Using Field Calculator in QGIS to update columns with centroid coordinates

Question

In QGIS I would like to update two columns with the centroid easting and northing of my polygons. I am using the field calculator. I have tried using $x and $y but this only seems to work for points.

I have checked the help but it does not seem to mention being able to do this.

hmm doesn't seem possible at the moment. Shouldn't be too hard to add in. — Nathan W, Jul 01 '11 at 09:22
Any easy thing should be adding centroids to the columns added by "Export geometry columns" — underdark, Jul 01 '11 at 10:44

score 21 · Answer 1 · edited Nov 10 '20 at 16:25

21

Not sure if it worked 5 years ago, but now the solution looks like this:

x(centroid($geometry))

and

y(centroid($geometry))

Results are the same as while using the "Join" option mentioned above:

edited Nov 10 '20 at 16:25

Taras

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answered Nov 21 '16 at 09:28

Mykola Kozyr

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score 15 · Accepted Answer · answered Jul 01 '11 at 10:30

15

A fast way (without field calculator) would be to

create a centroid layer: Vector - Geometry Tools - Polygon Centroids
join the centroid layer to the polygon layer: (Polygon) Layer Properties - Join tab

answered Jul 01 '11 at 10:30

underdark

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Thanks for the answer. I had figured out I could do it this way, I just wondered if there was a way to do it through field calculator like for points. – James S Jul 01 '11 at 10:37

score 0 · Answer 3 · answered Jul 01 '11 at 09:19

If you would consider doing it in workaround method here's how I did it:

Export your polygon as MapInfo file

Calculate centroids with Vector > Geometry Tools > Polygon Centroids

Export centroids as MapInfo File

Remove all unneeded info from Centroid MIF file, leave just coordinates

In your polygon MIF file add information that you have 2 more columns (x and y/lat and long) don't forget to update column count information.

In your polygon MID file copy all columns from centroid MIF file (excel will help here)

There might be a shorter/direct way to do this, but maybe my answer will help you.

Using Field Calculator in QGIS to update columns with centroid coordinates

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