Hi Don:
Both java date and joda-time use a long to represent millisecs since ref
date.
so min/max year is:
max = 292,278,994
min = -292,275,055
heres what im getting with your example in CDM 4.3 using joda-time:
50000000 years since 1970-01-01 00:00:00Z == 50001928-10-07T01:30:00.064Z
50000000 calendar years since 1970-01-01 00:00:00Z ==
50001970-01-01T00:00:00.000Z
calendar periods are integers, so you are limited to +/- 2 Gyears.
It seems to me it would be better to somehow denote the "epoch"
seperately, because its kind of silly keeping track of # millisecs
between two dates separated by 50 million years. plus its hard.
what about:
"01-01-01 12:00 epoch 50m BCE"
where the "epoch 50m BCE" is probably just carried along in the string
representation of the date.
(Im not sure why Myears is even accepted in Stu's example, since its a
time unit, not a date unit).
john
On 8/22/2011 9:16 AM, Don Murray wrote:
> John-
>
> An example of how this could be handled (provided by Stuart Wier of
> UNAVCO) is available here:
>
> http://geon.unavco.org/unavco/geodynamics/Lithgow-Bertelloni_Richards_Mesozoic_Cenozoic_Plate_Velocities.cdl
>
>
> described on the page:
>
> http://geon.unavco.org/unavco/IDV_datasource_plates.html#c
>
> Here, the time coordinate is listed as:
>
> float time(time) ;
> time:units = "Myear" ;
> time:standard_name = "time" ;
>
> with values of:
>
> time = -170.0, -96.0, -94.0, -84.0, -74.0, -64.0, -56.0, -48.0, -43.0,
> -25.0, -10.0 ;
>
> The problem is that udunits ends up computing times for -64 Myear as:
>
> 63998634-12-14 00:00:00 BCE
>
> so you lose precision on the year.
>
> Don
>
>
> On 8/19/11 10:45 AM, John Caron wrote:
>>
>>>> Regarding paleoclimate, a point I forgot is that some modellers may
>>>> wish to
>>>> have years which are very large negative numbers (many more than four
>>>> digits)
>>>> if they set up the model with the "true" date for the run. Although
>>>> for
>>>> geological timescales you might say that this isn't necessary and you
>>>> might
>>>> as well choose an arbitrary year, there is a good reason for it in
>>>> Pleistocene
>>>> when you might be using the dates to relate to orbital forcing or
>>>> atmospheric
>>>> composition.
>>>
>>> so the idea is that you are simulating some year, so you really need
>>> time down to the hour or second. but the climate is from 5 million
>>> years ago, so you need the year field to be able to handle that?
>>
>> Im just thinking that fitting this into the ISO date format
>> "5000000-01-01 12:00" seems awkward, esp as it indicates unwarranted
>> precision.
>>
>> seems something like "01-01 12:00 reference 50m BCE" would be better.
>> What do paleo modellers actually use, eg in the figures that they
>> publish?
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>
Received on Tue Aug 23 2011 - 16:25:42 BST
