[ros-users] Base Local Planner function visualization

[Eric Perko]

Hey all,

So, last time I worked with tuning the cost scoring parameters of
base_local_planner it was tricky due to no way to easily tell how each term
in the cost function was influencing the scored trajectories. To address
this problem, I've created a class that outputs a PointCloud2 on a topic
called cost_cloud under the base_local_planner namespace that contains the
cost information for each component of the cost function as well as the
total cost for each point the MapGrid maintained by the TrajectoryPlanner
class. You can find the code here:
https://github.com/ericperko/ros_navigation . You can find some sample
images from rviz at
http://www.dropbox.com/gallery/1970299/1/BaseLocalPlannerVizSamples?h=885d40 ,
files named by which cost value they are visualizing (hover over the
thumbnails to see the filenames or click for the gallery view and it will be
listed below the thumbnails at the top), to give you all an idea of what
this code outputs (red is lowest cost).

There are a few steps to actually being able to use this functionality:


   1. Checkout the updated Nav Stack from
   https://github.com/ericperko/ros_navigation or otherwise apply commit
   https://github.com/ericperko/ros_navigation/commit/00ec9847100942767a80524b401fc8c26e652d02
to
   your existing base_local_planner package & recompile it.
   2. Update your base_local_planner_params.yaml file with two more
   parameters:
      1. "publish_cost_grid_pc" to true. Default is false so that people who
      aren't interested in seeing the point cloud aren't wasting
cycles making &
      publishing it.
      2. "global_frame_id" to whatever your local costmap's global frame is.
      By default, this is "odom" to match the setup in the nav stack setup (
      http://www.ros.org/wiki/navigation/Tutorials/RobotSetup ). This is the
      frame id set for the output point cloud so will determine how it draws in
      the map.
   3. Now you should be able to verify that base_local_planner is outputting
   a PointCloud using something like "rostopic hz
   /move_base/TrajectoryPlannerROS/cost_cloud"
   4. In order to visualize the PointCloud in a meaningful way, you will
   have to apply the patch in https://code.ros.org/trac/ros-pkg/ticket/4610 to
   RViz so that you can treat arbitrary channels as intensity data. The
   visualization will be much more readable if you also make sure to check the
   "Use full RGB spectrum" box so that gradients are more apparent.
   5. Have fun selecting different components of the cost function and
   seeing what sort of affect they have on the potential field that
   base_local_planner is sampling trajectories from! Note that we don't output
   any points that have any cost component greater than max cost and would
   therefore be illegal for the planner to try to execute.

Feedback would be very welcome and I hope this comes in handy. I know it's
already helped me out by letting me see that my obstacle cost field doesn't
extend as far as I might like.

Eitan, any feedback on changes that are required to make this more general
for use in, for example, dwa_local_planner would be great. Also, the C++ API
of TrajectoryPlanner would likely have to change slightly if we wanted to
move the visualizer and it's use of ROS topics and parameters up to
TrajectoryPlannerROS. Specifically, the MapGrid would either need to become
public or we'd need to add a getter for it; currently it's private to the
TrajectorPlanner, so that's where the MapGridVisualizer is instantiated.
Either that or pass in a number of variables in the constructor/setter
methods (especially the scaling values). Let me know what you think would be
the best idea for improving it, as I was currently going for a minimally
invasive patch to start with and would like to get a more finalized patch
together before opening a ticket to add this to the nav_stack.

- Eric
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