THIS SUBROUTINE RETURNS THE ORTHONORMAL BASIS VECTORS, WITH RESPECT TO THE GCRS (GEOCENTRIC ICRS), OF THE CELESTIAL INTERMEDIATE SYSTEM DEFINED BY THE CELESTIAL INTERMEDIATE POLE (CIP) (IN THE Z DIRECTION) AND THE CELESTIAL INTERMEDIATE ORIGIN (CIO) (IN THE X DIRECTION). A TDB JULIAN DATE AND THE RIGHT ASCENSION OF THE CIO AT THAT DATE IS REQUIRED AS INPUT. THE RIGHT ASCENSION OF THE CIO CAN BE WITH RESPECT TO EITHER THE GCRS ORIGIN OR THE TRUE EQUINOX OF DATE -- DIFFERENT ALGORITHMS ARE USED IN THE TWO CASES.
TJD = TDB JULIAN DATE (IN)
RACIO = RIGHT ASCENSION OF THE CIO, IN HOURS (IN)
K = REFERENCE SYSTEM IN WHICH RIGHT ASCENSION IS
EXPRESSED (IN)
SET K=1 FOR GCRS
SET K=2 FOR TRUE EQUATOR AND EQUINOX OF DATE
X = UNIT VECTOR TOWARD THE CIO, EQUATORIAL RECTANGULAR
COORDINATES, REFERRED TO THE GCRS (OUT)
Y = UNIT VECTOR TOWARD THE Y-DIRECTION, EQUATORIAL
RECTANGULAR COORDINATES, REFERRED TO THE GCRS (OUT)
Z = UNIT VECTOR TOWARD NORTH CELESTIAL POLE (CIP),
EQUATORIAL RECTANGULAR COORDINATES, REFERRED TO
THE GCRS (OUT)
Type | Intent | Optional | Attributes | Name | ||
---|---|---|---|---|---|---|
real(kind=wp) | :: | tjd | ||||
real(kind=wp) | :: | racio | ||||
integer | :: | k | ||||
real(kind=wp), | dimension(3) | :: | x | |||
real(kind=wp), | dimension(3) | :: | y | |||
real(kind=wp), | dimension(3) | :: | z |