Selecting the closest lines to a point in QGIS

Question

I need to select the closest (and only the closest) lines to a point in QGIS. The lines may belong to different layers. The idea is to be able to combine the selected lines to form the smallest polygon that contains the point used to select the lines. This is an example of my situation:

The yellow point is the one i should use to make the selection; the lines can be blue, red, yellow, green or black, and they may belong to different layers. I tried the NNJoin plugin, but it doesn't work for me. Also the Nearest Neighbor tool doesn't work (it returns a List Index Out of Range error).

Does anybody have a suggestion?

Answer 1

In QGIS there is the DB Manager where you can execute SQL code. I am assuming you are using shapefiles, which can have SQL applied to them in the DB Manager and can be found in the 'Virtual Layers' data list.

So in the SQL Window, use the following code below, except replace 'linelayer' and 'pointlayer' with the datasets that contain your line and point data. Then the point_id is the field name for what ever uniquely identifies the point you want to run the query on.

 SELECT  linelayer.*
 FROM linelayer,
      (SELECT geometry FROM pointlayer WHERE point_id = <POINTID>) as point
 ORDER BY ST_Distance(point.geometry,linelayer.geometry)
 LIMIT 1

Hit execute and you should get one feature returned that is the closest to your point. You can then create a temporary layer by selecting the 'Load as new layer' check box right at the bottom of the window.