This routine ensures that the number of axes in the current Frame of the supplied FrameSet is the same as the number in the base Frame. If this is not the case on entry, one or more new Frames with the required number of axes are created and added into the FrameSet, one of which becomes the new current Frame. The only case in which more than one new Frame is added is if the current Frame has too many axes, and the FrameSet contains more than one " ROI" Frame (that is, Frames which are Regions and which have a Domain name beginning with " ROI" ). If the FrameSet contains zero or one ROI Frame, then only a single new Frame is added into the FrameSet.

If the original current Frame has too few axes, the new Frame is a copy of the original current Frame with extra simple axes added to the end. These extra axes are supplied a value of AST__BAD by the Mapping which connects the original current Frame to the new current Frame.

If the original current Frame has too many axes, one or more new Frames will be created by picking the specified axes from the original current Frame. Each of these Frames is added into the FrameSet using a Mapping which has a forward transformation which simply drops the values for the unselected axes. The inverse transformation (from new to old Frame) attempts to assign usable values for the dropped axes if possible. If this is not possible, then AST__BAD is assigned to the dropped axes.

Two methods are used for finding suitable values to assign to dropped axes. The first is only possible if the value for a dropped axis can be determined uniquely from the value of one of the retained axes. This may be the case for instance in a situation where (RA,wavelength) axes were selected from the (RA,Dec,Wavelength) axes describing a 2D longslit spectrum. The missing Dec value can probably be determined from the RA value because the relationship between RA and Dec is determined by the position and orientation of the slit on the sky.

If it is not possible to determine the value for a dropped axis in this way, then a search is made for Frames that are Regions having a Domain name beginning with " ROI" . If any are found, then a new Frame is added into the FrameSet for each ROI Region found, connected to the original current Frame via a PermMap. The values to be assigned to the dropped axes by the inverse PermMap transformation are determined by transforming the bounding box of the corresponding ROI Region into the original current Frame. The assigned axis values are the mean values of the transformed bounding box on each dropped axis. The Domain name of the corresponding ROI Region is stored in the Ident attribute of each new Frame so that later code can identify the corresponding ROI Region, and is also appended to the end of the Frame’ s Domain. The new Frame corresponding to the first ROI Region found in the FrameSet is left as the current Frame on exit.

CALL ATL_AXTRM( IWCS, AXES, LBND, UBND, WORK, STATUS )

IWCS = INTEGER (Given)

AXES( $\ast$ ) = INTEGER (Given)

LBND( $\ast$ ) = INTEGER (Given)

UBND( $\ast$ ) = INTEGER (Given)

WORK( $\ast$ ) = INTEGER (Given)

STATUS = INTEGER (Given and Returned)