A number of the ESP application allows image regions to be defined as being of poor quality by two basic methods; by use of an NDF whose data component values are set bad (either explicitly or by use of the quality component and the badbits flag — see SUN/33) or by interpreting bad-region commands contained within an ordinary text file (an ASCII Region Definition file — ARD file — see SUN/183)
An NDF, with the appropriate pixels set to the bad value, can be produced interactively using the KAPPA applications ARDGEN and ARDMASK (SUN/95).
The capabilities of the ARD option (which uses little disk and could form part of a ‘database’ of data masking information) are described below.
As things stand, with images generated using a known CCD, the bad or hot pixels, rows or columns might be defined by ARDGEN so that they are always set to bad and excluded from all subsequent processing. The information required is often supplied by the observatory operating the CCD and can placed in a text file using any text editor.
The shapes of regions which can be defined are specified by the following KEYWORDS:
Regions are specified using the keywords suffixed by the following information.
Only one KEYWORD is allowed per line and the parameters must be enclosed in parentheses. The parameters must be separated by commas. Any amount of white space (blanks) is allowed between keywords and numerics. Tabs are not allowed.
Comments are indicated by the characters ‘#’ and may be in-line or whole line at any place within the file. The presence of a comment terminates the current line immediately.
Any line within the file may be continued on to another by terminating with the continuation
Thus an ARD file might contain the following information:
The co-ordinates used by ARD by default refer to the co-ordinate system defined by the image bounds for the current NDF. Further details are available from SUN/183.