A general purpose distance and area calculator, capable of performing ellipsoid based calculations. More...

#include <qgsdistancearea.h>

Public Member Functions
	QgsDistanceArea ()
	Constructor. More...

QgsUnitTypes::AreaUnit	areaUnits () const
	Returns the units of area for areal calculations made by this object. More...

double	bearing (const QgsPointXY &p1, const QgsPointXY &p2) const
	Computes the bearing (in radians) between two points. More...

QgsPointXY	computeSpheroidProject (const QgsPointXY &p1, double distance=1, double azimuth=M_PI_2) const
	Given a location, an azimuth and a distance, computes the location of the projected point. More...

double	convertAreaMeasurement (double area, QgsUnitTypes::AreaUnit toUnits) const
	Takes an area measurement calculated by this QgsDistanceArea object and converts it to a different areal unit. More...

double	convertLengthMeasurement (double length, QgsUnitTypes::DistanceUnit toUnits) const
	Takes a length measurement calculated by this QgsDistanceArea object and converts it to a different distance unit. More...

QString	ellipsoid () const
	Returns ellipsoid's acronym. More...

double	ellipsoidInverseFlattening () const
	Returns ellipsoid's inverse flattening. More...

double	ellipsoidSemiMajor () const
	Returns the ellipsoid's semi major axis. More...

double	ellipsoidSemiMinor () const
	Returns ellipsoid's semi minor axis. More...

QgsUnitTypes::DistanceUnit	lengthUnits () const
	Returns the units of distance for length calculations made by this object. More...

double	measureArea (const QgsGeometry &geometry) const
	Measures the area of a geometry. More...

double	measureLength (const QgsGeometry &geometry) const
	Measures the length of a geometry. More...

double	measureLine (const QVector< QgsPointXY > &points) const
	Measures the length of a line with multiple segments. More...

double	measureLine (const QgsPointXY &p1, const QgsPointXY &p2) const
	Measures the distance between two points. More...

double	measureLineProjected (const QgsPointXY &p1, double distance=1, double azimuth=M_PI_2, QgsPointXY *projectedPoint=nullptr) const
	Calculates the distance from one point with distance in meters and azimuth (direction) When the sourceCrs() is geographic, computeSpheroidProject() will be called otherwise QgsPoint.project() will be called after QgsUnitTypes::fromUnitToUnitFactor() has been applied to the distance. More...

double	measurePerimeter (const QgsGeometry &geometry) const
	Measures the perimeter of a polygon geometry. More...

double	measurePolygon (const QVector< QgsPointXY > &points) const
	Measures the area of the polygon described by a set of points. More...

bool	setEllipsoid (const QString &ellipsoid)
	Sets the ellipsoid by its acronym. More...

bool	setEllipsoid (double semiMajor, double semiMinor)
	Sets ellipsoid by supplied radii. More...

void	setSourceCrs (const QgsCoordinateReferenceSystem &crs, const QgsCoordinateTransformContext &context)
	Sets source spatial reference system crs. More...

QgsCoordinateReferenceSystem	sourceCrs () const
	Returns the source spatial reference system. More...

bool	willUseEllipsoid () const
	Returns whether calculations will use the ellipsoid. More...

Static Public Member Functions
static QString	formatArea (double area, int decimals, QgsUnitTypes::AreaUnit unit, bool keepBaseUnit=false)
	Returns an area formatted as a friendly string. More...

static QString	formatDistance (double distance, int decimals, QgsUnitTypes::DistanceUnit unit, bool keepBaseUnit=false)
	Returns an distance formatted as a friendly string. More...

Detailed Description

A general purpose distance and area calculator, capable of performing ellipsoid based calculations.

Measurements can either be performed on existing QgsGeometry objects, or using lists of points.

If a valid ellipsoid() has been set for the QgsDistanceArea, all calculations will be performed using ellipsoidal algorithms (e.g. using Vincenty's formulas). If no ellipsoid has been set, all calculations will be performed using Cartesian formulas only. The behavior can be determined by calling willUseEllipsoid().

In order to perform accurate calculations, the source coordinate reference system of all measured geometries must first be specified using setSourceCrs().

Usually, the measurements returned by QgsDistanceArea are in meters. If no valid ellipsoid is set, then the units may not be meters. The units can be retrieved by calling lengthUnits() and areaUnits().

Definition at line 49 of file qgsdistancearea.h.

Constructor & Destructor Documentation

QgsDistanceArea::QgsDistanceArea ( )

Constructor.

