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Re: [netcdf-java] Grib File Dump not correct?/Grib Code to read Grib Parameter Names & Values
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- Subject: Re: [netcdf-java] Grib File Dump not correct?/Grib Code to read Grib Parameter Names & Values
- Date: Tue, 6 Oct 2009 15:44:44 -0600 (MDT)
Chad,I've been answering many Grib questions lately, it seems that most programmers can use the CDM layer above the grib layer and remove themselves from the details of the Grib file, ie such as offsets, etc.
The CDM layer should have all the information that you need. On Tue, 6 Oct 2009, Chad Saxon wrote:
Robb, i have been looking at the doc and been trying out some code. By the way thanks for the updates and quick replies. The crux of what i want to do is really read in and store: - the unit parameter of the data (i.e. temperature) - the data coupled with the lat/lon in each record - the offset of lat/lon(resolution) so i can loop through the data and store appropriate parameter values.
Basically you would open the file as GridDataset, this will perform all the low level Grib actions for you.
Here's a tutorial to help get you get started: http://www.unidata.ucar.edu/software/netcdf-java/tutorial/
I would look at GridDatatype, NetcdfFile, and NetcdfDatasetsThere are also javaDocs at: http://www.unidata.ucar.edu/software/netcdf-java/v2.2.20/javadoc/index.html
Sample code: http://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2009/msg00233.html
http://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2009/msg00235.htmlThe above messages have urls to javaDocs about GridDatasets, if you do some searching I believe you will be able to get all the information that you need. On the netcdf-java home page:
http://www.unidata.ucar.edu/software/netcdf-javaThere is a reference to a program ToolsUI GUI that will permit you to look at the files. I would launch it by webstart so you can get the feel for it. There isn't any documentation but it intutitive. Hope this gets you out the low levels of Grib.
Robb...
right now i have this:
*testfile = whateverfile.grb
List<GridRecord> gribRecords;
ucar.unidata.io.RandomAccessFile gribfile = new
ucar.unidata.io.RandomAccessFile(testfile, "rw");
index = new GribReadIndex();
gridindex = new GridIndex();
gridindex = index.open(testfile);
gribRecords = gridindex.getGridRecords();
i wanted to declare gribRecords to the class GribGridRecord since it seems i
have access to the offset parameters i would need to do my seek that you
suggested
a while back for looking at all the data but the getGridRecords only returns of
type GridRecord which, according to the doc, doesnt have any functionality to
look
at the offsets, etc.
Once i get the list of records i just want to be able to do a seek on each
one,
loop through its data and start on the next record. The outdated Index class
seemed to have that capability before. Maybe i am just overlooking something.
thanks for your help...
Chad
On Sep 14, 2009, at 10:07 AM, Robb Kambic wrote:
Chad,
Thanks for pointing out that the Java Docs need to be updated on the
Decoders page, I'll do it sometime this afternoon.
Robb...
On Mon, 14 Sep 2009, Chad Saxon wrote:
Robb,
thanks for the input and feedback. i went ahead and got
the grib-8.0 library
and have to work through some of the depreciated stuff in
my code now but i
was wondering the the javadoc reflects the grib 8.0
changes? Some of the
functionality like, for
example, Grib1GridDefinitionSection.getGdsVars();
doesnt appear in the API javadoc that i am looking at.
thanks...
Chad
On Sep 8, 2009, at 2:03 PM, Robb Kambic wrote:
On Mon, 7 Sep 2009, Chad Saxon wrote:
I am writing some low level code(because i need
to),
to read grib files and all the values that i
print out
on the console do not match the values when i
dump
them out to a file. The grib file that i am
testing
against is including in this e-mail for those
that
want to take a look.
Also i seem to be having problems getting
actual
String literals for certain codes.. like the
parameter
name for code 11 is Temperature and the Unit
type is K
in this case but it seems that the way to get
these
are not very intuitive to get using Index and
my
GribRecords variable in the code below. Maybe
someone
could shed some light on this??
In advance, i want to thank all those that can
take
the time to look through this.
--Chad
Chad,
The Grib library usually reads the records of the
grib file in
sequence of the sections, there are 5 sections to
Grib1. See:
http://www.nco.ncep.noaa.gov/pmb/docs/on388/
To read a particular section, the filePointer must be
moved to the
start of the section to have a proper read. There is
an index file
that has some of the offsets to the sections, such as
the GDS
section. Here's the index of your sample file:
------------------------------------------------------------------
10 0 -1 11 96 1 0.0 255 0.0 2009-09-07T06:00:00Z 24
284494432 36
68 1 false 7 0 2
10 0 -1 11 96 1 0.0 255 0.0 2009-09-07T06:00:00Z 48
284494432 390
422 1 false 7 0 2
10 0 -1 11 96 1 0.0 255 0.0 2009-09-07T06:00:00Z 72
284494432 744
776 1 false 7 0 2
------------------------------------------------------------------
The offsets 36, 390, and 744 are the GDS offsets for
the 3 records
in the file. If you would modify you code to do the
seeks and then
read the GDS, then the values will be correct.
gribfile.seek( 36 );
Grib1GridDefinitionSection gds =
Grib1GridDefinitionSection(gribfile);
Here are some files that will help you understand the
how the
index works.
