org.tinfour.interpolation

Class InverseDistanceWeightingInterpolator

java.lang.Object

org.tinfour.interpolation.InverseDistanceWeightingInterpolator

All Implemented Interfaces:

IProcessUsingTin, IInterpolatorOverTin

public class InverseDistanceWeightingInterpolator
extends Object
implements IInterpolatorOverTin

Provides interpolation based on the classic method of inverse distance weighting (IDW).

This class is intended primarily for diagnostic purposes and does not implement a comprehensive set of options in support of the inverse distance-weighting concept.

Constructor Summary

Constructors

Constructor and Description
InverseDistanceWeightingInterpolator(IIncrementalTin tin) Construct an interpolator that operates on the specified TIN.
InverseDistanceWeightingInterpolator(IIncrementalTin tin, double parameter, boolean gaussian) Constructs an interpolator using the specified method.

Method Summary

Modifier and Type	Method and Description
static double	computeAverageSampleSpacing(IIncrementalTin tin) Computes the average sample spacing.
static double	estimateNominalBandwidth(double pointSpacing) Estimates a nominal bandwidth for the Gaussian kernal method of interpolation using the mean length of the distances between samples
String	getMethod() Gets a string describing the interpolation method that can be used for labeling graphs and printouts.
double[]	getSurfaceNormal() Not supported at this time.
double	interpolate(double x, double y, IVertexValuator valuator) Perform inverse distance weighting interpolation.
boolean	isSurfaceNormalSupported() Indicates whether the interpolation class supports the computation of surface normals through the getUnitNormal() method.
void	printDiagnostics(PrintStream ps) Prints diagnostic information about sample sizes and spacing used for interpolation
void	resetForChangeToTin() Used by an application to reset the state data within the interpolator when the content of the TIN may have changed.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

InverseDistanceWeightingInterpolator

public InverseDistanceWeightingInterpolator(IIncrementalTin tin)

Construct an interpolator that operates on the specified TIN. Because the interpolator will access the TIN on a read-only basis, it is possible to construct multiple instances of this class and allow them to operate in parallel threads.

Important Synchronization Issue

To improve performance, the classes in this package frequently maintain state-data about the TIN that can be reused for query to query. They also avoid run-time overhead by not implementing any kind of Java synchronization or or even the concurrent-modification testing provided by the Java collection classes. If an application modifies the TIN, instances of this class will not be aware of the change. In such cases, interpolation methods may fail by either throwing an exception or, worse, returning an incorrect value. The onus is on the calling application to manage the use of this class and to ensure that no modifications are made to the TIN between interpolation operations. If the TIN is modified, the internal state data for this class must be reset using a call to resetForChangeToTIN().

This constructor creates an interpolator based on Shepard's classic weight = 1/(d^2) formula.

Parameters:

tin - a valid instance of an incremental TIN.

InverseDistanceWeightingInterpolator

public InverseDistanceWeightingInterpolator(IIncrementalTin tin,
                                            double parameter,
                                            boolean gaussian)

Constructs an interpolator using the specified method.

Gaussian Kernel: If the Gaussian Kernel option is specified, the parameter will be interpreted as the bandwidth (lambda) for the formula weight = exp(-(1/2)(d/lambda)).

Power formula: If the Gaussian Kernel options is not specified, the parameter will be interpreted as a power for the formula weight = 1/pow(d, power);

Parameters:

tin - a valid TIN

parameter - a parameter specifying either bandwidth (for Gaussian) or power. In both cases the parameter must be greater than zero.

gaussian - true if the Gaussian kernel is to be used; otherwise the non-Gaussian method (power) will be used

Method Detail

resetForChangeToTin

public void resetForChangeToTin()

Used by an application to reset the state data within the interpolator when the content of the TIN may have changed. Resetting the state data unnecessarily may result in a performance reduction when processing a large number of interpolations, but is otherwise harmless.

Specified by:

resetForChangeToTin in interface IProcessUsingTin

interpolate

public double interpolate(double x,
                          double y,
                          IVertexValuator valuator)

Perform inverse distance weighting interpolation.

This interpolation is not defined beyond the convex hull of the TIN and this method will produce a Double.NaN if the specified coordinates are exterior to the TIN.

Specified by:

interpolate in interface IInterpolatorOverTin

Parameters:

x - the x coordinate for the interpolation point

y - the y coordinate for the interpolation point

valuator - a valid valuator for interpreting the z value of each vertex or a null value to use the default.

Returns:

if the interpolation is successful, a valid floating point value; otherwise, a NaN.

isSurfaceNormalSupported

public boolean isSurfaceNormalSupported()

Description copied from interface: IInterpolatorOverTin

Indicates whether the interpolation class supports the computation of surface normals through the getUnitNormal() method.

Specified by:

isSurfaceNormalSupported in interface IInterpolatorOverTin

Returns:

true if the class implements the ability to compute surface normals; otherwise, false.

getSurfaceNormal

public double[] getSurfaceNormal()

Not supported at this time.

Specified by:

getSurfaceNormal in interface IInterpolatorOverTin

Returns:

a zero-sized array.

getMethod

public String getMethod()

Description copied from interface: IInterpolatorOverTin

Gets a string describing the interpolation method that can be used for labeling graphs and printouts. Because this string may be used as a column header in a table, its length should be kept short.

Specified by:

getMethod in interface IInterpolatorOverTin

Returns:

A valid string

estimateNominalBandwidth

public static double estimateNominalBandwidth(double pointSpacing)

Estimates a nominal bandwidth for the Gaussian kernal method of interpolation using the mean length of the distances between samples

Parameters:

pointSpacing - a positive value

Returns:

if successful, a positive value; otherwise, Double.NaN

computeAverageSampleSpacing

public static double computeAverageSampleSpacing(IIncrementalTin tin)

Computes the average sample spacing.

In many cases, the sample spacing of the perimeter edges of a TIN is much larger than the mean sample spacing for the interior. So if the TIN contains more than 3 points, the perimeter edges are not included in the tabulation.

Parameters:

tin - a valid instance

Returns:

if the TIN is valid, a positive value; otherwise Double.NaN

printDiagnostics

public void printDiagnostics(PrintStream ps)

Prints diagnostic information about sample sizes and spacing used for interpolation

Parameters:

ps - a valid instance (such as System.out).

toString

public String toString()

Overrides:

toString in class Object