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Re: Fwd: Polar stereo projection parameter name problem

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  • Subject: Re: Fwd: Polar stereo projection parameter name problem
  • Date: Thu, 18 Oct 2007 10:13:31 -0600 (MDT)
On Thu, 18 Oct 2007, Ben Domenico wrote:


Hi John and Robb,

This is a follow up on an error in a variable name in a file served by the
NCDC NOMADS TDS.  It turns out the source file is from ncep in grib.
Perhaps the GRIB iosp for these files is putting the wrong variable name in
for the polar stereographic case.



All,
This is a GRIB table problem and it occurs because the desired table wasn't available, so the code uses the closes table available. 

dumping a radar file gives table info:
center = 7
sub_center = 4
table_version = 2

table used was:

center = 7
sub_center = -1 default sub_center table_version = 2
The fix is to get table 7 4 2 and to include in the resources and make a release or if you don't want to change your release, then the table can be added and referenced. This is a more time consuming process. 

Does anyone have table 7 4 2 in NWS format ?
Once the correct table is added to the code, no modifications need to be done since Grib uses numbers internally so the parameters will be correct. 



Thanks,
Robb...



The THREDDS catalog for such datasets is

at:


http://nomads.ncdc.noaa.gov:8085/thredds/catalogServices?catalog=http://nomads.ncdc.noaa.gov:8085/thredds/catalog/radar/StIV/2006/catalog.xml

The NCDC folks are talking about using ncML to correct the problem, but it
could be that the grib iosp is putting the wrong name in.  I thought this
was worth checking because, if it is the iosp, it will pop up on any TDS
that serves grib files in polar stereographic.

-- Ben

---------- Forwarded message ----------
From: Steve.Ansari <address@hidden>
Date: Oct 18, 2007 7:09 AM
Subject: Re: Polar stereo projection parameter name problem
To: "Glenn.Rutledge" <address@hidden>
Cc: Ben Domenico <address@hidden>, John Caron <address@hidden>,
Nomads NCDC <address@hidden>, Brian Nelson <address@hidden>,
Rich Baldwin <address@hidden>

Hello all,

The STIV (Stage-4 Multisensor Precip from NCEP) are in GRIB files from
NCEP.

John,
Is this a parameter that should be different in the GRIB file?  Can we use
NcML to describe an 'alias' for this parameter?  If so, can you send a
sample.

Thanks,
Steve



Glenn.Rutledge said the following on 10/18/2007 8:24 AM:

Hi Ben,
This server data is populated and maintained (mostly) by Steve Ansari and
Brian Nelson.  They are cc;ed to this and I'm certain they'll look into it.


It turns out that this data, and some others (GOES),k and projected grids
have some " incompatibility" issues for their datum description while being
access with the GeoPortal Tooklit by ESRI (aka our ACCESS conversions of
late)- as reported by Rich Baldwin here and he's also cc:ed just in case
this might be germane.

Regards, Glenn

Ben Domenico wrote the following on 10/17/2007 3:36 PM:

Hi Glenn,

You may not be the right person for this note, but I'll start with you with
the idea you can forward it to the appropriate person.  As the note below
from John Caron indicates, there is a problem with the name being used to
specify the latitude coordinate for the polar stereographic coordinate
system being used to serve STIV radar data on the nomads server.  The
prescribed CF name is "straight_vertical_longitude_from_pole"  but the
netCDF file uses "longitude_of_projection_origin."  According to John, this
is not an uncommon error, but it would be good to fix it.

Thanks.

-- Ben

---------- Forwarded message ----------
From: John Caron <address@hidden >
Date: Oct 17, 2007 1:08 PM
Subject: Re: attached file
To: Ben Domenico <address@hidden>
Cc: Nawajish Noman <address@hidden >, address@hidden

Hi Noman:

Unfortunately its common for these files to not follow the conventions
exactly.

"longitude_of_projection_origin" should be
"straight_vertical_longitude_from_pole". Its a common error, and we tend to
try to be lenient in these cases, so our software would probably look for
both names.

