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.
à votre santé!
John
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