QGIS 3x capturing coordinates for multitude of objects at once

Question

I would like to ask about the possibility of capturing coordinates for more than 1 object in QGIS.

I used to use the coordinate capture plugin, but what is the problem there I have to collect coordinates one by one.

Is there any way to collect coordinates i.e. for all points from the given layer and export them to excel? Following their names or different features from data attribute table?

I will by more than happy if someone clarifies it for me.

UPDATE:

Following the answer below, I tried to run the $x expression, but it returns NULL.

What am I missing here?

Please define what you mean by "capturing" and what you're doing with the coordinates afterwards. — Erik, Sep 04 '20 at 08:18
Capturing - implicitly - gathering the coordinates, as you do with coordinate capture plugin. I need them as a list in Excel. There are about 30-40 of them from each layer. — Geographos, Sep 04 '20 at 08:47

score 5 · Answer 1 · answered Sep 04 '20 at 08:56

5

You may use the field calculator to add the coordinates of a feature to the attribute table. In cases like yours I usually create two fields, one for the X coordinate, and one for Y.

The expression is utterly simple:

$x

This writes the X coordinate in a column. The same goes for $y. Afterwards you can copy & paste the attribute table to excel.

You should choose the column type according to your CRS.

answered Sep 04 '20 at 08:56

Erik

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I suppose @Erik can refer to this thread Exporting x,y coordinates as latitude,longitude – Taras Sep 04 '20 at 09:01
Pay attention that when applying copy & paste the attribute table into Excel, it is not 100% sure whether Excel will maintain the type/format of the output data, I will suggest using one of solutions provided here Exporting attribute table to Excel from QGIS?. – Taras Sep 04 '20 at 09:05
if I type $x it returns NULL. What am I missing? – Geographos Sep 10 '20 at 08:41
NULL can appear when you use $x or $y for polylines and polygons – Taras Sep 10 '20 at 09:16
yes, exactly i've got the polygons. Shall I make it for the points only then? – Geographos Sep 10 '20 at 09:19
yes, I think @Erik meant points in his answer – Taras Sep 10 '20 at 09:22
Oh that sucks. I have the polygons lines and polylines mostly. Is there any way to set the coordinates for polygons at least? – Geographos Sep 10 '20 at 09:29
1

@MKR since you're talking about "all points from the given layer" I assumed you had points. My solution doesn't work for lines/polygons. – Erik Sep 10 '20 at 13:22
Ok thank you for clarification. I will definitely use it for points in the future. – Geographos Sep 10 '20 at 13:27

Taras · Accepted Answer · 2020-09-18T09:04:02.680

You get NULL while using $x or $y because your geometry is probably either Polylines or Polygons.

So, I will suggest employing this expression to capture coordinates for a multitude of objects at once

map_to_json(
    map(
        'x', array_to_string(array_foreach(generate_series(1, num_points($geometry)), x(point_n($geometry, @element)))),
        'y', array_to_string(array_foreach(generate_series(1, num_points($geometry)), y(point_n($geometry, @element))))
     )
)

So, the result will look as following

{"x":"5395496.429117461,5395494.155999963,5395489.773418307","y":"5659901.713053187,5659897.333999608,5659899.601836967"}
{"x":"5396759.156386755,5396761.318999965,5396764.051999965,5396762.000375618,5396760.367999964,5396755.841312531","y":"5660769.610787445,5660770.32399961,5660769.08599961,5660764.5589490365,5660760.95699961,5660763.009167434"}
{"x":"5397230.945016465,5397230.575999966,5397225.642692687","y":"5660956.466597664,5660951.539999611,5660951.8752865605"}
...

There is also a possibility of using this expression with a different formatting

array_to_string(
               array_foreach(generate_series(1, num_points($geometry)),
                             'Point_'  || @element || ': (' || x(point_n($geometry, @element))|| ', ' || y(point_n($geometry, @element)) || ')'
                )
)

That will lead to this

Point_1: (5395496.429117461, 5659901.713053187),Point_2: (5395494.155999963, 5659897.333999608),Point_3: (5395489.773418307, 5659899.601836967)
Point_1: (5396759.156386755, 5660769.610787445),Point_2: (5396761.318999965, 5660770.32399961),Point_3: (5396764.051999965, 5660769.08599961),Point_4: (5396762.000375618, 5660764.5589490365),Point_5: (5396760.367999964, 5660760.95699961),Point_6: (5396755.841312531, 5660763.009167434)
Point_1: (5397230.945016465, 5660956.466597664),Point_2: (5397230.575999966, 5660951.539999611),Point_3: (5397225.642692687, 5660951.8752865605)
...

Both cases are approachable in the "Field Calculator" via creating a new text(string) field and using those expressions in Expression Dialog.

Note: it shall do the work for all geometry types

The expression works, but how to use it really. I plotted it into my data attribute table, where is the "e" - expression symbol and I saw your result at the very bottom like you wrote (points with coordinates) but I couldn't plot them into my data attribute table column. Is there any way to do this? — Geographos, Sep 18 '20 at 07:47
Simply create a new a new text(string) field and use those expressions there — Taras, Sep 18 '20 at 07:58
Hi,
Is that the way that I should use?

https://imgur.com/gallery/fdp1atX

It doesn't provide any result. Where should I roughly place this formula? — Geographos, Sep 18 '20 at 08:41
OK, now sorted. Could you tell me how to use your expression for the decimal type? — Geographos, Sep 18 '20 at 10:41
Can you please explain to me how would you like to have that decimal type, how will it look like? — Taras, Sep 19 '20 at 15:43
I think, that I already solved my problem, as I can run the centroid expression, which makes a perfect shortcut.
https://gis.stackexchange.com/questions/374849/merging-attributes-of-selected-features-not-working-in-qgis-3

Thank you very much for the help. I will definitely take into account your option when working with geoJSON or sth. — Geographos, Sep 24 '20 at 09:38

QGIS 3x capturing coordinates for multitude of objects at once

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