Subgroup: Geometry

Class: QgsGeometryUtils¶

class qgis.core.QgsGeometryUtils

Bases: sip.wrapper

Contains various geometry utility functions.

New in version 2.10: Methods

 angleBetweenThreePoints Calculates the angle between the lines AB and BC, where AB and BC described by points a, b and b, c. angleOnCircle Returns true if an angle is between angle1 and angle3 on a circle described by angle1, angle2 and angle3. averageAngle Angle between two linear segments ccwAngle Returns the counter clockwise angle between a line with components dx, dy and the line with dx > 0 and dy = 0 circleAngleBetween Returns true if, in a circle, angle is between angle1 and angle2 circleCenterRadius Returns radius and center of the circle through pt1, pt2, pt3 circleClockwise Returns true if circle is ordered clockwise circleLength Length of a circular string segment defined by pt1, pt2, pt3 circleTangentDirection Calculates the direction angle of a circle tangent (clockwise from north in radians) closestPoint Returns the nearest point on a segment of a geometry for the specified point. closestVertex Returns the closest vertex to a geometry for a specified point. coefficients Return the coefficients (a, b, c for equation “ax + by + c = 0”) of a line defined by points pt1 and pt2. distanceToVertex Returns the distance along a geometry from its first vertex to the specified vertex. extractLineStrings Returns list of linestrings extracted from the passed geometry. gradient Return the gradient of a line defined by points pt1 and pt2. interpolateArcValue Interpolate a value at given angle on circular arc given values (zm1, zm2, zm3) at three different angles (a1, a2, a3). interpolatePointOnLine Interpolates the position of a point a fraction of the way along the line from (x1, y1) to (x2, y2). interpolatePointOnLineByValue Interpolates the position of a point along the line from (x1, y1) to (x2, y2). leftOfLine Returns a value < 0 if the point (x, y) is left of the line from (x1, y1) -> ( x2, y2). lineAngle Calculates the direction of line joining two points in radians, clockwise from the north direction. lineCircleIntersection Compute the intersection of a line and a circle. lineIntersection Computes the intersection between two lines. linePerpendicularAngle Calculates the perpendicular angle to a line joining two points. midpoint Returns a middle point between points pt1 and pt2. normalizedAngle Ensures that an angle is in the range 0 <= angle < 2 pi. perpendicularSegment Create a perpendicular line segment from p to segment [s1, s2] pointOnLineWithDistance Returns a point a specified distance toward a second point. projectPointOnSegment Project the point on a segment segmentIntersection Compute the intersection between two segments segmentMidPoint Calculates midpoint on circle passing through p1 and p2, closest to given coordinate. segmentSide For line defined by points pt1 and pt3, find out on which side of the line is point pt3. segmentizeArc Convert circular arc defined by p1, p2, p3 (p1/p3 being start resp. setZValueFromPoints A Z dimension is added to point if one of the point in the list points is in 3D. sqrDistToLine Returns the squared distance between a point and a line. sqrDistance2D Returns the squared 2D distance between two points. sweepAngle Calculates angle of a circular string part defined by pt1, pt2, pt3 verticesAtDistance Retrieves the vertices which are before and after the interpolated point at a specified distance along a linestring (or polygon boundary).

Signals

Attributes

angleBetweenThreePoints(x1: float, y1: float, x2: float, y2: float, x3: float, y3: float) → float

Calculates the angle between the lines AB and BC, where AB and BC described by points a, b and b, c.

Parameters: x1 – x-coordinate of point a y1 – y-coordinate of point a x2 – x-coordinate of point b y2 – y-coordinate of point b x3 – x-coordinate of point c y3 – y-coordinate of point c angle between lines in radians. Returned value is undefined if two or more points are equal.
angleOnCircle(angle: float, angle1: float, angle2: float, angle3: float) → bool

Returns true if an angle is between angle1 and angle3 on a circle described by angle1, angle2 and angle3.

averageAngle(x1: float, y1: float, x2: float, y2: float, x3: float, y3: float) → float

Angle between two linear segments

averageAngle(a1: float, a2: float) -> float Averages two angles, correctly handling negative angles and ensuring the result is between 0 and 2 pi.

