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.help preces Jun99 "Slalib Package"
.nf
SUBROUTINE slPRCE (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 char precession to be applied: 'FK4' or '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 slPRCE ('FK4', 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
Copyright (C) 1995 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
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.endhelp
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