# Use global planner to "DETECT" obstacles (not simply avoid or re-plan path)

Hi All,

I'm not sure if this is a silly question that has a simple solution or if I missed something. However, using the Turtlebot 2 with the DWA planner and a known map when an obstacle causes a major re-planning of trajectory to its goal, but still succeeds in performing the task (i.e. causes the message) DWA planner failed to produce path.  the actionlib goal status doesn't have a message to deal with this. Therefore, if I want to count how many times an obstacle caused a path to be re-planned or I want to count how many times a robot encountered an obstacle I can't. (Note: This is true most of the time, as long as the obstacle doesn't cause enough of an issue for the robot to send an abort message to actionlib)

Currently the robot immediately re-plans the path and continues until it gets to the goal (unless it can't reach the goal in which case it normally sends goalstatus.msg = 4, i.e. aborted). Did I miss something obvious, is there a way to check when a path is altered because of an obstacle? As a side note, no I don't want to use the camera to "detect" an obstacle in this case as it will defeat the point and do let me know if more information is required.

Thanks, Tiz

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Since dwa failing to produce a path will result in the global planner being retriggered, you could listen to the global planner / plan topic.

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Thanks. This might actually be the only possible way. Since no-one else has given better answers and I couldn't come up with anything better, I'll mark your answer as the solution. Hope it helps others as well.

( 2018-05-29 11:19:27 -0600 )edit