Parameters: a1 – first angle (in radians) a2 – second angle (in radians) average angle (in radians)
ccwAngle(dy: float, dx: float) → float

Returns the counter clockwise angle between a line with components dx, dy and the line with dx > 0 and dy = 0

circleAngleBetween(angle: float, angle1: float, angle2: float, clockwise: bool) → bool

Returns true if, in a circle, angle is between angle1 and angle2

circleCenterRadius(pt1: QgsPoint, pt2: QgsPoint, pt3: QgsPoint) → Tuple[float, float, float]

Returns radius and center of the circle through pt1, pt2, pt3

circleClockwise(angle1: float, angle2: float, angle3: float) → bool

Returns true if circle is ordered clockwise

circleLength(x1: float, y1: float, x2: float, y2: float, x3: float, y3: float) → float

Length of a circular string segment defined by pt1, pt2, pt3

circleTangentDirection(tangentPoint: QgsPoint, cp1: QgsPoint, cp2: QgsPoint, cp3: QgsPoint) → float

Calculates the direction angle of a circle tangent (clockwise from north in radians)

closestPoint(geometry: QgsAbstractGeometry, point: QgsPoint) → QgsPoint

Returns the nearest point on a segment of a geometry for the specified point. The z and m values will be linearly interpolated between the two neighbouring vertices.

closestVertex(geom: QgsAbstractGeometry, pt: QgsPoint) → Tuple[QgsPoint, QgsVertexId]

Returns the closest vertex to a geometry for a specified point. On error null point will be returned and “id” argument will be invalid.

coefficients(pt1: QgsPoint, pt2: QgsPoint) → Tuple[float, float, float]

Return the coefficients (a, b, c for equation “ax + by + c = 0”) of a line defined by points pt1 and pt2.

Parameters: pt1 – first point. pt2 – second point. a – Output parameter, a coefficient of the equation. b – Output parameter, b coefficient of the equation. c – Output parameter, c coefficient of the equation.

New in version 3.0.

distanceToVertex(geom: QgsAbstractGeometry, id: QgsVertexId) → float

Returns the distance along a geometry from its first vertex to the specified vertex.

Parameters: geom – geometry id – vertex id to find distance to distance to vertex (following geometry)

New in version 2.16.

extractLineStrings(geom: QgsAbstractGeometry) → object

Returns list of linestrings extracted from the passed geometry. The returned objects have to be deleted by the caller.

gradient(pt1: QgsPoint, pt2: QgsPoint) → float

Return the gradient of a line defined by points pt1 and pt2.

Parameters: pt1 – first point. pt2 – second point. The gradient of this linear entity, or infinity if vertical

New in version 3.0.

interpolateArcValue(angle: float, a1: float, a2: float, a3: float, zm1: float, zm2: float, zm3: float) → float

Interpolate a value at given angle on circular arc given values (zm1, zm2, zm3) at three different angles (a1, a2, a3).

New in version 3.0.

interpolatePointOnLine(x1: float, y1: float, x2: float, y2: float, fraction: float) → QgsPointXY

Interpolates the position of a point a fraction of the way along the line from (x1, y1) to (x2, y2).

Usually the fraction should be between 0 and 1, where 0 represents the point at the start of the line (x1, y1) and 1 represents the end of the line (x2, y2). However, it is possible to use a fraction < 0 or > 1, in which case the returned point is extrapolated from the supplied line.

New in version 3.0.2.

interpolatePointOnLine(p1: QgsPoint, p2: QgsPoint, fraction: float) -> QgsPoint Interpolates the position of a point a fraction of the way along the line from p1 to p2.

Usually the fraction should be between 0 and 1, where 0 represents the point at the start of the line (p1) and 1 represents the end of the line (p2). However, it is possible to use a fraction < 0 or > 1, in which case the returned point is extrapolated from the supplied line.

Any Z or M values present in the input points will also be interpolated and present in the returned point.

New in version 3.0.2.

interpolatePointOnLineByValue(x1: float, y1: float, v1: float, x2: float, y2: float, v2: float, value: float) → QgsPointXY

Interpolates the position of a point along the line from (x1, y1) to (x2, y2).

The position is interpolated using a supplied target value and the value at the start of the line (v1) and end of the line (v2). The returned point will be linearly interpolated to match position corresponding to the target value.

New in version 3.0.2.

leftOfLine(x: float, y: float, x1: float, y1: float, x2: float, y2: float) → int

Returns a value < 0 if the point (x, y) is left of the line from (x1, y1) -> ( x2, y2). A positive return value indicates the point is to the right of the line.

