The following statistics are displayed:
A pixel is included if its centre is within the aperture, and is not included otherwise. This simple approach may not be suitable for accurate aperture photometry, especially where the aperture diameter is less than about ten times the pixel size. A specialist photometry package should be used if accuracy, rather than speed, is paramount.
The co-ordinate system in which positions within the ARD file are given should be indicated by including suitable COFRAME or WCS statements within the file (see SUN/183), but will default to pixel co-ordinates in the absence of any such statements. For instance, starting the file with a line containing the text "COFRAME(SKY,System=FK5)" would indicate that positions are specified in RA/DEC (FK5,J2000). The statement "COFRAME(PIXEL)" indicates explicitly that positions are specified in pixel co-ordinates. [!]
A list of acceptable values is displayed if an illegal value is supplied. If a null (!) value is supplied, the axes with the same indices as the two used pixel axes within the NDF are used. [!]
KAPPA --- Kernel Application Package