LV2IDL, a software package for automatic data transfer between LabVIEW and IDL

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LV2IDL, a software package for automatic data
transfer between LabVIEW and IDL

• Gelu M. Nita
• New Jersey Institute of Technology

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Purpose

• To provide several means of in-line or off-line
  automatic data transfer between the LabVIEW and
  IDL programming environments.

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Retrieving LabVIEW datalog records

• Any LabVIEW 7.x datalog file record can be
  restored as an IDL structure without any prior
  knowledge of the original record template. Since
  this option is not currently provided by the
  LabVIEW environment, one may also use this
  feature to recover data stored in undocumented
  LabVIEW datalog files.

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Retrieving and returning LabVIEW variant records
using temporary files

• Any arbitrary LabVIEW data structure converted in
  a variant variable and stored as a data file
  record may be restored as an IDL structure,
  processed inside IDL, and saved as a LabVIEW
  variant record.
• Provided that IDL does not change the original
  template of the data, one may return the
  processed variant variable back to the LabVIEW
  application.

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Storing the variant record in LabVIEW
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Restoring and processing the variant record in IDL
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Retrieving in LabVIEW the variant record
processed by the IDL application
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Adding flexibility to the IDL Scriptnode for
LabVIEW

• The IDL Scriptnode for LabVIEW allows the user to
  perform in-line data transfer between LabVIEW 7.x
  and IDL. However, the user has to explicitly
  define at the development stage the data types of
  input and output terminals of the script node,
  which are limited to a few basic unstructured
  data types.
• This package allows the user to pass any LabVIEW
  data structure in a variant format, dynamically
  process it inside the script, and pass the result
  back to LabVIEW, as well as any dynamically
  created variables, as variant structures.

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Data type incompatibility issues

• The LV2IDL package does not provide support for
  special data types that would be out of scope
  outside the LabVIEW environment, such as variable
  or file references.
• Since IDL does not support the unsigned short
  integer data type (i8), such LabVIEW variables
  are automatically converted to unsigned IDL byte
  variables, while a warning message is issued. It
  is the full responsibility of the user to convert
  these variables to any of the available IDL
  signed integer data types (integer or long).
• LabVIEW empty arrays are converted to a special
  IDL structure named empty_array which contains
  only the element descriptor.
• LabVIEW variants are converted to anonymous IDL
  structures that combine the variant data fields
  and its attributes. Empty variants are converted
  to a special IDL structure named empty_variant
  which contains only a null pointer field.
• The LabVIEW extended numerical data types (8
  bytes) are not supported by the current version,
  but they could be converted in a Lo32,Hi32 IDL
  structure in a future release.

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LabVIEW 8.x compatibility

• Starting with version 8.0, National Instruments
  changed the LabVIEWs internal type descriptors,
  which makes the current version of the LV2IDL
  package being incompatible with the LabVIEW 8.x
  data types.
• However, any data structure may be still passed
  between the LabVIEW 8.x and IDL applications as a
  variant file record provided it is explicitly
  converted to the 7.x format by using the LabVIEW
  8.x flatten to string function with the
  appropriate option selected.

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Saving a variant structure as a LabVIEW 7.x
variant record using the flatten to string
LabVIEW 8.x function. Restoring the variant
record as an IDL structure, modifying its
contents while preserving its original template,
and saving it as an LabVIEW 7.x variant
record. Restoring the LabVIEW 7.x variant record
as a binary string, converting it to a LabVIEW
8.x variant using the unflatten from string
function, and to its original data format using
the variant to data function.