If the return value is 0, then the test was unsuccessful (e.g. due to testing a point exactly on the line, or exactly in line with the segment) and the result is undefined.

lineAngle(x1: float, y1: float, x2: float, y2: float) → float

Calculates the direction of line joining two points in radians, clockwise from the north direction.

Parameters: x1 – x-coordinate of line start y1 – y-coordinate of line start x2 – x-coordinate of line end y2 – y-coordinate of line end angle in radians. Returned value is undefined if start and end point are the same.
lineCircleIntersection(center: QgsPointXY, radius: float, linePoint1: QgsPointXY, linePoint2: QgsPointXY, intersection: QgsPointXY) → Tuple[bool, QgsPointXY]

Compute the intersection of a line and a circle. If the intersection has two solutions (points), the closest point to the initial intersection point is returned. @param center the center of the circle @param radius the radius of the circle @param linePoint1 a first point on the line @param linePoint2 a second point on the line @param intersection the initial point and the returned intersection point @return true if an intersection has been found

lineIntersection(p1: QgsPoint, v1: QgsVector, p2: QgsPoint, v2: QgsVector) → Tuple[bool, QgsPoint]

Computes the intersection between two lines. Z dimension is supported and is retrieved from the first 3D point amongst p1 and p2.

Parameters: p1 – Point on the first line v1 – Direction vector of the first line p2 – Point on the second line v2 – Direction vector of the second line intersection – Output parameter, the intersection point Whether the lines intersect
linePerpendicularAngle(x1: float, y1: float, x2: float, y2: float) → float

Calculates the perpendicular angle to a line joining two points. Returned angle is in radians, clockwise from the north direction.

Parameters: x1 – x-coordinate of line start y1 – y-coordinate of line start x2 – x-coordinate of line end y2 – y-coordinate of line end angle in radians. Returned value is undefined if start and end point are the same.
midpoint(pt1: QgsPoint, pt2: QgsPoint) → QgsPoint

Returns a middle point between points pt1 and pt2. Z value is computed if one of this point have Z. M value is computed if one of this point have M.

Parameters: pt1 – first point. pt2 – second point. New point at middle between points pt1 and pt2.
• Example:
p = QgsPoint( 4, 6 ) # 2D point
pr = midpoint ( p, QgsPoint( 2, 2 ) )
# pr is a 2D point: 'Point (3 4)'
pr = midpoint ( p, QgsPoint( QgsWkbTypes.PointZ, 2, 2, 2 ) )
# pr is a 3D point: 'PointZ (3 4 1)'
pr = midpoint ( p, QgsPoint( QgsWkbTypes.PointM, 2, 2, 0, 2 ) )
# pr is a 3D point: 'PointM (3 4 1)'
pr = midpoint ( p, QgsPoint( QgsWkbTypes.PointZM, 2, 2, 2, 2 ) )
# pr is a 3D point: 'PointZM (3 4 1 1)'

New in version 3.0.

normalizedAngle(angle: float) → float

Ensures that an angle is in the range 0 <= angle < 2 pi.

Parameters: angle – angle in radians equivalent angle within the range [0, 2 pi)
perpendicularSegment(p: QgsPoint, s1: QgsPoint, s2: QgsPoint) → QgsLineString

Create a perpendicular line segment from p to segment [s1, s2]

Parameters: p – The point s1 – The segment start point s2 – The segment end point A line (segment) from p to perpendicular point on segment [s1, s2]
pointOnLineWithDistance(startPoint: QgsPoint, directionPoint: QgsPoint, distance: float) → QgsPoint

Returns a point a specified distance toward a second point.

projectPointOnSegment(p: QgsPoint, s1: QgsPoint, s2: QgsPoint) → QgsPoint

Project the point on a segment

Parameters: p – The point s1 – The segment start point s2 – The segment end point The projection of the point on the segment
segmentIntersection(p1: QgsPoint, p2: QgsPoint, q1: QgsPoint, q2: QgsPoint, tolerance: float = 1e-08, acceptImproperIntersection: bool = False) → Tuple[bool, QgsPoint, bool]

