gr_id	IN:	GR interface identifier returned by GRstart
	index	IN:	Index of the raster image in the file

	Purpose	Selects the existing raster image.
	Return value	Returns the raster image identifier if successful or FAIL (or -1) otherwise.
	Description	GRselect obtains the identifier of the raster image specified by the its index, index.
		Valid values of the parameter index range from 0 to the total number of raster images in the file - 1. The total number of the raster images in the file can be obtained by using GRfileinfo.

	FORTRAN	integer function mgselct(gr_id, index)
		integer gr_id, index