org.tinfour.common

Class Thresholds

java.lang.Object

org.tinfour.common.Thresholds

public class Thresholds
extends Object

Provides a standard calculation of threshold values appropriate for use in an incremental TIN implementation based on nominal point spacing. With the exception of vertex tolerance, all thresholds are computed using a small multiplier times the Unit of Least Precision (ULP) computed from the nominal point spacing. The vertex tolerance is a fixed fraction of the nominal point spacing.

Field Summary

Fields

Modifier and Type	Field and Description
static double	DELAUNAY_THRESHOLD_FACTOR Factor for computing the delaunay threshold.
static double	HALF_PLANE_THRESHOLD_FACTOR Factor for computing the half-plane threshold.
static double	IN_CIRCLE_THRESHOLD_FACTOR Factor for computing the in-circle threshold.
static double	PRECISION_THRESHOLD_FACTOR Factor for computing precision threshold.
static double	VERTEX_TOLERANCE_FACTOR_DEFAULT Factor for computing the vertex tolerance.

Constructor Summary

Constructors

Constructor and Description
Thresholds() Constructs thresholds for a nominal point spacing of 1.
Thresholds(double nominalPointSpacing) Constructs threshold values for the specified nominalPointSpacing.

Method Summary

Modifier and Type	Method and Description
double	getDelaunayThreshold() Gets the computed value for evaluating whether a triangle pair is within sufficient tolerance when testing to see if they approximately meet the Delaunay criterion using the in-circle calculation.
double	getHalfPlaneThreshold() Gets a threshold value giving guidelines for the smallest absolute value result that can be trusted in geometric calculations for determining on which side of a point a plane lies (the "half-plane calculation").
double	getInCircleThreshold() Gets the threshold value indicating when an extended-precision calculation must be used for the in-circle determination.
double	getNominalPointSpacing() Gets the nominal point spacing value specified in the constructor.
double	getPrecisionThreshold() Get a threshold value giving guidelines for the smallest absolute value result from a geometric calculations that can be accepted without concern for an excessive loss of precision.
double	getVertexTolerance() Gets a threshold value indicating the distance at which a pair of (x,y) coordinates will be treated as effectively a match for a vertex.
double	getVertexTolerance2() Gets a threshold value indicating the square of the distance at which a pair of (x,y) coordinates will be treated as effectively a match for a vertex.

Methods inherited from class java.lang.Object

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

Field Detail

PRECISION_THRESHOLD_FACTOR

public static final double PRECISION_THRESHOLD_FACTOR

Factor for computing precision threshold.

See Also:

Constant Field Values

HALF_PLANE_THRESHOLD_FACTOR

public static final double HALF_PLANE_THRESHOLD_FACTOR

Factor for computing the half-plane threshold.

See Also:

Constant Field Values

DELAUNAY_THRESHOLD_FACTOR

public static final double DELAUNAY_THRESHOLD_FACTOR

Factor for computing the delaunay threshold.

See Also:

Constant Field Values

IN_CIRCLE_THRESHOLD_FACTOR

public static final double IN_CIRCLE_THRESHOLD_FACTOR

Factor for computing the in-circle threshold.

See Also:

Constant Field Values

VERTEX_TOLERANCE_FACTOR_DEFAULT

public static final double VERTEX_TOLERANCE_FACTOR_DEFAULT

Factor for computing the vertex tolerance.

See Also:

Constant Field Values

Constructor Detail

Thresholds

public Thresholds()

Constructs thresholds for a nominal point spacing of 1.

Thresholds

public Thresholds(double nominalPointSpacing)

Constructs threshold values for the specified nominalPointSpacing. In general, the nominal point spacing is a rough estimate of the mean distance between neighboring points (or vertices). It is used for estimating threshold values for logic used by the IncrementalTin and related classes. A perfect value is not necessary. An estimate within a couple orders of magnitude of the actual value is sufficient.

Parameters:

nominalPointSpacing - a positive, non-zero value

Method Detail

getInCircleThreshold

public double getInCircleThreshold()

Gets the threshold value indicating when an extended-precision calculation must be used for the in-circle determination.

Returns:

a positive value scaled according to the nominal point spacing of the TIN.

getVertexTolerance

public double getVertexTolerance()

Gets a threshold value indicating the distance at which a pair of (x,y) coordinates will be treated as effectively a match for a vertex.

Returns:

a distance in the system of units consistent with the TIN.

getVertexTolerance2

public double getVertexTolerance2()

Gets a threshold value indicating the square of the distance at which a pair of (x,y) coordinates will be treated as effectively a match for a vertex.

Returns:

a distance squared in the system of units consistent with the TIN.

getPrecisionThreshold

public double getPrecisionThreshold()

Get a threshold value giving guidelines for the smallest absolute value result from a geometric calculations that can be accepted without concern for an excessive loss of precision. This value is based on general assumptions about the what constitutes a significant distance given the nominal point spacing of the vertices in the TIN.

Returns:

a small, positive value.

getNominalPointSpacing

public double getNominalPointSpacing()

Gets the nominal point spacing value specified in the constructor. In general, this value is a rough estimate of the mean distance between neighboring points (or vertices).

Returns:

a positive, non-zero value.

getDelaunayThreshold

public double getDelaunayThreshold()

Gets the computed value for evaluating whether a triangle pair is within sufficient tolerance when testing to see if they approximately meet the Delaunay criterion using the in-circle calculation. A positive (non-zero) in-circle value indicates that the pair violates the criterion, but for case where floating-point limitations may result in conflicts, a very small positive value may be acceptable for approximation purposes.

This value is primarily used in test procedures that evaluate the correctness of a TIN constructed by the IncrementalTin class.

Returns:

A positive value much smaller than the nominal point spacing.

getHalfPlaneThreshold

public double getHalfPlaneThreshold()

Gets a threshold value giving guidelines for the smallest absolute value result that can be trusted in geometric calculations for determining on which side of a point a plane lies (the "half-plane calculation"). If the absolute value of the result is smaller than this threshold, extended-precision arithmetic is advised.

Returns:

a positive, non-zero value much smaller than the nominal point spacing.