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Hello all,

I've followed the tutorial here http://www.ros.org/wiki/navigation/Tutorials/RobotSetup and also checked the website for similar questions but I am still quite confused and unable to produce the result I need.

I'm hooking up GMapping to the Costmap by setting static_map: true for global_costmap_params.yaml and static_map: falase for local_cost_map_params. However I wish to allow the robot, Pionneer3-AT to auto navigate itself in that environment. I thought of pointing the 2D Nav Goal to the unknown space from local_costmap but I've received errors and there's no reaction from the robot whatsoever.

Error from Costmap launch

[ERROR] [1371710574.377069274]: Client [/rostopic_25335_1371710566077] wants topic /move_base/local_costmap/unknown_space to have datatype/md5sum [geometry_msgs/PoseStamped/d3812c3cbc69362b77dc0b19b345f8f5], but our version has [nav_msgs/GridCells/b9e4f5df6d28e272ebde00a3994830f5]. Dropping connection.

Error from RVIZ

[ERROR] [1371710524.998325539]: md5sum mismatch making local subscription to topic /move_base/local_costmap/unknown_space. [ERROR] [1371710524.998429812]: Subscriber expects type nav_msgs/GridCells, md5sum b9e4f5df6d28e272ebde00a3994830f5 [ERROR] [1371710524.998484870]: Publisher provides type geometry_msgs/PoseStamped, md5sum d3812c3cbc69362b77dc0b19b345f8f5

rostopic echo /move_base/local_costmap/unknown_space would also most of the time not return anything.

I also applied unknown_cost_value: 255 and track_unknown_space: true to the costmap_common_params

It'll be great to get some help to achieve autonavigation in an unknown environment.

** EDIT 1 The errors were eliminated by setting static_map: false for global_costmap. However, there doesn't seem to be any path planning occuring. No errors were found in rxgraph and roswtf too.

** EDIT 2 The global_costmap_params.yaml has settings of static_map: false and rolling_window:true.

I've created a simple publisher and subscriber to subscribe to nav_msgs/GridCells on topic move_base/local_costmap/unknown_space and publish geometry_msgs/PoseStamped on topic /move_base_simple/goal. Since there are a bunch of coordinates of unknown space, a random coordinate is chosen.

The basic ROS tutorial for writing a subscriber/publisher should be referred to as an example.


Originally posted by barrybear on ROS Answers with karma: 57 on 2013-06-19

Post score: 1

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2 Answers 2

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To say what Felix said a slightly different way...

As input, move_base takes a PoseStamped, which specifies a particular pose (location and orientation)

The published topic unknown_space is of type GridCells. This is a visualization message that specifies an area of the map.

To get the behavior you want, you'll have to write a node that takes in the GridCells message and pick a (random?) point and send that as a PoseStamped to move_base.


Originally posted by David Lu with karma: 10932 on 2013-06-26

This answer was ACCEPTED on the original site

Post score: 2


Original comments

Comment by barrybear on 2013-06-26:
Ohhhhh! That makes sense! So, the random point, should I make any changes to it? Or just simply sending it to the move_base?

Comment by David Lu on 2013-06-26:
What do you mean, any changes?

Comment by barrybear on 2013-06-26:
If there's any necessary to add/subtract the values depending/relative to the map

Comment by David Lu on 2013-06-26:
That's what the Stamped portion refers to. If there's a header stamp on the Pose which specifies the correct reference frame, then move_base will translate it accordingly.

Comment by barrybear on 2013-06-26:
Hey guess what David! It works! Thanks for clarifying on the problem! :D Now to work on sending a goal only if the previous goal has succeeded. Thanks for your time man!

Comment by David Lu on 2013-06-27:
This should help: http://www.ros.org/wiki/navigation/Tutorials/SendingSimpleGoals

Comment by Gazer on 2013-06-27:
sorry.... I don't get it....... @barrybear, how did you solve your problem? do you mind re-edit your question to include your current setting?????

Comment by barrybear on 2013-06-28:
@Gazer editted :) hopefully the explanation's clear enough. sorry I can't post the codes here..still a work in progress!

Comment by Gazer on 2013-06-28:
ok. I see. thank you for this reply

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To your errors:

The costmap2d wiki states unknown_space to be of type GridCells, so the rostopic node you started is wrong.

If you remove that, and don't make roscore and everything believe that this topic is a PoseStamped, which it's not, the second error will vanish.


Originally posted by felix k with karma: 1650 on 2013-06-19

This answer was NOT ACCEPTED on the original site

Post score: 1


Original comments

Comment by barrybear on 2013-06-19:
Hey I'm a little unsure, what do I remove? the 2D Nav Goal? If I remove it, what do I replace it with?

Comment by felix k on 2013-06-20:
The error states a /rostopic node that's running. Don't do that/remove it from your launch file. Don't start it in publishing mode, and the safe is to start it only after a working node on that topic.

Comment by barrybear on 2013-06-20:
Oh.. I only use three launch files. One to launch p2os driver. Second to launch laser driver & GMapping. The third is to launch costmap and the base_local_planner..i do them in order and usually wait for each launch to succesfully load completely. After all that I run rviz.

Comment by barrybear on 2013-06-20:
Hey! I'm still experiencing the same error..and totally unsure of how to fix it :(

Comment by barrybear on 2013-06-24:
Hello! I'm still facing this problem :( Even more so when I switch the 2D Nav Goal to /move_base/goal. Any help please?

Comment by felix k on 2013-06-25:
Please look carefully at the error message you (currently) get. E.g. if theres still some Client [/rostopic_ named, you have some rostopic node running (with wrong msg type). And check that any node you start (maybe indirectly) that accesses the topic named in the error uses the same msg type.

Comment by felix k on 2013-06-25:
Maybe running roswtf gives a hint. roswtf wiki

Comment by barrybear on 2013-06-25:
Hey Felix! I'll try that tomorrow with the robot. Just to make sure again..its not necessary to run roscore right? And launching three launch files as I've stated in that order is okay?

Comment by barrybear on 2013-06-25:
I managed to use roswtf and eliminate the errors. Now there's no errors! However it doesnt seem to conduct any path planning when set to unknown space.. :(

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