Method filter

filters/LOFFilter.cpp:73–140

}

void LOFFilter::filter(PointView& view)
{
    const KD3Index& index = view.build3dIndex();

    // Increment the minimum number of points, as knnSearch will be returning
    // the neighbors along with the query point.
    m_minpts++;

    // First pass: Compute the k-distance for each point.
    // The k-distance is the Euclidean distance to k-th nearest neighbor.
    log()->get(LogLevel::Debug) << "Computing k-distances...\n";

    typedef std::pair<PointId, size_t> PointIdKPair;
    typedef std::pair<PointId, double> PointIdDistPair;
    typedef std::map<PointIdKPair, PointIdDistPair> AdjacencyMap;
    AdjacencyMap mat;

    for (PointId i = 0; i < view.size(); ++i)
    {
        PointIdList indices(m_minpts);
        std::vector<double> sqr_dists(m_minpts);
        index.knnSearch(i, m_minpts, &indices, &sqr_dists);

        for (size_t j = 0; j < m_minpts; ++j)
            mat[std::make_pair(i, j)] = std::make_pair(indices[j], std::sqrt(sqr_dists[j]));

        view.setField(Id::NNDistance, i, std::sqrt(sqr_dists[m_minpts - 1]));
    }

    // Second pass: Compute the local reachability distance for each point.
    // For each neighbor point, the reachability distance is the maximum value
    // of that neighbor's k-distance and the distance between the neighbor and
    // the current point. The lrd is the inverse of the mean of the reachability
    // distances.
    log()->get(LogLevel::Debug) << "Computing lrd...\n";
    for (PointId i = 0; i < view.size(); ++i)
    {
        double M1 = 0.0;
        point_count_t n = 0;
        for (size_t j = 0; j < m_minpts; ++j)
        {
            auto val = mat[std::make_pair(i, j)];
            double k = view.getFieldAs<double>(Id::NNDistance, val.first);
            double reachdist = (std::max)(k, val.second);
            M1 += (reachdist - M1) / ++n;
        }
        view.setField(Id::LocalReachabilityDistance, i, 1.0 / M1);
    }

    // Third pass: Compute the local outlier factor for each point.
    // The LOF is the average of the lrd's for a neighborhood of points.
    log()->get(LogLevel::Debug) << "Computing LOF...\n";
    for (PointId i = 0; i < view.size(); ++i)
    {
        double lrdp = view.getFieldAs<double>(Id::LocalReachabilityDistance, i);
        double M1 = 0.0;
        point_count_t n = 0;
        for (size_t j = 0; j < m_minpts; ++j)