public class

LinearInterpolator

extends Plottable
java.lang.Object
   ↳ org.rrd4j.data.Plottable
     ↳ org.rrd4j.data.LinearInterpolator

Class Overview

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.

Summary

Constants
int INTERPOLATE_LEFT constant used to specify LEFT interpolation.
int INTERPOLATE_LINEAR constant used to specify LINEAR interpolation (default interpolation method).
int INTERPOLATE_REGRESSION constant used to specify LINEAR REGRESSION as interpolation method.
int INTERPOLATE_RIGHT constant used to specify RIGHT interpolation.
Public Constructors
LinearInterpolator(long[] timestamps, 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(Calendar[] dates, double[] values)
Creates LinearInterpolator from arrays of timestamps and corresponding datasource values.
Public Methods
double getValue(long timestamp)
Method overriden from the base class.
void setInterpolationMethod(int interpolationMethod)
Sets interpolation method to be used.
[Expand]
Inherited Methods
From class org.rrd4j.data.Plottable
From class java.lang.Object

Constants

public static final int INTERPOLATE_LEFT

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

Constant Value: 0 (0x00000000)

public static final int INTERPOLATE_LINEAR

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

Constant Value: 2 (0x00000002)

public static final int INTERPOLATE_REGRESSION

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

Constant Value: 3 (0x00000003)

public static final int INTERPOLATE_RIGHT

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

Constant Value: 1 (0x00000001)

Public Constructors

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.

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.

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.

Public Methods

public double getValue (long timestamp)

Method overriden from the base class. This method will be called by the framework. Call this method only if you need interpolated values in your code.

Parameters
timestamp timestamp in seconds
Returns
  • inteprolated datasource value

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 inteprolation 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).