IndexFormat.txt locate in the root directory of the
package.
ucar/grib/grib1 directory:
Grib1WriteIndex.java
Grib1Dump.java
Grib1GetData.java
Grib1Data.java
Grib1Input.java
also look at the following files on how to extract
particular PDS
and GDS values;
GribReadIndex.java
ShowGribIndex.java
I must warn you that the Grib library has been
refactored, so the
Index api will be slightly different then the 6.0
release. I would
suggest that you get the latest 8.0 release on the
decoders page
located at:
http://www.unidata.ucar.edu/software/decoders/
Robb...
here is my code below with output:
public class GribPlugin {
java.io.PrintStream ps;
String[] fileDump;
Grib1GridDefinitionSection gridSection;
String testfile = "gfs20090907162501123.grb";
public GribPlugin() throws IOException,
NoValidGribException, NotSupportedException{
ucar.unidata.io.RandomAccessFile gribfile = new
ucar.unidata.io.RandomAccessFile(testfile,
"rw");
type = file.getEdition(gribfile);
System.out.println("File read in: " + testfile
+ ",
Type of Grib File is " + type);
fileDump = new String[3];
fileDump[0] = "gfs20090907162501123.grb";
fileDump[1] = "gribdump.out";
fileDump[2] = "true";
try{
gridSection = new
Grib1GridDefinitionSection(gribfile);
System.out.println("defining a new
gridsection");
}
catch(IOException e){
throw new IOException("Grid Section " + e);
}
System.out.println("grid definition section");
System.out.println("dx: " + gridSection.getDx()
+ ",
dy: " + gridSection.getDy() + ", La1: " +
gridSection.getLa1() + ", La2: " +
gridSection.getLa2() + ", Lo1: " +
gridSection.getLo1() + ", Lo2: " +
gridSection.getLo2() + ", Nx: " +
gridSection.getNx()
+ ", Ny: " + gridSection.getNy() + ", Grid
Section
Name: " + gridSection.getName());
System.out.println("File Dump Information");
gribDump.main(fileDump);
System.out.println("Dump GridFile Info Out To
File");
ps = new java.io.PrintStream("grib.out");
index = gribIndex.writeFileIndex(gribfile, ps,
true);
//this is printing out the grib records
System.out.println("Grib Records");
gribRecords = index.getGribRecords();
System.out.println("Number of Grib Records: " +
gribRecords.size());
for(int i = 0; i < gribRecords.size(); i++){
System.out.println(gribRecords.get(i).category
+ " " +
gribRecords.get(i).center + " " +
gribRecords.get(i).discipline + " " +
gribRecords.get(i).paramNumber + " " +
<--how
do you convert this to the equivalent param
name??
gribRecords.get(i).productType + " " +
gribRecords.get(i).decimalScale + " " +
gribRecords.get(i).gdsKey + " " +
gribRecords.get(i).typeGenProcess + " " +
gribRecords.get(i).forecastTime + " " +
gribRecords.get(i).refTime + " " +
gribRecords.get(i).subCenter + " " +
gribRecords.get(i).bmsExists);
} //end for
} //end public class constructor
} // end class GribPlugin
Console Output:
File read in: gfs20090907162501123.grb, Type of
Grib
File is 1
GribPDSLevel: Table 3 level 96 is not
implemented yet
PDS: Time Unit 9 is not yet supported
Using default
table:resources/grib/tables/wmo_2_v1.tab
(0:0:-1)
defining a new gridsection
Grid 28 not configured yet
grid definition section
dx: 2.632, dy: 0.0, La1: -8355.851, La2:
591.622, Lo1:
65.536, Lo2: 0.256, Nx: 540, Ny: 24583, Grid
Section
Name: Latitude/Longitude Grid
File Dump Information
gds exception was caught
Dump GridFile Info Out To File
Grib Records
Number of Grib Records: 3
-1 7 0 11 10 1 2350466037 96 24
2009-09-07T06:00:00Z 0
false
-1 7 0 11 10 1 2350466037 96 48
2009-09-07T06:00:00Z 0
false
-1 7 0 11 10 1 2350466037 96 72
2009-09-07T06:00:00Z 0
false
*****
Now you will notice that my grid definition
section
does not match any of the parameters from the
grid
dump below(except for the grid section name).
My
question is, is why is this and/or what am i
doing
wrong here??? Those numbers that i get from the
Console output just do not make any sense to me
at
all.
*****
GridDump Output:
Header : GRIB1
Discipline : 0 Meteorological
Products
GRIB Edition : 1
GRIB length : 354
Originating Center : 7 US National
Weather
Service (NCEP)
Originating Sub-Center : 0 WMO Secretariat
Product Definition : 10 product valid
at
reference time P1
Parameter Category : -1 Meteorological
Parameters
Parameter Name : 11 TMP
Temperature
Parameter Units : K
Reference Time :
2009-09-07T06:00:00Z
Time Units : hour
Time Range Indicator : product valid at
RT + P1
Time 1 (P1) : 24
Time 2 (P2) : 0
Generating Process Type : 96 Global
Forecast
System Model (formerly known as the Aviation)
Level Type : 1 surface
Level Value 1 : 0.0
Level Value 2 : 0.0
GDS Exists : true
BMS Exists : false
Number of data points : 3447
Grid Name :
Latitude/Longitude Grid
Grid Shape: 0 spherical
Spherical earth radius: 6367.47
Nx : 16
Ny : 15
La1 : 0.0
Lo1 : -100.0
Resolution & Component flags : 128
Winds : True
La2 : 29.0
Lo2 : -70.0
=============================================================================
==
Robb Kambic Unidata Program Center
Software Engineer III Univ. Corp for Atmospheric
Research
address@hidden WWW:
http://www.unidata.ucar.edu/
=============================================================================
==
===============================================================================
Robb Kambic Unidata Program Center
Software Engineer III Univ. Corp for Atmospheric Research
address@hidden WWW: http://www.unidata.ucar.edu/
===============================================================================
=============================================================================== Robb Kambic Unidata Program Center Software Engineer III Univ. Corp for Atmospheric Research address@hidden WWW: http://www.unidata.ucar.edu/ ===============================================================================
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