Ben, can we notify the writer? Also, can I get a sample of the file for my
tests?

John

Ben Domenico wrote:

Noman,

I'm forwarding this message to John Caron who can help you with the
details of the projection in that netCDF file.

-- Ben

On 10/16/07, * Nawajish Noman* <address@hidden
<mailto: address@hidden>> wrote:

    Hi Ben,

    We are working on the problem with Polar stereographic projection. I
    am comparing the grid_mapping parameters in the file (see your email
    below) and the parameters listed on the CF Convention page at _
    
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.0/cf-conventions.html#appendix-grid-mappings_



    Example F.5.

    *Example F.5. Polar stereographic*

    grid_mapping_name = polar_stereographic



    */Map parameters:/*

    straight_vertical_longitude_from_pole

    latitude_of_projection_origin - Either +90. or -90.

    Either standard_parallel or scale_factor_at_projection_origin

    false_easting

    false_northing

    *Parameters in file are:***

    char Polar_Stereographic_projection_Grid;

         :grid_mapping_name = "polar_stereographic";

         :longitude_of_projection_origin = - 105.0; // double

         :scale_factor_at_projection_origin = 0.933; // double

    Here are my questions:

    Q1: Some of the parameters are missing in file. What do we do about
    missing parameters?

    Q2: You have " longitude_of_projection_origin " in file but the CF
    convention says " latitude_of_projection_origin" - What do with
    "longitude_of_projection_origin "?

    We look for parameters listed in CF Conventions and map them to our
    Spatial reference parameters. If parameters are missing in file we
    assume default value. If incorrect parameters are specified - we
    ignore them.

    I want to make sure we are reading the parameters from your file
    correctly. Please comment…

    Thanks,

    Noman

    -----Original Message-----
    From: address@hidden <mailto:address@hidden> [
    mailto: address@hidden] On Behalf Of Ben Domenico
    Sent: Tuesday, June 05, 2007 1:56 PM
    To: Steve Kopp
    Cc: Nawajish Noman
    Subject: Re: attached file

    Steve,

    I'll attach jpegs of the dataset as displayed in arcMap and one from

    the IDV.  In each case, you can see at the bottom of the screen, the

    lat/lon values associated with the cursor position.  I'll also append

    the ncDump output which shows the projection information -- in netCDF

    terms (i.e., Polar_Stereographic_projection_Grid) anyway.

    -- Ben

    ncDump output

    ===================================================

    netcdf C:/Documents and
    Settings/ben/Desktop/ST4.2006010100.06hWithLatLon.nc {

     dimensions:

       time = 1;   // (has coord.var)

       y = 815;   // (has coord.var)

       x = 1121;   // (has coord.var)

     variables:

       float Total_precipitation(time=1, y=815, x=1121);

         :units = "kg/m^2";

         :long_name = "Total precipitation @ surface";

         :missing_value = -9999.0f; // float

         :grid_mapping = "Polar_Stereographic_projection_Grid";

         :GRIB_param_name = "Total precipitation";

         :GRIB_center_id = 7; // int

         :GRIB_table_id = 2; // int

         :GRIB_param_number = 61; // int

         :GRIB_param_id = 1, 7, 2, 61; // int

         :GRIB_product_definition_type = "Accumulation";

         :GRIB_level_type = 1; // int

       int time(time=1);

         :long_name = "forecast time";

         :units = "hour since 2005-12-31T12:00:00Z";

         :GRIB_orgReferenceTime = "2005-12-31T12:00:00Z";

         :GRIB2_significanceOfRTName = "Start of forecast";

         :_CoordinateAxisType = "Time";

       double y(y=815);

         :units = "km";

         :long_name = "y coordinate of projection";

         :standard_name = "projection_y_coordinate";

         :grid_spacing = "4.763 km";

         :_CoordinateAxisType = "GeoY";

       double x(x=1121);

         :units = "km";

         :long_name = "x coordinate of projection";

         :standard_name = "projection_x_coordinate";

         :grid_spacing = "4.763 km";

         :_CoordinateAxisType = "GeoX";

       char Polar_Stereographic_projection_Grid;

