Re: [netcdf-java] NCEP 174 Grid scanMode 64 flipped grids

  • To: Bonny Strong - NOAA Affiliate <bonny.strong@xxxxxxxx>
  • Subject: Re: [netcdf-java] NCEP 174 Grid scanMode 64 flipped grids
  • From: John Caron <caron@xxxxxxxx>
  • Date: Wed, 28 Jan 2015 18:17:06 -0700
Ok, thanks all for checking it out. I will put it on hold until its clear
if its in error, etc. I think its a simple fix if we need to support it.

John

On Wed, Jan 28, 2015 at 5:38 PM, Bonny Strong - NOAA Affiliate <
bonny.strong@xxxxxxxx> wrote:

> For info, I spoke briefly to Ning Wang about this.  He can talk to NCEP
> software people he works with, but this isn't his highest priority, and
> this may take some time.
>
> I wonder if there is a more formal route for a request-for-change that we
> could follow to get this change made officially.  Bob, any experience with
> this?
>
> On Wed, Jan 28, 2015 at 5:21 PM, Bob Lipschutz - NOAA Affiliate <
> robert.c.lipschutz@xxxxxxxx> wrote:
>
>> Hi John. Thanks for the ping. No, I don't have access to other sample
>> GRIB files with this property. The only progress we've made is that we had
>> an exchange with a fellow in the NCEP marine modeling group (EMC/MMAB) who
>> said this about their sea ice products:
>>
>> The 1/8th degree grid never went to production.  I'm amazed that there
>>> was a table entry for it.  The high resolution ice grids in production are
>>> number 171, 172, 173 -- northern hemisphere, southern hemisphere, global,
>>> respectively.  The hemispheric grids are 1/30 bedient, and global is 1/12th
>>> degree.
>>
>>
>> This leads me to believe that the scanMode setting in the grid 174
>> definition is in error, and that 174 probably had never really been used
>> until we came along. We need to talk to the maintainers of the NCEP tables,
>> and see if we can get it corrected.
>>
>>     Thanks again for your support on this!
>>
>>            -Bob
>>
>>
>> On Wed, Jan 28, 2015 at 11:52 PM, John Caron <caron@xxxxxxxx> wrote:
>>
>>> Hi Bob:
>>>
>>> Any word from NCEP on this issue? Or sample files that already use
>>> scanmode 64?
>>>
>>> John
>>>
>>> On Wed, Jan 14, 2015 at 10:30 AM, Bob Lipschutz - NOAA Affiliate <
>>> robert.c.lipschutz@xxxxxxxx> wrote:
>>>
>>>> John,
>>>>
>>>> Thanks for looking at this. Sorry, I don't have any particular
>>>> recommendation here. The grid specification does seem odd and inconsistent
>>>> with other domains with scanMode=64 that give south-to-north corner
>>>> coordinates. It's also inconsistent with the similar 1/12th degree '173'
>>>> grid, which has scanMode=0 and north-to-south corners. We will check with
>>>> NCEP to see if there's an error in the table, but it's not a new entry and
>>>> ostensibly used by someone out there (it's described as a Sea Ice grid)...
>>>>
>>>> Thanks again,
>>>>
>>>>     -Bob
>>>>
>>>> On Wed, Jan 14, 2015 at 1:14 AM, Bonny Strong - NOAA Affiliate <
>>>> bonny.strong@xxxxxxxx> wrote:
>>>>
>>>>> John, I don't have Bob's expertise, but I know that during discussions
>>>>> here at GSD trying to figure this out, one developer gave his opinion that
>>>>> the lats of the first and last point were unrelated related to the scan
>>>>> direction.  Bob may wish to add to that tomorrow.
>>>>>
>>>>> Bonny
>>>>>
>>>>> On Tue, Jan 13, 2015 at 6:07 PM, John Caron <caron@xxxxxxxx> wrote:
>>>>>
>>>>>> Hi Bob:
>>>>>>
>>>>>> Thanks for reporting this problem. Im looking at it now. Do you have
>>>>>> any idea how these various parameters interact? They have first lat in
>>>>>> north, last lat in south, but a positive Dj. Then with scanMode 64, they
>>>>>> say "Points of first row or column scan in the +j (+y) direction". Seems
>>>>>> overspecified with the possibility of inconsistent results. Im looking
>>>>>> though my data samples now to see if I can detect if there is are 
>>>>>> problems,
>>>>>> but im not exactly sure what combinations should be legal. Any thoughts?
>>>>>>
>>>>>> heres my dump on your record:
>>>>>>
>>>>>>  47:                                                         La1 -
>>>>>> latitude of first grid point ==   89938000
>>>>>>  56:                                                          La2 -
>>>>>> latitude of last grid point == -89938000
>>>>>>  68:
>>>>>>  Dj - j direction increment ==  125000
>>>>>>  72:
>>>>>>                Scanning mode == 64
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon, Jan 12, 2015 at 4:02 PM, Bob Lipschutz - NOAA Affiliate <
>>>>>> Robert.C.Lipschutz@xxxxxxxx> wrote:
>>>>>>
>>>>>>>
>>>>>>> Java NetCDF Folks,
>>>>>>>
>>>>>>> We have recently begun generating global 1/8 degree GRIB files
