All positions and distances, both given by the user and
returned by program, now refer to the Current Frame of the NDF.
For instance, this means that if the Current Frame of the NDF
is a SKY Frame, then:
- celestial co-ordinates must be provided for the star
positions.
- the FWHM will be displayed in arcseconds.
- the radial distance in the plot will be displayed in
arcseconds.
- the orientation of the major axis will be given as a
position angle (from north through east).
Note, it is assumed that the image scale does not vary
significantly across the image, so you should be cautious
about using PSF with very large images.
If, instead, the Current Frame of the NDF is the PIXEL Frame,
then:
- pixel co-ordinates must be provided for the star
positions.
- the FWHM will be displayed in pixels.
- the plot will be annotated in pixels.
- the orientation of the major axis will be given as the
angle from the first (X) axis through the second (Y) axis.