SETNORM - Sets a new value for one or all of an NDF's axis-normalisation flags

Description:

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 modified.

If an AXIS structure does not exist, a new one whose centres are pixel co-ordinates is created.

Usage:

setnorm ndf dim

Parameters:

ANORM = _LOGICAL (Read)

The normalisation flag for the axis. TRUE 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 altered.

A 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.

Examples:

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 false.

setnorm borg 3 anorm

This sets the normalisation flag for the third dimension in the NDF structure borg.

Axis Normalisation

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.

Related Applications

KAPPA: SETAXIS.