Hi,
Using 1-1-1 wasn't the best choice, but there are tens of thousands of
files using that as the time origin without an explicit calendar attribute.
Rewriting them doesn't seem practical. It seems to me that if the files
conform to the convention (namely that a lack of calendar attribute implies
the default of Gregorian) it's wrong for the software tool to interpret the
time axis as Proleptic Gregorian.
Roland
On Tue, Dec 4, 2012 at 5:51 PM, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
> Hi Don:
>
>
> On 12/4/2012 4:09 PM, Don Murray (NOAA Affiliate) wrote:
>
>> Hi-
>>
>> I was just trying to access the NOAA/ESRL/PSD Outgoing Longwave
>> Radiation (OLR) data using netCDF-Java 4.3 ToolsUI and noticed that the
>> times are wrong. If you open:
>>
>> dods://www.esrl.noaa.gov/psd/**thredds/dodsC/Datasets/**
>> uninterp_OLR/olr.day.mean.nc<http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/uninterp_OLR/olr.day.mean.nc>
>>
>>
>> in the ToolsUI grid viewer, the last time in the file is shown as
>> 2012-12-04 00Z. However, the last time in the file is actually
>> 2012-12-02 00Z. Here is the time variable in that file:
>>
>> double time(time=3989);
>> :units = "hours since 1-1-1 00:00:0.0";
>> :long_name = "Time";
>> :actual_range = 1.7540448E7, 1.763616E7; // double
>> :delta_t = "0000-00-01 00:00:00";
>> :avg_period = "0000-00-01 00:00:00";
>> :standard_name = "time";
>> :axis = "T";
>>
>> netCDF-Java 4.2 and ncdump -t -v time (C version) show the correct
>> date/times.
>>
>
> hours from 1-1-1 is rather problematic, since you are crossing the
> julian/gregorian weirdness line (i think thats the technical term ;)
>
> Im guessing the trouble lies here:
>
> "Default calendar: for udunits, and therefore for CF, the default calendar
> is gregorian ("Mixed Gregorian/Julian calendar"). For CDM, the default
> calendar is proleptic_gregorian (ISO8601 standard). This only matters for
> dates before 1582."
>
> I have to say relying uncritically on a calendar implementation like
> udunits is a mistake. putting the reference date unnecessarily to include
> the problem is, um, unnecessary.
>
> is there any way those files can be updated? specifying the gregorian
> calendar explicitly should do it, but changing to use a reference date
> after 1582 would be much better.
>
>
>
>> BTW, is there an easier way to see human readable dates through toolsUI
>> than loading it into the grid viewer (akin to ncdump -t)?
>>
>
> open in coordSys tab; in bottom table, select time coord, right-click and
> choose "show values as date"
>
>
>
>> Thanks for your help.
>>
>> Don
>>
>
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