Add Nearest Neighbors search structure and algorithms

[jalvesz]

Motivation

It would be a very useful feature to add Nearest Neighbors search such as KDtree, BallTree and/or Octree

Prior Art

Some Fortran references:

• https://github.com/dongli/fortran-kdtree

• https://github.com/dongli/fortran-octree

• https://github.com/travissluka/geoKdTree

• https://leonfoks.github.io/coretran/type/kdtree.html

• https://arxiv.org/abs/physics/0408067 and https://github.com/jmhodges/kdtree2

• https://github.com/tchlux/balltree/tree/master

Scikit-learn Nearest Neighbors: https://scikit-learn.org/stable/modules/neighbors.html

• KDTree: https://scikit-learn.org/stable/modules/generated/sklearn.neighbors.KDTree.html
• Ball Tree : https://scikit-learn.org/stable/modules/generated/sklearn.neighbors.BallTree.html#sklearn.neighbors.BallTree

SciPy Nearest-neighbor queries https://docs.scipy.org/doc/scipy/reference/spatial.html#nearest-neighbor-queries

• KDTree: https://docs.scipy.org/doc/scipy/reference/generated/scipy.spatial.KDTree.html#scipy.spatial.KDTree

Some Julia implementations:
https://github.com/sadit/SimilaritySearch.jl
https://github.com/KristofferC/NearestNeighbors.jl

Additional Information

No response