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RE: [Fwd: [netcdf-java] FW: Adding a new projection to GRIB netcdf decoder] (fwd)

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  • Subject: RE: [Fwd: [netcdf-java] FW: Adding a new projection to GRIB netcdf decoder] (fwd)
  • Date: Sat, 6 Dec 2008 13:55:12 -0700 (MST)

Tor,
There is a problem with the sample file coordinate pamameters or the projection equation. 

Using your equations:

Location of pole of rotated grid as seen in non-rotated grid:
Lon=0.0, Lat=-25.0
Additional axial rotation about pole of rotated grid:0.0

Location of chosen point in non-rotated grid:
Lon=-46.5, Lat=-36.5
Location of chosen point as seen in rotated grid:
Lon=-117.63130026466261, Lat=-48.84029857829332

I believe the rotated point should be near lon 46W lat 28N

Location of chosen point in non-rotated grid:
Lon=46.9, Lat=38.9
Location of chosen point as seen in rotated grid:
Lon=35.59515325886277, Lat=-12.506087977741661

The makes the image show south of the equator.
Also, it seems that Dx and Dy might be wrong. If I use 46W, 28N as the lower left corner, then the upper right corner is off the earth, lat > 90. 

Can you check?


Robb...


On Thu, 20 Nov 2008, Tor Christian Bekkvik wrote:


Hi,
I have been a little busy; Sorry for the bad example file I sent first,
the attached file should have more meaningful values.
Some file info, logged from a java-application using JGRIB (JGRIB
supports rotated latlon for GRIB-1) :

  Gribfile: rotatedlatlon.grb
  Records: 1
  Grid:
      GDS section:
          Rotated LatLon Grid  (468x378)
          lon: -46.5 to 46.9  (dx 9.99990041077413E24)
          lat: -36.5 to 38.9  (dy 9.99990041077413E24)
          south pole: lon 0.0 lat -25.0
          rot angle: 0.0
        mode(17):0x88
        type(6) :0xa
        scan(28):0x40
      PDS cent tab proc: 96 1 1
                    -> 96 -1 1 ncep_opn.tab
   Z type(105): fixed height above ground
   Z #levels: 1
   Dates(1):
         min Mon Dec 15 19:00:00 CET 2003
         max Mon Dec 15 19:00:00 CET 2003
   Param: 7 HGT [gpm] Geopotential height [-275.23438  4048.7656]




PS. Hoping that rotated latlon projection could be supported for GRIB-2

Thanks,
Tor C



-----Original Message-----
From: Robb Kambic [mailto:address@hidden]
Sent: 20. november 2008 00:44
To: Tor Christian Bekkvik
Subject: Re: [Fwd: [netcdf-java] FW: Adding a new projection
to GRIB netcdf decoder] (fwd)

Tor,

An image of the result would be appreciated.

Thanks,
Robb...





On Wed, 19 Nov 2008, Robb Kambic wrote:


Tor,

I've been working on this problem but the sample file you

sent has all

the data values equal to 0.  could you make available

another sample

file with a description so I can tell if I am displaying correctly.

Robb...


-------- Original Message --------
Subject: [netcdf-java] FW: Adding a new projection to GRIB netcdf
decoder
Date: Wed, 29 Oct 2008 09:35:55 +0100
From: Tor Christian Bekkvik <address@hidden>
To: netcdf-java <address@hidden>



-----Original Message-----
From: Tor Christian Bekkvik
Sent: 27. oktober 2008 14:48
To: 'address@hidden'
Cc: Kjell Rĝang
Subject: Adding a new projection to GRIB netcdf decoder

Hi,
We would like to add support for Rotated LatLon projection when
reading GRIB files. (using netcdf decoders)


To open the gribfile, we have used class  NetcdfDataset:
NetcdfDataset.openDataset(gribFile,...)
But this fails for with rotated latlong projection, as it

is not supported:

 ucar.grib.NoValidGribException: GDS: Unknown Grid Type :

10) is not

supported.
    at


ucar.grib.grib1.Grib1GridDefinitionSection.<init>(Grib1GridDef
initionSection.java:401)

    at ucar.grib.grib1.Grib1Input.scan(Grib1Input.java:155)
    at

ucar.grib.grib1.Grib1Indexer.writeFileIndex(Grib1Indexer.java:90)

    at


ucar.nc2.iosp.grib.GribServiceProvider.writeIndex(GribServiceP
rovider.java:163)

    at


ucar.nc2.iosp.grib.GribServiceProvider.getIndex(GribServicePro
vider.java:139)

    at


ucar.nc2.iosp.grib.GribServiceProvider.open(GribServiceProvide
r.java:75)

    at ucar.nc2.NetcdfFile.<init>(NetcdfFile.java:1092)
    at ucar.nc2.NetcdfFile.open(NetcdfFile.java:485)
    at ucar.nc2.NetcdfFile.open(NetcdfFile.java:278)
    at

ucar.nc2.dataset.NetcdfDataset.openFile(NetcdfDataset.java:341)

    at

ucar.nc2.dataset.NetcdfDataset.openDataset(NetcdfDataset.java:175)

    at

ucar.nc2.dataset.NetcdfDataset.openDataset(NetcdfDataset.java:161)




To add this new projection, it seems that at least the

following code

needs
update:
1) ProjectionImpl  (I can implement RotLatLonProjection extends
ProjectionImpl)
2) Grib1GridDefinitionSection  (to fix

NoValidGribException, listed above)

3) GribHorizCoordSys.makeProjection   (read necessary

parameters from Grib

GDS section and return RotLatLonProjection):
 private void makeProjection(NetcdfFile ncfile) {
   switch (lookup.getProjectionType(gdsIndex)) {
     case TableLookup.PolarStereographic:
       makePS();
       break;
     case TableLookup.LambertConformal:
       makeLC();
       break;
     case TableLookup.Mercator:
       makeMercator();
       break;
     case TableLookup.Orthographic:
       makeSpaceViewOrOthographic();
       break;
     default:
       throw new UnsupportedOperationException("unknown

projection = "

+ gdsIndex.grid_type);
   }





Currently, I don't have sufficient GRIB/NetCDF knowledge (or source
code) to do this.
But I have already added Rotated LatLon projection for the JGRIB
project (http://jgrib.sourceforge.net/), and we would like

to do the

same with NetCDF/GRIB.




- Any comments how to best do this ?



Thanks,
Tor Chr Bekkvik


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==============================================================
=================
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/
===============================================================================