## Changes Introduced in V4.1

The following describes the most significant changes which occurred in the AST library between versions V4.0 and V4.1:

1. A new control flag has been added to the AST_RESAMPLE<X>/astResample<X> functions which produces approximate flux conservation.

2. New constants AST__SOMB and AST__SOMBCOS have been added to ast.h. These specify kernels for astResample and astRebin based on the “Sombrero” function ( 317#317 where 318#318 is the first order Bessel function of the first kind).

3. The SkyFrameSkyFrame class now supports a SystemSystem value of AZEL corresponding to horizon (azimuth/elevation) coordinates.

4. The FitsChanFitsChan class allows the non-standard strings “AZ–” and “EL–” to be used as axis types in FITS-WCS CTYPE keyword values.

5. The FrameFrame class now has attributes ObsLonObsLon and ObsLatObsLat to specify the geodetic longitude and latitude of the observer.

6. The ClockLon and ClockLat attributes have been removed from the TimeFrameTimeFrame class. Likewise, the GeoLon and GeoLat attributes have been removed from the SpecFrameSpecFrame class. Both classes now use the ObsLon and ObsLat attributes of the parent Frame class instead. However, the old attribute names can be used as synonyms for ObsLat and ObsLon. Also, dumps created using the old scheme can be read succesfully by AST V4.1 and converted to the new form.

7. A new function astMapSplitastMapSplit has been added to the MappingMapping class. This splits a Mapping into two component Mappings which, when combined in parallel, are equivalent to the original Mapping.

8. The default value for the SkyRefIsSkyRefIs attribute has been changed from “Origin” to “Ignored”. This means that if you want to use a SkyFrame to represent offsets from some origin position, you must now set the SkyRefIs attribute explicitly to either “Pole” or “Origin”, in addition to assigning the required origin position to the SkyRef attribute.