OPREP: Open a Batch Surface Photometry Preparation File

OPREP opens a "batch photometry preparation file" used for batch-type surface photometry reductions. The files contain the following information (one record per image):

This information is written by WPREP command, and read by RPREP. This routine initialized the PREPCON common block, which records the status of the prep-file (whether open to read or write). The filename is supplied as a keyword. Default directory is V_DATADIR, with the default extension ``.pre''. If no name is given on the command line, the default name PREPFILE is used. If there is a prep-file already open, this routine closes it and opens a new one.

NOTE: You must compute the image parameters above ahead of time, either outside of VISTA or using the AXES command without the CORR option.