/* tai_et.c
********************************************************************************
* tai_et.c
*
* This pair of functions converts between TAI (atomic time) and ET (ephemeris
* time).
*
* RL_FLT8 Jul_TAIofET(et)
* converts from ephemeris time to atomic time.
* RL_FLT8 Jul_ETofTAI(tai)
* converts from atomic time to ephemeris time.
*
* Mark R. Showalter, PDS Ring-Moon Systems Node, November 1995
*******************************************************************************/
#include <math.h>
#include "julian.h"
#include "fortran.h"
/*
********************************************************************************
* EXPORTED USER ROUTINES
********************************************************************************
*$ Component_name:
* Jul_TAIofET (tai_et.c)
*$ Abstract:
* Converts from ET (ephemeris time) to TAI (Atomic time).
*$ Keywords:
* JULIAN, TIME, UNIVERSAL_TIME, EPHEMERIS_TIME
* C, PUBLIC
*$ Declarations:
* RL_FLT8 Jul_TAIofET(et)
* RL_FLT8 et;
*$ Inputs:
* et ephmeris time (seconds relative to J2000 ET).
*$ Outputs:
* none
*$ Returns:
* corresponding atomic time (seconds relative to J2000 TAI).
*$ Side_effects:
* none
*$ Detailed_description:
* This function converts from ET (ephemeris time) to TAI (Atomic time).
* All times are given as seconds relative to J2000. The algorithm is
* based on that used in the SPICE toolkit.
*$ External_references:
* none
*$ Examples:
* none
*$ Error_handling:
* none
*$ Limitations:
* none
*$ Author_and_institution:
* Mark R. Showalter
* PDS Ring-Moon Systems Node
* NASA/Ames Research Center
*$ Version_and_date:
* 1.0: November 1995
*$ Change_history:
* none
*******************************************************************************/
#define M0 6.239996
#define M1 1.99096871e-7
#define EB 1.671e-2
#define K 1.657e-3
#define DELTA_T_A 32.184
RL_FLT8 Jul_TAIofET(et)
RL_FLT8 et;
{
RL_FLT8 mean_anom, ecc_anom;
mean_anom = M0 + M1 * et;
ecc_anom = mean_anom + EB * sin(mean_anom);
return et - DELTA_T_A - K * sin(ecc_anom);
}
/*
********************************************************************************
*$ Component_name:
* Jul_ETofTAI (tai_et.c)
*$ Abstract:
* Converts from TAI (Atomic time) to ET (ephemeris time).
*$ Keywords:
* JULIAN, TIME, UNIVERSAL_TIME, EPHEMERIS_TIME
* C, PUBLIC
*$ Declarations:
* RL_FLT8 Jul_ETofTAI(tai)
* RL_FLT8 tai;
*$ Inputs:
* tai atomic time (seconds relative to J2000 TAI).
*$ Outputs:
* none
*$ Returns:
* corresponding ephmeris time (seconds relative to J2000 ET).
*$ Side_effects:
* none
*$ Detailed_description:
* This function converts from TAI (Atomic time) to ET (ephemeris time).
* All times are given as seconds relative to J2000. This is the inverse
* of function Jul_TAIofET().
*$ External_references:
* Jul_TAIofET()
*$ Examples:
* none
*$ Error_handling:
* none
*$ Limitations:
* none
*$ Author_and_institution:
* Mark R. Showalter
* PDS Ring-Moon Systems Node
* NASA/Ames Research Center
*$ Version_and_date:
* 1.0: November 1995
*$ Change_history:
* none
*******************************************************************************/
RL_FLT8 Jul_ETofTAI(tai)
RL_FLT8 tai;
{
RL_FLT8 et, et_prev;
/* Take an initial guess at the ephemeris time */
et = tai + DELTA_T_A;
/* Iterate until time converges */
do {
et_prev = et;
et += tai - Jul_TAIofET(et);
}
while (et != et_prev);
return et;
}
/*
********************************************************************************
* FORTRAN INTERFACE ROUTINES
********************************************************************************
*$ Component_name:
* FJul_TAIofET (tai_et.c)
*$ Abstract:
* Converts from ET (ephemeris time) to TAI (Atomic time).
*$ Keywords:
* JULIAN, TIME, UNIVERSAL_TIME, EPHEMERIS_TIME
* FORTRAN, PUBLIC
*$ Declarations:
* real*8 function FJul_TAIofET(et)
* real*8 et
*$ Inputs:
* et ephmeris time (seconds relative to J2000 ET).
*$ Outputs:
* none
*$ Returns:
* corresponding atomic time (seconds relative to J2000 TAI).
*$ Side_effects:
* none
*$ Detailed_description:
* This function converts from ET (ephemeris time) to TAI (Atomic time).
* All times are given as seconds relative to J2000. The algorithm is
* based on that used in the SPICE toolkit.
*$ External_references:
* Jul_TAIofET(), RL_FortInit()
*$ Examples:
* none
*$ Error_handling:
* none
*$ Limitations:
* none
*$ Author_and_institution:
* Mark R. Showalter
* PDS Ring-Moon Systems Node
* NASA/Ames Research Center
*$ Version_and_date:
* 1.0: November 1995
*$ Change_history:
* none
*******************************************************************************/
RL_FLT8 FORTRAN_NAME(fjul_taiofet) (et)
RL_FLT8 *et;
{
FORT_Init();
return Jul_TAIofET(*et);
}
/*
********************************************************************************
*$ Component_name:
* FJul_ETofTAI (tai_et.c)
*$ Abstract:
* Converts from TAI (Atomic time) to ET (ephemeris time).
*$ Keywords:
* JULIAN, TIME, UNIVERSAL_TIME, EPHEMERIS_TIME
* FORTRAN, PUBLIC
*$ Declarations:
* real*8 function FJul_ETofTAI(tai)
* real*8 tai
*$ Inputs:
* tai atomic time (seconds relative to J2000 TAI).
*$ Outputs:
* none
*$ Returns:
* corresponding ephmeris time (seconds relative to J2000 ET).
*$ Side_effects:
* none
*$ Detailed_description:
* This function converts from TAI (Atomic time) to ET (ephemeris time).
* All times are given as seconds relative to J2000. This is the inverse
* of function FJul_TAIofET().
*$ External_references:
* Jul_ETofTAI(), RL_FortInit()
*$ Examples:
* none
*$ Error_handling:
* none
*$ Limitations:
* none
*$ Author_and_institution:
* Mark R. Showalter
* PDS Ring-Moon Systems Node
* NASA/Ames Research Center
*$ Version_and_date:
* 1.0: November 1995
*$ Change_history:
* none
*******************************************************************************/
RL_FLT8 FORTRAN_NAME(fjul_etoftai) (tai)
RL_FLT8 *tai;
{
FORT_Init();
return Jul_ETofTAI(*tai);
}
/*******************************************************************************
*/