Description of IDL DBase merged catalogues

IDL database are made from the merged files in the same way as for the unmerged files, by concatenating the 4 CCDs together, then sorting by RA. However there are a few additional considerations to take into account:

• The user is prompted to enter the order in which he or she wants bands to be entered into the database. In the case where there are several occurences of the same band only one occurence should be selected.
• Information for one object occupies only one row, and there are 5 sets of columns per object (columns corresponding to absent bands are filled with zeros).
• The X-- and Y--coordinates have to be converted to RA and DEC using a tangent plane calculation.
• The databases are named after the bands they contain in the order chosen by the user e.g. izrgu if all bands are present. They are found at the same location as the unmerged databases.

A typical database description file is shown in Appendix 6.