celter Subroutine

public subroutine celter(tjdh, tjdl, xp, yp, vec1, vec2)

THIS SUBROUTINE ROTATES A VECTOR FROM THE CELESTIAL TO THE TERRESTRIAL SYSTEM. SPECIFICALLY, IT TRANSFORMS A VECTOR IN THE GCRS (A LOCAL SPACE-FIXED SYSTEM) TO THE ITRS (A ROTATING EARTH-FIXED SYSTEM) BY APPLYING ROTATIONS FOR THE GCRS-TO- DYNAMICAL FRAME TIE, PRECESSION, NUTATION, EARTH ROTATION, AND POLAR MOTION.

 TJDH   = UT1 JULIAN DATE, HIGH-ORDER PART (IN)
 TJDL   = UT1 JULIAN DATE, LOW-ORDER PART (IN)
          THE JULIAN DATE MAY BE SPLIT AT ANY POINT, BUT
          FOR HIGHEST PRECISION, SET TJDH TO BE THE INTEGRAL
          PART OF THE JULIAN DATE, AND SET TJDL TO BE THE
          FRACTIONAL PART
 XP     = CONVENTIONALLY-DEFINED X COORDINATE OF CELESTIAL
          INTERMEDIATE POLE WITH RESPECT TO ITRS POLE,
          IN ARCSECONDS (IN)
 YP     = CONVENTIONALLY-DEFINED Y COORDINATE OF CELESTIAL
          INTERMEDIATE POLE WITH RESPECT TO ITRS POLE,
          IN ARCSECONDS (IN)
 VEC1   = POSITION VECTOR, GEOCENTRIC EQUATORIAL RECTANGULAR
          COORDINATES, REFERRED TO GCRS AXES (CELESTIAL
          SYSTEM) (IN)
 VEC2   = POSITION VECTOR, GEOCENTRIC EQUATORIAL RECTANGULAR
          COORDINATES, REFERRED TO ITRS AXES (TERRESTRIAL
          SYSTEM) (OUT)

NOTE 1: SET XP=YP=0.D0 TO ELIMINATE POLAR MOTION ROTATION.

NOTE 2: SEE ALSO SUBROUTINE SETDT TO SET THE VALUE OF DELTA-T (DELTA-T = TT - UT1) TO BE USED HERE.

NOTE 3: BOTH TJDH AND TJDL SHOULD BE NON-NEGATIVE FOR NORMAL USE (TJDL=0.D0 IS OK). A NEGATIVE VALUE OF TJDH IS USED TO INVOKE A SPECIAL OPTION WHERE THE INPUT VECTOR IS ASSUMED TO BE WITH RESPECT TO THE EQUATOR AND EQUINOX OF DATE, AND THE DATE FOR WHICH THE TRANSFORMATION APPLIES IS TAKEN FROM TJDL ONLY. THIS OPTION WORKS ONLY IN 'EQUINOX' MODE.

Arguments