Re: display points using log scale

Hi Celine-

Attached is a program that lets the user switch between
log and non-log Y axis.  It's based on the LogTest file
I sent you earlier off list.  Note that as before you
need to explicitly set the range for the logMap.  I'm
not sure why it doesn't autoscale.

Hope it helps.


Don Murray wrote:
Hi Celine-

I'm travelling and don't have time to do this justice, but
here's my take on it.  I have not been able to follow your
code in detail, but here's my take on it.  You have some
X or Y values.  You can use X or Y for those real types.
For the Log values, you can create a RealType (e.g. LogX,
LogY) which is used for the reference realtype of the
LogCoordinateSystem.  VisAD automatically does the calculations
converting the values to the log values.  What you have below
looks like you are trying to go the other way.  Your Integer1DSet
has index as the reference of the CS so values of 0,1,2,3 will
get converted to the log of those values when index is mapped
to a scale.  I would think you would want it the other way.

Another question is are you removing the non-log scalar maps
when you switch to log displays and vice-versa?

Again, I'm travelling so may not answer until I get back.


Celine Gestas wrote:
Thank you for your answer but there is no change : points are displayed but
not in the log scale, it keeps the default scale. What I changed is :

                       index = RealType.getRealType("index",
                       indexLog = RealType.getRealType("indexLog",
CommonUnit.promiscuous);                            // new RealType
                       referenceIndex = new RealTupleType(index);
                       LogCoordinateSystem logCSindex = new
LogCoordinateSystem(referenceIndex, base);
rangeIndex = new RealTupleType(indexLog, logCSindex, null); // use the new RealType
                       index_set = new Integer1DSet(rangeIndex,
x_vals[0].length, logCSindex, null, null);

2007/3/26, Bill Hibbard <hiding@xxxxxxxxx>:

 Hi Celine,

If someone has an idea ...

        RealTupleType rangeIndex = null;

       // create the index
        if (log.equals("logX") || log.equals("logY")
||log.equals("loglog")) {
index = RealType.getRealType("index", CommonUnit.promiscuous);
            RealTupleType referenceIndex = new RealTupleType(index);
            LogCoordinateSystem logCSindex = new
LogCoordinateSystem(referenceIndex, base);
            rangeIndex = new RealTupleType(index, logCSindex, null);
            index_set = new Integer1DSet(rangeIndex, x_vals[0].length,
logCSindex, null, null);

I think the problem is that the RealTupleTypes referenceIndex and
rangeIndex are both
defined as (index), that is they are both a RealTupleType of the same
single RealType.
This may also explain the very mysterious Exception you reported in your
other recent
message to the list. Try using different RealTypes in the constructors for
and rangeIndex.

Good luck,



Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307

import visad.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import visad.java2d.*;
import java.util.Hashtable;

public class LogDisplay {

    public LogDisplay(double base) 
      throws VisADException, java.rmi.RemoteException {

        // Set up the metadata
          // make a realtype for the values and for log values
          // create a CS that transforms from values to log values
        RealType values = RealType.getRealType("Values");
        RealType logValues = 
            RealType.getRealType("LogValues", CommonUnit.promiscuous);
        RealTupleType reference = new RealTupleType(logValues);
        CoordinateSystem logCS = new LogCoordinateSystem(reference, base);
        RealTupleType range = new RealTupleType(values, logCS, null);

        // Create realtype for domain
        RealType exponent = RealType.getRealType("Exponent");
        FunctionType fType = new FunctionType(exponent, range);
        Integer1DSet domain = new Integer1DSet(exponent, 4);

        // make a field to hold the data
        FlatField field = new FlatField(fType, domain);
        float[][] rangeValues = new float[][] { { 1, 10, 100, 1000 } };

        // Create the display
        final DisplayImpl display = new DisplayImplJ2D("log display");
        final ScalarMap yMap = new ScalarMap(values, Display.YAxis);
        final ScalarMap logMap = new ScalarMap(logValues, Display.YAxis);
        Hashtable logLabels = new Hashtable();
        logLabels.put(new Double(0), "1");
        logLabels.put(new Double(1), "10");
        logLabels.put(new Double(2), "100");
        logLabels.put(new Double(3), "1000");
        logMap.getAxisScale().setTitle("Log Values");
        display.addMap(new ScalarMap(exponent, Display.XAxis));
        DataReference ref = new DataReferenceImpl("ref");

        JFrame frame = new JFrame("Log Display");
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
        JPanel p = new JPanel();
        ButtonGroup b = new ButtonGroup();
        JRadioButton rb = new JRadioButton("Y",true);
        rb.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e) {
              try {
              } catch (Exception ve) { ve.printStackTrace(); }

        rb = new JRadioButton("Log Y");
        rb.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e) {
              try {
              } catch (Exception ve) { ve.printStackTrace(); }
        frame.getContentPane().add(p, BorderLayout.SOUTH);


    public static void main(String[] args) 
        throws Exception {
        double base = 10.0;
        if (args.length > 0) {
          try {
              base = Double.parseDouble(args[0]);
          catch (Exception e) { base = 10.0; }
        LogDisplay lt = new LogDisplay(base);

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