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
wcsslide ndf abs
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
"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)
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=
NDF = NDF (Update)
The NDF to
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=
STYPE = LITERAL (Read)
The sort of
shift to be used. The choice is
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.
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).
stype=abs abs=0.5 This does just the same as the previous example.
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
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