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slalib/ecor.f

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+      SUBROUTINE sla_ECOR (RM, DM, IY, ID, FD, RV, TL)
+*+
+*     - - - - -
+*      E C O R
+*     - - - - -
+*
+*  Component of Earth orbit velocity and heliocentric
+*  light time in a given direction (single precision)
+*
+*  Given:
+*     RM,DM    real    mean RA, Dec of date (radians)
+*     IY       int     year
+*     ID       int     day in year (1 = Jan 1st)
+*     FD       real    fraction of day
+*
+*  Returned:
+*     RV       real    component of Earth orbital velocity (km/sec)
+*     TL       real    component of heliocentric light time (sec)
+*
+*  Notes:
+*
+*  1  The date and time is TDB (loosely ET) in a Julian calendar
+*     which has been aligned to the ordinary Gregorian
+*     calendar for the interval 1900 March 1 to 2100 February 28.
+*     The year and day can be obtained by calling sla_CALYD or
+*     sla_CLYD.
+*
+*  2  Sign convention:
+*
+*     The velocity component is +ve when the Earth is receding from
+*     the given point on the sky.  The light time component is +ve
+*     when the Earth lies between the Sun and the given point on
+*     the sky.
+*
+*  3  Accuracy:
+*
+*     The velocity component is usually within 0.004 km/s of the
+*     correct value and is never in error by more than 0.007 km/s.
+*     The error in light time correction is about 0.03s at worst,
+*     but is usually better than 0.01s. For applications requiring
+*     higher accuracy, see the sla_EVP and sla_EPV routines.
+*
+*  Called:  sla_EARTH, sla_CS2C, sla_VDV
+*
+*  Last revision:   5 April 2005
+*
+*  Copyright P.T.Wallace.  All rights reserved.
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the 
+*    Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
+*    Boston, MA  02111-1307  USA
+*
+*-
+
+      IMPLICIT NONE
+
+      REAL RM,DM
+      INTEGER IY,ID
+      REAL FD,RV,TL
+
+      REAL sla_VDV
+
+      REAL PV(6),V(3),AUKM,AUSEC
+
+*  AU to km and light sec (1985 Almanac)
+      PARAMETER (AUKM=1.4959787066E8,
+     :           AUSEC=499.0047837)
+
+
+
+*  Sun:Earth position & velocity vector
+      CALL sla_EARTH(IY,ID,FD,PV)
+
+*  Star position vector
+      CALL sla_CS2C(RM,DM,V)
+
+*  Velocity component
+      RV=-AUKM*sla_VDV(PV(4),V)
+
+*  Light time component
+      TL=AUSEC*sla_VDV(PV(1),V)
+
+      END