         :grid_mapping_name = "polar_stereographic";

         :longitude_of_projection_origin = -105.0; // double

         :scale_factor_at_projection_origin = 0.933 ; // double

         :earth_shape = "spherical";

         :GRIB_param_Dx = 4763.0; // double

         :GRIB_param_Dy = 4763.0; // double

         :GRIB_param_GDSkey = 1294122487; // int

         :GRIB_param_La1 = 23.117; // double

         :GRIB_param_Lo1 = -119.023; // double

         :GRIB_param_LoV = -105.0; // double

         :GRIB_param_Nx = 1121; // int

         :GRIB_param_Ny = 881; // int

         :GRIB_param_ProjFlag = 0; // int

         :GRIB_param_ResCompFlag = 8; // int

         :GRIB_param_ScanningMode = 64; // int

         :GRIB_param_grid_name = "Polar Stereographic projection Grid";

         :GRIB_param_grid_radius_spherical_earth = 6367.47; // double

         :GRIB_param_grid_shape = "spherical";

         :GRIB_param_grid_shape_code = 0; // int

         :GRIB_param_grid_type = 5; // int

         :_CoordinateTransformType = "Projection";

         :_CoordinateAxisTypes = "GeoX GeoY";

       double lat(y=815, x=1121);

         :units = "degrees_north";

         :long_name = "latitude coordinate";

         :standard_name = "latitude";

         :_CoordinateAxisType = "Lat";

       double lon(y=815, x=1121);

         :units = "degrees_east";

         :long_name = "longitude coordinate";

         :standard_name = "longitude";

         :_CoordinateAxisType = "Lon";

     :History = "GridDatatype extracted from dataset

    /eclipse1a/ftp/pub/radar/StIV/2006/01/01/hr/ST4.2006010100.06h";

     :Conventions = "CF-1.0";

     :Originating_center = "US National Weather Service (NCEP) subcenter
    = 4";

     :Generating_Process_or_Model = "River Forecast Center Quantitative

    Precipitation estimate mosaic generated by NCEP";

     :Product_Type = "Accumulation";

     :cdm_data_type = "Grid";

     :creator_name = "US National Weather Service (NCEP) subcenter = 4";

     :file_format = "GRIB-1";

     :location =
    "/eclipse1a/ftp/pub/radar/StIV/2006/01/01/hr/ST4.2006010100.06h";

     :history = "Direct read of GRIB into NetCDF-Java 2.2 API";

     :_CoordinateModelRunDate = "2005-12-31T12:00:00Z";

    =====================================================

    On 6/5/07, Steve Kopp < address@hidden <mailto:address@hidden>> wrote:

   >

   >  Ben, the dataset contains no projection information. Without this,

we


   >  won't know where else to draw anything.

   >

   >  Could you send us a screen shot of what you are seeing?

   >

   >  Thanks,

   >

   >  Steve

   >

   >

   >  -----Original Message-----

   >  From: address@hidden <mailto:address@hidden> [
    mailto:address@hidden] On Behalf Of

   >  Ben Domenico

   >  Sent: Tuesday, June 05, 2007 11:32 AM

   >  To: Steve Kopp

   >  Subject: attached file

   >

   >  Hi Steve,

   >

   >  Don't know if this will work, but I'm attaching one of the

CF-netCDF


   >  files I got from that NCDC radar data server.  Let me know whether

   >  this comes through OK.

   >

   >  -- Ben

   >

   >





--
Glenn K. Rutledge
Services Team Leader
Remote Sensing and Applications Division
NOMADS Project Manager
National Oceanic and Atmospheric Administration
National Climatic Data Center
Asheville NC 28801
Phone: (828) 271-4097
Fax: (828) 271-4328

NOMADS: http://nomads.ncdc.noaa.gov/


--
Steve Ansari
Physical Scientist
NOAA's National Climatic Data Center
Veach-Baley Federal Building
151 Patton Avenue
Asheville, NC 28801
Ph: 828-271-4611
Fax: 828-271-4022



===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
===============================================================================