John-
On 3/26/11 12:51 PM, John Caron wrote:
> It seems like the essential thing you need is calendar field
> manipulation, to get around the variable month problem.
yes.
If you didnt
> have the 3 in "3 months since 2011-04-01", you could just multiply by 3
> in your coordinate values.
However, then you lose the semantics of a 3 month interval. As Benno
(sorry for spelling your name wrong last time) showed, the semantics of
the qualifier for x since have real meaning in climate datasets.
> I am looking at how hard that would be to support, but it does add
> perhaps unneeded complexity.
But it adds semantics of the time periods in question.
Don
> On 3/26/2011 7:46 AM, Don Murray wrote:
>> John-
>>
>> On 3/25/11 4:54 PM, John Caron wrote:
>>> On 3/22/2011 6:53 AM, John Caron wrote:
>>>> Consider:
>>>>
>>>> int time(sample=1001);
>>>> :long_name = "Measurement time";
>>>> :standard_name = "time";
>>>> :units = "days since 1970-01-01";
>>>>
>>>> vs
>>>>
>>>> int time(sample=1001);
>>>> :long_name = "Measurement time";
>>>> :standard_name = "time";
>>>> :units = "3 days since 1970-01-01";
>>>>
>>>> values = 1, 2, 3, ...
>>>>
>>>> are these equivalent or does the second one mean every 3 days ? Is the
>>>> second one illegal ?
>>>
>>> Im am going to assume that the second form is illegal, that is, you may
>>> not have a number in front of the unit in a "time coordinate unit" (CF
>>> section 4.4)
>>
>> I agree with Beno that it should be legal. GrADS gives their units in
>> terms of N (minutes, hours, days, months, years) from a reference
>> time. When I wrote the GrADS IOSP, I originally was using this syntax,
>> because then your time coordinate values are 0,1,2,..... However, 3mo
>> intervals came up with the problems that you have shown here, so I
>> converted everything to hours since the base date. But, if we had a
>> library that would compute 3mo since 2011-04-01 as 2011-07-01, I would
>> revert to that syntax because it is closer to the original GrADS
>> definition.
>>
>> Don
>
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--
Don Murray
NOAA/ESRL/PSD and CIRES
303-497-3596
http://www.esrl.noaa.gov/psd/people/don.murray/
Received on Sun Mar 27 2011 - 08:06:35 BST
