Add velocity based polygon

nav2_collision_monitor/README.md

@@ -36,6 +36,8 @@ The zones around the robot can take the following shapes:
 * Arbitrary user-defined polygon relative to the robot base frame, which can be static in a configuration file or dynamically changing via a topic interface.
 * Robot footprint polygon, which is used in the approach behavior model only. Will use the static user-defined polygon or the footprint topic to allow it to be dynamically adjusted over time.
 * Circle: is made for the best performance and could be used in the cases where the zone or robot footprint could be approximated by round shape.
+* VelocityPolygon: allow switching of polygons based on the command velocity. This is useful for robots to set different safety zones based on their velocity (e.g. a robot that has a larger safety zone when moving at 1.0 m/s than when moving at 0.5 m/s). 
+
 
 The data may be obtained from different data sources:
 
@@ -48,7 +50,7 @@ The data may be obtained from different data sources:
 The Collision Monitor is designed to operate below Nav2 as an independent safety node.
 This acts as a filter on the `cmd_vel` topic coming out of the Controller Server. If no such zone is triggered, then the Controller's `cmd_vel` is used. Else, it is scaled or set to stop as appropriate.
 
-The following diagram is showing the high-level design of Collision Monitor module. All shapes (Polygons and Circles) are derived from base `Polygon` class, so without loss of generality we can call them as polygons. Subscribed footprint is also having the same properties as other polygons, but it is being obtained a footprint topic for the Approach Model.
+The following diagram is showing the high-level design of Collision Monitor module. All shapes (`Polygon`, `Circle` and `VelocityPolygon`) are derived from base `Polygon` class, so without loss of generality we can call them as polygons. Subscribed footprint is also having the same properties as other polygons, but it is being obtained a footprint topic for the Approach Model.
 ![HLD.png](doc/HLD.png)
 ### Configuration
 

nav2_collision_monitor/params/collision_monitor_params.yaml

@@ -55,12 +55,10 @@ collision_monitor:
     VelocityPolygonStop:
       type: "velocity_polygon"
       action_type: "stop"
-      time_before_collision: 2.0
-      simulation_time_step: 0.1
       min_points: 6
       visualize: True
       enabled: True
-      polygon_pub_topic: "polygon_approach"
+      polygon_pub_topic: "velocity_polygon_stop"
       velocity_polygons: ["rotation", "translation_forward", "translation_backward", "stopped"]
       holonomic: false
       rotation: