# geos::geom::PrecisionModel Class Reference

Specifies the precision model of the Coordinate in a Geometry. More...

`#include <geos.h>`

List of all members.

## Public Types

enum | Type { FIXED, FLOATING, FLOATING_SINGLE }
| The types of Precision Model which GEOS supports. More...

## Public Member Functions

| PrecisionModel (void)
| Creates a PrecisionModel with a default precision of FLOATING.
| PrecisionModel (Type nModelType)
| Creates a PrecisionModel specifying an explicit precision model type.
| PrecisionModel (double newScale, double newOffsetX, double newOffsetY)
| Creates a `PrecisionModel` with Fixed precision.
| PrecisionModel (double newScale)
| Creates a PrecisionModel with Fixed precision.
| PrecisionModel (const PrecisionModel &pm)
| ~PrecisionModel (void)
| destructor
double | makePrecise (double val) const
| Rounds a numeric value to the PrecisionModel grid.
void | makePrecise (Coordinate &coord) const
| Rounds the given Coordinate to the PrecisionModel grid.
void | makePrecise (Coordinate *coord) const
bool | isFloating () const
| Tests whether the precision model supports floating point.
int | getMaximumSignificantDigits () const
| Returns the maximum number of significant digits provided by this precision model.
Type | getType () const
| Gets the type of this PrecisionModel.
double | getScale () const
| Returns the multiplying factor used to obtain a precise coordinate.
double | getOffsetX () const
| Returns the x-offset used to obtain a precise coordinate.
double | getOffsetY () const
| Returns the y-offset used to obtain a precise coordinate.
std::string | toString () const
| Sets `internal` to the precise representation of `external`.
int | compareTo (const PrecisionModel *other) const
| Compares this PrecisionModel object with the specified object for order.

## Static Public Attributes

static const double | maximumPreciseValue
| The maximum precise value representable in a double.

## Friends

class | io::Unload

## Detailed Description

Specifies the precision model of the Coordinate in a Geometry.

In other words, specifies the grid of allowable points for all `Geometry`s.

The makePrecise method allows rounding a coordinate to a "precise" value; that is, one whose precision is known exactly.

Coordinates are assumed to be precise in geometries. That is, the coordinates are assumed to be rounded to the precision model given for the geometry. JTS input routines automatically round coordinates to the precision model before creating Geometries. All internal operations assume that coordinates are rounded to the precision model. Constructive methods (such as boolean operations) always round computed coordinates to the appropriate precision model.

Currently three types of precision model are supported:

- FLOATING - represents full double precision floating point. This is the default precision model used in JTS
- FLOATING_SINGLE - represents single precision floating point.
- FIXED - represents a model with a fixed number of decimal places. A Fixed Precision Model is specified by a scale factor. The scale factor specifies the grid which numbers are rounded to. Input coordinates are mapped to fixed coordinates according to the following equations:
  - jtsPt.x = round( (inputPt.x * scale ) / scale
  - jtsPt.y = round( (inputPt.y * scale ) / scale

Coordinates are represented internally as Java double-precision values. Since Java uses the IEEE-394 floating point standard, this provides 53 bits of precision. (Thus the maximum precisely representable integer is 9,007,199,254,740,992).

JTS methods currently do not handle inputs with different precision models.

## Member Enumeration Documentation

enum geos::geom::PrecisionModel::Type

The types of Precision Model which GEOS supports.

Enumerator:

  FIXED | Fixed Precision indicates that coordinates have a fixed number of decimal places. The number of decimal places is determined by the log10 of the scale factor.
  FLOATING | Floating precision corresponds to the standard Java double-precision floating-point representation, which is based on the IEEE-754 standard
  FLOATING_SINGLE | Floating single precision corresponds to the standard Java single-precision floating-point representation, which is based on the IEEE-754 standard

## Constructor & Destructor Documentation

geos::geom::PrecisionModel::PrecisionModel | ( | Type | nModelType ) |

Creates a PrecisionModel specifying an explicit precision model type.

If the model type is FIXED the scale factor will default to 1.

Parameters:

  nModelType | the type of the precision model

geos::geom::PrecisionModel::PrecisionModel | ( | double | newScale,
|  | double | newOffsetX,
|  | double | newOffsetY
| ) |  |

Creates a `PrecisionModel` with Fixed precision.

Fixed-precision coordinates are represented as precise internal coordinates, which are rounded to the grid defined by the scale factor.

Parameters:

  scale | amount by which to multiply a coordinate after subtracting the offset, to obtain a precise coordinate
  offsetX | not used.
  offsetY | not used.

Deprecated:
  offsets are no longer supported, since internal representation is rounded floating point

geos::geom::PrecisionModel::PrecisionModel | ( | double | newScale ) |

Creates a PrecisionModel with Fixed precision.

Fixed-precision coordinates are represented as precise internal coordinates which are rounded to the grid defined by the scale factor.

Parameters:

  newScale | amount by which to multiply a coordinate after subtracting the offset, to obtain a precise coordinate

## Member Function Documentation

int geos::geom::PrecisionModel::compareTo | ( | const PrecisionModel * | other ) | const

Compares this PrecisionModel object with the specified object for order.

A PrecisionModel is greater than another if it provides greater precision. The comparison is based on the value returned by the getMaximumSignificantDigits method. This comparison is not strictly accurate when comparing floating precision models to fixed models; however, it is correct when both models are either floating or fixed.

Parameters:

  other | the PrecisionModel with which this PrecisionModel is being compared

Returns:
  a negative integer, zero, or a positive integer as this PrecisionModel is less than, equal to, or greater than the specified PrecisionModel.

int geos::geom::PrecisionModel::getMaximumSignificantDigits | ( | ) | const

Returns the maximum number of significant digits provided by this precision model.

Intended for use by routines which need to print out precise values.

Returns:
  the maximum number of decimal places provided by this precision model

double geos::geom::PrecisionModel::getOffsetX | ( | ) | const

Returns the x-offset used to obtain a precise coordinate.

Returns:
  the amount by which to subtract the x-coordinate before multiplying by the scale

Deprecated:
  Offsets are no longer used

double geos::geom::PrecisionModel::getOffsetY | ( | ) | const

Returns the y-offset used to obtain a precise coordinate.

Returns:
  the amount by which to subtract the y-coordinate before multiplying by the scale

Deprecated:
  Offsets are no longer used

Type geos::geom::PrecisionModel::getType | ( | ) | const

Gets the type of this PrecisionModel.

Returns:
  the type of this PrecisionModel

bool geos::geom::PrecisionModel::isFloating | ( | ) | const

Tests whether the precision model supports floating point.

Returns:
  `true` if the precision model supports floating point

double geos::geom::PrecisionModel::makePrecise | ( | double | val ) | const

Rounds a numeric value to the PrecisionModel grid.

Asymmetric Arithmetic Rounding is used, to provide uniform rounding behaviour no matter where the number is on the number line.

Note: Java's `Math::rint` uses the "Banker's Rounding" algorithm, which is not suitable for precision operations elsewhere in JTS.

std::string geos::geom::PrecisionModel::toString | ( | ) | const

Sets `internal` to the precise representation of `external`.

Parameters:

  external | the original coordinate
  internal | the coordinate whose values will be changed to the precise representation of `external`

Deprecated:
  use makePrecise instead

## Member Data Documentation

const double geos::geom::PrecisionModel::maximumPreciseValue`[static]`

The maximum precise value representable in a double.

Since IEE754 double-precision numbers allow 53 bits of mantissa, the value is equal to 2^53 - 1. This provides almost 16 decimal digits of precision.

The documentation for this class was generated from the following file:

- PrecisionModel.h