[Qgis-user] getting QgsMapCanvasSnapper to work

[Stefanie Tellex]

Here's what I do for snapping in python:
   def canvasReleaseEvent(self, e):
         print "mouse click", e
         mapcoords = 
self.canvas.getCoordinateTransform().toMapCoordinates(e.x(), e.y())
         print "map position", mapcoords
         snapdist = 2
         r = qgis_utils.snap(self.layer, mapcoords,
                             QgsSnapper.SnapToVertexAndSegment,
                             snapdist=0.3)
         if r != None:
             fid = r.snappedAtGeometry
             self.emit(SIGNAL("selectedFeature(int)"), (fid))





def snap(layer, point, snaptype, snapdist=1):
     print "\nsnapping"
     x, reslist = layer.snapWithContext(point, snapdist, snaptype)
     print "x", x
     if x != 0:
         return None
     return getBestSnapResult(reslist)

def getBestSnapResult(snapresult):
     print "result", snapresult
     keys = snapresult.keys()
     keys.sort()
     for k in keys:
         l = snapresult[k]
         for r in l:
             return r


It works, but not great.  It doesn't always get a snap result, even when 
I think it really should.  I think part of the problem is that I'm using 
a fixed snapdist no matter what the zoom level is... but I haven't 
looked at it closely.

Möri Cedric pisze:
> Hi all!
> 
> I'm trying to snap a vertex with my python plugin. (Many thanks to Martin for the quick work with the bindings!)
> 
> My code looks like this:
> 
> def canvasReleaseEvent(self,event):
>     x = event.pos().x()
>     y = event.pos().y()
>            
>     startingPoint = QPoint(x,y)
>     result = []
>     excludePoints = []
>       
>     snapper = QgsMapCanvasSnapper(self.canvas)
>        
>     snapper.snapToCurrentLayer (startingPoint,result,QgsSnapper.SnapToVertex, 10000, excludePoints)
>     print "result: ",result
> 
> The problem is, whatever I do, the result keeps empty. I tried to play with tolerance and scale and I'm quite sure it has to find a vertex but without any success (the layer unit is meter).
> 
> So I thought about using QgsSnapper directly. But I'm not able to set it up properly. Doing the following snippet always leads to a attribut error on the snapLayer struct.
> 
>   snapLayer = QgsSnapper.SnapLayer
>   snapLayer.mLayer = self.iface.mapCanvas().currentLayer()
>   snapLayer.mTolerance = 1000
>   snapLayer.mSnapTo = QgsSnapper.SnapToVertex
> 
> 
> So, if anyone has a hint why the QgsMapCanvasSnapper doesn't want to give me a result or how I set up the struct correctly, it would be wonderful to share it with me :-)
> 
> Best regards and kudos to all the helping people here on the list!
> Cédric
> 
> 
> mit freundlichen Grüssen
> 
> Cédric Möri
> GIS-Informatiker
> 
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