## Changes Introduced in V5.7-0

The following describes the most significant changes which occurred in the AST library between versions V5.6-1 and V5.7-0:

1. The FitsChanFitsChan class support for the IRAF-specific “TNX” projection has been extended to include reading TNX headers that use a Chebyshev representation for the distortion polynomial.

2. The FitsChan class support for the IRAF-specific “ZPX” projection has been extended to include reading ZPX headers that use simple or Chebyshev representation for the distortion polynomial.

3. A bug has been fixed in the FitsChan class that caused headers including the Spitzer “-SIP” distortion code to be read incorrectly if no inverse polynomial was specified in the header.

4. A new attribute called PolyTanPolyTan has been added to the FitsChan class. It can be used to indicate that FITS headers that specify a TAN projection should be interpreted according to the “distorted TAN” convention included in an early draft of FITS-WCS paper II. Such headers are created by (for instance) the SCAMP tool (`http://www.astromatic.net/software/scamp`).

5. The PolyMapPolyMap class now provides a method called astPolyTranastPolyTran that adds an inverse transformation to a PolyMap by sampling the forward transformation on a regular grid, and then fitting a polynomial function from the resulting output values to the grid of input values.