11 IFU headers

The ifu_profile.dat and the appropriate grism data file are read by the _LOCATE_SLICES_ primitive, which does nothing to the frame except put the positions of the slices and the offsets which should be applied to them into the header of the frame for use by subsequent primitives. The values are written into the entries IFU_start, IFU_end, IFU_xshift and IFU_yshift. Each of these headers contains an $n$ element array (indices 0 to $n-1$), where $n$ is the number of slices. An additional header entry, IFU_slices $=n$, is also written.

When the positions of the slices in the frame is changed by a primitive (for example, when the slices are re-ordered and shifted by the _EXTRACT_SLICES_ primitive) the new positions of the slices should be written into the header of the output file to be available for subsequent primitives.