QGIS API Documentation 3.33.0-Master (bf22a165b3)
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QgsCircle Class Reference

Circle geometry type. More...

`#include <qgscircle.h>`

Inheritance diagram for QgsCircle: [legend]

## Public Member Functions

QgsCircle ()

QgsCircle (const QgsPoint &center, double radius, double azimuth=0)
Constructs a circle by defining all the members.

double area () const override
The area of the ellipse.

QDomElement asGml2 (QDomDocument &doc, int precision=17, const QString &ns="gml", QgsAbstractGeometry::AxisOrder axisOrder=QgsAbstractGeometry::AxisOrder::XY) const
Returns a GML2 representation of the geometry.

QDomElement asGml3 (QDomDocument &doc, int precision=17, const QString &ns="gml", QgsAbstractGeometry::AxisOrder axisOrder=QgsAbstractGeometry::AxisOrder::XY) const
Returns a GML3 representation of the geometry.

QgsRectangle boundingBox () const override
Returns the minimal bounding box for the ellipse.

bool contains (const QgsPoint &point, double epsilon=1E-8) const
Returns `true` if the circle contains the point.

int innerTangents (const QgsCircle &other, QgsPointXY &line1P1, QgsPointXY &line1P2, QgsPointXY &line2P1, QgsPointXY &line2P2) const
Calculates the inner tangent points between this circle and an other circle.

int intersections (const QgsCircle &other, QgsPoint &intersection1, QgsPoint &intersection2, bool useZ=false) const
Calculates the intersections points between this circle and an other circle.

The four quadrants of the ellipse.

int outerTangents (const QgsCircle &other, QgsPointXY &line1P1, QgsPointXY &line1P2, QgsPointXY &line2P1, QgsPointXY &line2P2) const
Calculates the outer tangent points between this circle and an other circle.

double perimeter () const override
The circumference of the ellipse using first approximation of Ramanujan.

Returns the radius of the circle.

Sets the radius of the circle.

void setSemiMajorAxis (double semiMajorAxis) override
Inherited method.

void setSemiMinorAxis (double semiMinorAxis) override
Inherited method.

bool tangentToPoint (const QgsPointXY &p, QgsPointXY &pt1, QgsPointXY &pt2) const
Calculates the tangent points between this circle and the point p.

QgsCircularStringtoCircularString (bool oriented=false) const
Returns a circular string from the circle.

QString toString (int pointPrecision=17, int radiusPrecision=17, int azimuthPrecision=2) const override
returns a string representation of the ellipse. Public Member Functions inherited from QgsEllipse
QgsEllipse ()=default
Constructor for QgsEllipse.

QgsEllipse (const QgsPoint &center, double semiMajorAxis, double semiMinorAxis, double azimuth=90)
Constructs an ellipse by defining all the members.

virtual ~QgsEllipse ()=default

double azimuth () const
Returns the azimuth.

QgsPoint center () const
Returns the center point.

virtual double eccentricity () const
The eccentricity of the ellipse.

virtual QVector< QgsPointfoci () const
Two foci of the ellipse.

virtual double focusDistance () const
The distance between the center and each foci.

virtual bool isEmpty () const
An ellipse is empty if axes are equal to 0.

virtual bool operator!= (const QgsEllipse &elp) const

virtual bool operator== (const QgsEllipse &elp) const

virtual QgsPolygonorientedBoundingBox () const
Returns the oriented minimal bounding box for the ellipse.

virtual QgsPointSequence points (unsigned int segments=36) const
Returns a list of points with segmentation from segments.

The four quadrants of the ellipse.

QgsPointrcenter ()
Returns a reference to the center point of this ellipse.

double semiMajorAxis () const
Returns the semi-major axis.

double semiMinorAxis () const
Returns the semi-minor axis.

void setAzimuth (double azimuth)
Sets the azimuth (orientation).

void setCenter (const QgsPoint &center)
Sets the center point.

virtual QgsLineStringtoLineString (unsigned int segments=36) const
Returns a segmented linestring.

virtual QgsPolygontoPolygon (unsigned int segments=36) const
Returns a segmented polygon.

