[netcdf-java] Problem with findXYindexFromLatLon() on a Geogrid subset

Hello,

I have problems with the findXYindexFromLatLon() method used with a
Geogrid subset.
gcs.getLatLon(0,0) gives me lat/long coordinates that I try to convert
back to XY coordinates. 
But I get -1 for the Y coordinate.
On the original grid, everything is fine.

I use one of the sample netCDF files from the Unidata website. I'm using
netcdfAll-4.5.jar dated March, 6. I guess it is  the 4.5.5 version.

Does anyone see what I did wrong ? Code and output below. The "start"
members look strange.

Thanks,
Franck

------------------------------
Grid name =area
WHOLE GRID
is lat/lon system ? true
gcs bounding box : latmin=-88.927734375 latmax=88.927734375 lonmin=0.0
lonmax=358.59375
projection       : LatLonProjection
width =256, height=128
X is regular     ? true
X is contiguous  ? true
X start          : 0.0
X increment      : 1.40625
Y is regular     ? false
Y is contiguous  ? true
Y start          : -88.927734375
Y increment      : 1.4004367618110236
index (0,0) --> lat/lon : -88.927734375 ; 0.0
index (1,1) --> lat/lon : -87.53870391845703 ; 1.40625
looking up lat=-87.53870391845703  lon=1.40625
index= (1, 1)

SUBGRID (latmin=-20.0  latmax=-10.0  lonmin=35.0  lonmax=45.0)
is lat/lon system ? true
gcs bounding box : latmin=-20.31112289428711 latmax=-10.505756378173828
lonmin=35.15625 lonmax=45.0
projection       : LatLonProjection
width =8, height=8
X is regular     ? true
X is contiguous  ? true
X start          : 0.0
X increment      : 1.40625
Y is regular     ? false
Y is contiguous  ? true
Y start          : 0.0
Y increment      : 1.4004367618110236
index (0,0) --> lat/lon : -20.31112289428711 ; 35.15625
index (1,1) --> lat/lon : -18.910356521606445 ; 36.5625
looking up lat=-18.910356521606445  lon=36.5625
index= (-1, 1)

-------------------------
                try {
                        GridDataset dataset =
GridDataset.open("http://www.unidata.ucar.edu/software/netcdf/examples/sresa1b_ncar_ccsm3_0_run1_200001.nc";);
                        
                        GridDatatype firstGridInfo = dataset.getGrids().get(0);

                        System.out.println("Grid name 
="+firstGridInfo.getName());
                        
                        GeoGrid firstGrid = (GeoGrid) dataset.getGrids().get(0);
                        

                        System.out.println("WHOLE GRID");
                        GridCoordSystem gcs    = 
firstGrid.getCoordinateSystem();
                        System.out.println("is lat/lon system ? 
"+gcs.isLatLon());

                        LatLonRect rect = gcs.getLatLonBoundingBox();
                        System.out.println("gcs bounding box : 
latmin="+rect.getLatMin()+"
latmax="+rect.getLatMax()+" lonmin="+rect.getLonMin()+"
lonmax="+rect.getLonMax());
                        System.out.println("projection       : 
"+gcs.getProjection());
                        System.out.println("width 
="+gcs.getXHorizAxis().getSize()+",
height="+gcs.getYHorizAxis().getSize());
                        System.out.println("X is regular     ? 
"+((CoordinateAxis1D)
gcs.getXHorizAxis()).isRegular());
                        System.out.println("X is contiguous  ?
"+gcs.getXHorizAxis().isContiguous());
                        System.out.println("X start          : 
"+((CoordinateAxis1D)
gcs.getXHorizAxis()).getStart()) ;
                        System.out.println("X increment      : 
"+((CoordinateAxis1D)
gcs.getXHorizAxis()).getIncrement()) ;
                        System.out.println("Y is regular     ? 
"+((CoordinateAxis1D)
gcs.getYHorizAxis()).isRegular());
                        System.out.println("Y is contiguous  ?
"+gcs.getYHorizAxis().isContiguous());
                        System.out.println("Y start          : 
"+((CoordinateAxis1D)
gcs.getYHorizAxis()).getStart()) ;
                        System.out.println("Y increment      : 
"+((CoordinateAxis1D)
gcs.getYHorizAxis()).getIncrement()) ;

