Class: QgsTracer

class qgis.core.QgsTracer

Bases: PyQt5.QtCore.QObject

Constructor for QgsTracer.

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

New in version 2.14: Enums

Methods

childEvent

configure

Allows derived classes to setup the settings just before the tracer is initialized.

connectNotify

customEvent

destinationCrs

Returns the CRS used for tracing.

disconnectNotify

extent

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

findShortestPath

Given two points, find the shortest path and return points on the way.

hasTopologyProblem

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

init

Build the internal data structures.

invalidateGraph

Destroy the existing graph structure if any (de-initialize)

isInitialized

Whether the internal data structures have been initialized

isPointSnapped

Find out whether the point is snapped to a vertex or edge (i.e.

isSignalConnected

layers

Gets layers used for tracing

maxFeatureCount

Gets maximum possible number of features in graph.

offset

Gets offset in map units that should be applied to the traced paths returned from findShortestPath().

offsetParameters

Gets extra parameters for offset curve algorithm (used when offset is non-zero)

receivers

sender

senderSignalIndex

setDestinationCrs

Sets the crs and transform context used for tracing.

setExtent

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

setLayers

Sets layers used for tracing

setMaxFeatureCount

Gets maximum possible number of features in graph.

setOffset

Set offset in map units that should be applied to the traced paths returned from findShortestPath().

setOffsetParameters

Set extra parameters for offset curve algorithm (used when offset is non-zero)

timerEvent

Signals

Attributes

ErrNoPath

ErrNone

ErrPoint1

ErrPoint2

ErrTooManyFeatures

ErrNoPath = 4
ErrNone = 0
ErrPoint1 = 2
ErrPoint2 = 3
ErrTooManyFeatures = 1
class PathError

Bases: int

childEvent()
configure(self)

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.

connectNotify()
customEvent()
destinationCrs(self) → QgsCoordinateReferenceSystem

Returns the CRS used for tracing.

disconnectNotify()
extent(self) → QgsRectangle

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

findShortestPath(self, p1: QgsPointXY, p2: QgsPointXY) → Tuple[List[QgsPointXY], QgsTracer.PathError]

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 null

Returns

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

hasTopologyProblem(self) → bool

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

New in version 2.16.

init(self) → bool

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.

invalidateGraph(self)

Destroy the existing graph structure if any (de-initialize)

isInitialized(self) → bool

Whether the internal data structures have been initialized

isPointSnapped(self, pt: QgsPointXY) → bool

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

isSignalConnected()
layers(self) → object

Gets layers used for tracing

maxFeatureCount(self) → int

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

offset(self) → float

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.

New in version 3.0.

offsetParameters(self) → Tuple[int, int, float]

Gets extra parameters for offset curve algorithm (used when offset is non-zero)

New in version 3.0.

receivers()
sender()
senderSignalIndex()
setDestinationCrs(self, crs: QgsCoordinateReferenceSystem, context: QgsCoordinateTransformContext)

Sets the crs and transform context used for tracing.

See also

destinationCrs()

setExtent(self, extent: QgsRectangle)

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

setLayers(self, layers: Iterable[QgsVectorLayer])

Sets layers used for tracing

setMaxFeatureCount(self, count: int)

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

setOffset(self, offset: float)

Set 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.

New in version 3.0.

setOffsetParameters(self, quadSegments: int, joinStyle: int, miterLimit: float)

Set extra parameters for offset curve algorithm (used when offset is non-zero)

New in version 3.0.

timerEvent()