Class: QgsCurve¶

Abstract base class for curved geometry type.

Note

This is an abstract class, with methods which must be implemented by a subclass.

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

Abstract Methods

`addToPainterPath`	Adds a curve to a painter path.
`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.
`mAt`	Returns the m-coordinate of the specified node in the line string.
`numPoints`	Returns the number of points in the curve.
`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.
`startPoint`	Returns the starting point 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.

Methods

`orientation`	Returns the curve's orientation, e.g. clockwise or counter-clockwise.
`sinuosity`	Returns the curve sinuosity, which is the ratio of the curve `length()` to curve `straightDistance2d()`.
`straightDistance2d`	Returns the straight distance of the curve, i.e. the direct/euclidean distance between the first and last vertex of the curve.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsCurve. See the FAQ for more details.

`asQPolygonF`	Returns a QPolygonF representing the points.
`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.
`segmentize`	Returns a geometry without curves.

class qgis.core.QgsCurve[source]¶

Bases: QgsAbstractGeometry

Orientation¶: alias of AngularDirection

abstract addToPainterPath(self, path: QPainterPath)[source]¶

Adds a curve to a painter path.

Parameters:: path (QPainterPath)

virtual asQPolygonF(self) → QPolygonF[source]¶

Returns a QPolygonF representing the points.

Return type:: QPolygonF

abstract curveSubstring(self, startDistance: float, endDistance: float) → QgsCurve | None[source]¶

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]

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

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]

abstract drawAsPolygon(self, p: QPainter)[source]¶

Draws the curve as a polygon on the specified QPainter.

Parameters:: p (QPainter) – destination QPainter

abstract endPoint(self) → QgsPoint[source]¶

Returns the end point of the curve.

See also

startPoint()

Return type:: QgsPoint

abstract equals(self, other: QgsCurve) → bool[source]¶

Checks whether this curve exactly equals another curve.

Parameters:: other (QgsCurve)
Return type:: bool

abstract indexOf(self, point: QgsPoint) → int[source]¶

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

abstract interpolatePoint(self, distance: float) → QgsPoint | None[source]¶

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]

virtual isClosed(self) → bool[source]¶

Returns True if the curve is closed.

See also

isClosed2D()

Return type:: bool

virtual isClosed2D(self) → bool[source]¶

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

virtual isRing(self) → bool[source]¶

Returns True if the curve is a ring.

Return type:: bool

abstract mAt(self, index: int) → float[source]¶

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.

abstract numPoints(self) → int[source]¶

Returns the number of points in the curve.

Return type:: int

orientation(self) → Qgis.AngularDirection[source]¶

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

abstract pointAt(self, node: int)[source]¶

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

abstract points(self) → List[QgsPoint][source]¶

Returns a list of points within the curve.

Return type:: List[QgsPoint]

abstract reversed(self) → QgsCurve | None[source]¶

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

Return type:: Optional[QgsCurve]

abstract scroll(self, firstVertexIndex: int)[source]¶

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)

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

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[source]¶

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

abstract startPoint(self) → QgsPoint[source]¶

Returns the starting point of the curve.

See also

endPoint()

Return type:: QgsPoint

straightDistance2d(self) → float[source]¶

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

abstract sumUpArea(self) → float[source]¶

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

Return type:: float

abstract xAt(self, index: int) → float[source]¶

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

abstract yAt(self, index: int) → float[source]¶

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

abstract zAt(self, index: int) → float[source]¶

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.