Class: QgsCurve

Abstract base class for curved geometry type

Class Hierarchy

Base classes

QgsAbstractGeometry

Abstract base class for all geometries

Subclasses

QgsCircularString	Circular string geometry type
QgsCompoundCurve	Compound curve geometry type
QgsLineString	Line string geometry type, with support for z-dimension and m-values.

Enums

Orientation

alias of AngularDirection

Methods

addToPainterPath	Adds a curve to a painter path.
asQPolygonF	Returns a QPolygonF representing the points.
curveSubstring	Returns a new curve representing a substring of this curve.
curveToLine	Returns a new line string geometry corresponding to a segmentized approximation of the curve.
drawAsPolygon	Draws the curve as a polygon on the specified QPainter.
endPoint	Returns the end point of the curve.
equals	Checks whether this curve exactly equals another curve.
indexOf	Returns the index of the first vertex matching the given point, or -1 if a matching vertex is not found.
interpolatePoint	Returns an interpolated point on the curve at the specified distance.
isClosed	Returns True if the curve is closed.
isClosed2D	Returns true if the curve is closed.
isRing	Returns True if the curve is a ring.
mAt	Returns the m-coordinate of the specified node in the line string.
numPoints	Returns the number of points in the curve.
orientation	Returns the curve's orientation, e.g. clockwise or counter-clockwise.
pointAt	Returns the point and vertex id of a point within the curve.
points	Returns a list of points within the curve.
reversed	Returns a reversed copy of the curve, where the direction of the curve has been flipped.
scroll	Scrolls the curve vertices so that they start with the vertex at the given index.
segmentize	Returns a geometry without curves.
sinuosity	Returns the curve sinuosity, which is the ratio of the curve length() to curve straightDistance2d().
startPoint	Returns the starting point of the curve.
straightDistance2d	Returns the straight distance of the curve, i.e. the direct/euclidean distance between the first and last vertex of the curve.
sumUpArea	Sums up the area of the curve by iterating over the vertices (shoelace formula).
xAt	Returns the x-coordinate of the specified node in the line string.
yAt	Returns the y-coordinate of the specified node in the line string.
zAt	Returns the z-coordinate of the specified node in the line string.

class qgis.core.QgsCurve

Bases: QgsAbstractGeometry

Orientation

alias of AngularDirection

addToPainterPath(self, path: QPainterPath)

Adds a curve to a painter path.

Parameters:

path (QPainterPath)

asQPolygonF(self) → QPolygonF

Returns a QPolygonF representing the points.

Return type:

QPolygonF

curveSubstring(self, startDistance: float, endDistance: float) → QgsCurve | None

Returns a new curve representing a substring of this curve.

The startDistance and endDistance arguments specify the length along the curve which the substring should start and end at. If the endDistance is greater than the total length of the curve then any “extra” length will be ignored.

If z or m values are present, the output z and m will be interpolated using the existing vertices’ z or m values.

Added in version 3.4.

Parameters:

• startDistance (float)

• endDistance (float)

Return type:

Optional[QgsCurve]

curveToLine(self, tolerance: float = M_PI_2 / 90, toleranceType: QgsAbstractGeometry.SegmentationToleranceType = QgsAbstractGeometry.MaximumAngle) → QgsLineString | None

Returns a new line string geometry corresponding to a segmentized approximation of the curve.

Parameters:

• tolerance (float = M_PI_2/90) – segmentation tolerance

• toleranceType (QgsAbstractGeometry.SegmentationToleranceType = QgsAbstractGeometry.MaximumAngle) – maximum segmentation angle or maximum difference between approximation and curve

Uses a MaximumAngle tolerance of 1 degrees by default (360 segments in a full circle)

Return type:

Optional[QgsLineString]

drawAsPolygon(self, p: QPainter)

Draws the curve as a polygon on the specified QPainter.

Parameters:

p (QPainter) – destination QPainter

endPoint(self) → QgsPoint

Returns the end point of the curve.

See also

startPoint()

Return type:

QgsPoint

equals(self, other: QgsCurve) → bool

Checks whether this curve exactly equals another curve.

Parameters:

other (QgsCurve)

Return type:

bool

indexOf(self, point: QgsPoint) → int

Returns the index of the first vertex matching the given point, or -1 if a matching vertex is not found.

Note

If the curve has m or z values then the search point must have exactly matching m and z values in order to be matched against the curve’s vertices.

Note

This method only matches against segment vertices, not curve vertices.

