NearestNeighborsSqrtApprox.h

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/* Author: Ioan Sucan */

#ifndef OMPL_DATASTRUCTURES_NEAREST_NEIGHBORS_SQRT_APPROX_
#define OMPL_DATASTRUCTURES_NEAREST_NEIGHBORS_SQRT_APPROX_

#include "ompl/datastructures/NearestNeighborsLinear.h"
#include <algorithm>
#include <cmath>

namespace ompl
{
    template <typename _T>
    class NearestNeighborsSqrtApprox : public NearestNeighborsLinear<_T>
    {
    public:
        NearestNeighborsSqrtApprox() = default;

        ~NearestNeighborsSqrtApprox() override = default;

        void clear() override
        {
            NearestNeighborsLinear<_T>::clear();
            checks_ = 0;
            offset_ = 0;
        }

        void add(const _T &data) override
        {
            NearestNeighborsLinear<_T>::add(data);
            updateCheckCount();
        }

        void add(const std::vector<_T> &data) override
        {
            NearestNeighborsLinear<_T>::add(data);
            updateCheckCount();
        }

        bool remove(const _T &data) override
        {
            bool result = NearestNeighborsLinear<_T>::remove(data);
            if (result)
                updateCheckCount();
            return result;
        }

        _T nearest(const _T &data) const override
        {
            const std::size_t n = NearestNeighborsLinear<_T>::data_.size();
            std::size_t pos = n;

            if (checks_ > 0 && n > 0)
            {
                double dmin = 0.0;
                for (std::size_t j = 0; j < checks_; ++j)
                {
                    std::size_t i = (j * checks_ + offset_) % n;

                    double distance = NearestNeighbors<_T>::distFun_(NearestNeighborsLinear<_T>::data_[i], data);
                    if (pos == n || dmin > distance)
                    {
                        pos = i;
                        dmin = distance;
                    }
                }
                offset_ = (offset_ + 1) % checks_;
            }
            if (pos != n)
                return NearestNeighborsLinear<_T>::data_[pos];

            throw Exception("No elements found in nearest neighbors data structure");
        }

    protected:
        inline void updateCheckCount()
        {
            checks_ = 1 + (std::size_t)floor(sqrt((double)NearestNeighborsLinear<_T>::data_.size()));
        }

        std::size_t checks_{0};

        mutable std::size_t offset_{0};
    };
}

#endif