Generating random not overlaping circles inside polygon in QGIS

Question

How to generate random circles with certain radius size that do not overlap, inside a polygon?

Answer 1

1. Create an image with a cell size equal to the circle radius.
2. Create an empty point vector file with the required CRS (the same as the CRS of the image).
3. Use the r.random tool located in the GRASS toolbox.
4. Use the buffer tool with the distance value equal to the image cell size.
5. Use select by location tool to select all circles that lays within your polygon.
6. Inverse selection and delete all circles that lays outside of the polygon.

Answer 2

In this solution : circles won't overlap but they can touch

Let's assume there is a polygon layer called 'poly_test' with several features in it, see image below.

Step 1. Firstly make use of the "Create grid" geoalgorithm

Please, keep in mind: Horizontal spacing = Vertical spacing = 2 * of the certain radius. So the radius of a circle in this example will be 10000/2 = 5000, that be later proved with this expression :

distance(centroid($geometry), point_on_surface(boundary($geometry)))

Step 2. Use the "Extract by location" geoalgorithm with 'are within' geometrical predicate

Step 3. Proceed with the "Geometry by expression" geoalgorithm

make_circle(centroid($geometry), distance(centroid($geometry), point_on_surface(boundary($geometry)))/sqrt(2), 36)

Step 4. On the last stage apply the "Random extract" geoalgorithm

and get the output like this :