[netCDFJava #WIK-413864]: Reading forecast dates from grib2

Hi Jitka:

We have a rewrite of the grib2 handler, which i think solves all or most of 
these issues. It is in the 4.3 branch, we should have a beta release next week 
if all goes well. Perhaps you would be able to test it on your files? It will 
be a while before its the stable release, though.

A few more comments are below.

john

> Full Name: Jitka Tacoma
> Email Address: address@hidden
> Organization: Deltares
> Package Version: 4.2.25
> Operating System:
> Hardware:
> Description of problem: Hi John,
> 
> some time ago I contacted you and now I have some questions again.
> Since we, at Deltares, use Netcdf-Java CDM to read grids from nc/grib1/grib2 
> formats for various clients, we find some issues from time to time.
> 
> Currently I encounter some problems while reading the 'dates' from grib2 
> files :
> 
> 
> ISSUE 1: Time offset in hours isn't determined properly
> 
> I read a forecast stored in several files:
> 20110719.00.APCP.gec00.t00z.pgrb2af06
> 20110719.00.APCP.gec00.t00z.pgrb2af12
> ....
> ....
> 20110719.00.APCP.gec00.t00z.pgrb2af384
> 
> Each file contains one message. The reference date is 19-07-2011 00:00:00 for 
> all files.
> Starting with 20110719.00.APCP.gec00.t00z.pgrb2af258, NetCdf-Java determines  
> a wrong time offset in hours compared to the reference date

yes, i see we arent multiplying by 6.

> 
> I attach 3 files from my set :
> 20110719.00.APCP.gec00.t00z.pgrb2af06  : time offset = 6 hours, o.k.
> 20110719.00.APCP.gec00.t00z.pgrb2af252 : time offset = 252 hours,  o.k.
> 20110719.00.APCP.gec00.t00z.pgrb2af258 : time offset = 43 hours , however it 
> should be 258 hours
> 
> 
> ISSUE 2: The file '2011_Tigge.grib' with several forecasts -  the different 
> forecast(reference) dates are not recognized properly
> (this file is on FTP)
> 
> With this file a lot of messages come, like
> WARN ucar.nc2.iosp.grid.GridTimeCoord  - 
> GribGridRecord{param=Total_precipitation_rate, levelType1=1, 
> levelValue1=-9.999E-252, forecastTime=0, pdsOffset=48107} does not have same 
> base date= Sat Jan 01 00:00:00 GMT 2011 != Sat Jan 01 06:00:00 GMT 2011 for 
> 2011_Tigge.grib

this is fixed in 4.3

> 
> To inspect this file, I have opened it with NDFD DeGrib and this viewer shows 
> the expected c.q. logical contents, i.e.
> 4 forecast a day, first forecats date=01/01/2011 00:00, last forecast 
> date=05/31/2011 18:00
> Length of the forecast=15 days (6 hours steps)
> 
> However , Netcdf-Java CDM reports this dimensions :
> Total_precipitation_rate: time=36844 (this is approximately the total number 
> of messages in the file for one variable)
> Temperature:  time1=664  ?
> 
> Both variables: ens=1 ? , actually I expect hier something like ens=400, 
> since the file  contains approximately 400 forecasts

it says its ensemble data, but all have perturbation = 0. So an ensemble 
dimension of 1 is created.

im seeing 2 variables, Temperature and "Total Precipitation rate". 

For Temperature:

  1) multiple runs (refDate), 6 hours apart.
  2) for each refDate, 6 hour forecasts out to 360 hours.

since these overlap, I end up with 664 unique forecast times. (this is in 4.3 
sorry you cant see it yet).

For Total Precipitation rate:

  1) multiple runs (refDate), 6 hours apart.
  2) for each refDate, 6 hour forecasts out to 360 hours
  3) each forecast is for the interval 0-foreast (0 = refDate), so one sees 
0-6, 0-12, 0-18 ,...0-360.

these constitute unique coordinates (no overlap) so you get 36844 of them. The 
only thing I can think of if I am misunderstanding what the intervals are. (?) 

what would you expect ?

> 
> Please can you have a look at this and tell if it is a Netcdf-Java problem ? 
> If so , is it possible to fix it ?
> 
> I use Netcdf Java 4.2.25 build on 20.july 2011
> 
> FTP info
> Host name: ftp.wldelft.nl
> User name: fewsgrib
> Password: naii6a7
> 
> 
> Thanks in advance
> 
> 
> Kind regards
> 
> Jitka Tacoma
> Deltares
> the Netherlands
> 
> 
> 
> 
> 
> 


Ticket Details
===================
Ticket ID: WIK-413864
Department: Support netCDF Java
Priority: Normal
Status: Open