Throughout the codebase, Parcels uses two different libraries for kdtree:

https://github.com/OceanParcels/parcels/blob/035159a1b4002bc1550cebd275f93c0adaa8513d/parcels/particleset.py#L18-L21

https://github.com/OceanParcels/parcels/blob/035159a1b4002bc1550cebd275f93c0adaa8513d/parcels/interaction/neighborsearch/kdtreeflat.py#L2

Perhaps we should standardise this and use only one of them? Since scipy is already a dependency, perhaps better to use scipy.spatial.KDTree throughout?