jd2cal.R

source("fix.R")

jd2cal <- function(jd){
  # % JD2CAL  Converts Julian date to calendar date using algorithm
  # %   from "Practical Ephemeris Calculations" by Oliver Montenbruck
  # %   (Springer-Verlag, 1989). Must use astronomical year for B.C.
  # %   dates (2 BC = -1 yr). Non-vectorized version. See also CAL2JD,
  # %   DOY2JD, GPS2JD, JD2DOW, JD2DOY, JD2GPS, JD2YR, YR2JD.
  # % Version: 24 Apr 99
  # % Usage:   [yr, mn, dy]=jd2cal(jd)
  # % Input:   jd - Julian date
  # % Output:  yr - year of calendar date
  # %          mn - month of calendar date
  # %          dy - day of calendar date (including decimal)
  # 
  # % Copyright (c) 2011, Michael R. Craymer
  # % All rights reserved.
  # % Email: mike@craymer.com
  
    if (jd < 0){
      print("jd2cal")
      outputCalenderDate<-list(-1,-1,-1)
      return(outputCalenderDate)
    }
    
  
  
  
  a = fixVal(jd+0.5);
  if (a < 2299161){
    c = a + 1524;}
  else{
    b = fixVal( (a-1867216.25) / 36524.25 );
    c = a + b - fixVal(b/4) + 1525;
  }
  d = fixVal( (c-122.1)/365.25 );
  e = fixVal(365.25*d);
  f = fixVal( (c-e) / 30.6001 );
  dy = c - e - fixVal(30.6001*f) + (jd+0.5)%%a;
  mn = f - 1 - 12*fixVal(f/14);
  yr = d - 4715 - fixVal( (7+mn)/10 );
  
  outputCalenderDate<-list(yr,mn,floor(dy))
  return(outputCalenderDate)
}