JDCALF Subroutine

  1. astro_module.f90
  2. astro_module
  3. JDCALF

public subroutine JDCALF(ndp, dj1, dj2, iymdf, j)

Julian Date to Gregorian Calendar, expressed in a form convenient for formatting messages: rounded to a specified precision, and with the fields stored in a single array.

Status: support routine.

Notes

  1. The Julian Date is apportioned in any convenient way between the arguments DJ1 and DJ2. For example, JD=2450123.7 could be expressed in any of these ways, among others:

         DJ1            DJ2

 2450123.7D0        0D0        (JD method)
  2451545D0      -1421.3D0     (J2000 method)
 2400000.5D0     50123.2D0     (MJD method)
 2450123.5D0       0.2D0       (date & time method)

  2. In early eras the conversion is from the "Proleptic Gregorian Calendar"; no account is taken of the date(s) of adoption of the Gregorian Calendar, nor is the AD/BC numbering convention observed.

  3. Refer to the routine JD2CAL.

  4. NDP should be 4 or less if internal overflows are to be avoided on machines which use 16-bit integers.

Reference

  • Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann (ed), University Science Books (1992), Section 12.92 (p604).

History

  • IAU SOFA revision: 2019 June 20

Arguments

TypeIntentOptionalAttributesName
integer, intent(in) :: ndp

number of decimal places of days in fraction
real(kind=wp), intent(in) :: dj1

DJ1+DJ2 = Julian Date (Note 1)
real(kind=wp), intent(in) :: dj2

DJ1+DJ2 = Julian Date (Note 1)
integer, intent(out), dimension(4):: iymdf

year, month, day, fraction in Gregorian calendar
integer, intent(out) :: j
  • -1 = date out of range
  • 0 = OK
  • +1 = NDP not 0-9 (interpreted as 0)

Calls

proc~~jdcalf~~CallsGraph proc~jdcalf JDCALF proc~jd2cal JD2CAL proc~jdcalf->proc~jd2cal

Contents

Source Code

JDCALF

Source Code

    subroutine JDCALF ( ndp, dj1, dj2, iymdf, j )

    implicit none

    integer,intent(in) :: ndp !! number of decimal places of days in fraction
    real(wp),intent(in) :: dj1 !! DJ1+DJ2 = Julian Date (Note 1)
    real(wp),intent(in) :: dj2 !! DJ1+DJ2 = Julian Date (Note 1)
    integer,dimension(4),intent(out) :: iymdf !! year, month, day, fraction in Gregorian calendar
    integer,intent(out) :: j !! status:
                             !! * -1 = date out of range
                             !! *  0 = OK
                             !! * +1 = NDP not 0-9 (interpreted as 0)

    integer :: js
    real(wp) :: denom, d1, d2, f1, f2, f

    !  Denominator of fraction (e.g. 100 for 2 decimal places).
    if ( ndp>=0 .and. ndp<=9 ) then
       j = 0
       denom = real(10**ndp,wp)
    else
       j = 1
       denom = 1.0_wp
    end if

    !  Copy the date, big then small, and realign to midnight.
    if ( abs(dj1) >= abs(dj2) ) then
       d1 = dj1
       d2 = dj2
    else
       d1 = dj2
       d2 = dj1
    end if
    d2 = d2 - 0.5_wp

    !  Separate days and fractions.
    f1 = mod(d1,1.0_wp)
    f2 = mod(d2,1.0_wp)
    d1 = anint(d1-f1)
    d2 = anint(d2-f2)

    !  Round the total fraction to the specified number of places.
    f = anint(( f1+f2 ) * denom) / denom

    !  Re-assemble the rounded date and re-align to noon.
    d2 = d2 + f + 0.5_wp

    !  Convert to Gregorian calendar.
    call JD2CAL ( d1, d2, iymdf(1), iymdf(2), iymdf(3), f, js )
    if ( js == 0 ) then
       iymdf(4) = nint(f*denom)
    else
       j = js
    end if

    end subroutine JDCALF