Joining dangling end in the vector layer using QGIS

Question

I have a large river network vector file, where there are disconnections between features. Is there any way to join the nearest dangling points as in the figure below?

I found there is a plugin "Join Multiple Lines" where we manually select the two lines and then they are joined. There are many such lines that are to be joined, so the manual process is quite not favourable for me.

I also tried the "Geometry by expression" tool in QGIS using>

close_line( $geometry)

but I cannot see any change in the output file.

Does anyone have ways to join this kind of dangling points in the MultiLineString vectors?

Answer 1

You can use "Snap Vertices to Nearest Points by Condition" Processing tool from ProcessX PlugIn.

It is made for this purpose. Before running it, just extract the vertices of your lines via "extract vertices" or "points along geometry", depending on your desired result. Then just choose your desired behavior in "snap vertices" and run it.

For your usecase Snap Endvertices of Geometry may suit. You can also use more than one snapping option, e.g. if you also want to snap the ends of multiline parts. You can also choose a maximum snapping distance and an attribute condition, so only the lines with e.g. the same name snap to each other, even if there are other lines within that tolerance distance. As a second condition you could choose that the lines should have a different ID, so they dont snap to a vertex belonging to itself even if they have the same name.

Example result:

Disclaimer: I am the author of this tool.

Answer 2

1. Extract start- and end-points of the lines using Menu Processing > Toolbox > Geometry by expression with this expression: union (start_point ($geometry), end_point($geometry)), then run Multipart to Single parts.

2. Connect each point to the closest point, respecting a maximum distance to get only those connections you want. Use this expression:

    make_line (
        $geometry,
        overlay_nearest(
            @layer,
            $geometry,
            max_distance:=2000 -- change this value to fit your needs
        )[0]
    )

Hint: First use Geometry generator with the same expression. Like this, you can manually adapt the distance in line 6 (here: 2000) and see in realtime how the line changes. This way, you can find the ideal length, then run Geometry by expression with this value.

Expression with Geometry generator: initial line in blue, with start- end end-points (red) and connecting lines (light red):