Class: QgsGeometryEngine

class qgis.core.QgsGeometryEngine

Bases: sip.wrapper

A geometry engine is a low-level representation of a QgsAbstractGeometry object, optimised for use with external geometry libraries such as GEOS.

QgsGeometryEngine objects provide a mechanism for optimized evaluation of geometric algorithms, including spatial relationships between geometries and operations such as buffers or clipping.

QgsGeometryEngine objects are not created directly, but are instead created by calling QgsGeometry.createGeometryEngine().

Many methods available in the QgsGeometryEngine class can benefit from pre-preparing geometries. For instance, whenever a large number of spatial relationships will be tested (such as calling intersects(), within(), etc) then the geometry should first be prepared by calling prepareGeometry() before performing the tests.

# polygon_geometry contains a complex polygon, with many vertices
polygon_geometry = QgsGeometry.fromWkt('Polygon((...))')

# create a :py:class:`.QgsGeometryEngine` representation of the polygon
polygon_geometry_engine = QgsGeometry.createGeometryEngine(polygon_geometry.constGet())

# since we'll be performing many intersects tests, we can speed up these tests considerably
# by first "preparing" the geometry engine
polygon_geometry_engine.prepareGeometry()

# now we are ready to quickly test intersection against many other objects
for feature in my_layer.getFeatures():
    feature_geometry = feature.geometry()
    # test whether the feature's geometry intersects our original complex polygon
    if polygon_geometry_engine.intersects(feature_geometry.constGet()):
        print('feature intersects the polygon!')

QgsGeometryEngine operations are backed by the GEOS library (https://trac.osgeo.org/geos/).

New in version 2.10:

Methods

area

param errorMsg

buffer

buffer(self, distance: float, segments: int, endCapStyle: Qgis.EndCapStyle, joinStyle: Qgis.JoinStyle, miterLimit: float, errorMsg: str = ‘’) -> QgsAbstractGeometry Buffers a geometry.

centroid

Calculates the centroid of this.

combine

Calculate the combination of this and geom.

contains

Checks if geom contains this.

convexHull

Calculate the convex hull of this.

crosses

Checks if geom crosses this.

difference

Calculate the difference of this and geom.

disjoint

Checks if geom is disjoint from this.

distance

Calculates the distance between this and geom.

distanceWithin

Checks if geom is within maxdistance distance from this geometry

envelope

param errorMsg

geometryChanged

Should be called whenever the geometry associated with the engine has been modified and the engine must be updated to suit.

interpolate

param distance

intersection

Calculate the intersection of this and geom.

intersects

Checks if geom intersects this.

isEmpty

param errorMsg

isEqual

Checks if this is equal to geom.

isSimple

Determines whether the geometry is simple (according to OGC definition).

isValid

Returns True if the geometry is valid.

length

param errorMsg

logError

Logs an error message encountered during an operation.

offsetCurve

Offsets a curve.

overlaps

Checks if geom overlaps this.

pointOnSurface

Calculate a point that is guaranteed to be on the surface of this.

prepareGeometry

Prepares the geometry, so that subsequent calls to spatial relation methods are much faster.

relate

Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between the geometries.

relatePattern

Tests whether two geometries are related by a specified Dimensional Extended 9 Intersection Model (DE-9IM) pattern.

setLogErrors

Sets whether warnings and errors encountered during the geometry operations should be logged.

simplify

param tolerance

splitGeometry

Splits this geometry according to a given line.

symDifference

Calculate the symmetric difference of this and geom.

touches

Checks if geom touches this.

within

Checks if geom is within this.

Attributes

EngineError

InvalidBaseGeometry

InvalidInput

MethodNotImplemented

NodedGeometryError

NothingHappened

SplitCannotSplitPoint

Success

EngineError = 1002
class EngineOperationResult

Bases: int

InvalidBaseGeometry = 1004
InvalidInput = 1005
MethodNotImplemented = 1001
NodedGeometryError = 1003
NothingHappened = 1000
SplitCannotSplitPoint = 1006
Success = 0
area(self, errorMsg: str = '') float
Parameters

errorMsg (str = '') –

Return type

float

buffer(self, distance: float, segments: int, errorMsg: str = '') QgsAbstractGeometry

buffer(self, distance: float, segments: int, endCapStyle: Qgis.EndCapStyle, joinStyle: Qgis.JoinStyle, miterLimit: float, errorMsg: str = ‘’) -> QgsAbstractGeometry Buffers a geometry.

