Changes Introduced in V1.5

The following describes the most significant changes which have occurred in the AST library between versions V1.4 and V1.5 (not the most recent version):

  1. The FitsChanFitsChan class has been modified to support the latest draft FITS WCS standard, described in the two papers “Representation of world coordinates in FITS” (E.W. Greisen and M. Calabretta, dated 30th November, 1999), and “Representation of celestial coordinates in FITS” (M. Calabretta and E.W. Greisen, dated 24th September, 1999). These are available at http://www.cv.nrao.edu/fits/documents/wcs/wcs.html.

    The FITS-WCS encoding now uses these updated conventions. The main changes are:

  2. Two new encodings have been added to the FitsChan class:
    FITS-PC
    This encoding uses the conventions of the now superseded FITS WCS paper by E.W. Greisen and M. Calabretta which used keywords CDELTj and PCjjjiii to describe axis scaling and rotation. These are the conventions which were used by the FITS-WCS encoding prior to version 1.5 of AST. This encoding is provided to allow existing data which use these conventions to be read. It should not in general be used to create new data.

    FITS-AIPS
    This encoding is based on the conventions described in the document “Non-linear Coordinate Systems in AIPS” by Eric W. Greisen (revised 9th September, 1994 and available by ftp from fits.cv.nrao.edu /fits/documents/wcs/aips27.ps.Z). This encoding uses CROTAi and CDELTi keywords to describe axis rotation and scaling.

  3. The FitsChan class now provides some support for the IRAF-specific “TNX” sky projection, which is converted transparently into the equivalent FITS “TAN” projection (see the description of the EncodingEncoding attribute for details).

  4. FrameSets originally read from a DSS encoded FITS header can now be written out using the FITS-WCS encoding (a TAN projection with correction terms will be used) in addition to the DSS encoding. The reverse is also possible: FrameSets originally read from a FITS-WCS encoded FITS header and which use a TAN projection can now be written out using the DSS encoding.

  5. The algorithm used by the FitsChan class to verify that a FrameSetFrameSet conforms to the FITS-WCS model has been improved so that FrameSets including more complex mixtures of parallel and serial Mappings can be written out using the FITS-WCS encoding.

  6. The FitsChan class has been changed so that long strings included in the description of an ObjectObject can be saved and restored without truncation when using the NATIVE encoding. Previously, very long FrameFrame titles, mathematical expressions, etc. were truncated if they exceeded the capacity of a single FITS header card. They are now split over several header cards so that they can be restored without truncation. Note, this facility is only available when using NATIVE encoding.

  7. The FitsChan class has a new attribute called WarningsWarnings which can be used to select potentially dangerous conditions under which warnings should be issued. These conditions include (for instance) unsupported features within non-standard projections, missing keywords for which default values will be used, etc.

  8. The WcsMapWcsMap class has been changed to support the changes made to the FITS-WCS encoding in the FitsChan class: