The number of dimensions given when specifying an NDF section need not necessarily correspond with the actual number of NDF dimensions, although usually it will do so.
If you specify fewer dimensions than there are NDF dimensions, then any unspecified bounds will be set to (1:1) for the purposes of identifying the pixels to which the section should refer. Conversely, if extra dimensions are given, then the shape of the NDF will be padded with extra bounds set to (1:1) in order to match the number of dimensions. In all cases, the resulting section will have the number of dimensions you have actually specified, the padding serving only to identify the pixels to which the section should refer.
In KAPPA there are a number of applications that can only
handle a fixed number of dimensions (e.g. DISPLAY, LINPLOT,
MEDIAN). NDF sections permit such applications to
have wider applicability, since the applications can operate on full
NDFs of arbitrary dimensionality. So for instance, DISPLAY could show
planes of a datacube.
KAPPA --- Kernel Application Package