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laser_scan_assembler outputs no data

asked 2015-04-21 13:09:39 -0500 gravatar image

Hi forum, this has been driving me mad for a couple of days, can anyone help? I'm running ROS Indigo on Xubuntu 14.04 with a Hokuyo lidar on a remote machine. On my base machine I can see the /scan topic and get read data off it using rostopic echo /scan the output shows the data is in the "laser" frame.

I am trying to assemble scans using the laser_scan_assembler as in the tutorial, currently with this launch,

<launch> <node type="laser_scan_assembler" pkg="laser_assembler" output="screen" name="my_assembler"> </node> </launch>

And I broadcast tf's so that rosrun tf tf_echo laser map gives At time 1429639619.311 - Translation: [-0.050, 1.000, -0.250] - Rotation: in Quaternion [0.000, 0.000, 0.000, 1.000] in RPY [0.000, -0.000, 0.000]

However when I examine the assembler output there's no data, rosservice call assemble_scans 0 10 cloud: header: seq: 0 stamp: secs: 0 nsecs: 10 frame_id: map points: [] channels: []

I can't find any further info on this, and the tutorial doesn't give a full example, so could anyone help? I'm running here on a live robot, but have had similar problems running from a bag.

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answered 2015-04-21 15:39:00 -0500 gravatar image

Answering my own question for future reference:

Problem was due to syntax of the "rosservice call assemble_scans 0 10". The two arguments should instead be the starttime and endtime of the requested scans in NANOSECONDS of ROS TIME, not seconds since sim start. It was useful to run the test scripts in to reach this -- maybe would useful to mention the nanosecond convention on the laser_assemble tutorial wiki to clarify?

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Asked: 2015-04-21 13:09:39 -0500

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Last updated: Apr 21 '15