Definition at line 41 of file qgsdistancearea.cpp.

Member Function Documentation

QgsUnitTypes::AreaUnit QgsDistanceArea::areaUnits ( ) const

Returns the units of area for areal calculations made by this object.

See also: lengthUnits()

Since: QGIS 2.14

Definition at line 462 of file qgsdistancearea.cpp.

double QgsDistanceArea::bearing	(	const QgsPointXY &	p1,
		const QgsPointXY &	p2
	)		const

Computes the bearing (in radians) between two points.

Definition at line 510 of file qgsdistancearea.cpp.

QgsPointXY QgsDistanceArea::computeSpheroidProject	(	const QgsPointXY &	p1,
		double	distance = `1`,
		double	azimuth = `M_PI_2`
	)		const

Given a location, an azimuth and a distance, computes the location of the projected point.

Based on Vincenty's formula for the geodetic direct problem as described in "Geocentric Datum of Australia Technical Manual", Chapter 4.

Parameters

p1	- location of first geographic (latitude/longitude) point as degrees.
distance	- distance in meters.
azimuth	- azimuth in radians, clockwise from North

Returns: p2 - location of projected point as longitude/latitude.

Note

code (and documentation) taken from rttopo project https://git.osgeo.org/gogs/rttopo/librttopo

spheroid_project.spheroid_project(...)
Valid bounds checking for degrees (latitude=+- 85.05115) is based values used for -> 'WGS84 Web Mercator (Auxiliary Sphere)' calculations –> latitudes outside these bounds cause the calculations to become unstable and can return invalid results

Since: QGIS 3.0

Definition at line 393 of file qgsdistancearea.cpp.

double QgsDistanceArea::convertAreaMeasurement	(	double	area,
		QgsUnitTypes::AreaUnit	toUnits
	)		const

Takes an area measurement calculated by this QgsDistanceArea object and converts it to a different areal unit.

Parameters

area	area value calculated by this class to convert. It is assumed that the area was calculated by this class, ie that its unit of area is equal to areaUnits().
toUnits	area unit to convert measurement to

Returns: converted area

See also: convertLengthMeasurement()

Since: QGIS 2.14

Definition at line 824 of file qgsdistancearea.cpp.

double QgsDistanceArea::convertLengthMeasurement	(	double	length,
		QgsUnitTypes::DistanceUnit	toUnits
	)		const

Takes a length measurement calculated by this QgsDistanceArea object and converts it to a different distance unit.

Parameters

length	length value calculated by this class to convert. It is assumed that the length was calculated by this class, ie that its unit of length is equal to lengthUnits().
toUnits	distance unit to convert measurement to

Returns: converted distance

See also: convertAreaMeasurement()

Since: QGIS 2.14

Definition at line 810 of file qgsdistancearea.cpp.

QString QgsDistanceArea::ellipsoid ( ) const

inline

Returns ellipsoid's acronym.

Calculations will only use the ellipsoid if a valid ellipsoid has been set.

See also: setEllipsoid(); willUseEllipsoid()

Definition at line 102 of file qgsdistancearea.h.

double QgsDistanceArea::ellipsoidInverseFlattening ( ) const

inline

Returns ellipsoid's inverse flattening.

The inverse flattening is calculated with invf = a/(a-b).

See also: ellipsoid(); ellipsoidSemiMajor(); ellipsoidSemiMinor()

Definition at line 127 of file qgsdistancearea.h.

double QgsDistanceArea::ellipsoidSemiMajor ( ) const

inline

Returns the ellipsoid's semi major axis.

See also: ellipsoid(); ellipsoidSemiMinor(); ellipsoidInverseFlattening()

Definition at line 110 of file qgsdistancearea.h.

double QgsDistanceArea::ellipsoidSemiMinor ( ) const

inline

Returns ellipsoid's semi minor axis.

See also: ellipsoid(); ellipsoidSemiMajor(); ellipsoidInverseFlattening()

Definition at line 118 of file qgsdistancearea.h.

QString QgsDistanceArea::formatArea	(	double	area,
		int	decimals,
		QgsUnitTypes::AreaUnit	unit,
		bool	keepBaseUnit = `false`
	)

static

Returns an area formatted as a friendly string.

Parameters

area	area to format
decimals	number of decimal places to show
unit	unit of area
keepBaseUnit	set to false to allow conversion of large areas to more suitable units, e.g., square meters to square kilometers

Returns: formatted area string

See also: formatDistance()

Since: QGIS 2.14

Definition at line 805 of file qgsdistancearea.cpp.

