Cartesian Logarithmic Axes

The logarithmic axis is use to chart numerical data. It can be placed on either the x or y axis. As the name suggests, logarithmic interpolation is used to determine where a value lies on the axis.

Here are some example how to create logarithmic axes:

// creates a logarithmic axis with default scale id "y" and default kind "y" 
CartesianLogarithmicAxis axis1 = new CartesianLogarithmicAxis(chart);

// creates a logarithmic axis with scale id "my-axis" and default kind "y" 
CartesianLogarithmicAxis axis2 = new CartesianLogarithmicAxis(chart, "my-axis");

// creates a logarithmic axis with scale id "my-axis" and default kind "y" 
CartesianLogarithmicAxis axis3 = new CartesianLogarithmicAxis(chart, ScaleId.create("my-axis"));

// creates a logarithmic axis with default scale id "y" and custom kind "y" 
CartesianLogarithmicAxis axis4 = new CartesianLogarithmicAxis(chart, AxisKind.Y);

// creates a logarithmic axis with scale id "my-axis" and custom kind "y" 
CartesianLogarithmicAxis axis5 = new CartesianLogarithmicAxis(chart, "my-axis", AxisKind.Y);

// creates a logarithmic axis with scale id "my-axis" and custom kind "y" 
ScaleId myAxis = ScaleId.create("my-axis");
CartesianLogarithmicAxis axis6 = new CartesianLogarithmicAxis(chart, myAxis, AxisKind.Y);

// adds axes to chart configuration
chart.getOptions().setAxes(axis1, ...);

Options

The cartesian logarithmic axis allows to define a number of properties, used to display the data.

// creates a logarithmic axis 
CartesianLogarithmicAxis axis = new CartesianLogarithmicAxis(chart);
// sets and gets the max value
axis.setMax(10000);

double max = axis.getMax();

The following are the attributes that you can set:

Name	Type	Description
alignToPixels	boolean	Align pixel values to device pixels.
backgroundColor	String - IsColor	The background color of scale area.
bounds	Bounds	Determines the scale bounds on axis.
display	boolean - Display	If Display.TRUE, the axis is shown.
max	double	User defined maximum number for the scale, overrides maximum value from data.
min	double	User defined minimum number for the scale, overrides minimum value from data.
offset	boolean	If true, extra space is added to the both edges and the axis is scaled to fit in the chart area.
position	AxisPosition	Position of the axis.
reverse	boolean	Reverses order of tick labels.
singleStacked	boolean	If you might want to stack positive and negative values together.
stack	String	Sets the stack group. Axes at the same position with same stack are stacked.
stacked	boolean	If the axis are stacked.
stackWeight	double	Sets the weight of the scale in stack group. Used to determine the amount of allocated space for the scale within the group.
suggestedMax	double	Adjustment used when calculating the maximum data value.
suggestedMin	double	Adjustment used when calculating the minimum data value.
weight	int	The weight used to sort the axis. Higher weights are further away from the chart area.

Ticks

The logarithmic axis provides the following options for configuring tick marks.

// creates a logarithmic axis 
CartesianLogarithmicAxis axis = new CartesianLogarithmicAxis(chart);
// sets and gets the max value
axis.getTicks().setColor(HtmlColor.RED);

IsColor color = axis.gteTicks().getColor();

The following are the attributes that you can set:

