IRAM Memo 2012-? Preparing GILDAS for large datasets II - GILDAS Data Format Version 2
Keywords: sic-gdfv2

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# IRAM Memo 2012-?
Preparing GILDAS for large datasets
II - GILDAS Data Format Version 2

S. Guilloteau, S. Bardeau, J. Pety, V. Pietu

24-jul-2019
version 1.4

1. LAB (Bordeaux)

### Abstract:

With the advent of large data sets, the original GILDAS Data Format (for hypercubes and tables) became outdated due to its initial pure 32-bit implementation. The advent of new capabilities in interferometers, such as on-the-fly mosaics or polarization, also require modification in the way information are stored in UV tables.

A new version of the GILDAS Data Format, called GDFV2, was designed and implemented to answer these challenges. This document details what was done and how it affects both programmers and users (in particular the backward compatibility aspects).

The new data format is detailed. The public FORTRAN application program interface (API) which can be used in programs to access the data format is described.

Related documents: GreG documentation, Programming in GILDAS, Task Programming Manual.

- Contents
- Introduction
- Design of the GILDAS Data Format
- GDF Images
  - Type description
    - Header description
    - Data description
  - Improvements between GDFV1 and GDFV2
    - Dimensions
    - Transposition of data hypercubes
    - New header parameters or facilities
  - Backward compatibility
- GDF UV Tables
  - Why a new implementation of the UV Tables in GILDAS?
  - UV tables subversions and Doppler factor
    - Version 2.0: Historical Frequency implementation
    - Version 2.1: Global Doppler implementation
    - Version 2.2: Local Doppler implementation
  - The new layout
    - Data Format Identification
    - Dap positions and size
      - Restriction on the use of `real(8)` daps
      - Are `real(4)` U,V,W coordinates sufficient?
    - Complex visibilities
    - Telescope information
  - The new layout for polarimetry data
    - Nomenclature
    - In practice
- Changes for end-users
  - Behaviour
  - SIC variables
  - New facilities
- Changes for programmers
  - Dealing with GDF files (any kind)
  - UV data format usage restrictions
  - GDF API
  - Obsolete routines
- Miscellaneous and pending items
  - Compatibility
  - Pending issues
- GILDAS Fortran derived type
- GDFV2 header
- UV tables column codes
- GDF API and programming tools
  - GILDAS_NULL
  - GDF_READ_HEADER
  - GDF_TRIM_HEADER
  - GDF_ALLOCATE
  - GDF_COPY_HEADER
  - GDF_RANGE
  - GDF_READ_GILDAS
  - GDF_READ_UVDATASET
  - GDF_READ_UVONLY_CODES
  - GDF_SETUV
  - Other less used or too specific or hidden routines... To be debated
- About this document ...