[CF-metadata] udunits time unit question

From: John Caron <caron>
Date: Sat, 26 Mar 2011 12:51:34 -0600

Hi Don:

It seems like the essential thing you need is calendar field
manipulation, to get around the variable month problem. If you didnt
have the 3 in "3 months since 2011-04-01", you could just multiply by 3
in your coordinate values.

I am looking at how hard that would be to support, but it does add
perhaps unneeded complexity.

John

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
Received on Sat Mar 26 2011 - 12:51:34 GMT