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
rkambic@xxxxxxxxxxxxxxxx WWW: http://www.unidata.ucar.edu/
===============================================================================
