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ANN is a library written in C++, which supports data structures and
algorithms for both exact and approximate nearest neighbor searching in
arbitrarily high dimensions.
In the nearest neighbor problem a set of data points in d-dimensional
space is given. These points are preprocessed into a data structure, so
that given any query point q, the nearest or generally k nearest points of
P to q can be reported efficiently. The distance between two points can be
defined in many ways. ANN assumes that distances are measured using any
class of distance functions called Minkowski metrics. These include the
well known Euclidean distance, Manhattan distance, and max distance.
Based on our own experience, ANN performs quite efficiently for point sets
ranging in size from thousands to hundreds of thousands, and in dimensions
as high as 20. (For applications in significantly higher dimensions, the
results are rather spotty, but you might try it anyway.)
The library implements a number of different data structures, based on
kd-trees and box-decomposition trees, and employs a couple of different
search strategies.
The library also comes with test programs for measuring the quality of
performance of ANN on any particular data sets, as well as programs for
visualizing the structure of the geometric data structures.
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