Dr. Kuang's Utilities

月曆日轉儒略日(c2j)

 
  • Oct 20, 2022
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背景

  • 有關儒略日轉月曆日的轉換，可詳見j2c說明。此處為其反轉程式。

date(os) and datetime(py)

  • 不論是bash或者是python的datetime，都有+%j格式，可以輸出成julian day。設若輸入月曆日值為$ymd(+%Y%m%d)

bash

  • date指令：yyyyjjj=$( date -d "$ymd" +%Y%j)
  • 一般linux的date指令似乎會自行辨識輸入的日期格式(不含小時)
    • 至少可以自動辨識+%Y%m%d及+%Y-%m-%d等2種。
    • 不必(也不能)指定輸入格式。
  • 如需此二者以外格式之輸入、或含有小時之日期

macOS

  • date指令：yyyyjjj=$( date -j -f "%Y%m%d" $ymd +%Y%j)
  • 輸入時間格式可以用-f 來指定

python datetime指令

  • strptime
    • point(export) the character string to datetime object
    • ymd_dt=datetime.datetime.strptime(ymd,'%Y%m%d')
  • strftime
    • create formatted string from datetime
    • yj=ymd_dt.strftime('%Y%j')

fortran程式碼(cal2jul.f)

  • 此副程式剪裁自UAM及CAMx程式系統，現已不再更新。如在fortran程式內需進行日期的轉換可參考使用。
C$ cat ~/bin/cal2jul.f
        character A100*100
        call getarg(1,A100)
        read(A100,*)jjj
        call juldate(jjj)
        write(*,'(I7)')2000000+jjj
        stop
        end

        subroutine caldate(idate)
c
c-----CAMx v4.01 030625
c
c     CALDATE converts date from Julian (YYJJJ) format to calender
c     (YYMMDD) format
c
c     Copyright 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
c     ENVIRON International Corporation
c
c     Modifications:
c        none
c
c     Input arguments:
c        idate               julian date (YYJJJ)
c
c     Output arguments:
c        idate               calender date (YYMMDD)
c
c     Routines Called:
c        none
c
c     Called by:
c        AREAPREP
c        BNDPREP
c        CNCPREP
c        DRYDEP
c        PIGPREP
c        RDPTHDR
c        READZP
c        STARTUP
c
      dimension nday(12)
      data nday/31,28,31,30,31,30,31,31,30,31,30,31/
c
c-----Entry point
c
c-----If it is already in calender date, return
c
      if (idate.gt.100000) goto 9999
      iyear = idate/1000
      jday = idate - iyear*1000
c
      nday(2) = 28
      if (mod(iyear,4).eq.0) nday(2) = 29
      mday = 0
      do 10 imonth = 1,12
        mday = mday + nday(imonth)
        if (mday.ge.jday) go to 20
 10   continue
 20   iday = jday - (mday - nday(imonth))
      idate = iyear*10000 + imonth*100 + iday
c
 9999 return
      end
c-------------------------------------------------------------
      subroutine juldate(idate)
      dimension nday(12)
      data nday/31,28,31,30,31,30,31,31,30,31,30,31/
c
c-----Entry point
c
      iyear = idate/10000
      imonth = (idate - iyear*10000)/100
      iday = idate - iyear*10000 - imonth*100
      nday(2) = 28
      if (mod(iyear,4).eq.0) nday(2) = 29

      IF(IDAY.GT.NDAY(IMONTH).OR.IDAY.LE.0) THEN
        IDATE=-1
        RETURN
      ENDIF
c
      mday = 0
      do 10 n = 1,imonth-1
        mday = mday + nday(n)
 10   continue
      jday = mday + iday
      idate = iyear*1000 + jday
c
      return
      end
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