This routine sets a new value for one or all the normalisation flags in
an NDF AXIS
data structure. The NDF is accessed in update mode. This flag determines how the
NDF’s data and variance arrays behave when the associated axis information is
If an AXIS structure does not exist, a new one whose centres are pixel co-ordinates is
setnorm ndf dim
ANORM = _LOGICAL (Read)
normalisation flag for the axis.
means that the data and variance values in the
NDF are normalised to the pixel width values for the chosen axis so that the product of
data value and width, and variance and the squared width are constant if the width is
FALSE value means that the data and variance need not alter as the pixel widths are
varied. This is the default for an axis. The suggested default is the current value.
DIM = _INTEGER (Read)
The axis dimension for which the normalisation flag is to be
modified. There are separate units for each NDF dimension. A value of
0 sets the
normalisation flag for all the axes. The value must lie between 0 and the number of
dimensions of the NDF. This defaults to 1 for a one-dimensional NDF. The suggested
default is the current value.
NDF = NDF (Read and Write)
The NDF data
structure in which an axis-normalisation flag is to be modified.
setnorm hd23568 0 anorm This sets the normalisation flags along all axes
of the NDF structure hd23568 to be true.
setnorm ndf=spect noanorm This
sets the normalisation flag of the one-dimensional NDF structure spect to be
setnorm borg 3 anorm This sets the normalisation flag for the third
dimension in the NDF structure borg.
In general, the
axis-normalisation property is not needed. An example where it is relevant is a
spectrum in which data values representing energy per unit wavelength and each
pixel has a known spread in wavelength. The sum of each pixel’s data value
multiplied by its width gives the energy in a part of the spectrum. A change to
the axis width, say to allow for the redshift, necessitates a corresponding
modification to the data value to retain this property. In two dimensions an example
is where the data measure flux per unit area of sky and the pixel widths are
defined in terms of angular size.