The CCDPACK routine DEBIAS allows regions to be defined as having poor quality by two basic methods, by use of an image whose data component values are set bad (either explicitly or by use of the NDF quality component and the badbits flag — see SUN/33) or by interpreting bad-region commands within an ordinary text file (an ASCII region definition file — ARD file).

Setting regions of an image to bad can be done graphically using the GAIA display tool (SUN/214) which can also create an ARD file to describe these regions. Alternatively KAPPA (SUN/95) also provides applications for this task (see ZAPLIN, SEGMENT ARDGEN and ARDMASK).

The capabilities of the ARD option (which uses considerably less disk space than the “image with bad regions” option and hence could form part of a ‘database’) are described below (for more details see SUN/183).

The shapes of regions which can be defined are specified by the following KEYWORDS:

BOX, CIRCLE, COLUMN, ELLIPSE, LINE, PIXEL, POLYGON, RECT, ROTBOX, ROW

Regions are specified using the keywords suffixed by the following information:

• BOX(XCENTRE,YCENTRE,XSIDE,YSIDE)
• CIRCLE(XCENTRE,YCENTRE,RADIUS)
• COLUMN(COLUMN1,COLUMN2,COLUMN3...)
• ELLIPSE(XCENTRE,YCENTRE,SEMIMAJOR,SEMIMINOR,ANGLE)
• LINE(XSTART,YSTART,XEND,YEND)
• PIXEL(XCENTRE1,YCENTRE1,XCENTRE2,YCENTRE2...)
• POLYGON(XCENTRE1,YCENTRE1,XCENTRE2,YCENTRE2...)
• RECT(XCORNER1,YCORNER1,XCORNER2,YCORNER2)
• ROTBOX(XCENTRE,YCENTRE,XSIDE,YSIDE,ANGLE)
• ROW(ROW1,ROW2,ROW3...)

The angles are measured X through Y positive.

A sample ARD description follows:

#
# ARD description file for bad regions of my CCD.

COLUMN( 41, 177, 212 )        # Three bad columns
PIXEL( 201, 143, 153, 167 )   # Two Bad pixels
BOX( 188, 313, 5, 5 )         # One Hot spot centred at 188,313
ELLIPSE( 99, 120, 21.2, 5.4, 45.0 )

# Polygons defining badly vignetted corners
POLYGON( 2.2, 96.4, 12.1, 81.5, 26.9, 63.7, 47.7, 41.9,
61.5, 24.1, 84.3, 0.0 , 0.0, 0.0 )
POLYGON( 6.2, 294.3, 27.9, 321.0, 52.6, 348.7, 74.4, 371.5,
80.0, 384.0, 0.0, 384.0 )
#

But you should use the ARDGEN application to produce these files.