WCSSLIDE

←Prev
KAPPA –- Kernel Application Package
Next→
TOC ↑

WCSSLIDE

Applies a translational correction to the WCS in an NDF

Description:

This application modifies the WCS information in an NDF so that the WCS position of a given pixel is moved by specified amount along each WCS axis. The shifts to use are specified either by an absolute offset vector given by the ABS parameter or by the difference between a fiducial point and a standard object given by the FID and OBJ parameters respectively. In each case the co-ordinates are specified in the NDF’s current WCS co-ordinate Frame.

Usage:

wcsslide ndf abs

Parameters:

ABS( ) = _DOUBLE (Read)

Absolute shift for each WCS axis. The number of values supplied must match the number of WCS axes in the NDF. It is only used if STYPE="Absolute". Offsets for celestial longitude and latitude axes should be specified in arcseconds. Offsets for all other types of axes should be given directly in the units of the axis.

FID = LITERAL (Read)

A comma-separated list of formatted axis values giving the position of the fiducial point in WCS co-ordinates. The number of values supplied must match the number of WCS axes in the NDF. It is only used if STYPE="Relative".

NDF = NDF (Update)

The NDF to be translated.

OBJ = LITERAL (Read)

A comma-separated list of formatted axis values giving the position of the standard object in WCS co-ordinates. The number of values supplied must match the number of WCS axes in the NDF. It is only used if STYPE="Relative".

STYPE = LITERAL (Read)

The sort of shift to be used. The choice is "Relative" or "Absolute". ["Absolute"]

Examples:

wcsslide m31 [32,23]

The (RA,Dec) axes in the NDF m31 are shifted by 32 arcseconds in right ascension and 23 arcseconds in declination.

wcsslide speca stype=rel fid=211.2 obj=211.7

The spectral axis in the NDF speca (which measures frequency in GHz), is shifted by 0.5 GHz (i.e. 211.7–211.2).

wcsslide speca stype=abs abs=0.5

This does just the same as the previous example.

Notes:

The correction is affected by translating pixel co-ordinates by a constant amount before projection them into WCS co-ordinates. Therefore, whilst the translation will be constant across the array in pixel co-ordinates, it may vary in WCS co-ordinates depending on the nature of the pixel $\to$ WCS transformation. The size of the translation in pixel co-ordinates is chosen in order to produce the required shift in WCS co-ordinates at the OBJ position (if STYPE is "Relative"), or at the array centre (if STYPE is "Absolute").

Related Applications

KAPPA: SLIDE.

Implementation Status:

There can be an arbitrary number of NDF dimensions.

←Prev
KAPPA –- Kernel Application Package
Next→
TOC ↑