WCSFRAME - Changes the current co-ordinate Frame in the WCS component of an NDF

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.

Related Applications

KAPPA: NDFTRACE, WCSATTRIB, WCSCOPY, WCSREMOVE.