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
>
