org.locationtech.jts.operation.overlayng

Class PrecisionUtil

java.lang.Object

org.locationtech.jts.operation.overlayng.PrecisionUtil

public class PrecisionUtil
extends Object

Functions for computing precision model scale factors that ensure robust geometry operations. In particular, these can be used to automatically determine appropriate scale factors for operations using limited-precision noding (such as OverlayNG).

WARNING: the inherentScale and robustScale functions can be very slow, due to the method used to determine number of decimal places of a number. These are not recommended for production use.

Author:

Martin Davis

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_ROBUST_DP_DIGITS A number of digits of precision which leaves some computational "headroom" to ensure robust evaluation of certain double-precision floating point geometric operations.

Constructor Summary

Constructors

Constructor and Description
PrecisionUtil()

Method Summary

Modifier and Type	Method and Description
static double	inherentScale(double value) Computes the inherent scale of a number.
static double	inherentScale(Geometry geom) Computes the inherent scale of a geometry.
static double	inherentScale(Geometry a, Geometry b) Computes the inherent scale of two geometries.
static PrecisionModel	robustPM(Geometry a) Determines a precision model to use for robust overlay operations for one geometry.
static PrecisionModel	robustPM(Geometry a, Geometry b) Determines a precision model to use for robust overlay operations.
static double	robustScale(Geometry a) Determines a scale factor which maximizes the digits of precision and is safe to use for overlay operations.
static double	robustScale(Geometry a, Geometry b) Determines a scale factor which maximizes the digits of precision and is safe to use for overlay operations.
static double	safeScale(double value) Computes a safe scale factor for a numeric value.
static double	safeScale(Geometry geom) Computes a safe scale factor for a geometry.
static double	safeScale(Geometry a, Geometry b) Computes a safe scale factor for two geometries.

Methods inherited from class java.lang.Object

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

Field Detail

MAX_ROBUST_DP_DIGITS

public static int MAX_ROBUST_DP_DIGITS

A number of digits of precision which leaves some computational "headroom" to ensure robust evaluation of certain double-precision floating point geometric operations. This value should be less than the maximum decimal precision of double-precision values (16).

Constructor Detail

PrecisionUtil

public PrecisionUtil()

Method Detail

robustPM

public static PrecisionModel robustPM(Geometry a,
                                      Geometry b)

Determines a precision model to use for robust overlay operations. The precision scale factor is chosen to maximize output precision while avoiding round-off issues.

NOTE: this is a heuristic determination, so is not guaranteed to eliminate precision issues.

WARNING: this is very slow.

Parameters:

a - a geometry

b - a geometry

Returns:

a suitable precision model for overlay

safeScale

public static double safeScale(double value)

Computes a safe scale factor for a numeric value. A safe scale factor ensures that rounded number has no more than MAX_ROBUST_DP_DIGITS digits of precision.

Parameters:

value - a numeric value

Returns:

a safe scale factor for the value

safeScale

public static double safeScale(Geometry geom)

Computes a safe scale factor for a geometry. A safe scale factor ensures that the rounded ordinates have no more than MAX_ROBUST_DP_DIGITS digits of precision.

Parameters:

geom - a geometry

Returns:

a safe scale factor for the geometry ordinates

safeScale

public static double safeScale(Geometry a,
                               Geometry b)

Computes a safe scale factor for two geometries. A safe scale factor ensures that the rounded ordinates have no more than MAX_ROBUST_DP_DIGITS digits of precision.

Parameters:

a - a geometry

b - a geometry (which may be null)

Returns:

a safe scale factor for the geometry ordinates

inherentScale

public static double inherentScale(double value)

Computes the inherent scale of a number. The inherent scale is the scale factor for rounding which preserves all digits of precision (significant digits) present in the numeric value. In other words, it is the scale factor which does not change the numeric value when rounded:

   num = round( num, inherentScale(num) )
 

Parameters:

value - a number

Returns:

the inherent scale factor of the number

inherentScale

public static double inherentScale(Geometry geom)

Computes the inherent scale of a geometry. The inherent scale is the scale factor for rounding which preserves all digits of precision (significant digits) present in the geometry ordinates.

This is the maximum inherent scale of all ordinate values in the geometry.

WARNING: this is very slow.

Parameters:

geom - geometry

Returns:

inherent scale of a geometry

inherentScale

public static double inherentScale(Geometry a,
                                   Geometry b)

Computes the inherent scale of two geometries. The inherent scale is the scale factor for rounding which preserves all digits of precision (significant digits) present in the geometry ordinates.

This is the maximum inherent scale of all ordinate values in the geometries.

WARNING: this is very slow.

Parameters:

a - a geometry

b - a geometry

Returns:

the inherent scale factor of the two geometries

robustPM

public static PrecisionModel robustPM(Geometry a)

Determines a precision model to use for robust overlay operations for one geometry. The precision scale factor is chosen to maximize output precision while avoiding round-off issues.

NOTE: this is a heuristic determination, so is not guaranteed to eliminate precision issues.

WARNING: this is very slow.

Parameters:

a - a geometry

Returns:

a suitable precision model for overlay

robustScale

public static double robustScale(Geometry a,
                                 Geometry b)

Determines a scale factor which maximizes the digits of precision and is safe to use for overlay operations. The robust scale is the minimum of the inherent scale and the safe scale factors.

WARNING: this is very slow.

Parameters:

a - a geometry

b - a geometry

Returns:

a scale factor for use in overlay operations

robustScale

public static double robustScale(Geometry a)

Determines a scale factor which maximizes the digits of precision and is safe to use for overlay operations. The robust scale is the minimum of the inherent scale and the safe scale factors.

Parameters:

a - a geometry

Returns:

a scale factor for use in overlay operations