This directory is supplied to match the default cache directory of xephem. If
you run xephem (from ../..) with the GSC CDROM and the GSC Cache Field Stars
both turned on with its default settings you will notice that directories
containing .ech files start to accumulate here. These files will serve as local
alternates to accessing the CD-ROMs directly. The file names are the GSC small
region designation plus an .ech suffix. Thus, the directory structure matches
that of the CD-ROM.

You may also load any portion of a CDROM here at once using the gscload utility.
It is located in the tools/gsc directory off the main xephem source directory.

The files are in a portable packed binary format but the header is one line of
plain ASCII. One way to view this line on UNIX is to use "head -1 <filename>".
The header line consists of the following fields. Because the absolute value of
the declination is stored one must also know that southern region ids are 4663
and greater.

	Version number
	Region ID
	Number of stars
	Western (smallest) RA, radians
	abs(Dec nearest 0), radians
	south (1 or 0)
	<newline>

The binary format then begins immediately following the newline and stores
each star in 8 bytes, as follows:

     2  delta ra, rads, 0 .. degrad(4) * cos(dec0), scaled 0 .. 0xffff
     2  delta dec, rads, 0 .. degrad(4), scaled 0 .. 0xffff
     2  small region id
     2  upper 2 bits are class, lower 14 are magnitude*900
     ---
     8  total bytes per entry

     all values stored in big-endian byte order.
       
