R: Help on Data Transect

• To: <dmurray@xxxxxxxxxxxxxxxx>
• Subject: R: Help on Data Transect
• From: "Antonio Benvenuti" <antonio.benvenuti@xxxxxxxxx>
• Date: Tue, 26 Sep 2006 16:26:50 +0200

Hi

I noticed I had inverted rt_lon and rt_lat in the domain used by the
Gridded2DDoubleSet of "makeLatitudeLineSet" and "makeLongitudeLineSet"...

The code works now correctly!


Thanks

Antonio Benvenuti



-----Messaggio originale-----
Da: Antonio Benvenuti [mailto:antonio.benvenuti@xxxxxxxxx] 
Inviato: martedì 26 settembre 2006 14.37
A: 'dmurray@xxxxxxxxxxxxxxxx'
Cc: 'visad@xxxxxxxxxxxxxxxx'
Oggetto: R: Help on Data Transect


Hi Don

I have tried integrating the IDV's data transect as suggested by you, but
found it too expensive for the time I have to spend on the project.
So I tried to implement a simple data transect functionality as the
P6_05.java example.
The example is very simple, but I can not understand why I get Nan values
for the transect line that results from the intersection of a flatfield and
a line.

Could you please give me a hint?

Here is my code:


        // Displays the transect line on the main display
        try {
            ConstantMap[] cMaps = { new ConstantMap( 1.0f, Display.Red ),
                                    new ConstantMap( 1.0f, Display.Green ),
                                    new ConstantMap( 1.0f, Display.Blue ),
                                    new ConstantMap( 5.50f,
Display.PointSize )  };
            
            final int numberOfPoints = 1000;
            
            // Line transect
            final double initLatitude
currentRangeLat[0]+(currentRangeLat[1]-currentRangeLat[0])/2;
            final double initLongitude
currentRangeLon[0]+(currentRangeLon[1]-currentRangeLon[0])/2;
            
            Real cursorCoords;
            
            if (cutLongitude == true) {
                cursorCoords  = new Real(rt_lon, initLongitude);    
            }
            else {
                cursorCoords  = new Real(rt_lat, initLatitude);
            }
            
                ...

                // White Point
                cursorDataRef = new DataReferenceImpl("cursorDataRef");
                cursorDataRef.setData(cursorCoords);
                
                // White Line
                wLineDataRef = new DataReferenceImpl("wLineDataRef");
                                
                display.addReferences( new DirectManipulationRendererJ3D(),
cursorDataRef, cMaps );
                display.addReference(wLineDataRef);

                if (cutLongitude == true) {
                    whiteLine = (Set) makeLongitudeLineSet(initLatitude,
numberOfPoints);
                }
                else {
                    whiteLine = (Set) makeLatitudeLineSet(initLongitude,
numberOfPoints);
                }
                
                wLineDataRef.setData(whiteLine);
                
                // Transect Line
                tLineDataRef = new DataReferenceImpl("tLineDataRef");

                ConstantMap[] tLineMaps = { new ConstantMap(2.0f,
Display.PointSize) };
                transectDisplay.addReference(tLineDataRef, tLineMaps);

                surfsField = (FlatField) baseMap_sequence;
                transectLine = (FlatField) surfsField.resample(whiteLine);
                tLineDataRef.setData(transectLine);

                CellImpl cell = new CellImpl() {
                    public void doAction() throws RemoteException,
VisADException {

                        if (cutLongitude == true) {
                            Real lon = (Real) cursorDataRef.getData();
                            double lat = initLatitude;

                            // Make a new line
                            whiteLine = (Set)
makeLongitudeLineSet(lon.getValue(), numberOfPoints);
                        }
                        else {
                            double lon = initLongitude;
                            Real lat = (Real) cursorDataRef.getData();

                            // Make a new line
                            whiteLine = (Set)
makeLatitudeLineSet(lat.getValue(), numberOfPoints);
                        }                        

                        // Re-set Data, will update display
                        wLineDataRef.setData(whiteLine);

                        // Transect Data
                        surfsField = (FlatField) baseMap_sequence;
                        
                        int resampMode = Data.NEAREST_NEIGHBOR;
                        int errorMode = Data.NO_ERRORS;
                        
                        transectLine = (FlatField)
surfsField.resample(whiteLine,          <--------------------------------
 
resampMode,             <- HERE I GET ONLY "NAN" VALUES! |
 
errorMode);             <--------------------------------
                        tLineDataRef.setData(transectLine);
                    }
                };
                cell.addReference(cursorDataRef);

                ...

        }
        catch (Exception e) {
                ...
        }


And the make line methods that seem to work correctly:


    private Set makeLongitudeLineSet(double northingValue, int pointsPerLine
)
        throws VisADException, RemoteException {

        // Arbitrary easting end values of the line
        double lowVal =  currentRangeLat[0];
        double hiVal  =  currentRangeLat[1];
        

        double[][] domainSamples = new double[2][pointsPerLine];

        double lonVal = lowVal;
        double increment = ( hiVal - lowVal )/ (double) (pointsPerLine-1) ;
        for(int i=0;i<pointsPerLine;i++){
            domainSamples[0][i] = lonVal;
            domainSamples[1][i] = northingValue;
            lonVal += increment;
        }
        
        RealTupleType domain = new RealTupleType(rt_lon, rt_lat);

        return new Gridded2DDoubleSet( domain, domainSamples,
pointsPerLine);
    }

    private Set makeLatitudeLineSet(double eastingValue, int pointsPerLine )
        throws VisADException, RemoteException {

        // Arbitrary northing end values of the line
        double lowVal =  currentRangeLon[0];
        double hiVal  =  currentRangeLon[1];


        double[][] domainSamples = new double[2][pointsPerLine];

        double latVal = lowVal;
        double increment = ( hiVal - lowVal )/ (double) (pointsPerLine-1) ;
        for(int i=0;i<pointsPerLine;i++){
            domainSamples[0][i] = eastingValue;
            domainSamples[1][i] = latVal;
            latVal += increment;
        }
        
        RealTupleType domain = new RealTupleType(rt_lon, rt_lat);

        return new Gridded2DDoubleSet( domain, domainSamples,
pointsPerLine);
    }


Thanks

Antonio Benvenuti



-----Messaggio originale-----
Da: Don Murray [mailto:dmurray@xxxxxxxxxxxxxxxx]
Inviato: lunedì 11 settembre 2006 15.55
A: Antonio Benvenuti
Cc: visad@xxxxxxxxxxxxxxxx
Oggetto: Re: Help on Data Transect

Hi Antonio-

Antonio Benvenuti wrote:

> I would like to implement a functionality like IDV's "Data Transect" 
> in my application.
> I am actually representing a base map from a netcdf file, mapping 
> latitude, longitude respectively on the Y, X axes and the altitude as RGB
values.
> Could you suggest me a way to do it?

The easiest thing would be too look through the
ucar.unidata.idv.control.DataTransectControl and work your way back. But for
a quick summary the IDV has:

3 Data References with RealTuples (XYZ) in them for the selector points (two
end points, one mid point).
1 Data Reference with a Gridded2DSet on a 1D manifold (for the line)
ActionImpls that listen for changes when the selector points are directly
manipulated and update the postions of the line and other points.

A listener on the line so that when it changes:
  - A sampling set of points along the line is generated
    (see ucar.unidata.data.grid.GridUtil.sliceAlongLatLonLine)
  - the data field is resamples along that line.

You could reinvent this all, or just use the pieces of the IDV library that
we've already developed.

Don
*************************************************************
Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************


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