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 "similar set" 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.
The value of the parameter can be one of the following:
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 "CCDPACK.LOG". [CCDPACK.LOG]
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]
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 follows:
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's Base frame.
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:
USE keyword argumentsCurrently 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.
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.