Parameters
  • distance (float) –

  • segments (int) –

  • errorMsg (str = '') –

Return type

QgsAbstractGeometry

centroid(self, errorMsg: str = '') QgsPoint

Calculates the centroid of this. May return a `None`.

New in version 3.0.

Parameters

errorMsg (str = '') –

Return type

QgsPoint

combine(self, geom: QgsAbstractGeometry, errorMsg: str = '') QgsAbstractGeometry

Calculate the combination of this and geom.

New in version 3.0.

combine(self, geomList: object, errorMsg: str) -> QgsAbstractGeometry Calculate the combination of this and geometries.

New in version 3.0.

combine(self, geometries: Iterable[QgsGeometry], errorMsg: str = ‘’) -> QgsAbstractGeometry Calculate the combination of this and geometries.

New in version 3.0.

Parameters
Return type

QgsAbstractGeometry

contains(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom contains this.

New in version 3.0.

Parameters
Return type

bool

convexHull(self, errorMsg: str = '') QgsAbstractGeometry

Calculate the convex hull of this.

Parameters

errorMsg (str = '') –

Return type

QgsAbstractGeometry

crosses(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom crosses this.

New in version 3.0.

Parameters
Return type

bool

difference(self, geom: QgsAbstractGeometry, errorMsg: str = '') QgsAbstractGeometry

Calculate the difference of this and geom.

New in version 3.0.

Parameters
Return type

QgsAbstractGeometry

disjoint(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom is disjoint from this.

New in version 3.0.

Parameters
Return type

bool

distance(self, geom: QgsAbstractGeometry, errorMsg: str = '') float

Calculates the distance between this and geom.

New in version 3.0.

Parameters
Return type

float

distanceWithin(self, geom: QgsAbstractGeometry, maxdistance: float, errorMsg: str = '') bool

Checks if geom is within maxdistance distance from this geometry

New in version 3.22.

Parameters
Return type

bool

envelope(self, errorMsg: str = '') QgsAbstractGeometry
Parameters

errorMsg (str = '') –

Return type

QgsAbstractGeometry

geometryChanged(self)

Should be called whenever the geometry associated with the engine has been modified and the engine must be updated to suit.

interpolate(self, distance: float, errorMsg: str = '') QgsAbstractGeometry
Parameters
  • distance (float) –

  • errorMsg (str = '') –

Return type

QgsAbstractGeometry

intersection(self, geom: QgsAbstractGeometry, errorMsg: str = '') QgsAbstractGeometry

Calculate the intersection of this and geom.

New in version 3.0.

Parameters
Return type

QgsAbstractGeometry

intersects(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom intersects this.

New in version 3.0.

Parameters
Return type

bool

isEmpty(self, errorMsg: str) bool
Parameters

errorMsg (str) –

Return type

bool

isEqual(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if this is equal to geom. If both are Null geometries, `False` is returned.

New in version 3.0.

Parameters
Return type

bool

isSimple(self, errorMsg: str = '') bool

Determines whether the geometry is simple (according to OGC definition).

New in version 3.0.

Parameters

errorMsg (str = '') –

Return type

bool

isValid(self, errorMsg: str = '', allowSelfTouchingHoles: bool = False, errorLoc: QgsGeometry = None) bool

Returns True if the geometry is valid.

If the geometry is invalid, errorMsg will be filled with the reported geometry error.

The allowSelfTouchingHoles argument specifies whether self-touching holes are permitted. OGC validity states that self-touching holes are NOT permitted, whilst other vendor validity checks (e.g. ESRI) permit self-touching holes.

If errorLoc is specified, it will be set to the geometry of the error location.

