adding missing example

Point_set_processing_3/examples/Point_set_processing_3/poisson_eliminate_from_mesh_example.cpp

@@ -0,0 +1,65 @@
+#include <vector>
+#include <iostream>
+#include <fstream>
+#include <filesystem>
+#include <string>
+
+#include <CGAL/Surface_mesh.h>
+#include <CGAL/Simple_cartesian.h>
+#include <CGAL/poisson_eliminate.h>
+#include <CGAL/Polygon_mesh_processing/distance.h>
+#include <CGAL/IO/write_points.h>
+
+using Point_3 = CGAL::Simple_cartesian<double>::Point_3;
+using Mesh = CGAL::Surface_mesh<Point_3>;
+
+int main(int argc, char* argv[])
+{
+  std::vector<Point_3> points;
+  std::size_t sampling_size = 20000;
+  std::size_t target_size = 10000;
+  Mesh mesh;
+
+  if (argc == 4) {
+    target_size = std::atoi(argv[2]);
+    sampling_size = std::atoi(argv[3]);
+    if (sampling_size < target_size) {
+      std::cout << "usage: poisson_eliminate_from_mesh_example input_mesh target_size sampling_size" << std::endl << "with sampling_size > target_size, e.g. by a factor of 2" << std::endl;
+      return -1;
+    }
+  }
+
+  if (argc == 3) {
+    target_size = std::atoi(argv[2]);
+    sampling_size = 2 * target_size;
+  }
+
+  if (argc < 2)
+    CGAL::IO::read_polygon_mesh(CGAL::data_file_path("meshes/elephant.off"), mesh);
+  else
+    CGAL::IO::read_polygon_mesh(argv[1], mesh);
+
+  if (mesh.number_of_faces() == 0) {
+    std::cout << "mesh could not be loaded" << std::endl;
+    std::cout << "usage: poisson_eliminate_from_mesh_example input_mesh target_size sampling_size" << std::endl << "with sampling_size > target_size, e.g. by a factor of 2" << std::endl;
+    return -1;
+  }
+
+  points.reserve(sampling_size);
+  CGAL::Polygon_mesh_processing::sample_triangle_mesh(mesh,
+    std::back_inserter(points),
+    CGAL::parameters::number_of_points_on_faces(sampling_size)
+    .do_sample_vertices(false)
+    .do_sample_edges(false));
+
+  CGAL::IO::write_points("out_sampled.xyz", points, CGAL::parameters::stream_precision(17));
+
+  std::vector<Point_3> output;
+  output.reserve(target_size);
+
+  CGAL::poisson_eliminate(points, target_size, std::back_inserter(output));
+
+  CGAL::IO::write_points("out_poisson_eliminated.xyz", output, CGAL::parameters::stream_precision(17));
+
+  return 0;
+}