Basic Information on region

Key: region
	This selects a subregion of an image. Multiple subregions can be
	selected, which are "ored" together. The following subcommands are
	recognized (each of which can be abbreviated to uniqueness).

	  images(z1,z2)
	Select image planes z1 to z2 inclusive. z2 defaults to z1.

	  quarter(z1,z2)
	Select the inner quarter of the image planes z1 to z2 inclusive.
	If both z1 and z2 are missing, then all planes are selected. If
	only z2 is omitted, z2 defaults	to z1.

          percentage(px,py)(z1,z2)
        Select the inner px and py percent of the image x and y axis 
        for planes z1 to z2 inclusive. If py is missing, it defaults to px.
        If both z1 and z2 are missing, then all planes are selected. If
        only z2 is omitted, z2 defaults to z1.

	  boxes(xmin,ymin,xmax,ymax)(z1,z2)
	Select the pixels within a box with corners xmin,ymin,xmax,ymax.
	z1 and z2 are the same as in the "image" subcommand. If z1 and z2
	are omitted, all planes are selected.

	  polygon(x0,y0,x1,y1,x2,y2,...)(z1,z2)
	Select the pixels within the polygon defined by the list of vertices.
	z1 and z2 are the same as in the "image" subcommand. If z1 and z2 are
	missing, all planes are selected. If only z2 is omitted, it defaults
	to z1.

	  mask(file)
	Select  pixels according to the mask given in the file.

	The units of the numbers given in the above commands are, in
	general, absolute pixels. But this can be changed (and rechanged)
	by using one of the following subcommands.

	  abspixel
	Coordinates are interpreted as absolute pixel values, the default.
	  relpixel
	Coordinates are relative to the reference pixel of the map.
	  relcenter
	Coordinates are relative to the central pixel of the map,
	(defined as (naxis1/2+1,naxis2/2+1)).
	  arcsec
	Coordinates are in arcseconds, relative to the reference pixel.
	  kms
	Coordinates in the third dimension are in km/s.