Subroutine:   IRCO_TRANSFORM
 
 Purpose:      Transform between coordinate systems
 
 Category	WORLD COORDINATES, IRAS

 File:         irco.shl
 
 Author:       Do Kester
 
 Person resp.: Do Kester
 
 Address:      guspace!do or rugfx4!do         (uucp)
 
 Use: call irco_transform(
	xyz1,		I	double precision array(3,n)
 	coor1,		I	integer
 	xyz2,		O	double precision array(3,n)
 	coor2,		I	integer
 	n )		I	integer
 		
       xyz1     vectors to be transformed                    
       coor1    coordinate system in which XYZ1 are given    
       coor2    desired coordinate system                    
       n        number of vectors to be transformed          
       xyz2     vectors in system coor2
 		
 Description:  
 	The vectors in XYZ1 and XYZ2 are three-dimensional unit vectors.
 	The vectors XYZ1 which are in coordinate system COOR1 are
 	transformed into vectors XYZ2 in coordinate system COOR2 by
 	multiplication with a transformation matrix. The matrix is
 	either given in advance (COORn <= 5), or it has to be (re)defined
 	using the routines IRCO_NEWCOOR, IRCO_PRECESS or IRCO_PLATE.
 
 	It is allowed that XYZ1 and XYZ2 are the same array.
 	It is not essential that XYZ1 are unit vectors; they will 
	retain their length upon transformation.
 Externals:    
 
 Updates:      850624 Albrecht de Jonge, original code
		900424 DK, documentation and rewrite