## Static Public Member Functions

static QgsCircle from2Points (const QgsPoint &pt1, const QgsPoint &pt2)
Constructs a circle by 2 points on the circle.

static QgsCircle from3Points (const QgsPoint &pt1, const QgsPoint &pt2, const QgsPoint &pt3, double epsilon=1E-8)
Constructs a circle by 3 points on the circle.

static QgsCircle from3Tangents (const QgsPoint &pt1_tg1, const QgsPoint &pt2_tg1, const QgsPoint &pt1_tg2, const QgsPoint &pt2_tg2, const QgsPoint &pt1_tg3, const QgsPoint &pt2_tg3, double epsilon=1E-8, const QgsPoint &pos=QgsPoint())
Constructs a circle by 3 tangents on the circle (aka inscribed circle of a triangle).

static QVector< QgsCirclefrom3TangentsMulti (const QgsPoint &pt1_tg1, const QgsPoint &pt2_tg1, const QgsPoint &pt1_tg2, const QgsPoint &pt2_tg2, const QgsPoint &pt1_tg3, const QgsPoint &pt2_tg3, double epsilon=1E-8, const QgsPoint &pos=QgsPoint())
Returns an array of circle constructed by 3 tangents on the circle (aka inscribed circle of a triangle).

static QgsCircle fromCenterDiameter (const QgsPoint &center, double diameter, double azimuth=0)
Constructs a circle by a center point and a diameter.

static QgsCircle fromCenterPoint (const QgsPoint &center, const QgsPoint &pt1)
Constructs a circle by a center point and another point.

static QgsCircle fromExtent (const QgsPoint &pt1, const QgsPoint &pt2)
Constructs a circle by an extent (aka bounding box / QgsRectangle).

static QgsCircle minimalCircleFrom3Points (const QgsPoint &pt1, const QgsPoint &pt2, const QgsPoint &pt3, double epsilon=1E-8)
Constructs the smallest circle from 3 points. Static Public Member Functions inherited from QgsEllipse
static QgsEllipse fromCenter2Points (const QgsPoint &ptc, const QgsPoint &pt1, const QgsPoint &pt2)
Constructs an ellipse by a central point and two other points.

static QgsEllipse fromCenterPoint (const QgsPoint &ptc, const QgsPoint &pt1)
Constructs an ellipse by a center point and a another point.

static QgsEllipse fromExtent (const QgsPoint &pt1, const QgsPoint &pt2)
Constructs an ellipse by an extent (aka bounding box / QgsRectangle).

static QgsEllipse fromFoci (const QgsPoint &pt1, const QgsPoint &pt2, const QgsPoint &pt3)
Constructs an ellipse by foci (pt1 and pt2) and a point pt3. Protected Attributes inherited from QgsEllipse
double mAzimuth = 90.0

QgsPoint mCenter

double mSemiMajorAxis = 0.0

double mSemiMinorAxis = 0.0

## Detailed Description

Circle geometry type.

A circle is defined by a center point with a radius and an azimuth. The azimuth is the north angle to the semi-major axis, in degrees. By default, the semi-major axis is oriented to the north (0 degrees).

Since
QGIS 3.0

Definition at line 43 of file qgscircle.h.

## ◆ QgsCircle() [1/2]

 QgsCircle::QgsCircle ( )

Definition at line 26 of file qgscircle.cpp.

## ◆ QgsCircle() [2/2]

 QgsCircle::QgsCircle ( const QgsPoint & center, double radius, double azimuth = `0` )

Constructs a circle by defining all the members.

Parameters
 center The center of the circle. radius The radius of the circle. azimuth Angle in degrees started from the North to the first quadrant.