>>>>>>> using NCEP's grid 174 definition (
>>>>>>> http://www.nco.ncep.noaa.gov/pmb/docs/on388/tableb.html#GRID174).
>>>>>>>
>>>>>>> Following that definition, we are setting the value of scanMode to
>>>>>>> 64, which
>>>>>>> per GRIB2 Table 3.4 indicates "points scan in the +j direction", and
>>>>>>> so filling
>>>>>>> the data arrays from south to north. However, the java-netCDF
>>>>>>> package (v4.5)
>>>>>>> does not seem to handle the scanMode flag properly, and consequently
>>>>>>> our
>>>>>>> grids appear flipped on display.  Meanwhile, I understand that NCL
>>>>>>> does handle
>>>>>>> the data mapping correctly, from which we conclude that java-netCDF
>>>>>>> is has a
>>>>>>> problem with this grid definition.
>>>>>>>
>>>>>>> As a work-around, we will set scanMode to 0 and write from north to
>>>>>>> south,
>>>>>>> which will fix the problem for us. But, we'd also hope to have the
>>>>>>> tools work
>>>>>>> correctly, too so that we can use the NCEP's grid as specified --
>>>>>>> which
>>>>>>> admittedly is strange in that it list the corner lons from north to
>>>>>>> south.
>>>>>>>
>>>>>>> I've posted a sample GRIB2 file and resulting flipped image here:
>>>>>>>
>>>>>>> ftp://aftp.fsl.noaa.gov/divisions/its/bob/grid174_scanmode_64_example.grb2
>>>>>>>   ftp://aftp.fsl.noaa.gov/divisions/its/bob/flipped_174grid.jpg
>>>>>>>
>>>>>>> FWIW, here is the output from the (v4.3) Grib2Dump utility on that
>>>>>>> data file:
>>>>>>>
>>>>>>>                                            Header : GRIB2
>>>>>>>                                        Discipline : 0 Meteorological
>>>>>>> products
>>>>>>>                                   GRIB Edition : 2
>>>>>>>                                    GRIB length : 2808735
>>>>>>>                        Originating Center : 59 The NOAA Forecast
>>>>>>> Systems Laboratory
>>>>>>>                Originating Sub-Center : 0
>>>>>>> Significance of Reference Time : 1 Start of forecast
>>>>>>>                            Reference Time : 2015-01-08T00:00:00Z
>>>>>>>                               Product Status : 0 Operational products
>>>>>>>                                 Product Type : 1 Forecast products
>>>>>>>                 Number of data points : 4147200
>>>>>>>                                     Grid Name : 0 Latitude_Longitude
>>>>>>>                                     Grid Shape: 0 Earth spherical
>>>>>>> with radius = 6,367,470 m
>>>>>>> Number of points along parallel: 2880
>>>>>>> Number of points along meridian: 1440
>>>>>>>                                       Basic angle : 0
>>>>>>>             Subdivisions of basic angle: 0
>>>>>>>               Latitude of first grid point : 89.938
>>>>>>>            Longitude of first grid point : 0.062
>>>>>>>      Resolution & Component flags : 48
>>>>>>>                                                 Winds : True
>>>>>>>                Latitude of last grid point : -89.938
>>>>>>>             Longitude of last grid point : 359.938
>>>>>>>                        i direction increment : 0.125
>>>>>>>                        j direction increment : 0.125
>>>>>>>                                            Grid Units : degrees
>>>>>>>                                  Scanning mode : 64
>>>>>>>                              Product Definition : 0
>>>>>>> Analysis/forecast at horizontal level/layer at a point in time
>>>>>>>                          Parameter Category : 0 Temperature
>>>>>>>                                Parameter Name : 0 Temperature
>>>>>>>                                  Parameter Units : K
>>>>>>>                  Generating Process Type : 2 Forecast
>>>>>>>                                      ForecastTime : 240
>>>>>>>                              First Surface Type : 1 Ground or water
>>>>>>> surface
>>>>>>>                             First Surface value : 0.0
>>>>>>>                        Second Surface Type : 255 Missing
>>>>>>>                       Second Surface value : 0.0
>>>>>>>
>>>>>>>    Thanks for any insights on this issue!
>>>>>>>
>>>>>>>          Bob Lipschutz
>>>>>>>          NOAA/ESRL/Global Systems Division
>>>>>>>          IT Services/Data Services Group
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> netcdf-java mailing list
>>>>>>> netcdf-java@xxxxxxxxxxxxxxxx
>>>>>>> For list information or to unsubscribe, visit:
>>>>>>> http://www.unidata.ucar.edu/mailing_lists/
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Bonny Strong
>>>>> NOAA Affiliate
>>>>> 303 497-3936
>>>>>
>>>>
>>>>
>>>
>>
>
>
> --
> Bonny Strong
> NOAA Affiliate
> 303 497-3936
>
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