Newbie Question


  Before I jumped in and started writing a GRIB file adapter,
I thought I'd just try to read one slice of temperature data that
the degrib routine prints out:  an binary array of floats,
with a header integer declaring the number of bytes to follow.
I tried looking at the Simple example and the Vis5DForm
code to come up with the following main method.

  Also included is a GIF image of the screen output from my program.
It is supposed to be a temperature map (values are in Kelvin).
It looks funky to me!  I tried changing the display from RGB
to IsoContour, but I got a NullPointer exception.  I printed out
the float values of array, and they look OK.  I'm not quite sure
what to test here...

In line 104 in my program, I set a scalarMap using field3d[0]
rather than something from the range I set up earlier like in
the example.  Am I accessing the temperature field data as I
thought?  I'm not sure how the connection between my FlatField
grid (where I store my array data) and the field3d variable
is made?

 If you need the 69K binary data file in order to run it, let me
know and I can send it to you.

Thanks for any insight!

KathyLee Simunich
Argonne National Lab

GIF image

// import needed classes
import visad.*;
import visad.java2d.DisplayImplJ2D;
//import visad.util.VisADSlider;
import java.rmi.RemoteException;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class WXView {

  public static void main(String args[])
         throws VisADException, RemoteException, IOException {

        if (args.length < 1) {
                System.err.println("Usage: java WXView <filename>");

        float[][] array= null;
        String filename = new String(args[0]);
        try {
                // read in the GRIB slice
                RandomAccessFile in = new RandomAccessFile(new 

                int numVals = WXView.readInteger(in);
                int val = numVals/4;

                array= new float[1][val];
                System.out.println("numVAls= "+numVals+" val = "+val);

                // reads in the number of bytes in file
                for (int i=0; i<val; i++) {
                        array[0][i] = WXView.readFloat(in); 

        } catch (FileNotFoundException e) {
    catch (IOException e) {

        // construct RealType components for grid coordinates
        RealType row = new RealType("row",null,null);
        RealType col = new RealType("column",null,null);
        RealType level = new RealType("level",null,null);

        // construct RealTupleType components for grid coordinates
        RealType[] type3d = {row, col, level};
        RealTupleType domain = new RealTupleType(type3d);

        // construct RealType components for grid fields
        RealType temperature = new RealType("temperature",null,null);

        // construct RealTupleType for grid fields
        RealType[] field3d = {temperature};
        RealTupleType range = new RealTupleType(field3d);

        // construct FunctionType for grid
        FunctionType grid_type = new FunctionType(domain,range);

        // construct RealType and RealTupleType for time domain
        RealType time = new RealType("time",null,null);
        RealTupleType time_type = new RealTupleType(time);

        // construct FunctionType for time sequence of grids
        FunctionType afwa_type = new FunctionType(time_type,grid_type);

        // construct an integer 3D grid - hardcoded dimensions thus far...KLS
        Set grid_set = new Integer3DSet(144,120,1); // what are the numlevs?
        // construct a sequence of hours - also hardcoded
        Set time_set = new Integer1DSet(1);

        // construct a FieldImple for a time sequence of grids
        FieldImpl grib = new FieldImpl(afwa_type,time_set);

        //loop on time hours...
                // construct a FlatField for the ith time step
                FlatField grid = new FlatField(grid_type,grid_set);

                // set the data values into the grid

                // set grid as the ith time sample

    // create a Display using Java2D
    DisplayImpl display = new DisplayImplJ2D("weather map");

        DataReference grid_ref = new DataReferenceImpl("grid");

    // map image coordinates to display coordinates
    display.addMap(new ScalarMap((RealType) domain.getComponent(0),
    display.addMap(new ScalarMap((RealType) domain.getComponent(1),
    // map image brightness values to RGB (default is grey scale)
    display.addMap(new ScalarMap((RealType) field3d[0],


    // create JFrame (i.e., a window) for display and slider
    JFrame frame = new JFrame("Simple VisAD Application");
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {System.exit(0);}
    // create JPanel in JFrame
    JPanel panel = new JPanel();
    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
    // add slider and display to JPanel
    // set size of JFrame and make it visible
    frame.setSize(500, 600);


        static int readInteger(RandomAccessFile input) throws IOException{
        int b1,b2,b3,b4;
        //return (int)(b4<<24|b3<<16|b2<<8|b1);
        return (int)(b1<<24|b2<<16|b3<<8|b4);

    static float readFloat(RandomAccessFile input) throws IOException{
        return Float.intBitsToFloat(readInteger(input));