Class: QgsGeometryCheck¶

Base class for geometry checks.

Geometry checks run over a set of features and can detect errors like topological or other issues which are reported in the geometry validation panel in QGIS and help a user to create valid geometries.

Implementing a custom geometry check consists of the following parts

Writing the check¶

A new subclass of QgsGeometryCheck needs to be written and at least the following abstract methods need to be implemented:

compatibleGeometryTypes(): A list of geometry types to which this check applies
availableResolutionMethods(): A list of resolution methods that can be used to fix errors of this type
description(): A description for the geometry check.
id(): A unique id for this check.
checkType(): One of QgsGeometryCheck.LayerCheck, QgsGeometryCheck.FeatureCheck, QgsGeometryCheck.FeatureNodeCheck
collectErrors(): This method will be called to validate geometries. All geometries which should be validated are passed into this method with the parameter ids and should be retrieved from the available featurePools to make use of caching. New errors should be appended to the error list and other message strings to messages. The method needs to return a tuple (errors, messages).

Creating a geometry check factory¶

A Geometry check factory manages meta information for checks. There will always be one single geometry check factory created per check type, but it’s possible that multiple QgsGeometryCheck instances are created and used in parallel.

A new subclass of QgsGeometryCheckFactory needs to be written and at least the following abstract methods need to be implemented:

QgsGeometryCheckFactory.createGeometryCheck(): Needs to return a new subclassed QgsGeometryCheck object that has been written in the previous step.
QgsGeometryCheckFactory.id(): A unique id for this geometry check.
QgsGeometryCheckFactory.description(): A description for this geometry check that can be presented to the user for more explanation.
QgsGeometryCheckFactory.isCompatible(): Returns a boolean that determines if this check is available for a given layer. This often checks for the geometry type of the layer.
QgsGeometryCheckFactory.flags(): Returns additional flags for a geometry check. If unsure return QgsGeometryCheck.AvailableInValidation.
QgsGeometryCheckFactory.checkType(): Returns the type of this geometry check.

Registering the geometry check¶

Finally the geometry check factory needs to be registered in QGIS, so the system is aware of the available geometry checks.

# Make sure you always keep a reference
checkFactory = MyGeometryCheckFactory()
QgsAnalysis.geometryCheckRegistry().registerGeometryCheck(checkFactory)

Note

This class is a technology preview and unstable API.

Added in version 3.4.

Note

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

The following methods must be implemented: checkType(), collectErrors(), compatibleGeometryTypes(), description(), id()

Class Hierarchy¶

Subclasses¶

QgsSingleGeometryCheck

Base class for geometry checks for a single geometry without any context of the layer or other layers in the project.

Abstract Methods

`checkType`	Returns the check type.
`collectErrors`	The main worker method.
`compatibleGeometryTypes`	A list of geometry types for which this check can be performed.
`description`	Returns a human readable description for this check.
`id`	Returns an id for this check.

Methods

context

Returns the context

Virtual Methods

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

`availableResolutionMethods`	Returns a list of available resolution methods.
`flags`	Flags for this geometry check.
`isCompatible`	Returns if this geometry check is compatible with layer.
`prepare`	Will be run in the main thread before `collectErrors()` is called (which may be run from a background thread).
`resolutionMethods`	Returns a list of descriptions for available resolutions for errors.

Attributes

`AvailableInValidation`
`ChangeAdded`
`ChangeChanged`
`ChangeFeature`
`ChangeNode`
`ChangePart`
`ChangeRemoved`
`ChangeRing`
`FeatureCheck`
`FeatureNodeCheck`
`LayerCheck`

class qgis.analysis.QgsGeometryCheck[source]¶

Bases: object

__init__(context: QgsGeometryCheckContext | None, configuration: Dict[str, Any])

Create a new geometry check.

Parameters:

context (Optional[QgsGeometryCheckContext])
configuration (Dict[str, Any])

__init__(a0: QgsGeometryCheck)

Parameters:: a0 (QgsGeometryCheck)

AvailableInValidation = 2¶

class Change¶

Bases: object

Descripts a change to fix a geometry.