Definition at line 32 of file qgscircle.cpp.

## ◆ area()

 double QgsCircle::area ( ) const
overridevirtual

The area of the ellipse.

Reimplemented from QgsEllipse.

Definition at line 397 of file qgscircle.cpp.

## ◆ asGml2()

 QDomElement QgsCircle::asGml2 ( QDomDocument & doc, int precision = `17`, const QString & ns = `"gml"`, QgsAbstractGeometry::AxisOrder axisOrder = `QgsAbstractGeometry::AxisOrder::XY` ) const

Returns a GML2 representation of the geometry.

Since GML2 does not supports curve, it will be converted to a LineString.

Parameters
 doc DOM document precision number of decimal places for coordinates ns XML namespace axisOrder Axis order for generated GML
asGml3()

Definition at line 478 of file qgscircle.cpp.

## ◆ asGml3()

 QDomElement QgsCircle::asGml3 ( QDomDocument & doc, int precision = `17`, const QString & ns = `"gml"`, QgsAbstractGeometry::AxisOrder axisOrder = `QgsAbstractGeometry::AxisOrder::XY` ) const

Returns a GML3 representation of the geometry.

From the GML3 description: A Circle is an arc whose ends coincide to form a simple closed loop. The three control points shall be distinct non-co-linear points for the circle to be unambiguously defined. The arc is simply extended past the third control point until the first control point is encountered.

Coordinates are taken from quadrant North, East and South.

Parameters
 doc DOM document precision number of decimal places for coordinates ns XML namespace axisOrder Axis order for generated GML
asGml2()

Definition at line 486 of file qgscircle.cpp.

## ◆ boundingBox()

 QgsRectangle QgsCircle::boundingBox ( ) const
overridevirtual

Returns the minimal bounding box for the ellipse.

Reimplemented from QgsEllipse.

Definition at line 458 of file qgscircle.cpp.

## ◆ contains()

 bool QgsCircle::contains ( const QgsPoint & point, double epsilon = `1E-8` ) const

Returns `true` if the circle contains the point.

Definition at line 453 of file qgscircle.cpp.

## ◆ from2Points()

 QgsCircle QgsCircle::from2Points ( const QgsPoint & pt1, const QgsPoint & pt2 )
static

Constructs a circle by 2 points on the circle.

The center point can have m value which is the result from the midpoint operation between pt1 and pt2. Z dimension is also supported and is retrieved from the first 3D point amongst pt1 and pt2. The radius is calculated from the 2D distance between pt1 and pt2. The azimuth is the angle between pt1 and pt2.

Parameters
 pt1 First point. pt2 Second point.

Definition at line 38 of file qgscircle.cpp.

## ◆ from3Points()

 QgsCircle QgsCircle::from3Points ( const QgsPoint & pt1, const QgsPoint & pt2, const QgsPoint & pt3, double epsilon = `1E-8` )
static

Constructs a circle by 3 points on the circle.

M value is dropped for the center point. Z dimension is supported and is retrieved from the first 3D point amongst pt1, pt2 and pt3. The azimuth always takes the default value. If the points are colinear an empty circle is returned.

Parameters
 pt1 First point. pt2 Second point. pt3 Third point. epsilon Value used to compare point.

Definition at line 84 of file qgscircle.cpp.

## ◆ from3Tangents()

 QgsCircle QgsCircle::from3Tangents ( const QgsPoint & pt1_tg1, const QgsPoint & pt2_tg1, const QgsPoint & pt1_tg2, const QgsPoint & pt2_tg2, const QgsPoint & pt1_tg3, const QgsPoint & pt2_tg3, double epsilon = `1E-8`, const QgsPoint & pos = `QgsPoint()` )
static

Constructs a circle by 3 tangents on the circle (aka inscribed circle of a triangle).

Z and m values are dropped for the center point. The azimuth always takes the default value.

