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why are the wait motions ignored in sipp dynamic path planner

asked 2011-11-03 01:18:39 -0500

Stefan Stiene gravatar image

Hi, I have tested the sipp library of the sbpl_dynamic_planner. I used the EnvIntervalLat I get the following warning:

WARN: wait motion in mprim file ignored

And the resulting path also looks like the warning is right. The robot drives slowly backwards until the obstacle disappears that blocks the way to the goal. Afterwards it drives forwards to the goal. The desired path is that the robot drives slowly forwards and wait in front of the obstacle. What is the reason why the wait motion is ignored?

Best Stefan

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answered 2011-11-30 07:40:22 -0500

mlphilli gravatar image

This warning is related to your problem (I'll probably get rid of the warning in the future). The sipp and interval environments assume that waiting is allowed as a prefix to every motion primitive therefore any "wait" action specified in the motion primitive file is ignored because the planner is going to use waits wherever it needs to.

While I can't say for sure without looking at it, the likely reason (especially if your epsilon is 1, optimal) for the behavior you are seeing is that it is at least as fast if not faster to get to the goal, by waiting for the obstacles to "disappear". When the dynamic obstacle trajectories end, it is as if they disappear. If you want to make sure the planner "deals with" the dynamic obstacles instead of waiting until they disappear you have to make sure the trajectories are long enough for it to be cheaper for the robot to do what you expect than waiting for trajectories to end.

Hope that helps!

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Asked: 2011-11-03 01:18:39 -0500

Seen: 253 times

Last updated: Nov 30 '11