Description:
This application displays the current
co-ordinate Frame associated with
an
NDF and then allows the user to specify a new Frame. The current co-ordinate Frame
determines the co-ordinate system in which positions within the NDF will be expressed
when communicating with the user.
Having selected a new current co-ordinate Frame, its attributes (such the specific
system it uses to represents points within its Domain, its units, etc.) can be changed
using Kappa command WCSATTRIB.
Usage:
wcsframe ndf frame epoch
Parameters:
EPOCH
= _DOUBLE (Read)
If a Sky Co-ordinate System specification is supplied (using
Parameter FRAME) for a celestial co-ordinate system, then an epoch value is needed to
qualify it. This is the epoch at which the supplied sky positions were determined. It
should be given as a decimal years value, with or without decimal places ("1996.8" for
example). Such values are interpreted as a Besselian epoch if less than 1984.0 and
as a Julian epoch otherwise.
FRAME = LITERAL (Read)
A string specifying
the new co-ordinate Frame. If a null parameter value is supplied, then the
current Frame is left unchanged. The suggested default is the Domain (or index
if the Domain is not set) of the current Frame. The string can be one of the
following:
-
A domain name such as SKY, SPECTRUM, AXIS, PIXEL. The two ‘pseudo-domains’ WORLD and
DATA may be supplied and will be translated into PIXEL and AXIS respectively,
so long as the WCS component of the NDF does not contain Frames with these
domains.
-
An integer value giving the index of the required Frame within the WCS component.
-
An IRAS90 Sky Co-ordinate System (SCS) values such as "EQUAT(J2000)" (see SUN/163).
Using an SCS value is equivalent to specifying "SKY" for this parameter and then
setting the System attribute (to "FK5", "Galactic", etc.) using Kappa command
WCSATTRIB. The specific system used to describe positions in other Domains (SPECTRUM,
for instance) must be set using WCSATTRIB.
NDF = NDF (Read and Write)
The NDF
data structure in which the current co-ordinate Frame is to be modified.
Examples:
wcsframe m51 pixel
This chooses pixel co-ordinates for the current co-ordinate Frame
in the NDF m51. wcsframe m51 sky
This chooses celestial co-ordinates for the
current co-ordinate Frame in the NDF m51 (if available). The specific celestial
co-ordinate system (FK5, Galactic, etc.) will depend on the contents of the WCS
component of the NDF, but may be changed by setting a new value for the System
attribute using the WCSATTRIB command. wcsframe m51 spectral
This chooses
spectral co-ordinates for the current co-ordinate Frame in the NDF m51 (if
available). The specific spectral co-ordinate system (wavelength, frequency,
etc.) will depend on the contents of the WCS component of the NDF, but may be
changed by setting a new value for the System attribute using the WCSATTRIB
command. wcsframe m51 equ(J2000) epoch=1998.2
This chooses equatorial (RA/DEC)
co-ordinates referred to the equinox at Julian epoch 2000.0 for the current
co-ordinate Frame in the NDF m51. The positions were determined at the Julian
epoch 1998.2 (this is needed to correct positions for the fictitious proper
motions which may be introduced when converting between different celestial
co-ordinate systems). wcsframe m51 2
This chooses the second co-ordinate
Frame in the WCS component of the NDF. wcsframe m51 data
This chooses a
co-ordinate Frame with domain DATA if one exists, or the AXIS co-ordinate Frame
otherwise. wcsframe m51 world
This chooses a co-ordinate Frame with domain
WORLD if one exists, or the PIXEL co-ordinate Frame otherwise. Notes:
-
The current co-ordinate Frame in the supplied NDF is not displayed if a value is
assigned to Parameter FRAME on the command line.
-
This routine may add a new co-ordinate Frame into the WCS component of the
NDF.
-
The NDFTRACE command can be used to examine the co-ordinate Frames in the WCS component
of an NDF.
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