Hi Steve:
On 3/15/2011 10:13 AM, Steve Hankin wrote:
John et. al.,
It looks like this thread has reached reasonable conclusions:
1. units of days (or secs or mins) can provide an accurate encoding
for months ("days since 1930-01-01")
2. "units of measure" should not be quantities that vary
3. udunits could in principle offer calendar type-sensitive support
for units of "months" or "years", but doing so would likely
break backwards compatibility and would get nasty-complicated as
a result of bullet #2
i guess the problem here is that i think date is not a unit of measure.
do we disagree on that?
1.
I'd like to add a response to this concern:
option 1 is suboptimal because one has to calculate the days
correctly. Also it makes the time coordinates not human readable, eg:
Here I think concerns of human-readable formatting and convenience are
sliding into issues of accurate encoding. ncdump already offers an
option to format these values as dates. Ncgen could in principle
offer conversions to encode various human-friendly formatting options.
im sure we agree that making things human readable is good, it makes it
more likely that errors will be noticed. we are just discussing the best
way to do that.
The larger question of "months" used as units of time measure is an
ingrained problem of sloppy earth science. =-O >:o (heresy!)
Regarding Gregorian months (unequal length) as a simple numbered
sequence, 1, 2, 3, 4 .... continues to promote countless sloppy
(wrong) calculations -- erroneous derivatives, integrals, variance,
... any calculation that attempts to use the month number as encoded
as a unit of time measure. Glossing over these errors seems often to
be the norm, rather than the exception. This is one of those rare
areas where our responsibility as software developers should be to
push back against sloppy science, by offering software that makes it
easy to do the calculations correctly, and help to end these sloppy
practices. I'd welcome seeing this discussion elevate to our science
colleagues.
- Steve
so im looking at a 100 year dataset of monthly averages. Theres nothing
sloppy about wanting to encode it using "month since start" or "year
since start" to indicate the starting and ending dates. Its the
limitation of udunit processing this as if dates are dimensional units
thats the problem.
John
_______________________________________________
CF-metadata mailing list
[email protected]
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
