Getting centroids for multiple lines in QGIS

Question

Is there a possibility to get the centroid of each line?

When using Vector > Analysis Tools > Mean Coordinates I always get a centroid of the whole lines. What I need is the centroid of each line without having to select individual lines.

score 9 · Answer 1 · edited Jun 08 '22 at 09:20

9

In the Field Calculator, create a new String field and set the length to be something high like 99. Then use the expression:

geomToWKT(centroid($geometry))

This should give centroid coordinate values like Point (-4.28930643 55.86506837).

edited Jun 08 '22 at 09:20

Taras

32,823
4
66
137

answered Mar 29 '17 at 11:12

Joseph

75,746
7
171
282

@MaFo - Most welcome, glad it was helpful :) – Joseph Mar 29 '17 at 11:43

score 9 · Accepted Answer · edited Jun 08 '22 at 09:19

9

In tool "Mean coordinate(s)" from the QGIS's Processing Toolbox (Ctrl+Alt+T) use Unique "ID" field.

edited Jun 08 '22 at 09:19

Taras

32,823
4
66
137

answered Mar 29 '17 at 11:20

tomalos

191
3

score 1 · Answer 3 · answered Jun 08 '22 at 10:45

There is a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer....

Let's assume there is a polyline layer called 'lines_test2', see image below.

With the following query, it is possible * to get the centroid of each line*.

SELECT
    "id",
    st_centroid(geometry) AS geom
FROM
    "lines_test2"

The output point layer with its attribute table will look like:

However, keep in mind the difference between Centroid | Midpoint | Center, more details here: Getting the line middle point with SQL in QGIS.

References:

Getting centroids for multiple lines in QGIS

3 Answers3

Linked