Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[DelazJ]

Hi,
Seem a good candidate for PyQGIS Cookbook ...

Regards,
Harrissou

2017-01-12 17:43 GMT+01:00 Martin Dobias :

> Hi Tom
>
> Try something like this:
>
> request = QgsFeatureRequest(iface.mapCanvas().extent())
> request.setFlags(QgsFeatureRequest.ExactIntersect)
> for f in layer.getFeatures(r):
>   print f.id()
>
> This feature request will only use features that intersect canvas
> view. The extra flag ExactIntersect is there to make sure that true
> intersection test is done, rather just doing fast intersection of
> geometry's bounding box with the canvas extent recangle.
>
> Cheers
> Martin
>
> On Fri, Jan 13, 2017 at 12:07 AM, Tom Chadwin 
> wrote:
> > Hello all
> >
> > I currently create a memory layer from an existing layer as follows
> > ('usedFields' is a subset of the original layer's attributes/fields):
> >
> > newlayer = QgsVectorLayer(uri, layer.name(), 'memory')
> > writer = newlayer.dataProvider()
> > outFeat = QgsFeature()
> > for feature in layer.getFeatures():
> > if feature.geometry() is not None:
> > outFeat.setGeometry(feature.geometry())
> > attrs = [feature[f] for f in usedFields]
> > if attrs:
> > outFeat.setAttributes(attrs)
> > writer.addFeatures([outFeat])
> >
> > What is the best way to add only features visible in the current QGIS
> view
> > of the canvas, rather than every feature in the layer?
> >
> > Thanks
> >
> > Tom
> >
> >
> >
> > -
> > Buy Pie Spy: Adventures in British pastry 2010-11 on Amazon
> > --
> > View this message in context: http://osgeo-org.1560.x6.
> nabble.com/Create-memory-layer-containing-only-
> features-visible-in-current-canvas-extent-tp5303218.html
> > Sent from the Quantum GIS - Developer mailing list archive at Nabble.com.
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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Tom Chadwin]

Many thanks, Matthias and Martin - I got it working exactly as you suggested.
Is this the mechanism which QGIS itself uses to determine which features are
in the viewport?

I'm running into some performance issue which I thought this would help, but
they are not solved yet, so I might soon have a more general question about
identifying bottlenecks in PyQGIS code.

Tom



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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Tom Chadwin]

This looks ideal. Thanks, both. Plus I could make ExactIntersect an option in
the GUI, as sometimes dotted could be more critical than accuracy.

Thanks again

Tom



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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Martin Dobias]

Hi Tom

Try something like this:

request = QgsFeatureRequest(iface.mapCanvas().extent())
request.setFlags(QgsFeatureRequest.ExactIntersect)
for f in layer.getFeatures(r):
  print f.id()

This feature request will only use features that intersect canvas
view. The extra flag ExactIntersect is there to make sure that true
intersection test is done, rather just doing fast intersection of
geometry's bounding box with the canvas extent recangle.

Cheers
Martin

On Fri, Jan 13, 2017 at 12:07 AM, Tom Chadwin  wrote:
> Hello all
>
> I currently create a memory layer from an existing layer as follows
> ('usedFields' is a subset of the original layer's attributes/fields):
>
> newlayer = QgsVectorLayer(uri, layer.name(), 'memory')
> writer = newlayer.dataProvider()
> outFeat = QgsFeature()
> for feature in layer.getFeatures():
> if feature.geometry() is not None:
> outFeat.setGeometry(feature.geometry())
> attrs = [feature[f] for f in usedFields]
> if attrs:
> outFeat.setAttributes(attrs)
> writer.addFeatures([outFeat])
>
> What is the best way to add only features visible in the current QGIS view
> of the canvas, rather than every feature in the layer?
>
> Thanks
>
> Tom
>
>
>
> -
> Buy Pie Spy: Adventures in British pastry 2010-11 on Amazon
> --
> View this message in context: 
> http://osgeo-org.1560.x6.nabble.com/Create-memory-layer-containing-only-features-visible-in-current-canvas-extent-tp5303218.html
> Sent from the Quantum GIS - Developer mailing list archive at Nabble.com.
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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Matthias Kuhn]

http://www.qgis.org/api/classQgsFeatureRequest.html#ac7c734b9cab6939a706ea53040afe6b3

that might help

On January 12, 2017 5:20:07 PM GMT+01:00, Tom Chadwin  
wrote:
>I've found this method:
>
>viewportPolygon =
>QgsGeometry().fromWkt(iface.mapCanvas().extent().asWktPolygon())
>layer = iface.activeLayer()
>
>resultlayer = QgsVectorLayer("Polygon", "result", "memory")
>resultlayer.dataProvider().addAttributes(list(layer.dataProvider().fields()))
>
>clippedFeatures = []
>for feature in layer.dataProvider().getFeatures():
>clippedGeometry = feature.geometry().intersection(viewportPolygon)
>
>
>From http://gis.stackexchange.com/a/74471/36921
>
>However, this loops through all features. I'm concerned that this will
>struggle with large layers. Is there a more efficient method?
>
>
>
>-
>Buy Pie Spy: Adventures in British pastry 2010-11 on Amazon 
>--
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>http://osgeo-org.1560.x6.nabble.com/Create-memory-layer-containing-only-features-visible-in-current-canvas-extent-tp5303218p5303223.html
>Sent from the Quantum GIS - Developer mailing list archive at
>Nabble.com.
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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Paolo Cavallini]

Il 12/01/2017 17:20, Tom Chadwin ha scritto:

> However, this loops through all features. I'm concerned that this will
> struggle with large layers. Is there a more efficient method?

I guess that's unsuitable for layers of millions of records.
all the best.
-- 
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QGIS & PostGIS courses: http://www.faunalia.eu/training.html
https://www.google.com/trends/explore?date=all=IT=qgis,arcgis
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Re: [Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Tom Chadwin]

I've found this method:

viewportPolygon =
QgsGeometry().fromWkt(iface.mapCanvas().extent().asWktPolygon())
layer = iface.activeLayer()

resultlayer = QgsVectorLayer("Polygon", "result", "memory")
resultlayer.dataProvider().addAttributes(list(layer.dataProvider().fields()))

clippedFeatures = []
for feature in layer.dataProvider().getFeatures():
clippedGeometry = feature.geometry().intersection(viewportPolygon)


From http://gis.stackexchange.com/a/74471/36921

However, this loops through all features. I'm concerned that this will
struggle with large layers. Is there a more efficient method?



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[Qgis-developer] Create memory layer containing only features visible in current canvas extent

[Tom Chadwin]

Hello all

I currently create a memory layer from an existing layer as follows
('usedFields' is a subset of the original layer's attributes/fields):

newlayer = QgsVectorLayer(uri, layer.name(), 'memory')
writer = newlayer.dataProvider()
outFeat = QgsFeature()
for feature in layer.getFeatures():
if feature.geometry() is not None:
outFeat.setGeometry(feature.geometry())
attrs = [feature[f] for f in usedFields]
if attrs:
outFeat.setAttributes(attrs)
writer.addFeatures([outFeat])

What is the best way to add only features visible in the current QGIS view
of the canvas, rather than every feature in the layer?

Thanks

Tom



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