Compute the intersection between two segments

Parameters: p1 – First segment start point p2 – First segment end point q1 – Second segment start point q2 – Second segment end point intersectionPoint – Output parameter, the intersection point isIntersection – Output parameter, return true if an intersection is found tolerance – The tolerance to use acceptImproperIntersection – By default, this method returns true only if segments have proper intersection. If set true, returns also true if segments have improper intersection (end of one segment on other segment ; continuous segments). Whether the segments intersect
• Example:
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, 0 ), QgsPoint( 0, 1 ), QgsPoint( 1, 1 ), QgsPoint( 1, 0 ) )
ret, ret.asWkt(), ret
# Whether the segments intersect, the intersection point, is intersect
# (False, 'Point (0 0)', False)
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, 0 ), QgsPoint( 0, 5 ), QgsPoint( 0, 5 ), QgsPoint( 1, 5 ) )
ret, ret.asWkt(), ret
# (False, 'Point (0 5)', True)
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, 0 ), QgsPoint( 0, 5 ), QgsPoint( 0, 5 ), QgsPoint( 1, 5 ), acceptImproperIntersection=True )
ret, ret.asWkt(), ret
# (True, 'Point (0 5)', True)
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, 0 ), QgsPoint( 0, 5 ), QgsPoint( 0, 2 ), QgsPoint( 1, 5 ) )
ret, ret.asWkt(), ret
# (False, 'Point (0 2)', True)
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, 0 ), QgsPoint( 0, 5 ), QgsPoint( 0, 2 ), QgsPoint( 1, 5 ), acceptImproperIntersection=True )
ret, ret.asWkt(), ret
# (True, 'Point (0 2)', True)
ret = QgsGeometryUtils.segmentIntersection( QgsPoint( 0, -5 ), QgsPoint( 0, 5 ), QgsPoint( 2, 0 ), QgsPoint( -1, 0 ) )
ret, ret.asWkt(), ret
# (True, 'Point (0 0)', True)
segmentMidPoint(p1: QgsPoint, p2: QgsPoint, radius: float, mousePos: QgsPoint) → Tuple[bool, QgsPoint]

Calculates midpoint on circle passing through p1 and p2, closest to given coordinate. Z dimension is supported and is retrieved from the first 3D point amongst p1 and p2.

segmentSide(pt1: QgsPoint, pt3: QgsPoint, pt2: QgsPoint) → int

For line defined by points pt1 and pt3, find out on which side of the line is point pt3. Returns -1 if pt3 on the left side, 1 if pt3 is on the right side or 0 if pt3 lies on the line.

New in version 3.0.

segmentizeArc(p1: QgsPoint, p2: QgsPoint, p3: QgsPoint, tolerance: float = M_PI_2/90, toleranceType: QgsAbstractGeometry.SegmentationToleranceType = QgsAbstractGeometry.MaximumAngle, hasZ: bool = False, hasM: bool = False) → List[QgsPoint]

Convert circular arc defined by p1, p2, p3 (p1/p3 being start resp. end point, p2 lies on the arc) into a sequence of points.

New in version 3.0.

setZValueFromPoints(points: object, point: QgsPoint) → bool

A Z dimension is added to point if one of the point in the list points is in 3D. Moreover, the Z value of point is updated with.

Parameters: points – List of points in which a 3D point is searched. point – The point to update with Z dimension and value. true if the point is updated, false otherwise

New in version 3.0.

sqrDistToLine(ptX: float, ptY: float, x1: float, y1: float, x2: float, y2: float, epsilon: float) → Tuple[float, float, float]

Returns the squared distance between a point and a line.

sqrDistance2D(pt1: QgsPoint, pt2: QgsPoint) → float

Returns the squared 2D distance between two points.

sweepAngle(centerX: float, centerY: float, x1: float, y1: float, x2: float, y2: float, x3: float, y3: float) → float

Calculates angle of a circular string part defined by pt1, pt2, pt3

verticesAtDistance(geometry: QgsAbstractGeometry, distance: float) → Tuple[bool, QgsVertexId, QgsVertexId]

Retrieves the vertices which are before and after the interpolated point at a specified distance along a linestring (or polygon boundary).

Parameters: geometry – line or polygon geometry distance – distance to traverse along geometry previousVertex – will be set to previous vertex ID nextVertex – will be set to next vertex ID true if vertices were successfully retrieved

Note

if the distance coincides exactly with a vertex, then both previousVertex and nextVertex will be set to this vertex

New in version 3.0.