Add 2D example of data structure.

Frechet_distance/examples/Frechet_distance/Frechet_DS_2.cpp

@@ -0,0 +1,42 @@
+#include <CGAL/Frechet_distance.h>
+#include <CGAL/Frechet_distance_traits_2.h>
+#include <CGAL/Frechet_distance/Neighbor_search.h>
+#include <CGAL/Simple_cartesian.h>
+#include <CGAL/IO/WKT.h>
+
+#include <ostream>
+#include <fstream>
+#include <filesystem>
+
+using Kernel = CGAL::Simple_cartesian<double>;
+using Traits = CGAL::Frechet_distance_traits_2<Kernel>;
+using Point = Traits::Point_d;
+using Curve = std::vector<Point>;
+using Curves = std::vector<Curve>;
+
+int main()
+{
+    Curves curves;
+    const std::filesystem::path data{"./data"};
+    for (auto const& dir_entry : std::filesystem::directory_iterator{data}){
+        std::ifstream in(dir_entry.path());
+        curves.push_back(Curve());
+        CGAL::IO::read_linestring_WKT(in, curves.back());
+    }
+
+    Curve query = curves.back();
+
+    curves.pop_back();
+
+    CGAL::Frechet_distance::Neighbor_search<Curve, Traits> ds;
+    ds.insert(curves);
+
+    for(const Curve& c : curves){
+        std::pair<double, double> res = CGAL::bounded_error_Frechet_distance(c, query, 0.000001);
+        std::cout << "The Frechet distance between the polylines is between " <<  res.first << " and " << res.second << std::endl;
+    }
+    double distance = 16;
+    std::vector<std::size_t> result = ds.get_close_curves(query, distance);
+
+    std::cout << result.size() << " curves at Frechet distance closer than " << distance << std::endl;
+}