Description:
Precess coordinates using the
appropriate system and epochs.
Invocation
void palPreces ( const char sys[3], double ep0, double
ep1, double ra,
double dc
);
Arguments
sys = const char [3] (Given)
Precession to be applied: FK4 or FK5. Case insensitive.
ep0 = double (Given)
Starting epoch.
ep1 = double (Given)
Ending epoch
ra = double
(Given & Returned)
On input the RA mean equator & equinox at epoch
ep0. On exit the RA mean equator & equinox of epoch ep1.
dec = double
(Given
& Returned)
On input the dec mean equator & equinox at epoch ep0. On exit the dec mean equator &
equinox of epoch ep1.
Notes:
-
Uses palPrec for FK5 data and palPrebn for FK4 data.
-
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: palPreces( " FK4" , 1900.0, 1950.0,
&ra, &dc );
-
This routine will NOT correctly convert between the old and the new systems - for example
conversion from B1950 to J2000. For these purposes see palFk425, palFk524, palFk45z and
palFk54z.
-
If an invalid SYSTEM is supplied, values of -99D0,-99D0 will be returned for both RA and DC.
Copyright © 2012 Science and Technology Facilities Council.
Copyright © 2014 Cornell University.
Copyright © 2015 Tim Jenness