL end-user license.  To implement this, someone who does
          not hold an IDL license would have to reverse-engineer a set of .SAV files sent to that person by
          someone else with an IDL license.

       Objects
          IDL objects contain compiled code.

FUNCTIONS

   ridl
       $a = ridl("foo.sav");

       Read an IDL save file from a file.

       Upon successful completion, $a is a hash ref containing all of the variables that are present in the save
       file, indexed by original variable name.

       IDL identifiers are case insensitive; they're all converted to upper-case in the hash that gets returned.
       This may be adjustable at a future date.  Furthermore, because IDL identifiers can't contain special
       characters, some fields that start with '+' are used to store metadata about the file itself.

       Numeric arrays are stored as PDLs, structures are stored as hashes, and string and structure arrays are
       stored as perl lists.  Named structure types don't exist in perl in the same way that they do in IDL, so
       named structures are described in the 'structs' field of the global metadata.  Anonymous structures are
       treated as simple hashes.  Named structures are also simple hashes, but they also contain a field '+name'
       that refers to the name of the structure type.

AUTHOR, LICENSE, NO WARRANTY

       THIS CODE IS PROVIDED WITH NO WARRANTY and may be distributed and/or modified under the same terms as PDL
       itself.

       This code is based on the analysis of the IDL save file format published by Craig Markwardt in 2002.

       IDL is a trademark of Research Systems Incorporated (RSI).  The PDL development team, and authors of this
       code, are not affiliated with RSI.