Subroutine:	IRCO_TWISTORECT.

 Purpose:	Transform twist angles to rectangular coordinates.

 Category	WORLD COORDINATES, IRAS

 File:		irco.shl

 Author:	900921	Do Kester

 Use:
	call IRCO_TWISTORECT (
		lon	  I	doubleprecision(n) 
		lat	  I	doubleprecision(n) 
		twist	  I	doubleprecision(n),
		xyz	  I	doubleprecision(3,n),
		twv	  O	doubleprecision(3,n),
		n 	  I	integer.
		)
	lon 	longitude of direction
	lat	latitude
	twist   (in radian:) twist angle perpendicular to XYZ, 
		counterclock from north
	xyz	rectangular coordinates of direction
	twv	rectangular coordinates of the twist angle
	n	number of coordinates to transform.
 Description:
	Transformation according to:
		x = cos(lat) * cos(lon),
 		y = cos(lat) * sin(lon),
		z = sin(lat).
		tx = cos(lon) * sin(lat) * cos(twist) + sin(lon) * sin(twist)
		ty = sin(lon) * sin(lat) * cos(twist) - cos(lon) * sin(twist)
		tz = cos(lat) * cos(twist)
	In this module (psi, theta,epsilon) is not applicable, use:
	call IRCO_TWISTORECT( psi, pi/2 - theta, epsilon + pi/2, xyz, twv, n) !!
 Updates:
	90 Apr 24 Sjag Steensma; documentation changed, n-coordinates,
	87 May 25 Timo Prusti; unification of versions,
	87 May 25 Romke Bontekoe; documentation changed.