nanoflann-knn/examples/pointcloud_adaptor_example.cpp

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#include <cstdlib>
#include <ctime>
#include <iostream>
#include <nanoflann.hpp>

// Declare custom container PointCloud<T>:
#include "utils.h"

void dump_mem_usage();

// And this is the "dataset to kd-tree" adaptor class:
template <typename Derived>
struct PointCloudAdaptor
{
    using coord_t = typename Derived::coord_t;

    const Derived& obj;  //!< A const ref to the data set origin

    /// The constructor that sets the data set source
    PointCloudAdaptor(const Derived& obj_) : obj(obj_) {}

    /// CRTP helper method
    inline const Derived& derived() const { return obj; }

    // Must return the number of data points
    inline size_t kdtree_get_point_count() const
    {
        return derived().pts.size();
    }

    // Returns the dim'th component of the idx'th point in the class:
    // Since this is inlined and the "dim" argument is typically an immediate
    // value, the
    //  "if/else's" are actually solved at compile time.
    inline coord_t kdtree_get_pt(const size_t idx, const size_t dim) const
    {
        if (dim == 0)
            return derived().pts[idx].x;
        else if (dim == 1)
            return derived().pts[idx].y;
        else
            return derived().pts[idx].z;
    }

    // Optional bounding-box computation: return false to default to a standard
    // bbox computation loop.
    //   Return true if the BBOX was already computed by the class and returned
    //   in "bb" so it can be avoided to redo it again. Look at bb.size() to
    //   find out the expected dimensionality (e.g. 2 or 3 for point clouds)
    template <class BBOX>
    bool kdtree_get_bbox(BBOX& /*bb*/) const
    {
        return false;
    }

};  // end of PointCloudAdaptor

template <typename num_t>
void kdtree_demo(const size_t N)
{
    PointCloud<num_t> cloud;

    // Generate points:
    generateRandomPointCloud(cloud, N);

    using PC2KD = PointCloudAdaptor<PointCloud<num_t>>;
    const PC2KD pc2kd(cloud);  // The adaptor

    // construct a kd-tree index:
    using my_kd_tree_t = nanoflann::KDTreeSingleIndexAdaptor<
        nanoflann::L2_Simple_Adaptor<num_t, PC2KD>, PC2KD, 3 /* dim */
        >;

    dump_mem_usage();

    auto do_knn_search = [](const my_kd_tree_t& index) {
        // do a knn search
        const size_t                   num_results = 1;
        size_t                         ret_index;
        num_t                          out_dist_sqr;
        nanoflann::KNNResultSet<num_t> resultSet(num_results);
        num_t                          query_pt[3] = {0.5, 0.5, 0.5};

        resultSet.init(&ret_index, &out_dist_sqr);
        index.findNeighbors(resultSet, &query_pt[0]);

        std::cout << "knnSearch(nn=" << num_results << "): \n";
        std::cout << "ret_index=" << ret_index
                  << " out_dist_sqr=" << out_dist_sqr << std::endl;
    };

    my_kd_tree_t index1(3 /*dim*/, pc2kd, {10 /* max leaf */});
    my_kd_tree_t index2(3 /*dim*/, pc2kd);

    dump_mem_usage();

    do_knn_search(index1);
    do_knn_search(index2);
}

int main()
{
    // Randomize Seed
    srand((unsigned int)time(NULL));
    kdtree_demo<float>(1000000);
    kdtree_demo<double>(1000000);
    return 0;
}