| Re: julday() and fractional days [message #56448] |
Wed, 31 October 2007 09:16  |
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Bob[3]
Messages: 60
Registered: December 2006
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Member |
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Perhaps I'm missing something but why would one expect a JULDAY
function that is passing hour, minute and second data to also accept
fractional days?
I can understand that if you did: print,julday(12,31.2,2005) one might
expect the fractional days to be handled, but not when the smaller
time units are explicitedly present.
What would the correct output of, say,
print,julday(12,31.2,2005,6,0,0) be?
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| Re: julday() and fractional days [message #56450 is a reply to message #56448] |
Wed, 31 October 2007 08:49  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Ed Hyer <ejhyer@gmail.com> writes:
> OK, if you search c.l.i-p for this you'll find a post from Craig
> Markwardt wherein he laments that JULDAY "doesn't handle fractional
> days". Someone replies to say yes it does, but I think that person
> misunderstood.
>
> IDL> print,julday(12,31,2005,0,0,0)
> 2453735.5
> IDL> print,julday(12,31.2,2005,0,0,0)
> 2453735.5
>
> I'm really unhappy with IDL right now.
I mostly use my own simple Julian day routine just to avoid all these
annoying surprises.
But in your case it would *almost* be easy enough to work around it
with something like,
IDL> print,julday(12,31,2005,0,0,0) + .2
2453735.7
or programmatically,
IDL> print,julday(month,floor(day),year,0,0,0) + (day-floor(day))
But the annoyance is in taking the time to discover these quirks, and
to remember them.
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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| Re: julday() and fractional days [message #56461 is a reply to message #56450] |
Tue, 30 October 2007 19:20 |
ben.bighair
Messages: 221
Registered: April 2007
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Senior Member |
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On Oct 30, 8:02 pm, Ed Hyer <ejh...@gmail.com> wrote:
> OK, if you search c.l.i-p for this you'll find a post from Craig
> Markwardt wherein he laments that JULDAY "doesn't handle fractional
> days". Someone replies to say yes it does, but I think that person
> misunderstood.
>
> IDL> print,julday(12,31,2005,0,0,0)
> 2453735.5
> IDL> print,julday(12,31.2,2005,0,0,0)
> 2453735.5
>
> I'm really unhappy with IDL right now.
Hi Ed,
Would this work for you?
IDL> print,eh_julday(12,31,2005,0,0,0)
2453735.5
IDL> print,eh_julday(12,31.2,2005,0,0,0)
2453735.7
***BEGIN
FUNCTION EH_JULDAY, mon, day, year, hour, min, sec
case N_PARAMS() of
6: j = JULDAY(mon, day, year, hour, min,sec)
3: j = JULDAY(mon, day, year)
ELSE: MESSAGE, '3 or 6 arguments required'
endcase
return, j + (day - FLOOR (day))
end
***END
Ben
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| Re: julday() and fractional days [message #56629 is a reply to message #56448] |
Thu, 01 November 2007 07:39 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Bob Crawford <Snowman42@gmail.com> writes:
> Perhaps I'm missing something but why would one expect a JULDAY
> function that is passing hour, minute and second data to also accept
> fractional days?
>
> I can understand that if you did: print,julday(12,31.2,2005) one might
> expect the fractional days to be handled, but not when the smaller
> time units are explicitedly present.
>
> What would the correct output of, say,
> print,julday(12,31.2,2005,6,0,0) be?
I don't know, but because of IDL JULDAY()'s insane behavior, I can
tell you that it would be different than,
print,julday(12,31.2,2005) + 0.25
Craig
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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