Data Exchange Format

This chapter describes how to exchange data between MIDAS and other systems. MIDAS supports the Flexible Image Transport System (FITS) as the official format for data interchange and long term storage. The FITS format is recommended by the IAU for exchange of digital information between astronomical institutes and provides a computer independent description of the data.

It is important to recognise that MIDAS officially only supports the FITS format for data exchange. For backwards compatibility, MIDAS can also read the IHAP format which was used by the old ESO image processing system and some data acquisition systems at La Silla. Other formats are not supported officially and no help will be provided to access such data.

Note data representation of internal MIDAS files is machine dependent in order to optimise performance. Further, their layout may change with time. The use of the FITS format for storage and exchange will always ensure that proper conversions are made. This is not the case with other formats. It is safer for you to save your data in FITS format, especially if you intend keeping them for a longer time.

For standard text files such as programs, procedures and ASCII data files, operating systems utilities can be used ( e.g. tar). Text files can also be saved as FITS headers using ASCII-catalogues in MIDAS, however, such files can only be decoded by the MIDAS FITS reader.

The MIDAS commands for data exchange ( INTAPE, OUTTAPE) can convert the FITS files directly to/from either sequence tape devices or disks. It is therefore also possible to convert to/from FITS on disk and afterward use general utilities ( e.g. tar or ftp) to do the actual transfer. In that case, proper options must be used to ensure that the files are transferred in binary mode and with correct blocking factors.

• FITS Format
  • Structure of FITS files
  • FITS data-types and extensions
  • FITS keywords
    • Standard keywords
    • Non-standard keywords
    • Hierarchical keywords
  • Restrictions
• IHAP Format
  • Translation of IHAP header
  • Restrictions
• Conversion between FITS and internal format
  • Devices
  • File naming
  • Reading FITS
  • Writing FITS