volumes

hello all,

Can someone tell me why this Linear3Dset is not a volume?!?!?!?

Cheers,
Tiago
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import visad.*;
import visad.java3d.*;
import visad.util.*;

public class tester
{
  private DisplayImpl display;

  public tester()
  {
    try {
      display = new DisplayImplJ3D("display");

      ScalarMap latMap = new ScalarMap(RealType.Latitude, Display.XAxis);
      ScalarMap lonMap = new ScalarMap(RealType.Longitude, Display.YAxis);
      ScalarMap hgtMap = new ScalarMap(RealType.Radius, Display.ZAxis);

      display.addMap(latMap);
      display.addMap(lonMap);
      display.addMap(hgtMap);

      latMap.setRange(-90.0, 90.0);
      lonMap.setRange(-180.0, 180.0);
      hgtMap.setRange(0.0f, 100.0f);

      RealTupleType fieldtuple = new RealTupleType(RealType.Latitude, 
RealType.Longitude, RealType.Radius);

      Linear3DSet layerLines = new Linear3DSet(fieldtuple, 0.0f, 50.0f, 30, 
20.0f, 60.0f, 30, 50.0f, 90.0f, 30);

      DataReference coast_linesref = new DataReferenceImpl("layerLines");
      coast_linesref.setData(layerLines);

      display.addReference(coast_linesref);

      JFrame frame = new JFrame("Tester");
      frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) { System.exit(0); }
      });

      frame.getContentPane().setLayout(new BorderLayout());
      frame.getContentPane().add(display.getComponent(), BorderLayout.CENTER);
      frame.setSize(800, 600);
      frame.setVisible(true);

      GraphicsModeControl dispGMC = display.getGraphicsModeControl();
      dispGMC.setScaleEnable(true);

    } catch (Exception ne) {
      ne.printStackTrace();
      System.exit(1);
    }
  }

  public static void main(String[] args)
  {
    tester satDisplay = new tester();
  }

}