Update remove_outlier example with change of API

Point_set_processing_3/examples/Point_set_processing_3/remove_outliers_example.cpp

@@ -1,5 +1,6 @@
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 #include <CGAL/property_map.h>
+#include <CGAL/compute_average_spacing.h>
 #include <CGAL/remove_outliers.h>
 #include <CGAL/IO/read_xyz_points.h>
 
@@ -28,11 +29,38 @@ int main(int argc, char*argv[])
 
   // Removes outliers using erase-remove idiom.
   // The Identity_property_map property map can be omitted here as it is the default value.
-  const double removed_percentage = 5.0; // percentage of points to remove
   const int nb_neighbors = 24; // considers 24 nearest neighbor points
+
+  // Estimate scale of the point set with average spacing
+  const double average_spacing = CGAL::compute_average_spacing<CGAL::Sequential_tag>
+    (points.begin(), points.end(), nb_neighbors);
+
+  //////////////////
+  // FIRST OPTION //
+  // I don't know the ratio of outliers present in the point set
+  std::vector<Point>::iterator first_to_remove
+    = CGAL::remove_outliers(points.begin(), points.end(),
+                            CGAL::Identity_property_map<Point>(),
+                            nb_neighbors,
+                            0.,                    // No minimum percentage to remove
+                            2. * average_spacing); // Point with distance above 2*average_spacing are considered outliers
+
+
+  std::cerr << (100. * std::distance(first_to_remove, points.end()) / (double)(points.size()))
+            << "% of the points are considered outliers when using a distance threshold of "
+            << 2. * average_spacing << std::endl;
+  
+
+  ///////////////////
+  // SECOND OPTION //
+  // I know the ratio of outliers present in the point set
+  const double removed_percentage = 5.0; // percentage of points to remove
+
   points.erase(CGAL::remove_outliers(points.begin(), points.end(),
                                      CGAL::Identity_property_map<Point>(),
-                                     nb_neighbors, removed_percentage), 
+                                     nb_neighbors,
+                                     removed_percentage, // Minimum percentage to remove
+                                     0.), // No distance threshold (can be omitted)
                points.end());
 
   // Optional: after erase(), use Scott Meyer's "swap trick" to trim excess capacity