Name	Type	Scriptable	Description
align	ElementAlign	-	The tick alignment along the axis.
autoSkip	boolean	-	If true, automatically calculates how many labels that can be shown and hides labels accordingly. Labels will be rotated up to maxRotation before skipping any. Turn autoSkip off to show all labels no matter what.
autoSkipPadding	int	-	The padding between the ticks on the horizontal axis when autoSkip is enabled.
backdropColor	String - IsColor	Yes	Color of label backdrops.
backdropPadding	Padding	-	The padding of tick backdrop. See padding documentation for more details.
color	String - IsColor	Yes	Color of ticks.
crossAlign	CrossAlign	-	The tick alignment perpendicular to the axis.
display	boolean	-	If true, the tick marks are shown.
font	IsFont	Yes	Font of ticks. See Font.
includeBounds	boolean	-	If true, the defined min and max values should be presented as ticks even if they are not "nice".
labelOffset	int	-	Distance in pixels to offset the label from the centre point of the tick (in the x-direction for the x-axis, and the y-direction for the y-axis). Note: This can cause labels at the edges to be cropped by the edge of the canvas.
maxRotation	int	-	The maximum rotation for tick labels when rotating to condense labels. Note: Rotation doesn't occur until necessary and only applicable to horizontal scales.
minRotation	int	-	The minimum rotation for tick labels.
mirror	boolean	-	The flips tick labels around axis, displaying the labels inside the chart instead of outside. Note: Only applicable to vertical scales.
numberFormat	NumberFormatOptions	Yes	The number format options used by the default label formatter. See INTL number format documentation
padding	int	-	The padding between the tick label and the axis.
sampleSize	int	-	The number of ticks to examine when deciding how many labels will fit. Setting a smaller value will be faster, but may be less accurate when there is large variability in label length.
showLabelBackdrop	boolean	Yes	If true, draw a background behind the tick labels
textStrokeColor	String - IsColor	Yes	The color of the stroke around the text.
textStrokeWidth	int	Yes	Stroke width around the text.
z	int	-	z-index of tick layer. Useful when ticks are drawn on chart area. Values less than or equals to 0 are drawn under data sets, greater than 0 on top.

The further customization of ticks, a callback is provided.

Scriptable

Scriptable options at ticks level accept a callback which is called for each of the underlying data values. See more details in Configuring charts section.

All scriptable options callbacks will get a ScaleContext instance.

// creates a logarithmic axis 
CartesianLogarithmicAxis axis = new CartesianLogarithmicAxis(chart);
// sets the option by a callback 
axis.getTicks().setColor(new ColorCallback<ScaleContext>(){

   @Override
   public IsColor invoke(ScaleContext context){
      // logic
      return color;
   }
});

The following options can be set by a callback:

Name	Callback	Returned types
backdropColor	ColorCallback<ScaleContext>	String - IsColor
color	ColorCallback<ScaleContext>	String - IsColor
font	FontCallback<ScaleContext>	FontItem
numberFormat	NumberFormatCallback	NumberFormatItem
showLabelBackdrop	ShowLabelBackdropCallback	boolean
textStrokeColor	ColorCallback<ScaleContext>	String - IsColor
textStrokeWidth	WidthCallback<ScaleContext>	int

Callback

It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$'). To do this, you need to implement a ticks callback in the axis configuration.

To apply a custom callback, you can set a TickCallback instance to the axis options, as following:

axis.getTicks().setCallback(new TickCallback(){

   /**
    * Changes the tick marks to include information about the data type.
    * 
    * @param axis axis instance where this callback as been defined
    * @param value value of tick
    * @param index index of tick
    * @param values list of all tick values
    * @return the tick to apply or if the callback returns null the associated grid line will be hidden.
    */
   public String onCallback(Axis axis, double value, int index, List<Double> values){
      // add $
      return "$" + value;
   }
         
});

See INTL number format documentation if you want to use a number formatter, provided out-of-the-box.

The callback can return a string (for single line) or a list of strings (for multiple lines).

NoSelectedDatasetTicksCallback callback

Charba provides a common implementation for tick callback to set the decimal digits of ticks in case of all data sets are hidden, to avoid the annoying standard format of doubles.

To apply the callback, you can set an instance to the axis options, as following:

// creates a logarithmic axis 
CartesianLogarithmicAxis axis = new CartesianLogarithmicAxis(chart);
// sets the option by a callback 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback());

The default decimal precision is 2. A custom precision can be set by the constructor of callback, as following:

// creates a logarithmic axis 
CartesianLogarithmicAxis axis = new CartesianLogarithmicAxis(chart);
// sets the option by a callback 
// 3 decimal digits 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback(3));