Parameters
 pt1_tg1 First point of the first tangent. pt2_tg1 Second point of the first tangent. pt1_tg2 First point of the second tangent. pt2_tg2 Second point of the second tangent. pt1_tg3 First point of the third tangent. pt2_tg3 Second point of the third tangent. epsilon Value used to compare point. pos Point to determine which circle use in case of multi return. If the solution is not unique and pos is an empty point, an empty circle is returned. – This case happens only when two tangets are parallels. (since QGIS 3.18)
from3TangentsMulti()

### Example

# [(0 0), (5 0)] and [(5 5), (10 5)] are parallels
QgsCircle.from3Tangents(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5))
# <QgsCircle: Empty>
QgsCircle.from3Tangents(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5), pos=QgsPoint(2, 0))
# <QgsCircle: Circle (Center: Point (1.46446609406726203 2.49999999999999911), Radius: 2.5, Azimuth: 0)>
QgsCircle.from3Tangents(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5), pos=QgsPoint(3, 0))
# <QgsCircle: Circle (Center: Point (8.53553390593273775 2.5), Radius: 2.5, Azimuth: 0)>
static QgsCircle from3Tangents(const QgsPoint &pt1_tg1, const QgsPoint &pt2_tg1, const QgsPoint &pt1_tg2, const QgsPoint &pt2_tg2, const QgsPoint &pt1_tg3, const QgsPoint &pt2_tg3, double epsilon=1E-8, const QgsPoint &pos=QgsPoint())
Constructs a circle by 3 tangents on the circle (aka inscribed circle of a triangle).
Point geometry type, with support for z-dimension and m-values.
Definition qgspoint.h:49

Definition at line 318 of file qgscircle.cpp.

## ◆ from3TangentsMulti()

 QVector< QgsCircle > QgsCircle::from3TangentsMulti ( const QgsPoint & pt1_tg1, const QgsPoint & pt2_tg1, const QgsPoint & pt1_tg2, const QgsPoint & pt2_tg2, const QgsPoint & pt1_tg3, const QgsPoint & pt2_tg3, double epsilon = `1E-8`, const QgsPoint & pos = `QgsPoint()` )
static

Returns an array of circle constructed by 3 tangents on the circle (aka inscribed circle of a triangle).

The vector can contain 0, 1 or 2 circles:

• 0: Impossible to construct a circle from 3 tangents (three parallel tangents)
• 1: The three tangents make a triangle or when two tangents are parallel there are two possible circles (see examples). If pos is not an empty point, we use its coordinates to determine which circle will be returned. More precisely the circle that will be returned will be the one whose center is on the same side as pos relative to the third tangent.
• 2: Returns both solutions when two tangents are parallel (this implies that pos is an empty point).

Z and m values are dropped for the center point. The azimuth always takes the default value.

Parameters
 pt1_tg1 First point of the first tangent. pt2_tg1 Second point of the first tangent. pt1_tg2 First point of the second tangent. pt2_tg2 Second point of the second tangent. pt1_tg3 First point of the third tangent. pt2_tg3 Second point of the third tangent. epsilon Value used to compare point. pos (optional) Point to determine which circle use in case of multi return.
from3Tangents()

