title: JavaFX 2.x : Logarithmic scale on Y axis
body: <p>As from this very good post here</p>
  
  <p><a href="http://blog.dooapp.com/2013/06/logarithmic-scale-strikes-back-in.html" rel="nofollow noreferrer">Logarithmic scale in Java FX 2</a></p>
  
  <p>I have changed this class to get log scale on Y axis, and it works fine. The only problem I have is that there are very few horizontal grid lines and scale always start ranges from 0 or near zero.</p>
  
  <p>Here is what I get</p>
  
  <p><img src="https://i.stack.imgur.com/ufVZT.png" alt="enter image description here"></p>
  
  <p>I would like to have tick values grid also in the min and max range of my data serie, in this case min = 19,35 max = 20,35; as of now all 10 horizontal grid lines are all plotted outside this range.</p>
  
  <p>How to accomplish this?</p>
  
  <p>Thanks all, here is my log code for Y axis</p>
  
  <pre><code>import java.text.NumberFormat;
  import java.util.ArrayList;
  import java.util.List;
  import javafx.beans.binding.DoubleBinding;
  import javafx.beans.property.DoubleProperty;
  import javafx.beans.property.SimpleDoubleProperty;
  import javafx.scene.chart.ValueAxis;
  
  //http://blog.dooapp.com/logarithmic-scale-strikes-back-in-javafx-20        
  public class LogarithmicAxis extends ValueAxis&lt;Number&gt; {
  
  //Create our LogarithmicAxis class that extends ValueAxis&lt;Number&gt; and define two properties that will represent the log lower and upper bounds of our axis.     
  private final DoubleProperty logUpperBound = new SimpleDoubleProperty();
  private final DoubleProperty logLowerBound = new SimpleDoubleProperty();
  //
  
  //we bind our properties with the default bounds of the value axis. But before, we should verify the given range according to the mathematic logarithmic interval definition.
  public LogarithmicAxis() {
      super(1, 100);
      bindLogBoundsToDefaultBounds();
  }
  
  public LogarithmicAxis(double lowerBound, double upperBound) {
      super(lowerBound, upperBound);
  try {
      validateBounds(lowerBound, upperBound);
      bindLogBoundsToDefaultBounds();
  } catch (IllegalLogarithmicRangeException e) {
      }
  }
  
  /**
   * Bind our logarithmic bounds with the super class bounds, consider the base 10 logarithmic scale.
   */
  private void bindLogBoundsToDefaultBounds() {
      logLowerBound.bind(new DoubleBinding() {
          {
              super.bind(lowerBoundProperty());
          }
  
          @Override
          protected double computeValue() {
              return Math.log10(lowerBoundProperty().get());
          }
      });
      logUpperBound.bind(new DoubleBinding() {
          {
              super.bind(upperBoundProperty());
          }
  
          @Override
          protected double computeValue() {
              return Math.log10(upperBoundProperty().get());
          }
      });
  }
  
  /**
   * Validate the bounds by throwing an exception if the values are not conform to the mathematics log interval:
   * ]0,Double.MAX_VALUE]
   *
   * @param lowerBound
   * @param upperBound
   * @throws IllegalLogarithmicRangeException
   */
  private void validateBounds(double lowerBound, double upperBound) throws IllegalLogarithmicRangeException {
      if (lowerBound &lt; 0 || upperBound &lt; 0 || lowerBound &gt; upperBound) {
          throw new IllegalLogarithmicRangeException(
                  "The logarithmic range should be include to ]0,Double.MAX_VALUE] and the lowerBound should be less than the upperBound");
      }
  }
  
  //Now we have to implement all abstract methods of the ValueAxis class.
  //The first one, calculateMinorTickMarks is used to get the list of minor tick marks position that you want to display on the axis. You could find my definition below. It's based on the number of minor tick and the logarithmic formula.
  @Override
  protected List&lt;Number&gt; calculateMinorTickMarks() {
      Number[] range = getRange();
      List&lt;Number&gt; minorTickMarksPositions = new ArrayList&lt;&gt;();
      if (range != null) {
  
