Ε-approximate nearest neighbor search

ε-approximate nearest neighbor search is a special case of the nearest neighbor search problem. The solution to the ε-approximate nearest neighbor search is a point or multiple points within distance (1+ε) R from a query point, where R is the distance between the query point and its true nearest neighbor.

Reasons to approximate nearest neighbor search include the space and time costs of exact solutions in high-dimensional spaces (see curse of dimensionality) and that in some domains, finding an approximate nearest neighbor is an acceptable solution.

Approaches for solving ε-approximate nearest neighbor search include kd-trees, Locality Sensitive Hashing and brute force search.