Subroutine:   IRCO_PLATE
 
 Purpose:      construct a plate coordinate system
 
 Category	WORLD COORDINATES, IRAS

 File:         irco.shl
 
 Author:       Do Kester
 
 Person resp.: Do Kester
 
 Address:      guspace!do or rugfx4!do         (uucp)
 
 Use: call irco_plate(
 	refcoor  	I  	integer 
 	center		I  	doubleprecision array(2)
	name		I	character*(*)
 	newcoor  	I/O 	integer )
 
 	refcoor		reference coordinate system
 	center		longitude and latitude of the plate
	name		of the new system
 	newcoor input: 0 => output: free coordinate number
		otherwise   output = input
 Description:  
 	A plate coordinate system will be created, defined with
 	respect to REFCOOR. Two angles are necessary to
 	define the new system: the longitude and the latitude
 	of the plate with respect to the reference system.
	The angles are given in radians. The plate system will
 	be aligned north-south along the meridian of the reference
	system running through the center of the plate.
	The central point of the plate has vector (1,0,0).

 	It is not allowed for NEWCOOR to be the same as REFCOOR.
	If NEWCOOR is 0 upon entry, a free coordinate number will 
	be returned, or 0 if none is available any more.
 	Upon output NEWCOOR contains the number of the new system.

	The connection to coordinate system nr 1 is always made, so that
	all connections with other systems will be present in one or
	two steps.

 Externals:    
 
 Updates:      5 May 1990 DK, documentation only
		17 DEC 1990 DK, make always connection with system nr 1