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I have a script that creates a square buffer of 1 degree around a point in QGIS, through the python console but I am unable to find a way to create circular buffers instead. Also, would it be possible to add to the script to add multiple buffers around the same point of different distances, as I currently have 1 degree but would like 5 degrees, 10 degrees... etc. The script I have currently written:

layer = iface.activeLayer()

feats = [ feat for feat in layer.getFeatures() ]

epsg = layer.crs().postgisSrid()

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=point_id:integer""&index=yes"

mem_layer = QgsVectorLayer(uri,
                           'circular_buffer',
                           'memory')

prov = mem_layer.dataProvider()

for i, feat in enumerate(feats):
    point = feat.geometry().asPoint()
    new_feat = QgsFeature()
    new_feat.setAttributes([i, point[0], point[1], feat.id()])
    tmp_feat = feat.geometry().buffer(1, -1).boundingBox().asWktPolygon()
    new_feat.setGeometry(QgsGeometry.fromWkt(tmp_feat))
    prov.addFeatures([new_feat])

QgsProject.instance().addMapLayer(mem_layer)
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    Have you tried to use: tmp_feat = feat.geometry().buffer(1, -1).asWktPolygon() instead. without the boundingbox function it should return a circular buffer
    – eurojam
    Commented Nov 18, 2020 at 16:35
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    A one degree buffer is an odd requirement, since degrees are angular measurements which measure wildly differing distances depending on latitude. A sixty nautical mile buffer would be slightly oblate over the Equator, and more and more egg-shaped as you increased latitude, so if you're doing a buffer in decimal degrees and see a circle, it's pretty much always wrong.
    – Vince
    Commented Nov 18, 2020 at 18:56
  • @eurojam Unfortunately after removing the bounding box function, it comes up with an error - AttributeError: 'QgsGeometry' object has no attribute 'asWktPolygon'. Any ideas?
    – LiamHems
    Commented Nov 19, 2020 at 11:20
  • @Vince I have tried to get a different CRS so that it would be in metres or another measurement other than degrees but every time I change the projection, I either can not see the geojson file or other files within my project
    – LiamHems
    Commented Nov 19, 2020 at 11:21
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    GeoJSON is restricted to WGS84 (4326), so that's nearly a different issue (GeoJSON isn't mentioned anywhere in the question). Note that projection "change" usually applies to clobbering the existing CRS, when "reprojection" is usually the goal.
    – Vince
    Commented Nov 19, 2020 at 12:25

1 Answer 1

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You can try the following, which will work anyway. Since the tmp_feat is from type geometry you can pass it directly to new_feat.setGeometry(tmp_feat)

layer = iface.activeLayer()
feats = [ feat for feat in layer.getFeatures() ]
epsg = layer.crs().postgisSrid()
uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&    field=y:real&field=point_id:integer""&index=yes"

mem_layer = QgsVectorLayer(uri,
                       'circular_buffer',
                       'memory')
prov = mem_layer.dataProvider()

for i, feat in enumerate(feats):
    point = feat.geometry().asPoint()
    new_feat = QgsFeature()
    new_feat.setAttributes([i, point[0], point[1], feat.id()])
    tmp_feat = feat.geometry().buffer(1, -1)
    new_feat.setGeometry(tmp_feat)
    prov.addFeatures([new_feat])

QgsProject.instance().addMapLayer(mem_layer)
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  • Thank you very much, it works now!
    – LiamHems
    Commented Nov 19, 2020 at 11:41
  • Do you know how I would be able to change the buffer opacity to 50% and to also change the color of the buffer to red too? Thanks
    – LiamHems
    Commented Nov 19, 2020 at 13:34
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    it is something like: sym =mem_layer.renderer().symbol() sym.setColor(QColor("red")) sym.setOpacity(50)
    – eurojam
    Commented Nov 19, 2020 at 17:40

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