Added in version 3.20.

Parameters:

point (QgsPoint)

Return type:

int

interpolatePoint(self, distance: float) → QgsPoint | None

Returns an interpolated point on the curve at the specified distance.

If z or m values are present, the output z and m will be interpolated using the existing vertices’ z or m values.

If distance is negative, or is greater than the length of the curve, None will be returned.

Added in version 3.4.

Parameters:

distance (float)

Return type:

Optional[QgsPoint]

isClosed(self) → bool

Returns True if the curve is closed.

See also

isClosed2D()

Return type:

bool

isClosed2D(self) → bool

Returns true if the curve is closed.

Unlike isClosed. It looks only for XY coordinates.

See also

isClosed()

Added in version 3.20.

Return type:

bool

isRing(self) → bool

Returns True if the curve is a ring.

Return type:

bool

mAt(self, index: int) → float

Returns the m-coordinate of the specified node in the line string.

Parameters:

index (int) – index of node, where the first node in the line is 0

Return type:

float

Returns:

m-coordinate of node, or 0.0 if index is out of bounds

Added in version 3.28.

numPoints(self) → int

Returns the number of points in the curve.

Return type:

int

orientation(self) → Qgis.AngularDirection

Returns the curve’s orientation, e.g. clockwise or counter-clockwise.

Warning

The result is not predictable for non-closed curves.

Added in version 3.6.

Return type:

Qgis.AngularDirection

pointAt(self, node: int)

Returns the point and vertex id of a point within the curve.

Parameters:

node (int) -> (bool) – node number, where the first node is 0

Returns:

• True if node exists within the curve

• point: point at corresponding node in the curve

• type: the vertex type of the node

points(self) → List[QgsPoint]

Returns a list of points within the curve.

Return type:

List[QgsPoint]

reversed(self) → QgsCurve | None

Returns a reversed copy of the curve, where the direction of the curve has been flipped.

Return type:

Optional[QgsCurve]

scroll(self, firstVertexIndex: int)

Scrolls the curve vertices so that they start with the vertex at the given index.

Warning

This should only be called on closed curves, or the shape of the curve will be altered and the result is undefined.

Warning

The firstVertexIndex must correspond to a segment vertex and not a curve point or the result is undefined.

Added in version 3.20.

Parameters:

firstVertexIndex (int)

segmentize(self, tolerance: float = M_PI_2 / 90, toleranceType: QgsAbstractGeometry.SegmentationToleranceType = QgsAbstractGeometry.MaximumAngle) → QgsCurve | None

Returns a geometry without curves. Caller takes ownership

Parameters:

• tolerance (float = M_PI_2/90) – segmentation tolerance

• toleranceType (QgsAbstractGeometry.SegmentationToleranceType = QgsAbstractGeometry.MaximumAngle) – maximum segmentation angle or maximum difference between approximation and curve

Return type:

Optional[QgsCurve]

sinuosity(self) → float

Returns the curve sinuosity, which is the ratio of the curve length() to curve straightDistance2d(). Larger numbers indicate a more “sinuous” curve (i.e. more “bendy”). The minimum value returned of 1.0 indicates a perfectly straight curve.

If a curve isClosed(), it has infinite sinuosity and will return NaN.

Added in version 3.2.

Return type:

float

startPoint(self) → QgsPoint

Returns the starting point of the curve.

See also

endPoint()

Return type:

QgsPoint

straightDistance2d(self) → float

Returns the straight distance of the curve, i.e. the direct/euclidean distance between the first and last vertex of the curve. (Also known as “as the crow flies” distance).

Added in version 3.2.

Return type:

float

sumUpArea(self) → float

Sums up the area of the curve by iterating over the vertices (shoelace formula).

Return type:

float

xAt(self, index: int) → float

Returns the x-coordinate of the specified node in the line string.

Parameters:

index (int) – index of node, where the first node in the line is 0

Return type:

float

Returns:

x-coordinate of node, or 0.0 if index is out of bounds

yAt(self, index: int) → float

Returns the y-coordinate of the specified node in the line string.

Parameters:

index (int) – index of node, where the first node in the line is 0

Return type:

float

Returns:

y-coordinate of node, or 0.0 if index is out of bounds

zAt(self, index: int) → float

Returns the z-coordinate of the specified node in the line string.

Parameters:

index (int) – index of node, where the first node in the line is 0

Return type:

float

Returns:

z-coordinate of node, or 0.0 if index is out of bounds

Added in version 3.28.