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, a new Frame with the required number of axes is created and added into the FrameSet and becomes the new current Frame.

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, the user is allowed to select a subset of the original axes using the environment parameter USEAXIS (see below). A new Frame is created by picking these selected axes from the original current Frame. This Frame 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. This is only possible if the value for a dropped axis can be determined uniquely from the value of one of the selected 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 what happens depends on whether or not any Frames can be found in the FrameSet that are Regions having a Domain name of " ROI$<$n$>$" , where "$<$n$>$" is a positive integer. If no such Frame can be found, AST__BAD is supplied for the dropped axis.

If the supplied current Frame has too many axes, and one or more ROI Regions are found in the FrameSet, then a new Frame is added into the FrameSet for each ROI Region found. These new Frames are all equivalent, containing axes from the supplied current Frame as specified by the USEAXIS parameter, and they are all connected to the supplied current Frame via a PermMap. Each PermMap has a forward transformation that simply drops the unwanted axis values. The inverse transformation of each PermMap supplies suitable values for the unwanted axes. These are determined by transforming the bounding box of the corresponding ROI Region into the original current Frame. The Domain name of the corresponding ROI Region is stored in the Ident attribute of the new Frame, and is also appended to the end of the Frame’ s Domain. The new Frame corresponding to the lowest numbered ROI Region is left as the current Frame on exit.

Various environment parameters may be used to obtain options, etc. The names of these parameters are hard-wired into this subroutine in order to ensure conformity between applications.

CALL KPG1_ASTRM( IWCS, DEFAX, LBND, UBND, WORK, STATUS )

IWCS = INTEGER (Given)

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

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

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

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

STATUS = INTEGER (Given and Returned)

USEAXIS = LITERAL (Read)