more explicit footprint info (ros-navigation#484)

Author: SteveMacenski

concepts/index.rst

@@ -196,6 +196,11 @@ Use of a separate smoother over one that is included as part of a planner is adv
 The general task in Nav2 for a smoother is to receive a path and return its improved version.
 However, for different input paths, criteria of the improvements and methods of acquiring them exist, creating space for a multitude of smoothers that can be registered in this server.
 
+Robot Footprints
+================
+
+It is worth remarking that in the cost maps, we set a robot's footprint either as a circle of radius ``robot_radius`` or as a vector of points ``footprint`` representing an arbitrary polygon if the robot is non-circular. This can also be adjusted over time using the costmap's ``~/footprint`` topic, which will update the polygon over time as needed due to changes in the robot's state, such as movement of an attached manipulator, picking up a pallet, or other actions that adjust a robot's shape. That polygon will then automatically be used by the planners and controllers.
+
 Waypoint Following
 ==================
 

configuration/packages/configuring-costmaps.rst

@@ -44,7 +44,7 @@ Costmap2D ROS Parameters
   ============== =======
 
   Description
-    Ordered set of footprint points passed in as a string, must be closed set. For example, the following defines a square base with side lengths of 0.2 meters `footprint: "[ [0.1, 0.1], [0.1, -0.1], [-0.1, -0.1], [-0.1, 0.1] ]"`.
+    Ordered set of footprint points passed in as a string, must be closed set. For example, the following defines a square base with side lengths of 0.2 meters `footprint: "[ [0.1, 0.1], [0.1, -0.1], [-0.1, -0.1], [-0.1, 0.1] ]"`. Note that this can also be adjusted over time using the costmap's ``~/footprint`` topic, which will update the polygon over time as needed due to changes in the robot's state, such as movement of an attached manipulator, picking up a pallet, or other actions that adjust a robot's shape.
 
 :global_frame:
 

setup_guides/footprint/setup_footprint.rst

@@ -19,6 +19,8 @@ For the global costmap footprint, the decision to choose between the ``robot_rad
 
 For the local costmap footprint, it is typical for non-circular robots to be set up with ``footprint`` (polygon). Some situations where this is not recommended is when you do not have enough computing resources to implement collision avoidance algorithms on a polygon-shaped footprint. Another possible reason to use ``robot_radius`` (circular) for the local costmap is when the robot is very small relative to its environment such that precise collision avoidance is not necessary. However, generally the local trajectory planner should use the actual footprint polygon of the robot. 
 
+Note that this can also be adjusted over time using the costmap's ``~/footprint`` topic, which will update the polygon over time as needed due to changes in the robot's state, such as movement of an attached manipulator, picking up a pallet, or other actions that adjust a robot's shape. That polygon will then automatically be used by the planners and controllers.
+
 Configuring the Robot's Footprint
 *********************************
 In this section, we will configure the footprint of ``sam_bot`` such that ``footprint`` (polygon) is used for the local costmap and ``robot_radius`` (circular) is used for the global costmap. We will utilize the default configuration file of Nav2 with a modified footprint parameter for the global and local costmaps.