                        LatLonPoint p = gcs.getLatLon(0,0);
                        System.out.println("index (0,0) --> lat/lon : 
"+p.getLatitude()+" ;
"+p.getLongitude());
                        p = gcs.getLatLon(1,1);
                        System.out.println("index (1,1) --> lat/lon : 
"+p.getLatitude()+" ;
"+p.getLongitude());

                        System.out.println("looking up lat="+p.getLatitude()+"
lon="+p.getLongitude());
                        int[] xy = gcs.findXYindexFromLatLon(p.getLatitude(),
p.getLongitude(), null);
                                System.out.println("index= ("+xy[0]+", 
"+xy[1]+")");


                         //
--------------------------------------------------------------------------
                        double latMin=-20.D, latMax=-10.D, lonMin=35.D, 
lonMax=45.D ;
                        System.out.println("\nSUBGRID (latmin="+latMin+"  
latmax="+latMax+"
lonmin="+lonMin+"  lonmax="+lonMax+")");

                        LatLonRect    latLonRect = new LatLonRect(
                    new LatLonPointImpl(latMin, lonMin),
                    new LatLonPointImpl(latMax, lonMax)) ;

                        GeoGrid   gridSubset = firstGrid.subset(null, null, 
latLonRect, 0, 1,
1) ;

                        GridCoordSystem gcs2    = 
gridSubset.getCoordinateSystem();

                        rect = gcs2.getLatLonBoundingBox();
                        System.out.println("is lat/lon system ? 
"+gcs2.isLatLon());
                        System.out.println("gcs bounding box : 
latmin="+rect.getLatMin()+"
latmax="+rect.getLatMax()+" lonmin="+rect.getLonMin()+"
lonmax="+rect.getLonMax());
                        System.out.println("projection       : 
"+gcs.getProjection());
                        System.out.println("width 
="+gcs2.getXHorizAxis().getSize()+",
height="+gcs2.getYHorizAxis().getSize());
                        System.out.println("X is regular     ? 
"+((CoordinateAxis1D)
gcs2.getXHorizAxis()).isRegular());
                        System.out.println("X is contiguous  ?
"+gcs2.getXHorizAxis().isContiguous());
                        System.out.println("X start          : 
"+((CoordinateAxis1D)
gcs2.getXHorizAxis()).getStart()) ;
                        System.out.println("X increment      : 
"+((CoordinateAxis1D)
gcs2.getXHorizAxis()).getIncrement()) ;
                        System.out.println("Y is regular     ? 
"+((CoordinateAxis1D)
gcs2.getYHorizAxis()).isRegular());
                        System.out.println("Y is contiguous  ?
"+gcs2.getYHorizAxis().isContiguous());
                        System.out.println("Y start          : 
"+((CoordinateAxis1D)
gcs2.getYHorizAxis()).getStart()) ;
                        System.out.println("Y increment      : 
"+((CoordinateAxis1D)
gcs2.getYHorizAxis()).getIncrement()) ;

                        p = gcs2.getLatLon(0,0);
                        System.out.println("index (0,0) --> lat/lon : 
"+p.getLatitude()+" ;
"+p.getLongitude());
                        p = gcs2.getLatLon(1,1);
                        System.out.println("index (1,1) --> lat/lon : 
"+p.getLatitude()+" ;
"+p.getLongitude());

                        System.out.println("looking up lat="+p.getLatitude()+"
lon="+p.getLongitude());
                        xy = gcs2.findXYindexFromLatLon(p.getLatitude(), 
p.getLongitude(),
null);
                        System.out.println("index= ("+xy[0]+", "+xy[1]+")");

                } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                } catch (InvalidRangeException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }

-- 
Franck Reinquin <franck.reinquin@xxxxxxxxxxxxxx>
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