Date truncated by cast to long

[mdtdhi]

Using netcdfAll-4.6.16.1 java library.

I've encountered multiple NetCDF files where the date is truncated by a second in DateUnit.makeStandardDateString(double). The implementation in 4.6.16.1 results in a date string with second precision, but I believe the date is only truncated by a millisecond.

i.e. secs = 89999.999999999985 is incorrectly rounded down to 89999999 milliseconds.

see /cdm/core/src/main/java/ucar/nc2/units/DateUnit.java
getDate (line 191)
makeDate (line 213):
return new Date(getDateOrigin().getTime() + (long) (1000 * secs));

Rounding prior to casting should solve the issue. Something like:
return new Date(getDateOrigin().getTime() + (long) Math.Round(1000 * secs));

[lesserwhirls]

Do you have an example file that you could share that triggers this issue?

[mdtdhi]

Do you have an example file that you could share that triggers this issue?

See attached.

Date time should be 2021-02-27 01:00:00. Result is 2021-02-27 00:59:59.

IDY25402.APS3.group2.slv.2021022600.025.surface.zip

[JohnLCaron]

Date time should be 2021-02-27 01:00:00.

Which exact Date time in the example file are you referring to?

…

On Mon, Mar 1, 2021 at 5:15 PM mdtdhi ***@***.***> wrote: Do you have an example file that you could share that triggers this issue? See attached. Date time should be 2021-02-27 01:00:00. Result is 2021-02-27 12:59:59. IDY25402.APS3.group2.slv.2021022600.025.surface.zip <https://github.com/Unidata/netcdf-java/files/6065225/IDY25402.APS3.group2.slv.2021022600.025.surface.zip> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <https://github.com/Unidata/netcdf-java/issues/620#issuecomment-788421838>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAEVZQBYI4WU56NGVQIMIIDTBQU3TANCNFSM4YL3YWOA> .

[JohnLCaron]

Date time should be 2021-02-27 01:00:00.

Which exact Date time in the example file are you referring to?

[JohnLCaron]

I dont see the problem in versions 5 and 6, though I dont have a particular field to check.
Its likely that their analysis is correct for 4.6.

[mdtdhi]

Date time should be 2021-02-27 01:00:00.

Which exact Date time in the example file are you referring to?

Variable: 'time'

Attributes:
'axis' 'T'
'bounds' 'time_bnds'
'units' 'days since 2021-02-26 00:00:00'
'standard_name' 'time'
'long_name' 'time'
'calendar' 'gregorian'
'_ChunkSize' 1
'_CoordinateAxisType' 'Time'

[JohnLCaron]

version 6:

double time(time=1);
  :axis = "T"; // String
  :bounds = "time_bnds"; // String
  :units = "days since 2021-02-26 00:00:00"; // String
  :standard_name = "time"; // String
  :long_name = "time"; // String
  :calendar = "gregorian"; // String
  :_ChunkSizes = 1U;

days since 2021-02-26 00:00:00
time =
{1.0416666666666665}

(-0.020833, 1.041667) == (2021-02-25T23:30:00Z, 2021-02-27T01:00:00Z)