C+
C NAME:
C	interpolate_latlon.f
C PURPOSE:
C	Interpolate the longitude of ASHI to use in a sidereal time determination
C CATEGORY:
C	I/O
C CALLING SEQUENCE:
C	call interpolate_latlon(JDXI,JD,alat,alon,NL,alaty,alonx)
C
C INPUTS:
C	JDXI        real*8	      Julian Date time to interpolate to
C	JD (NL)     real*8	      Julian dates of the tracked values where longitudes and latitudes exist
C
C OUTPUTS:
C	NL		integer		# valid number of tracked longitudes and latitudes recorded
C	alaty       real              interpolated tracked latitude value
C	alonx       real              interpolated tracked longitude value
C
C FUNCTIONS/SUBROUTINES:
C
C MODIFICATION HISTORY:
C	April-2022, Bernard Jackson (UCSD)
C-
	subroutine interpolate_latlon(JDXI,JD,alat,alon,NL,alaty,alonx)
        real            alat(NL),
     &                  alon(NL)
        real*8          JD  (NL)
        real*8          JDXI

C          print*, ' Into interpolate_latlon'

            IX = 0
            do I=1,NL-1
              if(JDXI.ge.JD(I).and.JDXI.lt.JD(I+1)) then
                alonx = ((JDXI-JD(I))/(JD(I+1)-JD(I)))*(alon(I+1)-alon(I)) + alon(I)
                alaty = ((JDXI-JD(I))/(JD(I+1)-JD(I)))*(alat(I+1)-alat(I)) + alat(I)
                IX = I
              end if
	      end do
            if(IX.eq.0) then
C              print*, 'The interpolate JDXI =',JDXI,' value is out of bounds.',JD(1),JD(NL)
              stop
            end if
C            write (*,'(2I5,3F15.6,6F9.4)')  IX,IX+1,JD(IX),JD(IX+1),JDXI,alat(IX),alat(IX+1),alaty,alon(IX),alon(IX+1),alonx
	  return
	end