Nearest distance between point and line layers in QGIS

Question

I have two layers, a line and a point layer.

I need to make a line layer which connects all the points to the nearest line feature. How can I do that?

Is there a plugin available for QGIS? This is a very important tool which is missing in QGIS.

ArcView has this tool: "Nearest Features"

Answer 1

As an alternative, you could:

1. Use the Convert Lines to Points tool from:

   Processing Toolbox > SAGA > Shapes - Points > Convert Lines to Points

   (Add points over small distances. E.g. add a point every 1m if the overall line is 100m)

   

2. Use the Distance to nearest hub from:

   Processing Toolbox > QGIS geoalgorithms > Vector analysis tools > Distance to nearest hub

   (Set the parameters, using the output layer of the Convert Lines to Points tool as the Destination hubs layer and setting the Output shape type as Line to hub)

   

3. Final result should be a line layer which connects the original points layer with the original line layer (with line-converted points):

   

   (without line-converted points):

   

I used QGIS 2.12.3-Lyon.

Answer 2

In QGIS I can suggest using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer....

Let's assume we have two layers 'points' and 'river' with their corresponding attribute tables, see image below.

With the following query, it is possible to create new lines that will represent the connection between points to the nearest line features.

SELECT
    ST_ShortestLine(r.geometry, p.geometry),
    p.id AS pid,
    r.id AS rid,
    ROUND(ST_Length(ST_ShortestLine(r.geometry, p.geometry)), 6) AS distance
FROM
    points AS p, river AS r
WHERE
    distance < 0.5
GROUP BY
    p.id
ORDER BY
    MIN(distance)

Note:

• WHERE distance < 0.5 specifies the longest acceptable distance between point to the line feature

The output Virtual Layer with its Attribute table will look as following

Answer 3

The ClosestPoint does what you are looking for, currently limited to selected features only. You can take a look at the code and modify it for your needs

Answer 4

Meanwhile (since QGIS 3.16), there is the new overlay_nearest() function you can use for that with QGIS expressions. For each point, 1) get the nearest line with overlay_nearest(), 2) get the closest point on this line to the point using closest_point().

The expression to be used with Geometry generator or Geometry by expression (see here for details) look like:

make_line (
    $geometry,
    closest_point (
        overlay_nearest ('line', $geometry)[0],
        $geometry
    )
)

• Replace line in line 4 with the name of your line layer.

Dotted lines to connect points to nearest lines are created with the above expression:

Answer 5

If you find the point over the line, the shortest point, with the coordinate 3D (X,Y,Z) you need an algorithm to calc the position over the shortest line. You can using this tool https://github.com/rafaelduartenom/findpointonline. You need postgres to execute this tool and shapefiles.