[Qgis-user] getting QgsMapCanvasSnapper to work

[Carson Farmer]

> I used your code lines and started the debugger. It seems that the QgsMapCanvasSnapper works correctly. I think the problem has to do with the QList reference in the binding:
>
> int snapToCurrentLayer( const QPoint& p, QList<QgsSnappingResult>& results, QgsSnapper::SnappingType snap_to, double snappingTol = -1, const QList<QgsPoint>& excludePoints = QList<QgsPoint>() );

I wonder if this is related to a similar problem I was having with
python bindings for uniqueValues on QgsVectorDataProvider?

> But then Python complains about a wrong type of the results parameter with your code. I tried to use a 'QList' instead of '[]', but it seems there is no QList in PyQt?
> Python experts: How can we deal with QList in PyQGIS?

Short answer: you should be able to use a python list in place of a QList


>
> Regards,
> Marco
>
>
> -----Ursprüngliche Nachricht-----
> Von: qgis-user-bounces at lists.osgeo.org im Auftrag von Möri Cedric
> Gesendet: Di 18.11.2008 18:43
> An: qgis-user at lists.osgeo.org
> Betreff: [Qgis-user] getting QgsMapCanvasSnapper to work
>
> 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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-- 
Carson Farmer
National Centre for Geocomputation
John Hume Building,
National University of Ireland, Maynooth,
Maynooth,
Co. Kildare,
Ireland.
www.carsonfarmer.com