Previous: Notation for commands
Up: Overview of the DAS
Previous Page: Notation for commands
Next Page: Using the DAS

Disk files for observations

Observations saved by the system computer are stored on disk in NDF structures, which can be read by Figaro, by DIPSO and by Starlink's ADAM-based software.

The NDF structure is a specific organization of objects in the disk format HDS and is described in the Starlink document SGP/38. NDFs are stored in HDS files with an extension `.SDF' to the file name.

Naming conventions are used to identify observations: RUN_FILES:R80200.SDF is an NDF containing run 80200; SCRATCH_FILES:S3.SDF is an NDF containing scratch exposure number 3.

The NDFs produced at the WHT contain images with an 16-bit unsigned-integer datum for each pixel. This is HDS type `_UWORD' which corresponds to Figaro's type `USHORT'. The headers are stored in a standard NDF-extension `FITS' (component name <file>.MORE.FITS) which is an array of 80-byte character strings, each string containing one FITS record.

Observations saved by the Observer's SPARCstation are stored on disk in IRAF's file format.