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Re: two issues with julian dates [message #54811 is a reply to message #54809]

Wed, 11 July 2007 15:43

Jean H.
Messages: 472
Registered: July 2006

Senior Member

Josh wrote:
> On Jul 11, 3:58 pm, David Fanning <n...@dfanning.com> wrote:
>> Josh writes:
>>> I've got date and time strings that I've parsed into their respective
>>> hour/minute/etc and month/day/etc form and I'm using the julday()
>>> function to turn them into julian dates. I've come across two
>>> problems that hopefully somebody can help me with.
>>> First off, according to NASA (http://ssd.jpl.nasa.gov/tc.cgi#top), the
>>> returned value of julday() is incorrect. When I use 11/18/2003 at
>>> 16:14:43, I get 2452955.2 from IDL and 2452962.1768866 from NASA.
>>> Thoughts?
>>> Second, the fact that julday() only returns a value with ONE digit
>>> after the decimal is not cool. If it returns a double floating point
>>> value, shouldn't I be able to get 14 sig figs? The time scales in my
>>> data set are such that I need that resolution. Thoughts?
>> Humm. Are you using *this* IDL!
>>
>> IDL> print, julday(11, 18, 2003, 16, 14, 43), format='(F 20.10)
>> 2452962.1768865748
>>
>> Cheers,
>>
>> David
>>
>> --
>> David Fanning, Ph.D.
>> Fanning Software Consulting, Inc.
>> Coyote's Guide to IDL Programming:http://www.dfanning.com/
>> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
>
>
> Perhaps it is because it is getting late into the afternoon, but I
> can't use that technique to stuff the new Julian date into a variable,
> correct? If I want to just save that beautifully long number in an
> array, how can I keep it formatted like that?
>

it is saved properly.... it is rounded when you display it only!
to convince yourself:
a = julday(11, 18, 2003, 16, 14, 43)
>> 2452962.1768865748
print, a - 2452962.0

Jean

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[Message index]

		Re: two issues with julian dates By: Josh on Thu, 12 July 2007 13:25
		Re: two issues with julian dates By: David Fanning on Thu, 12 July 2007 12:51
		Re: two issues with julian dates By: David Fanning on Thu, 12 July 2007 12:32
		Re: two issues with julian dates By: Josh on Thu, 12 July 2007 11:02
		Re: two issues with julian dates By: Jean H. on Wed, 11 July 2007 15:43
		Re: two issues with julian dates By: David Fanning on Wed, 11 July 2007 15:37
		Re: two issues with julian dates By: news.qwest.net on Wed, 11 July 2007 15:36
		Re: two issues with julian dates By: Josh on Wed, 11 July 2007 15:25
		Re: two issues with julian dates By: David Fanning on Wed, 11 July 2007 14:58
		Re: two issues with julian dates By: Josh on Mon, 16 July 2007 15:11

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