On 3/21/2011 11:14 AM, Steve Hankin wrote:
>
>
> On 3/17/2011 5:20 PM, John Caron wrote:
>> On 3/17/2011 12:19 PM, Steve Hankin wrote:
>>>
>>>
>>> On 3/17/2011 9:50 AM, Christopher Barker wrote:
>>>> On 3/16/11 8:47 AM, John Caron wrote:
>>>>
>>>>> 1. time instants vs time duration
>>>>> - one must distinguish between dimensional time ("time duration",
>>>>> units="secs"), and calendar time ("time instant", or "point on the
>>>>> time
>>>>> continuum") *which is not dimensional. *
>>>>
>>>> yup -- key clarification in all this.
>>>
>>> I think we are leading ourselves astray here. _A point in time has a
>>> dimension._ It has dimensions of "time". Whether the units happen
>>> to be days, months, years or whatever depends upon the encoding.
>>> But it definitely has dimensions of time. The date-time string
>>> loses its meaning if we see it as detached from the axis that gives
>>> it a dimensionality.
>>
>> in "dimensional units", "secs" is a base dimensional unit, and it
>> means "duration", eg watts = joules/sec, the sec is a time duration,
>> not an instant of time.
>>
>> "time" is not a dimensional unit, it refers to a point on the time
>> continuum. it does not have dimensional units of "secs", that is, it
>> cannot be converted to a duration in "secs".
>
> Hi John,
>
> Beg to differ on these most fundamental of issues. *All times* (all
> "points on the time continuum") indicate intervals. Typical
> date-time strings (e.g. "21-MAR-2011:10:10") are an artfully contrived
> way of stating an interval of time relative to a precise zero
> reference that is 2011+ years ago, while still retaining high
> resolution (fractions of seconds) in that interval measurement. But
> perhaps this is not a point to pursue much deeper without beer in hand.
>
> To me the most important point is just this: before proposing new
> libraries and new data models, there should be an effort to see
> whether there is any functionality that cannot be very satisfactorily
> handled by adding some convenience methods to the encodings that CF
> and udunits have already standardized.
>
> - Steve
Hi Steve:
Well I havent had a beer yet today (6:30 am), but ill try to simulate
the vibe ;^)
I think Im using "units" in a more restrictive sense then you are. Im
thinking about "dimensional units", which udunits handles well.
Dimensional units are powers of base units, m^2/sec^2 for example. A
"calendar time unit" is different, in that one never combines it with
base units or takes powers of it. m^2 / (2011-11-01)^2 wouldnt make sense.
Whether one wants to consider an instant of calendar time or an interval
of calendar time doesnt matter so much as the fact that its not a
dimensional unit.
? votre sant?!
John
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Received on Tue Mar 22 2011 - 06:30:28 GMT
