nav2_collision_monitor: collision detector (ros-navigation#3500)

Author: Tony Najjar

nav2_collision_monitor/README.md

@@ -29,7 +29,6 @@ The following models of safety behaviors are employed by Collision Monitor:
 
 * **Stop model**: Define a zone and a point threshold. If more that `N` obstacle points appear inside this area, stop the robot until the obstacles will disappear.
 * **Slowdown model**: Define a zone around the robot and slow the maximum speed for a `%S` percent, if more than `N` points will appear inside the area.
-* **Limit model**: Define a zone around the robot and clamp the maximum speed below a fixed value, if more than `N` points will appear inside the area.
 * **Approach model**: Using the current robot speed, estimate the time to collision to sensor data. If the time is less than `M` seconds (0.5, 2, 5, etc...), the robot will slow such that it is now at least `M` seconds to collision. The effect here would be to keep the robot always `M` seconds from any collision.
 
 The zones around the robot can take the following shapes:

nav2_collision_monitor/src/collision_monitor_node.cpp

@@ -280,8 +280,9 @@ bool CollisionMonitor::configurePolygons(
   try {
     auto node = shared_from_this();
 
+    // Leave it to be not initialized: to intentionally cause an error if it will not set
     nav2_util::declare_parameter_if_not_declared(
-      node, "polygons", rclcpp::ParameterValue(std::vector<std::string>()));
+      node, "polygons", rclcpp::PARAMETER_STRING_ARRAY);
     std::vector<std::string> polygon_names = get_parameter("polygons").as_string_array();
     for (std::string polygon_name : polygon_names) {
       // Leave it not initialized: the will cause an error if it will not set