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I have a point layer, and a polygon layer with buffers of a given radius around each point. I need to move points, and check that each buffer is not above forbidden land/plots.

In autocad, you can move a circle snapping its center, so you can see immediately the circle limits, and make sure it is not above forbidden land.

Here in qgis, I can only :

  1. move my point
  2. buffer my point
  3. check the buffer doesn't come over forbidden plots.

and if it does, do the process all over again. A pain !

So I would like to :

  1. move at the same time point and buffer by the centre, although it is probably impossible as it's on two different layers,

  2. move a circle by its center, so I can directly snap it to my point and check the circle position.

Any ideas ?

I guess, it could be a plugin doing polygon centroid + move item snapping by its centroid. I didn't find anything of the kind.

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  • 1
    You can use the move feature of the digitizing toolbar. Before doing that you can set a snapping threshold at settings/snapping options and there select the point/polygon layer you want to sanp to and set a treshold of 10-15 pixels. After that you have to select the layer where you want to move features, put this layer in edit mode, select the feature you want to move and chose the move feature icon and move your feature where you want to be.
    – Gerardo Jimenez
    Sep 29, 2014 at 15:25
  • Hello, thank you for your reply. What you're describing is how to move an object snapping to existing points of that object. What I want is to be able to move object snapping to inferred points, the way autocad does it. Because if I don't snap by the center, I can't precisely place my circle/buffer around a given point on my point layer..
    – Gilles
    Oct 2, 2014 at 15:03
  • If your points have to be in the center of the buffers you can calculate the centroid of the buffers (vector, geometry tools, polygon centroids). That will give you a shape layer with the center of each buffer. Later you can move the desired points to the center of the buffer as described before.
    – Gerardo Jimenez
    Oct 3, 2014 at 16:40
  • Hi, thank you Gerardo for you reply. What you're describing is a workaround, indeed that's what I've been doing so far. I'd like, however, to move the buffer snapping it by its center point (this point beeing only virtual, with no real existence as a data). Of course, it could be moving a line by its middle point, moving a rectangle by its center or the middle of a side... it's the same principle of snapping to inferred points, the way DAO softwares do it. An idea for a plugin ?
    – Gilles
    Oct 6, 2014 at 15:47
  • I do not know if this could help, but have you tried CADTools plugin?
    – Gerardo Jimenez
    Oct 6, 2014 at 16:49

1 Answer 1

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QGIS 2.14 +

Geometry generator has made "dynamic geometries" possible.

On your point layer's Layer Properties window:

  1. Click on green plus button.
  2. Set Symbol layer type to Geometry generator
  3. Select Polygon / Multipolygon as the Geometry type
  4. Create an Expression such as buffer($geometry, 2000) (depend on your radius)

enter image description here

Generated buffer(s) will follow the points as you move them.

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