EXT# FITSNAME FILENAME EXTVE DIMENS BITPI 0 ngc1140_1bftf ngc1140_4645_c1_000.f 1 BINTABLE 4Fx517R 2 IMAGE SCI 1 1024x508 -32 3 IMAGE VAR 1 1024x508 -32 4 IMAGE DQ 1 1024x508 -32 5 IMAGE TIME 1 1024x508 -32
Depending on if the image has been mosaiced or not it should look something like BINTABLE.txt which was read form the .fits file with
tdump ngc1140_1bftfsub_cal.ms.fits > BINTABLE.txt
The table contains four columns; FibreID, xcord, ycord and apnum. ID and apnum are generally identical in the current format IFU. Apnum gives the order of the spectra in the _cal.ms.fits file (starting at 1 NOT 0). xcord and ycord predictably give the x/y [position of the lense in the IFU. The current (2002) lense map is found here. A more detailed description of the interpretation of x/y positions is contained in Andrew Deans PhD thesis, more information will be added here soon.
The main potential error associated with using this file is in handling calibration fibers and missing lenses. There are 10 entries in the table for calibration fibers which appear on the slit (and in processed images which have not been mosaiced) but which have no lense in the IFU and hence have xcord/ycord=-999. There is also a broken lense in the IFU. This lense has no fiber attached and hence no entry in the spectral image (_cal.ms.fits[sci,1]) BUT the lense x/y coordinate in the IFU are still recorded in the Table. This lense (sitting between lenses 359 and 360) can be identified in the table by it's FibreID=-999 and apnum=-999. The corollary of all this is that apnum in the table extension corresponds to the apnum in the _cal.ms.fits (counting starting at 1 NOT 0). Line N in the table extension does not usually correspond to spectrum N'th in the spectral image.
Once multiple dithers have been mosaiced the dead lense and the calibration fibers are removed form the image and the table extension is updated to reflect the new fiber to lense map.