Subroutine:	IRPL_PLATECENTER.

 Purpose:	Delivering plate centres for the celestial sphere.

 File:		irpl_standard.shl

 Author: 	85 Aug 23  Wim van Oosterom.

 Use:
	call IRPL_PLATECENTER (
		size  	  I	doubleprecision array (*),
		overlp    I	doubleprecision,
		nplate    I/O	integer,
		plcenter  O	doubleprecision array(2,nplate),
		plsize	  O	doubleprecision array(2,nplate),
		)
	size  	Size of a layer of square plates;
	overlp  Size of overlap between plates;
	nplate  Maximum nr. of plates allowed storage for,
		Nr. of plates actually returned;
	plcenter longitude and latitude of the plate (in radians)
	plsize	lon. and lat. size of the plate (in radian)

 Description:
	IRPL_PLATECENTER starts at the equator with the first SIZE
	and goes up to the pole taking for each layer of plates
	the next SIZE. IRPL_PLATECENTER stops when the new centre
	would lie below the equator. The southern sky will be a symmetric
	copy of the northern sky. The caller is responsible to give enough
	plate sizes in size.
	This subroutine will produce a number of plate centres for the
	celestial sphere. The order of plates will be first the plates
	at the equator then the plates in layers above the equator fol-
	lowed by the plates in the layers below the equator in a symmetric
	way.
	The centers and the sizes are valid in any coordinate system;
	Both IRAS plate systems though are defined in the ECLIPTIC
	system of epoch 1983.5
 Externals:
	ERROR, IRPL_CORNERS, IRCO_PLATE, IRCO_TRANSFORM
 Updates:
	90 Jul 12  Do Kester, change in CALL and clean up
	90 May  1  Sjag Steensma; documentation only,
	89 Jan 09  Timo Prusti, unification of versions,
	87 May 11  WvO, Repaired documentation error,
	85 Dec 03  WvO, Forgotten declaration added.