C++11 header-only library for Nearest Neighbor Search with KD-Trees

 Nanoflann is a fork of the FLANN library. Originally born as a child project
 of the Mobile Robot Programming Toolkit, nanoflann is now available as
 stand-alone library.
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 It trades some of the flexibility of FLANN for raw execution speed and is much
 more memory efficient, as it avoids unnecessary copies of point cloud data.