nanoflann-knn/examples/vector_of_vectors_example.cpp

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#include <nanoflann.hpp>
using namespace nanoflann;

#include <cstdlib>
#include <ctime>
#include <iostream>

#include "KDTreeVectorOfVectorsAdaptor.h"

const int SAMPLES_DIM = 15;

typedef std::vector<std::vector<double>> my_vector_of_vectors_t;

void generateRandomPointCloud(
    my_vector_of_vectors_t& samples, const size_t N, const size_t dim,
    const double max_range = 10.0)
{
    std::cout << "Generating " << N << " random points...";
    samples.resize(N);
    for (size_t i = 0; i < N; i++)
    {
        samples[i].resize(dim);
        for (size_t d = 0; d < dim; d++)
            samples[i][d] = max_range * (rand() % 1000) / (1000.0);
    }
    std::cout << "done\n";
}

void kdtree_demo(const size_t nSamples, const size_t dim)
{
    my_vector_of_vectors_t samples;

    const double max_range = 20;

    // Generate points:
    generateRandomPointCloud(samples, nSamples, dim, max_range);

    // Query point:
    std::vector<double> query_pt(dim);
    for (size_t d = 0; d < dim; d++)
        query_pt[d] = max_range * (rand() % 1000) / (1000.0);

    // construct a kd-tree index:
    // Dimensionality set at run-time (default: L2)
    // ------------------------------------------------------------
    typedef KDTreeVectorOfVectorsAdaptor<my_vector_of_vectors_t, double>
        my_kd_tree_t;

    my_kd_tree_t mat_index(dim /*dim*/, samples, 10 /* max leaf */);

    // do a knn search
    const size_t        num_results = 3;
    std::vector<size_t> ret_indexes(num_results);
    std::vector<double> out_dists_sqr(num_results);

    nanoflann::KNNResultSet<double> resultSet(num_results);

    resultSet.init(&ret_indexes[0], &out_dists_sqr[0]);
    mat_index.index->findNeighbors(resultSet, &query_pt[0]);

    std::cout << "knnSearch(nn=" << num_results << "): \n";
    for (size_t i = 0; i < resultSet.size(); i++)
        std::cout << "ret_index[" << i << "]=" << ret_indexes[i]
                  << " out_dist_sqr=" << out_dists_sqr[i] << std::endl;
}

int main()
{
    // Randomize Seed
    srand(static_cast<unsigned int>(time(nullptr)));
    kdtree_demo(1000 /* samples */, SAMPLES_DIM /* dim */);
}