Parameters
  • errorMsg (str = '') –

  • allowSelfTouchingHoles (bool = False) –

  • errorLoc (QgsGeometry = None) –

Return type

bool

length(self, errorMsg: str = '') float
Parameters

errorMsg (str = '') –

Return type

float

logError(self, engineName: str, message: str)

Logs an error message encountered during an operation.

See also

setLogErrors()

New in version 3.16.

Parameters
  • engineName (str) –

  • message (str) –

offsetCurve(self, distance: float, segments: int, joinStyle: Qgis.JoinStyle, miterLimit: float, errorMsg: str = '') QgsAbstractGeometry

Offsets a curve.

Parameters
  • distance (float) –

  • segments (int) –

  • joinStyle (Qgis.JoinStyle) –

  • miterLimit (float) –

  • errorMsg (str = '') –

Return type

QgsAbstractGeometry

overlaps(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom overlaps this.

New in version 3.0.

Parameters
Return type

bool

pointOnSurface(self, errorMsg: str = '') QgsPoint

Calculate a point that is guaranteed to be on the surface of this. May return a `None`.

New in version 3.0.

Parameters

errorMsg (str = '') –

Return type

QgsPoint

prepareGeometry(self)

Prepares the geometry, so that subsequent calls to spatial relation methods are much faster.

This should be called for any geometry which is used for multiple relation tests against other geometries.

relate(self, geom: QgsAbstractGeometry, errorMsg: str = '') str

Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between the geometries.

Parameters
  • geom (QgsAbstractGeometry) – geometry to relate to

  • errorMsg (str = '') – destination storage for any error message

Return type

str

Returns

DE-9IM string for relationship, or an empty string if an error occurred

New in version 2.12.

relatePattern(self, geom: QgsAbstractGeometry, pattern: str, errorMsg: str = '') bool

Tests whether two geometries are related by a specified Dimensional Extended 9 Intersection Model (DE-9IM) pattern.

Parameters
  • geom (QgsAbstractGeometry) – geometry to relate to

  • pattern (str) – DE-9IM pattern for match

  • errorMsg (str = '') – destination storage for any error message

Return type

bool

Returns

True if geometry relationship matches with pattern

New in version 2.14.

setLogErrors(self, enabled: bool)

Sets whether warnings and errors encountered during the geometry operations should be logged.

By default these errors are logged to the console and in the QGIS UI. But for some operations errors are expected and logging these just results in noise. In this case setting enabled to False will avoid the automatic error reporting.

New in version 3.16.

Parameters

enabled (bool) –

simplify(self, tolerance: float, errorMsg: str = '') QgsAbstractGeometry
Parameters
  • tolerance (float) –

  • errorMsg (str = '') –

Return type

QgsAbstractGeometry

splitGeometry(self, splitLine: QgsLineString, topological: bool, topologyTestPoints: Iterable[QgsPoint], errorMsg: str = '', skipIntersectionCheck: bool = False) Tuple[QgsGeometryEngine.EngineOperationResult, List[QgsGeometry]]

Splits this geometry according to a given line.

Parameters

splitLine (QgsLineString) – the line that splits the geometry

param[out] newGeometries list of new geometries that have been created with the split :type topological: bool :param topological: True if topological editing is enabled param[out] topologyTestPoints points that need to be tested for topological completeness in the dataset param[out] errorMsg error messages emitted, if any :type skipIntersectionCheck: bool = False :param skipIntersectionCheck: set to True to skip the potentially expensive initial intersection check. Only set this flag if an intersection

test has already been performed by the caller!

Return type

Tuple[QgsGeometryEngine.EngineOperationResult, List[QgsGeometry]]

Returns

0 in case of success, 1 if geometry has not been split, error else

Parameters
  • topologyTestPoints (Iterable[QgsPoint]) –

  • errorMsg (str = '') –

symDifference(self, geom: QgsAbstractGeometry, errorMsg: str = '') QgsAbstractGeometry

Calculate the symmetric difference of this and geom.

New in version 3.0.

Parameters
Return type

QgsAbstractGeometry

touches(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom touches this.

New in version 3.0.

Parameters
Return type

bool

within(self, geom: QgsAbstractGeometry, errorMsg: str = '') bool

Checks if geom is within this.

New in version 3.0.

Parameters
Return type

bool