          Number lowerBound = range[0];
          Number upperBound = range[1];
          double logUpperBound = Math.log10(upperBound.doubleValue());
          double logLowerBound = Math.log10(lowerBound.doubleValue());
  
          int minorTickMarkCount = getMinorTickCount();
  
          for (double i = logLowerBound; i &lt;= logUpperBound; i += 1) {
              for (double j = 0; j &lt;= 10; j += (1. / minorTickMarkCount)) {
                  double value = j * Math.pow(10, i);
                  minorTickMarksPositions.add(value);
              }
          }
      }
      return minorTickMarksPositions;
  }
  
  //Then, the calculateTickValues method is used to calculate a list of all the data values for each tick mark in range, represented by the second parameter. The formula is the same than previously but here we want to display one tick each power of 10.
  @Override
  protected List&lt;Number&gt; calculateTickValues(double length, Object range) {
      List&lt;Number&gt; tickPositions = new ArrayList&lt;Number&gt;();
      if (range != null) {
          Number lowerBound = ((Number[]) range)[0];
          Number upperBound = ((Number[]) range)[1];
          double logLowerBound = Math.log10(lowerBound.doubleValue());
          double logUpperBound = Math.log10(upperBound.doubleValue());
          System.out.println("lower bound is: " + lowerBound.doubleValue());
  
          for (double i = logLowerBound; i &lt;= logUpperBound; i += 1) {
              for (double j = 1; j &lt;= 10; j++) {
                  double value = (j * Math.pow(10, i));
                  tickPositions.add(value);
              }
          }
      }
      return tickPositions;
  }
  
  //The getRange provides the current range of the axis. A basic implementation is to return an array of the lowerBound and upperBound properties defined into the ValueAxis class.
  @Override
  protected Number[] getRange() {
      return new Number[] { lowerBoundProperty().get(), upperBoundProperty().get() };
  }
  
  //The getTickMarkLabel is only used to convert the number value to a string that will be displayed under the tickMark. Here I choose to use a number formatter.
  @Override
  protected String getTickMarkLabel(Number value) {
      NumberFormat formatter = NumberFormat.getInstance();
      formatter.setMaximumIntegerDigits(6);
      formatter.setMinimumIntegerDigits(1);
      return formatter.format(value);
  }
  
  //The method setRange is used to update the range when data are added into the chart. There is two possibilities, the axis is animated or not. The simplest case is to set the lower and upper bound properties directly with the new values.
  @Override    
  protected void setRange(Object range, boolean animate) {
      if (range != null) {
          Number lowerBound = ((Number[]) range)[0];
          Number upperBound = ((Number[]) range)[1];
          try {
              validateBounds(lowerBound.doubleValue(), upperBound.doubleValue());
          } catch (IllegalLogarithmicRangeException e) {
          }
  
          lowerBoundProperty().set(lowerBound.doubleValue());
          upperBoundProperty().set(upperBound.doubleValue());
      }
  }
  
  //We are almost done but we forgot to override 2 important methods that are used to perform the matching between data and the axis (and the reverse).
  @Override
  public Number getValueForDisplay(double displayPosition) {
      double delta = logUpperBound.get() - logLowerBound.get();
      if (getSide().isVertical()) {
          return Math.pow(10, (((displayPosition - getHeight()) / -getHeight()) * delta) + logLowerBound.get());
      } else {
          return Math.pow(10, (((displayPosition / getWidth()) * delta) + logLowerBound.get()));
      }
  }
  
  @Override
  public double getDisplayPosition(Number value) {
      double delta = logUpperBound.get() - logLowerBound.get();
      double deltaV = Math.log10(value.doubleValue()) - logLowerBound.get();
      if (getSide().isVertical()) {
          return (1. - ((deltaV) / delta)) * getHeight();
      } else {
          return ((deltaV) / delta) * getWidth();
      }
  }
  
  /**
   * Exception to be thrown when a bound value isn't supported by the logarithmic axis&lt;br&gt;
   *
   *
   * @author Kevin Senechal mailto: kevin.senechal@dooapp.com
   *
   */
  public class IllegalLogarithmicRangeException extends Exception {
  /**
   * @param string
   */
      public IllegalLogarithmicRangeException(String message) {
          super(message);
      }
  }
  }
  </code></pre>