Suppose, you have two point clouds cloud 1 and cloud 2. Suppose, for each point P from cloud 1 you would like to get all the points from cloud 2 that are not farther then a given radius from P.
Then, you could use points-join --all:
> cat cloud-1.csv | points-join cloud-2.csv --radius 1.5 --all
Now, you also can specify variable radius for points in cloud 1. (E.g. your radius may vary depending on your point cloud density or structure, as it happened in our use case.)
Then you could run:
> cat cloud-1.csv | points-join --fields x,y,z,radius cloud-2.csv --radius 1.5 --all
(Note that, as a limitation, the point-specific radius should not exceed --radius value.)