NASA Ocean Color

ocssw V2022

       subroutine eci2ecef(time,ecivec,ecrvec)
 c
 c  Converts inertial Earth-centered coordinates of position and
 c  velocity into Earth-centered, Earth-fixed (ECEF) coordinates,
 c  using the Greenwich Hour Angle as the rotation angle.
 c
       implicit none
 c
       real*8    time            ! julian vector time
       real*8    ecivec(6)       ! eci vector (x,y,z,vx,vy,vz)
       real*8    ecrvec(6)       ! eci vector (x,y,z,vx,vy,vz)
 c
       real*8    gha
       integer*4 year
       integer*4 day
       real*8    sec
 c
       logical*4 firstCall
       real*8 pi,radeg,re,rem,f,omf2,omegae
       common /gconst/pi,radeg,re,rem,f,omf2,omegae
       data firstcall / .true. /
 c
       if (firstcall) then
           firstcall = .false.
           call cdata
       endif
 c
       call jul2yds(time,year,day,sec)
       call gha2000(year,day+sec/86400.d0,gha)
 c
       call ecef(gha,ecivec(1),ecivec(4),ecrvec(1),ecrvec(4))
  
 c      rgha   = gha/radeg
 c      cosgha = dcos(rgha)
 c      singha = dsin(rgha)
  
 c
 c  Position rotation
 c      ecrvec(1) =  ecivec(1)*cosgha + ecivec(2)*singha
 c      ecrvec(2) = -ecivec(1)*singha + ecivec(2)*cosgha
 c      ecrvec(3) =  ecivec(3)
  
 c
 c  Velocity rotation
 c
 c      term1 = ecivec(4)*cosgha + ecivec(5)*singha
 c      term2 = omegae*(-ecivec(4)*singha + ecivec(5)*cosgha)
 c      ecrvec(4) = term1+term2
 c
 c      term1 = -ecivec(4)*singha + ecivec(5)*cosgha
 c      term2 = omegae*(-ecivec(4)*cosgha - ecivec(5)*singha)
 c      ecrvec(5) = term1+term2
 c
 c      ecrvec(6) = ecivec(6)
 c
       return
       end