### Example

# [(0 0), (5 0)] and [(5 5), (10 5)] are parallels
QgsCircle.from3TangentsMulti(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5))
# [<QgsCircle: Circle (Center: Point (8.53553390593273775 2.5), Radius: 2.5, Azimuth: 0)>, <QgsCircle: Circle (Center: Point (1.46446609406726203 2.49999999999999911), Radius: 2.5, Azimuth: 0)>]
QgsCircle.from3TangentsMulti(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5), pos=QgsPoint(2, 0))
# [<QgsCircle: Circle (Center: Point (1.46446609406726203 2.49999999999999911), Radius: 2.5, Azimuth: 0)>]
QgsCircle.from3TangentsMulti(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(2.5, 0), QgsPoint(7.5, 5), pos=QgsPoint(3, 0))
# [<QgsCircle: Circle (Center: Point (8.53553390593273775 2.5), Radius: 2.5, Azimuth: 0)>]
# [(0 0), (5 0)], [(5 5), (10 5)] and [(15 5), (20 5)] are parallels
QgsCircle.from3TangentsMulti(QgsPoint(0, 0), QgsPoint(5, 0), QgsPoint(5, 5), QgsPoint(10, 5), QgsPoint(15, 5), QgsPoint(20, 5))
# []
static QVector< QgsCircle > from3TangentsMulti(const QgsPoint &pt1_tg1, const QgsPoint &pt2_tg1, const QgsPoint &pt1_tg2, const QgsPoint &pt2_tg2, const QgsPoint &pt1_tg3, const QgsPoint &pt2_tg3, double epsilon=1E-8, const QgsPoint &pos=QgsPoint())
Returns an array of circle constructed by 3 tangents on the circle (aka inscribed circle of a triangl...

Definition at line 278 of file qgscircle.cpp.

## ◆ fromCenterDiameter()

 QgsCircle QgsCircle::fromCenterDiameter ( const QgsPoint & center, double diameter, double azimuth = `0` )
static

Constructs a circle by a center point and a diameter.

The center point keeps z and m values from center.

Parameters
 center Center point. diameter Diameter of the circle. azimuth Azimuth of the circle.

Definition at line 177 of file qgscircle.cpp.

## ◆ fromCenterPoint()

 QgsCircle QgsCircle::fromCenterPoint ( const QgsPoint & center, const QgsPoint & pt1 )
static

Constructs a circle by a center point and another point.

The center point keeps z and m values from center. Axes are calculated from the 2D distance between center and pt1. The azimuth is the angle between center and pt1.

Parameters
 center Center point. pt1 A point on the circle.

Definition at line 182 of file qgscircle.cpp.

## ◆ fromExtent()

 QgsCircle QgsCircle::fromExtent ( const QgsPoint & pt1, const QgsPoint & pt2 )
static

Constructs a circle by an extent (aka bounding box / QgsRectangle).

The center point can have m value which is the result from the midpoint operation between pt1 and pt2. Z dimension is also supported and is retrieved from the first 3D point amongst pt1 and pt2. Axes are calculated from the 2D distance between pt1 and pt2. The azimuth always takes the default value.

Parameters
 pt1 First corner. pt2 Second corner.

Definition at line 382 of file qgscircle.cpp.

## ◆ innerTangents()

 int QgsCircle::innerTangents ( const QgsCircle & other, QgsPointXY & line1P1, QgsPointXY & line1P2, QgsPointXY & line2P1, QgsPointXY & line2P2 ) const

Calculates the inner tangent points between this circle and an other circle.

The inner tangent points correspond to the points at which the two lines which are drawn so that they are tangential to both circles but on different sides, touching the circles and crossing each other.

The first tangent line is described by the points stored in line1P1 and line1P2, and the second line is described by the points stored in line2P1 and line2P2.

Returns the number of tangents (either 0 or 2).

Note that this method is 2D only and does not consider the z-value of the circle.

tangentToPoint() and outerTangents()
Since
QGIS 3.6

Definition at line 376 of file qgscircle.cpp.

## ◆ intersections()

 int QgsCircle::intersections ( const QgsCircle & other, QgsPoint & intersection1, QgsPoint & intersection2, bool useZ = `false` ) const

Calculates the intersections points between this circle and an other circle.

If found, the intersection points will be stored in intersection1 and intersection2.

By default this method does not consider any z values and instead treats the circles as 2-dimensional. If useZ is set to `true`, then an intersection will only occur if the z values of both circles are equal. In this case the points returned for intersection1 and intersection2 will contain the z value of the circle intersections.

Returns
number of intersection points found.
Since
QGIS 3.2

Definition at line 342 of file qgscircle.cpp.

