Re: [thredds] WMS time dimension different from OPeNDAP

we interpret months as implying calendar 360,  with a calendar month like
conversion between calendar 360 and standard calendars, which amounts to
the same thing as John's code.   So there are definitely useful
interpretations of months, it is just the udunits interpretation which is
useless.  And we have even a modified version of udunits, which keeps
second-based and year-based time separately, and avoids messing things up.

In any case, it is a shame that a flaw in udunits incapacitates CF.


On Fri, Apr 12, 2013 at 3:52 AM, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:

>  Hi all:
>
> I assume that someone who uses "months" really wants "calendar months",
> which manipulates the calendar fields, rather than using a fixed duration
> in seconds. The CDM implements this :
>
>
> http://www.unidata.ucar.edu/software/netcdf-java/CDM/CalendarDateTime.html<http://www.unidata.ucar.edu/software/netcdf-java/CDM/CalendarDateTime.html>
>
> and i think i still have to make a formal proposal to CF for it.
>
> However, concerns about backwards compatibility have scuttled most
> attempts to extend datetime handling in CF.
>
> John
>
>
> On 4/10/2013 11:59 PM, Signell, Richard wrote:
>
> Patrick, Lansing & Co:
>
> I note that the time units for this dataset are:
>  "units: months since 1901-01-01 00:00:00"
> with
> "calendar: standard"
>
> In the CF 
> documentationhttp://cf-pcmdi.llnl.gov/documents/cf-conventions/1.6/ch04s04.html
> it warns about units of "month":
>
> " We recommend that the unit year be used with caution. The Udunits
> package defines a year to be exactly 365.242198781 days (the interval
> between 2 successive passages of the sun through vernal equinox). It
> is not a calendar year. Udunits includes the following definitions for
> years: a common_year is 365 days, a leap_year is 366 days, a
> Julian_year is 365.25 days, and a Gregorian_year is 365.2425 days.
>
> For similar reasons the unit month, which is defined in udunits.dat to
> be exactly year/12, should also be used with caution."
>
> Perhaps the WMS and OPeNDAP service are not handling units of month in
> the same way?
>
> -Rich
>
> On Wed, Apr 10, 2013 at 5:45 PM, Lansing Madry <madry@xxxxxxxxxxxxxxxx> 
> <madry@xxxxxxxxxxxxxxxx> wrote:
>
>  Hi Patrick,
>
> I pulled down the file via http service and looked at it in ToolsUI.
> ToolsUI (perhaps unsurprisingly) gives the "1951-07-16T12:12:04.339Z" value.
> I'm not familiar with ferret as an OpenDAP client or viewer, have you heard
> from anyone on that front?
>
> Regards,
>   Lansing Madry
>   Unidata
>   Boulder, Colorado
>
>
> On 4/9/2013 11:08 AM, Patrick Brockmann wrote:
>
>  Hi all,
>
> I have a strange behaviour with time dimension values exposed by the
> GetCapabilities
> and values get from an OPeNDAP access.
> Could someone explain me what is the source of the problem ?
>
> http://webportals.ipsl.jussieu.fr/thredds/wms/CARBON/CARBONES_PRIOR_orchidee_hadgem2-es_historical_nosoc_co2_npp_monthly_1951_2004_yearmonmean_3.nc?service=WMS&version=1.3.0&request=GetCapabilities
>
> ---> 1951-07-16T12:12:04.339Z, ....
>
> And from the OPeNDAP access with ferret client, I get
>
> ferret
> yes? 
> use"http://webportals.ipsl.jussieu.fr/thredds/dodsC/CARBON/CARBONES_PRIOR_orchidee_hadgem2-es_historical_nosoc_co2_npp_monthly_1951_2004_yearmonmean_3.nc";
>  
> <http://webportals.ipsl.jussieu.fr/thredds/dodsC/CARBON/CARBONES_PRIOR_orchidee_hadgem2-es_historical_nosoc_co2_npp_monthly_1951_2004_yearmonmean_3.nc>
> yes? sg/t/l=1:10 npp2
>     GRID GTL2
>  name       axis              # pts   start                end
>  MYLON     LONGITUDE          720mr   0E                   0.5W
>  LAT       LATITUDE           360 r   89.75S               89.75N
>  normal    Z
>  TIME      TIME                54 r   16-JUL-1951 12:33 15-JUL-2004 09:01
>
>        L     T                   TBOX      TBOXLO TSTEP (months)
>        1>  16-JUL-1951 12:33:59  12         14-JAN-1951 21:39:23 606.4526
>        2>  15-JUL-1952 18:23:11  12         15-JAN-1952 03:28:35 618.4526
>        3>  16-JUL-1953 00:12:23  12         14-JAN-1953 09:17:47 630.4526
>
> --> Note the difference between 1951-07-16T12:12:04.339Z and 16-JUL-1951
> 12:33:59
>
> My TDS version is Version 4.3.15 - 20121218.1126
>
> Regards
> Patrick
>
>
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-- 
Dr. M. Benno Blumenthal          benno@xxxxxxxxxxxxxxxx
International Research Institute for climate and society
The Earth Institute at Columbia University
Lamont Campus, Palisades NY 10964-8000   (845) 680-4450
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