Used together, the framesets written out to an AST file can thus contain information about the positioning of images in a set of related images.
AST files written out by this application can be applied to other images of similar origin using the
ASTIMP or MAKESET programs, so that registration information present in the WCS components of
one set of images (put there for instance by the REGISTER or WCSEDIT applications) can be
transferred using ASTIMP and ASTEXP to another similar set. This
" will typically be one
from chips in the same mosaic camera instrument.
A 2-frame frameset is output for each image. The Base frame is one selected by the BASEFRAME parameter, and is identical in the exported frameset to the one in the original image. The Current frame in the exported frameset is the same as the Current frame in the original image, but may be given a different Domain name by the OUTDOMAIN parameter.
Under normal circumstances, the Current frames of all the input images should share the same Domain name, and so should the frames identified by the BASEFRAME parameter. A warning will be issued if this is not the case. Warnings will also be issued if the image identifiers are not all unique.
"Sky Co-ordinate System
"specification is supplied (using parameter BASEFRAME) 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 (
"for example). Such values are interpreted as a Besselian epoch if less than 1984.0 and as a Julian epoch otherwise.
The value of the parameter can be one of the following:
"Sky Co-ordinate System
"(SCS) value such as EQUAT(J2000) (see section
"Sky Co-ordinate Systems
Unlike the Current frame, the frame selected using this parameter is copied to the AST file unmodified; in particular it retains the same Domain name. [PIXEL]
If the logging system has been initialised using CCDSETUP, then the value specified there will be
used. Otherwise, the default is
TERMINAL – Send output to the terminal only
LOGFILE – Send output to the logfile only (see the LOGFILE parameter)
BOTH – Send output to both the terminal and the logfile
NEITHER – Produce no output at all
If the logging system has been initialised using CCDSETUP then the value specified there will be
used. Otherwise, the default is
Note that the frames which are written to the AST file are always the Current frames of the images supplied; this parameter only gives the name that the frames will have in the AST file, and consequently the name by which they will be known when the WCS information is imported into other images using ASTIMP or MAKESET.
The name is converted to upper case, and whitespace is removed. [CCD_EXPORT]
’to the file
’, calling the alignment domain
’. The file
’can later be used by the ASTIMP or MAKESET applications to add the same coordinate information to a different set of images from the same instrument. Before running this, the images
’should be correctly aligned in their Current domain. CHIPNUM must be the name of a FITS header keyword present in the FITS extension of each image whose value distinguishes the CCDs from each other (presumably present in the unreduced data). The mappings between the pixel coordinates and Current coordinates of the input images are recorded.
"astfile=camera.ast baseframe=axis title=
"Focal plane alignment
’, but mappings are between the Current coordinates of the input images and their
’coordinates. This could be a good idea if the images had been shrunk using KAPPA
’s COMPAVE or something similar, which modifies the PIXEL coordinates but leaves the AXIS coordinates unchanged. No suitable FITS header is available to distinguish the different types of image, so the IDTYPE parameter is allowed to assume its default value of INDEX. When camera.ast is used for importing frameset information, the images from the three different chips must be listed in the same order as when this command was invoked. The title of the output Current frame will be as given.
"wfc.ast outdomain=wfc idtype=fitsid fitsid=CHIPNAME fitsrot=ROTSKYPA
The AST file consists of the following, in order:
frameset 1 modifiers
frameset 2 modifiers
(end of file)
Characters after a
’ character are normally ignored. The constituent parts are composed as
A single blank line, which may contain spaces but no comments.
The framesets are written in AST native format, as explained in SUN/210.
Each frameset has an ID, and contains two frames (a Base frame and a Current frame) and a mapping
between them. The domains of all the Base frames should normally be the same, and likewise
for all the Current frames. For the images to which the file will be applied by ASTIMP,
their WCS components should contain frames in the same domain as the AST file
The ID of each frameset is used to determine, for each image, which of the framesets in the file should be applied to it. This ID is a string which can assume one of the following forms:
"FITSID KEY VALUE
" — This will match an image if the first FITS header card with the keyword
KEY has the value VALUE. If the value is of type CHARACTER it must be in single quotes. KEY
may be compound (of the form keyword1.keyword2 etc) to permit reading of hierarchical
" — This associates a frameset with an integer N. Usually N will take the values 1,2,3,... for
the framesets in the file. Typically the N
’th image in a list will match the one with an ID of
" — This will match an image if the Set Index attribute iin its CCDPACK Set header is equal to
the integer N.
USE keyword arguments
Currently the only modifier defined is FITSROT, which defines the name of a FITS header which specifies how many degrees to rotate the image before use. This rotation is carried out after the mapping defined by the frameset itself.
Global modifiers affect all images processed with the AST file. Frameset modifiers affect only those images which correspond to their frameset.
Rigorous error checking of the AST file is not performed, so that unhelpful modifications to the WCS components of the target images may occur if it is not in accordance with these requirements.
"value is the value assigned on the last run of the application. If the application has not been run then the
"defaults, as shown in the parameter help, apply.
Retaining parameter values has the advantage of allowing you to define the default behaviour of the application but does mean that additional care needs to be taken when re-using the application after a break of sometime. The intrinsic default behaviour of the application may be restored by using the RESET keyword on the command line.
Certain parameters (LOGTO, LOGFILE and NDFNAMES) have global values. These global values will always take precedence, except when an assignment is made on the command line. Global values may be set and reset using the CCDSETUP and CCDCLEAR commands.