;+ ; - - - - - - - - ; s l a P R E C ; - - - - - - - - ; ; Form the matrix of precession between two epochs (IAU 1976, FK5) ; (double precision) ; ; Given: ; EP0 dp beginning epoch ; EP1 dp ending epoch ; ; Returned: ; RMATP dp(3,3) precession matrix ; ; Notes: ; ; 1) The epochs are TDB (loosely ET) Julian epochs. ; ; 2) The matrix is in the sense V(EP1) = RMATP * V(EP0) ; ; References: ; Lieske,J.H., 1979. Astron.Astrophys.,73,282. ; equations (6) & (7), p283. ; Kaplan,G.H., 1981. USNO circular no. 163, pA2. ; ; Called: sla_DEULER ; ; P.T.Wallace Starlink 12 April 1990 ;- pro slaPREC, EP0, EP1, RMATP ; Arc seconds to radians AS2R=0.4848136811095359949D-05 ; Interval between basic epoch J2000.0 and beginning epoch (JC) T0 = (EP0-2000D0)/100D0 ; Interval over which precession required (JC) T = (EP1-EP0)/100D0 ; Euler angles TAS2R = T*AS2R W = 2306.2181D0+(1.39656D0-0.000139D0*T0)*T0 ZETA = (W+((0.30188D0-0.000344D0*T0)+0.017998D0*T)*T)*TAS2R Z = (W+((1.09468D0+0.000066D0*T0)+0.018203D0*T)*T)*TAS2R THETA = ((2004.3109D0+(-0.85330D0-0.000217D0*T0)*T0)+\$ ((-0.42665D0-0.000217D0*T0)-0.041833D0*T)*T)*TAS2R ; Rotation matrix slaDEULER,'ZYZ',-ZETA,THETA,-Z,RMATP end