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.help precss Jun99 "Slalib Package"
.nf
SUBROUTINE slPRCS (SYSTEM, EP0, EP1, RA, DC)
- - - - - - -
P R C E
- - - - - - -
Precession - either FK4 (Bessel-Newcomb, pre IAU 1976) or
FK5 (Fricke, post IAU 1976) as required.
Given:
SYSTEM int precession to be applied: 1 = FK4 or 2 = FK5
EP0,EP1 dp starting and ending epoch
RA,DC dp RA,Dec, mean equator & equinox of epoch EP0
Returned:
RA,DC dp RA,Dec, mean equator & equinox of epoch EP1
Called: slDA2P, slPRBN, slPREC, slDS2C,
slDMXV, slDC2S
Notes:
1) Lowercase characters in SYSTEM are acceptable.
2) The epochs are Besselian if SYSTEM=FK4 and Julian if FK5.
For example, to precess coordinates in the old system from
equinox 1900.0 to 1950.0 the call would be:
CALL slPRCS (1, 1900D0, 1950D0, RA, DC)
3) This routine will NOT correctly convert between the old and
the new systems - for example conversion from B1950 to J2000.
For these purposes see slFK45, slFK54, slF45Z and
slF54Z.
4) If an invalid SYSTEM is supplied, values of -99D0,-99D0 will
be returned for both RA and DC.
P.T.Wallace Starlink 20 April 1990
.fi
.endhelp
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