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*To*: orekit-users@orekit.org*Subject*: Re: [Orekit Users] Time question - julian date*From*: MAISONOBE Luc <luc.maisonobe@c-s.fr>*Date*: Fri, 27 May 2011 19:16:25 +0200*In-reply-to*: <BANLkTik2BLdqDhUDgG8d0_Us0HczFTaakA@mail.gmail.com>*References*: <BANLkTik8dg_k_D-XN+_RK-9iAyz9xWs+ZQ@mail.gmail.com> <BANLkTi=d54OgC+v0jJ-N3dghAA3kNgeRHA@mail.gmail.com> <BANLkTin+i5RLbsAHY3p09KE2HAqUXNR+Zg@mail.gmail.com> <BANLkTik2BLdqDhUDgG8d0_Us0HczFTaakA@mail.gmail.com>*User-agent*: Internet Messaging Program (IMP) H3 (4.3.9)

Petrus Hyvönen <petrus.hyvonen@gmail.com> a écrit :

Hi, Haven't managed to try that algorithm, but downloaded the SPG4 package from Vallado, and I get same Julian Date there as my previous algoritm. If I create a own date reference on: ad_jd = AbsoluteDate(-4712,01,01,12,00,00.000,utc) and use; epoch_date=AbsoluteDate(ad_jd,my_jd,utc) I get conversions from julian date to .. time ... same as the Vallado routines. Why is orekit using a reference point at -4712-01-01T11:59:27.816 ? Is it different timescales?

Yes, Orekit uses the TT time scale for this referene date.

Another way to achieve what you want could be something like: AbsoluteDate t = new AbsoluteDate(DateComponents.JULIAN_EPOCH, my_jd, utc); Luc

Best regards /PetrusOn Fri, May 20, 2011 at 5:53 PM, beowulf zhang<beowulf.zhang@gmail.com>wrote:This algorithm is in the JAT. link is http://jat.sourceforge.net/ 2011/5/20, beowulf zhang <beowulf.zhang@gmail.com>: > I can't find the reason of this question, but I give you a piece of > program that could give correct answer. > > /** Create a CalDate object using MJD. From Montenbruck C++ code. > * @param mjd Modified Julian Date. > */ > public CalDate(double mjd){ > long a,b,c,d,e,f; > double Hours,x; > > // Convert Julian day number to calendar date > a = (long)(mjd+2400001.0); > > if ( a < 2299161 ) { // Julian calendar > b = 0; > c = a + 1524; > } > else { // Gregorian calendar > b = (long)((a-1867216.25)/36524.25); > c = a + b - (b/4) + 1525; > } > > d = (long)( (c-122.1)/365.25 ); > e = 365*d + d/4; > f = (long)( (c-e)/30.6001 ); > > long temp = (long)(30.6001*f); > this.Day = (int)(c - e - temp); > temp = (long)(f/14); > this.Month = (int)(f - 1 - 12*temp); > temp = (long)((7+Month)/10); > this.Year = (int)(d - 4715 - temp); > > Hours = 24.0*(mjd-Math.floor(mjd)); > > this.Hour = (int)Hours; > x = (Hours-Hour)*60.0; > this.Min = (int) x; > this.Sec = (x-Min)*60.0; > this.DOY = day2doy(this.Year, this.Month, this.Day); > } > > > 2011/5/19, Petrus Hyvönen <petrus.hyvonen@gmail.com>: >> Hi, >> >> This maybe is a FAQ but anyway... >> >> I'm trying to create an absolute date based on a julian date created in >> another software. >> >> My julian date is 2.456413500000000e+006, corresponding to 01-May-2013 >> 00:00:00 UTC according to that software and some web conversion i checked >> it >> with. >> >> with orekit i do: >> ad_jd = AbsoluteDate.JULIAN_EPOCH >> ad_jd = >> -4712-01-01T11:59:27.816 >> >> AbsoluteDate(ad_jd,t*24*3600) >> ans = >> 2013-04-30T23:58:53.816 >> >> There must be some kind of time scale or different references here I >> suppose, how can convert this properly? >> >> Best regards >> /Petrus >> >-- _____________________________________________ Petrus Hyvönen, Uppsala, Sweden Mobile Phone/SMS:+46 73 803 19 00

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**Follow-Ups**:**Re: [Orekit Users] Time question - julian date***From:*beowulf zhang <beowulf.zhang@gmail.com>

**References**:**[Orekit Users] Time question - julian date***From:*Petrus Hyvönen <petrus.hyvonen@gmail.com>

**Re: [Orekit Users] Time question - julian date***From:*Petrus Hyvönen <petrus.hyvonen@gmail.com>

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