QString QgsDistanceArea::formatDistance	(	double	distance,
		int	decimals,
		QgsUnitTypes::DistanceUnit	unit,
		bool	keepBaseUnit = `false`
	)

static

Returns an distance formatted as a friendly string.

Parameters

distance	distance to format
decimals	number of decimal places to show
unit	unit of distance
keepBaseUnit	set to false to allow conversion of large distances to more suitable units, e.g., meters to kilometers

Returns: formatted distance string

See also: formatArea()

Since: QGIS 2.16

Definition at line 800 of file qgsdistancearea.cpp.

QgsUnitTypes::DistanceUnit QgsDistanceArea::lengthUnits ( ) const

Returns the units of distance for length calculations made by this object.

See also: areaUnits()

Since: QGIS 2.14

Definition at line 457 of file qgsdistancearea.cpp.

double QgsDistanceArea::measureArea ( const QgsGeometry & geometry ) const

Measures the area of a geometry.

Parameters

geometry geometry to measure

Returns: area of geometry. For geometry collections, non surface geometries will be ignored. The units for the returned area can be retrieved by calling areaUnits().

See also: measureLength(); measurePerimeter(); areaUnits()

Since: QGIS 2.12

Definition at line 180 of file qgsdistancearea.cpp.

double QgsDistanceArea::measureLength ( const QgsGeometry & geometry ) const

Measures the length of a geometry.

Parameters

geometry geometry to measure

Returns: length of geometry. For geometry collections, non curve geometries will be ignored. The units for the returned distance can be retrieved by calling lengthUnits().

See also: lengthUnits(); measureArea(); measurePerimeter()

Since: QGIS 2.12

Definition at line 189 of file qgsdistancearea.cpp.

double QgsDistanceArea::measureLine ( const QVector< QgsPointXY > & points ) const

Measures the length of a line with multiple segments.

Parameters

points list of points in line

Returns: length of line. The units for the returned length can be retrieved by calling lengthUnits().

See also: lengthUnits()

Definition at line 270 of file qgsdistancearea.cpp.

double QgsDistanceArea::measureLine	(	const QgsPointXY &	p1,
		const QgsPointXY &	p2
	)		const

Measures the distance between two points.

Parameters

p1	start of line
p2	end of line

Returns: distance between points. The units for the returned distance can be retrieved by calling lengthUnits().

See also: lengthUnits()

Definition at line 312 of file qgsdistancearea.cpp.

double QgsDistanceArea::measureLineProjected	(	const QgsPointXY &	p1,
		double	distance = `1`,
		double	azimuth = `M_PI_2`,
		QgsPointXY *	projectedPoint = `nullptr`
	)		const

Calculates the distance from one point with distance in meters and azimuth (direction) When the sourceCrs() is geographic, computeSpheroidProject() will be called otherwise QgsPoint.project() will be called after QgsUnitTypes::fromUnitToUnitFactor() has been applied to the distance.

Parameters

p1	start point [can be Cartesian or Geographic]
distance	must be in meters
azimuth	- azimuth in radians, clockwise from North
projectedPoint	calculated projected point

Returns: distance in mapUnits

See also: sourceCrs(); computeSpheroidProject()

Note: The input Point must be in the coordinate reference system being used

Since: QGIS 3.0

Definition at line 347 of file qgsdistancearea.cpp.

double QgsDistanceArea::measurePerimeter ( const QgsGeometry & geometry ) const

Measures the perimeter of a polygon geometry.

Parameters

geometry geometry to measure

Returns: perimeter of geometry. For geometry collections, any non-polygon geometries will be ignored. The units for the returned perimeter can be retrieved by calling lengthUnits().

See also: lengthUnits(); measureArea(); measurePerimeter()

Since: QGIS 2.12

Definition at line 198 of file qgsdistancearea.cpp.

double QgsDistanceArea::measurePolygon ( const QVector< QgsPointXY > & points ) const

Measures the area of the polygon described by a set of points.

Definition at line 483 of file qgsdistancearea.cpp.

bool QgsDistanceArea::setEllipsoid ( const QString & ellipsoid )

Sets the ellipsoid by its acronym.

Known ellipsoid acronyms can be retrieved using QgsEllipsoidUtils::acronyms(). Calculations will only use the ellipsoid if a valid ellipsoid has been set.