Added in version 3.4.

type: QgsGeometryCheck.ChangeType¶: What action this change performs.

vidx: QgsVertexId¶: The index of the part / ring / vertex, depending on what().

what: QgsGeometryCheck.ChangeWhat¶: What level this change affects.

ChangeAdded = 0¶

ChangeChanged = 2¶

ChangeFeature = 0¶

ChangeNode = 3¶

ChangePart = 1¶

ChangeRemoved = 1¶

ChangeRing = 2¶

class ChangeType¶: Bases: int

class ChangeWhat¶: Bases: int

class CheckType¶: Bases: int

FeatureCheck = 1¶

FeatureNodeCheck = 0¶

class Flag¶: Bases: int

class Flags¶
class Flags(f: QgsGeometryCheck.Flags | QgsGeometryCheck.Flag)
class Flags(a0: QgsGeometryCheck.Flags): Bases: object

LayerCheck = 2¶

class LayerFeatureIds¶

Bases: object

A list of layers and feature ids for each of these layers. In C++, the member ids can be accessed directly. In Python some accessor methods will need to be written.

Added in version 3.4.

virtual availableResolutionMethods(self) → List[QgsGeometryCheckResolutionMethod]¶

Returns a list of available resolution methods.

Added in version 3.12.

Return type:: List[QgsGeometryCheckResolutionMethod]

abstract checkType(self) → QgsGeometryCheck.CheckType[source]¶

Returns the check type.

Added in version 3.4.

Return type:: QgsGeometryCheck.CheckType

abstract collectErrors(self, featurePools: Any, errors: Iterable[QgsGeometryCheckError], messages: Iterable[str | None], feedback: QgsFeedback | None, ids: QgsGeometryCheck.LayerFeatureIds = QgsGeometryCheck.LayerFeatureIds())[source]¶

The main worker method. Check all features available from featurePools and write errors found to errors. Other status messages can be written to messages. Progress should be reported to feedback. Only features and layers listed in ids should be checked.

Added in version 3.4.

Parameters:

featurePools (Any)
errors (Iterable[QgsGeometryCheckError])
messages (Iterable[Optional[str]])
feedback (Optional[QgsFeedback])
ids (QgsGeometryCheck.LayerFeatureIds = QgsGeometryCheck.LayerFeatureIds()) -> (List[QgsGeometryCheckError])

abstract compatibleGeometryTypes(self) → List[Qgis.GeometryType]¶

A list of geometry types for which this check can be performed.

Added in version 3.4.

Return type:: List[Qgis.GeometryType]

context(self) → QgsGeometryCheckContext | None[source]¶

Returns the context

Added in version 3.4.

Return type:: Optional[QgsGeometryCheckContext]

abstract description(self) → str[source]¶

Returns a human readable description for this check.

Added in version 3.4.

Return type:: str

virtual flags(self) → QgsGeometryCheck.Flags[source]¶

Flags for this geometry check.

Return type:: QgsGeometryCheck.Flags

abstract id(self) → str[source]¶

Returns an id for this check.

Added in version 3.4.

Return type:: str

virtual isCompatible(self, layer: QgsVectorLayer | None) → bool[source]¶

Returns if this geometry check is compatible with layer. By default it checks for the geometry type in compatibleGeometryTypes().

Added in version 3.4.

Parameters:: layer (Optional[QgsVectorLayer])
Return type:: bool

virtual prepare(self, context: QgsGeometryCheckContext | None, configuration: Dict[str, Any])[source]¶

Will be run in the main thread before collectErrors() is called (which may be run from a background thread).

Added in version 3.10.

Parameters:

context (Optional[QgsGeometryCheckContext])
configuration (Dict[str, Any])

virtual resolutionMethods(self) → List[str][source]¶

Returns a list of descriptions for available resolutions for errors. The index will be passed as method to fixError().

Deprecated since version 3.12: Use availableResolutionMethods() instead.

Added in version 3.4.

Return type:: List[str]