Class: QgsTracer¶

Utility class that constructs a planar graph from the input vector layers and provides shortest path search for tracing of existing features.

Class Hierarchy¶

Base classes¶

QObject

Subclasses¶

QgsMapCanvasTracer

Extension of QgsTracer that provides extra functionality.

class qgis.core.QgsTracer[source]¶

Bases: QObject

__init__(): Constructor for QgsTracer.

ErrNoPath = 4¶

ErrNone = 0¶

ErrPoint1 = 2¶

ErrPoint2 = 3¶

ErrTooManyFeatures = 1¶

class PathError¶: Bases: int

addPointsOnIntersectionsEnabled(self) → bool[source]¶

Returns whether the shortest path’s straight segments will include vertices where the input layers intersect, even if no such vertex existed on the input layers

Added in version 3.40.

Return type:: bool

virtual configure(self)[source]¶: Allows derived classes to setup the settings just before the tracer is initialized. This allows the configuration to be set in a lazy way only when it is really necessary. Default implementation does nothing.

destinationCrs(self) → QgsCoordinateReferenceSystem[source]¶

Returns the CRS used for tracing.

See also

setDestinationCrs()

Return type:: QgsCoordinateReferenceSystem

extent(self) → QgsRectangle[source]¶

Gets extent to which graph’s features will be limited (empty extent means no limit)

Return type:: QgsRectangle

findShortestPath(self, p1: QgsPointXY, p2: QgsPointXY)¶

Given two points, find the shortest path and return points on the way. The optional “error” argument may receive error code (PathError enum) if it is not None

Returns:

array of points - trace of linestrings of other features (empty array one error)

Parameters:

p1 (QgsPointXY)
p2 (QgsPointXY) -> (List[QgsPointXY])

hasTopologyProblem(self) → bool[source]¶

Whether there was an error during graph creation due to noding exception, indicating some input data topology problems

Return type:: bool

init(self) → bool[source]¶

Build the internal data structures. This may take some time depending on how big the input layers are. It is not necessary to call this method explicitly - it will be called by findShortestPath() if necessary.

Return type:: bool

invalidateGraph(self)[source]¶: Destroy the existing graph structure if any (de-initialize)

isInitialized(self) → bool[source]¶

Whether the internal data structures have been initialized

Return type:: bool

isPointSnapped(self, pt: QgsPointXY) → bool[source]¶

Find out whether the point is snapped to a vertex or edge (i.e. it can be used for tracing start/stop)

Parameters:: pt (QgsPointXY)
Return type:: bool

layers(self) → List[QgsVectorLayer]¶

Gets layers used for tracing

Return type:: List[QgsVectorLayer]

maxFeatureCount(self) → int[source]¶

Gets maximum possible number of features in graph. If the number is exceeded, graph is not created.

Return type:: int

offset(self) → float[source]¶

Gets offset in map units that should be applied to the traced paths returned from findShortestPath(). Positive offset for right side, negative offset for left side.

Return type:: float

offsetParameters(self)[source]¶: Gets extra parameters for offset curve algorithm (used when offset is non-zero)

setAddPointsOnIntersectionsEnabled(self, enable: bool)[source]¶

When enable is True, the shortest path’s straight segments will include vertices where the input layers intersect, even if no such vertex existed on the input layers

Added in version 3.40.

Parameters:: enable (bool)

setDestinationCrs(self, crs: QgsCoordinateReferenceSystem, context: QgsCoordinateTransformContext)[source]¶

Sets the crs and transform context used for tracing.