## Changes Introduced in V3.4

The following describes the most significant changes which have occurred in the AST library between versions V3.3 and V3.4:

1. The MappingMapping class has a new method (astLinearApproxastLinearApprox) which calculates the co-efficients of a linear approximation to a Mapping.

2. The Format attribute for simple Frames and SkyFrames has been extended. It has always been possible, in both classes, to specify a precision by including a dot in the Format value followed by an integer (e.g. “`dms.1`” for a SkyFrameSkyFrame, or “`%.10g`” for a simple FrameFrame). The precision can now also be specified using an asterisk in place of the integer (e.g. “`dms.*`” or “`%.*g`”). This causes the precision to be derived on the basis of the Digits attribute value.

3. The PlotPlot class has been changed so that the default value used for the Digits attribute is chosen to be the smallest value which results in no pair of adjacent labels being identical. For instance, if an annotated grid is being drawn describing a SkyFrame, and the Format(1) value is set to “`hms.*g`” (the “g” causes field delimiters to be drawn as superscripts), and the Digits(1) value is unset, then the seconds field will have a number of decimal places which results in no pair of labels being identical.

4. Addition of a new class classed DSBSpecFrameDSBSpecFrame. This is a sub-class of SpecFrameSpecFrame which can be used to describe spectral axes associated with dual sideband spectral data.

5. The FitsChanFitsChan class will now read headers which use the old “-GLS” projection code, converting them to the corresponding modern “-SFL” code, provided that the celestial axes are not rotated.

6. The FitsChan class has a new EncodingEncoding, “FITS-CLASS”, which allows the reading and writing of FITS headers using the conventions of the CLASS package - see `http://www.iram.fr/IRAMFR/GILDAS/doc/html/class-html/class.html`).