## ◆ minimalCircleFrom3Points()

 QgsCircle QgsCircle::minimalCircleFrom3Points ( const QgsPoint & pt1, const QgsPoint & pt2, const QgsPoint & pt3, double epsilon = `1E-8` )
static

Constructs the smallest circle from 3 points.

Z and m values are dropped for the center point. The azimuth always takes the default value. If the points are colinear an empty circle is returned.

Parameters
 pt1 First point. pt2 Second point. pt3 Third point. epsilon Value used to compare point.

Definition at line 326 of file qgscircle.cpp.

 QVector< QgsPoint > QgsCircle::northQuadrant ( ) const

The four quadrants of the ellipse.

They are oriented and started from North.

Returns

Definition at line 419 of file qgscircle.cpp.

## ◆ outerTangents()

 int QgsCircle::outerTangents ( const QgsCircle & other, QgsPointXY & line1P1, QgsPointXY & line1P2, QgsPointXY & line2P1, QgsPointXY & line2P2 ) const

Calculates the outer tangent points between this circle and an other circle.

The outer tangent points correspond to the points at which the two lines which are drawn so that they are tangential to both circles touch the circles.

The first tangent line is described by the points stored in line1P1 and line1P2, and the second line is described by the points stored in line2P1 and line2P2.

Returns the number of tangents (either 0 or 2).

Note that this method is 2D only and does not consider the z-value of the circle.

tangentToPoint() and innerTangents()
Since
QGIS 3.2

Definition at line 370 of file qgscircle.cpp.

## ◆ perimeter()

 double QgsCircle::perimeter ( ) const
overridevirtual

The circumference of the ellipse using first approximation of Ramanujan.

Reimplemented from QgsEllipse.

Definition at line 402 of file qgscircle.cpp.

inline

Returns the radius of the circle.

Definition at line 311 of file qgscircle.h.

inline

Sets the radius of the circle.

Definition at line 313 of file qgscircle.h.

## ◆ setSemiMajorAxis()

 void QgsCircle::setSemiMajorAxis ( double semiMajorAxis )
overridevirtual

Inherited method.

Reimplemented from QgsEllipse.

Definition at line 407 of file qgscircle.cpp.

## ◆ setSemiMinorAxis()

 void QgsCircle::setSemiMinorAxis ( double semiMinorAxis )
overridevirtual

Inherited method.

Reimplemented from QgsEllipse.

Definition at line 413 of file qgscircle.cpp.

## ◆ tangentToPoint()

 bool QgsCircle::tangentToPoint ( const QgsPointXY & p, QgsPointXY & pt1, QgsPointXY & pt2 ) const

Calculates the tangent points between this circle and the point p.

If found, the tangent points will be stored in pt1 and pt2.

Note that this method is 2D only and does not consider the z-value of the circle.

Returns
`true` if tangent was found.
outerTangents() and innerTangents()
Since
QGIS 3.2

Definition at line 365 of file qgscircle.cpp.

## ◆ toCircularString()

 QgsCircularString * QgsCircle::toCircularString ( bool oriented = `false` ) const

Returns a circular string from the circle.

Parameters
 oriented If oriented is `true` the start point is from azimuth instead from north.

Definition at line 430 of file qgscircle.cpp.

## ◆ toString()

 QString QgsCircle::toString ( int pointPrecision = `17`, int axisPrecision = `17`, int azimuthPrecision = `2` ) const
overridevirtual

returns a string representation of the ellipse.

Members will be truncated to the specified precision.

Reimplemented from QgsEllipse.

Definition at line 463 of file qgscircle.cpp.

The documentation for this class was generated from the following files:
• /build/qgis-3.33.0+git20230922+bf22a165b3+99sid/src/core/geometry/qgscircle.h
• /build/qgis-3.33.0+git20230922+bf22a165b3+99sid/src/core/geometry/qgscircle.cpp