Did you mean 'coarse'?

As a note; there is no need to sqrt(...) for all N^2 of the distances. Instead, simply square your threshold; that is a much cheaper operation, only needing to be done once.

If you have a large number of coordinates, you could also break the world up into a grid of buckets. Each entry then only needs to check distance to the entries in the nearest four adjacent buckets. Use a 2D hash of buckets since most buckets will be unused/empty out in the countryside.

In reply to Re^2: CSV Cross Referencing by SuicideJunkie
in thread CSV Cross Referencing by Jalcock501

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