QGIS » QGIS Application

Executing the following python code and then clicking the map canvas works on QGIS 2.2.

On QGIS 2.4 it needs to be adapted, so a new snapper gets created in the callback to restore functionality (Minor issue as the workaround is backwards compatible).

At the same time, a warning gets printed to the log about deprecation of .mapRenderer() and a suggestion to use .mapSettings() instead.

If this is done

• QGIS 2.4 freezes
• QGIS 2.5 (master) crashes (sometimes) in the crs transformation code and never returns any snapped points

also when moving the snapper instantiation to the callback there are no snapping results.

Code working in 2.2 but no longer in 2.4¶

from qgis.gui import QgsMapToolEmitPoint
from PyQt4.QtCore import QPoint

l = iface.activeLayer()
sl = QgsSnapper.SnapLayer()
sl.mLayer = l
sl.mTolerance = 10
sl.mUnitType = QgsTolerance.Pixels
sl.mSnapTo = QgsSnapper.SnapToVertex
s = QgsSnapper( iface.mapCanvas().mapRenderer() )
s.setSnapLayers( [sl] )

mt = QgsMapToolEmitPoint( iface.mapCanvas() )

def canvasclicked( mpt, e ):
    # transform map to device coordinate
    dpt = iface.mapCanvas().getCoordinateTransform().transform( mpt )
    ( _, sp ) = s.snapPoint( QPoint( dpt.x(), dpt.y() ) )
    print '{} points found'.format( len( sp ) )

mt.canvasClicked.connect( canvasclicked )
iface.mapCanvas().setMapTool( mt )

QGIS 2.4 deprecation adapted code: no snapping results are found¶

from qgis.gui import QgsMapToolEmitPoint
from PyQt4.QtCore import QPoint

l = iface.activeLayer()

mt = QgsMapToolEmitPoint( iface.mapCanvas() )

def canvasclicked( mpt, e ):
    sl = QgsSnapper.SnapLayer()
    sl.mLayer = l
    sl.mTolerance = 10
    sl.mUnitType = QgsTolerance.Pixels
    sl.mSnapTo = QgsSnapper.SnapToVertex
    s = QgsSnapper( iface.mapCanvas().mapSettings() )
    s.setSnapLayers( [sl] )
    # transform map to device coordinate
    dpt = iface.mapCanvas().getCoordinateTransform().transform( mpt )
    ( _, sp ) = s.snapPoint( QPoint( dpt.x(), dpt.y() ) )
    print '{} points found'.format( len( sp ) )

mt.canvasClicked.connect( canvasclicked )
iface.mapCanvas().setMapTool( mt )