QgsScaleCalculator Class Reference

Calculates scale for a given combination of canvas size, map extent, and monitor dpi. More...

#include <qgsscalecalculator.h>

Public Member Functions
	QgsScaleCalculator (double dpi=0, Qgis::DistanceUnit mapUnits=Qgis::DistanceUnit::Meters)
	Constructor.
double	calculate (const QgsRectangle &mapExtent, double canvasWidth) const
	Calculate the scale denominator.
double	calculateGeographicDistance (const QgsRectangle &mapExtent) const
	Calculate the distance in meters, horizontally across the specified map extent (in geographic coordinates).
double	calculateGeographicDistanceAtLatitude (double latitude, double longitude1, double longitude2) const
	Calculate the distance in meters, horizontally between two longitudes at a specified latitude.
QSizeF	calculateImageSize (const QgsRectangle &mapExtent, double scale) const
	Calculate the image size in pixel (physical) units.
double	dpi () const
	Returns the DPI (dots per inch) used in scale calculations.
Qgis::DistanceUnit	mapUnits () const
	Returns current map units.
Qgis::ScaleCalculationMethod	method () const
	Returns the method to use for map scale calculations.
void	setDpi (double dpi)
	Sets the dpi (dots per inch) for the output resolution, to be used in scale calculations.
void	setMapUnits (Qgis::DistanceUnit mapUnits)
	Set the map units.
void	setMethod (Qgis::ScaleCalculationMethod method)
	Sets the method to use for map scale calculations.

Detailed Description

Calculates scale for a given combination of canvas size, map extent, and monitor dpi.

The calculation defaults to using the scale calculated horizontally across the center of the map, however this may be changed by calling setMethod().

Definition at line 37 of file qgsscalecalculator.h.

Constructor & Destructor Documentation

QgsScaleCalculator()

QgsScaleCalculator::QgsScaleCalculator	(	double	dpi = 0,
		Qgis::DistanceUnit	mapUnits = Qgis::DistanceUnit::Meters
	)

Constructor.

Parameters

dpi	Monitor resolution in dots per inch
mapUnits	Units of the data on the map

Definition at line 26 of file qgsscalecalculator.cpp.

Member Function Documentation

calculate()

double QgsScaleCalculator::calculate	(	const QgsRectangle &	mapExtent,
		double	canvasWidth
	)		const

Calculate the scale denominator.

Parameters

mapExtent	QgsRectangle containing the current map extent. Units are specified by mapUnits().
canvasWidth	Width of the map canvas in pixel (physical) units

Returns

scale denominator of current map view, e.g. 1000.0 for a 1:1000 map.

Definition at line 57 of file qgsscalecalculator.cpp.

calculateGeographicDistance()

double QgsScaleCalculator::calculateGeographicDistance

(

const QgsRectangle &

mapExtent

)

const

Calculate the distance in meters, horizontally across the specified map extent (in geographic coordinates).

Used to calculate scale for map views with geographic (decimal degree) data.

This method respects the scale method().

Parameters

mapExtent

the map extent, in geographic (degrees) coordinates

Returns

distance in meters across the map extent

Definition at line 168 of file qgsscalecalculator.cpp.

calculateGeographicDistanceAtLatitude()

double QgsScaleCalculator::calculateGeographicDistanceAtLatitude	(	double	latitude,
		double	longitude1,
		double	longitude2
	)		const

Calculate the distance in meters, horizontally between two longitudes at a specified latitude.

Used to calculate scale for map views with geographic (decimal degree) data.

Parameters

latitude	latitude (in degrees) to calculate distance at
longitude1	first longitude (left side of map, or x-minimum) to calculate distance between
longitude2	second longitude (right side of map, or x-maximum) to calculate distance between

Returns

distance in meters between the two longitudes

Since

QGIS 3.44

Definition at line 203 of file qgsscalecalculator.cpp.

calculateImageSize()

QSizeF QgsScaleCalculator::calculateImageSize	(	const QgsRectangle &	mapExtent,
		double	scale
	)		const

Calculate the image size in pixel (physical) units.

Parameters

mapExtent	QgsRectangle containing the current map extent. Units are specified by mapUnits()
scale	Scale denominator, e.g. 1000.0 for a 1:1000 map

Returns

image size

Since

QGIS 3.24

Definition at line 74 of file qgsscalecalculator.cpp.

dpi()

double QgsScaleCalculator::dpi

(

)

const

Returns the DPI (dots per inch) used in scale calculations.

See also

setDpi()

Definition at line 40 of file qgsscalecalculator.cpp.

mapUnits()

Qgis::DistanceUnit QgsScaleCalculator::mapUnits

(

)

const

Returns current map units.

See also

setMapUnits()

Definition at line 51 of file qgsscalecalculator.cpp.

method()

Qgis::ScaleCalculationMethod QgsScaleCalculator::method ( ) const

inline

Returns the method to use for map scale calculations.

See also

setMethod()

Since

QGIS 3.44

Definition at line 56 of file qgsscalecalculator.h.

setDpi()

void QgsScaleCalculator::setDpi

(

double

dpi

)

Sets the dpi (dots per inch) for the output resolution, to be used in scale calculations.

See also

dpi()

Definition at line 36 of file qgsscalecalculator.cpp.

setMapUnits()

void QgsScaleCalculator::setMapUnits

(

Qgis::DistanceUnit

mapUnits

)

Set the map units.

See also

mapUnits()

Definition at line 45 of file qgsscalecalculator.cpp.

setMethod()

void QgsScaleCalculator::setMethod

(

Qgis::ScaleCalculationMethod

method

)

Sets the method to use for map scale calculations.

See also

method()

Since

QGIS 3.44

Definition at line 31 of file qgsscalecalculator.cpp.

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

• /build/qgis-3.43.0+git20250408+c67cf405802+99sid/src/core/qgsscalecalculator.h
• /build/qgis-3.43.0+git20250408+c67cf405802+99sid/src/core/qgsscalecalculator.cpp