org.rrd4j.data

Class LinearInterpolator

java.lang.Object

org.rrd4j.data.Plottable

org.rrd4j.data.LinearInterpolator

public class LinearInterpolator
extends Plottable

Class used to interpolate datasource values from the collection of (timestamp, values) points. This class is suitable for linear interpolation only.

Interpolation algorithm returns different values based on the value passed to setInterpolationMethod(). If not set, interpolation method defaults to standard linear interpolation (INTERPOLATE_LINEAR). Interpolation method handles NaN datasource values gracefully.

Field Summary

Fields

Modifier and Type	Field and Description
static int	INTERPOLATE_LEFT constant used to specify LEFT interpolation.
static int	INTERPOLATE_LINEAR constant used to specify LINEAR interpolation (default interpolation method).
static int	INTERPOLATE_REGRESSION constant used to specify LINEAR REGRESSION as interpolation method.
static int	INTERPOLATE_RIGHT constant used to specify RIGHT interpolation.

Constructor Summary

Constructors

Constructor and Description
LinearInterpolator(Calendar[] dates, double[] values) Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
LinearInterpolator(Date[] dates, double[] values) Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
LinearInterpolator(long[] timestamps, double[] values) Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.

Method Summary

Methods

Modifier and Type	Method and Description
double	getValue(long timestamp) Retrieves datapoint value based on a given timestamp.
void	setInterpolationMethod(int interpolationMethod) Sets interpolation method to be used.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

INTERPOLATE_LEFT

public static final int INTERPOLATE_LEFT

constant used to specify LEFT interpolation. See setInterpolationMethod() for explanation.

See Also:

Constant Field Values

INTERPOLATE_RIGHT

public static final int INTERPOLATE_RIGHT

constant used to specify RIGHT interpolation. See setInterpolationMethod() for explanation.

See Also:

Constant Field Values

INTERPOLATE_LINEAR

public static final int INTERPOLATE_LINEAR

constant used to specify LINEAR interpolation (default interpolation method). See setInterpolationMethod() for explanation.

See Also:

Constant Field Values

INTERPOLATE_REGRESSION

public static final int INTERPOLATE_REGRESSION

constant used to specify LINEAR REGRESSION as interpolation method. See setInterpolationMethod() for explanation.

See Also:

Constant Field Values

Constructor Detail

LinearInterpolator

public LinearInterpolator(long[] timestamps,
                  double[] values)

Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.

Parameters:

timestamps - timestamps in seconds

values - corresponding datasource values

Throws:

IllegalArgumentException - Thrown if supplied arrays do not contain at least two values, or if timestamps are not ordered, or array lengths are not equal.

LinearInterpolator

public LinearInterpolator(Date[] dates,
                  double[] values)

Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.

Parameters:

dates - Array of Date objects

values - corresponding datasource values

Throws:

IllegalArgumentException - Thrown if supplied arrays do not contain at least two values, or if timestamps are not ordered, or array lengths are not equal.

LinearInterpolator

public LinearInterpolator(Calendar[] dates,
                  double[] values)

Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.

Parameters:

dates - array of GregorianCalendar objects

values - corresponding datasource values

Throws:

IllegalArgumentException - Thrown if supplied arrays do not contain at least two values, or if timestamps are not ordered, or array lengths are not equal.

Method Detail

setInterpolationMethod

public void setInterpolationMethod(int interpolationMethod)

Sets interpolation method to be used. Suppose that we have two timestamp/value pairs:
(t, 100) and (t + 100, 300). Here are the results interpolator returns for t + 50 seconds, for various interpolationMethods:

• INTERPOLATE_LEFT: 100
• INTERPOLATE_RIGHT: 300
• INTERPOLATE_LINEAR: 200

If not set, interpolation method defaults to INTERPOLATE_LINEAR.

The fourth available interpolation method is INTERPOLATE_REGRESSION. This method uses simple linear regression to interpolate supplied data with a simple straight line which does not necessarily pass through all data points. The slope of the best-fit line will be chosen so that the total square distance of real data points from from the best-fit line is at minimum.

The full explanation of this interpolation method can be found here.

Parameters:

interpolationMethod - Should be INTERPOLATE_LEFT, INTERPOLATE_RIGHT, INTERPOLATE_LINEAR or INTERPOLATE_REGRESSION. Any other value will be interpreted as INTERPOLATE_LINEAR (default).

getValue

public double getValue(long timestamp)

Retrieves datapoint value based on a given timestamp. Use this method if you only have one series of data in this class. Method overridden from the base class. This method will be called by the framework. Call this method only if you need interpolated values in your code.

Overrides:

getValue in class Plottable

Parameters:

timestamp - Timestamp in seconds for the datapoint.

Returns:

Double value of the datapoint.