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ROS : laser_assembler

asked 2021-07-23 20:15:39 -0600

ManChrys gravatar image

OS : Ubuntu 18,04 Distro : melodic

Hello guys,

im trying the laser_assembler but i have the following error :

[ERROR] [1627088238.325826329]: Client [/my_assembler] wants topic /livox/lidar to have datatype/md5sum [sensor_msgs/LaserScan/90c7ef2dc6895d81024acba2ac42f369], but our version has [sensor_msgs/PointCloud2/1158d486dd51d683ce2f1be655c3c181]. Dropping connection.

I am using livox mid 40, which topic list about laser os /livox/lidar.

The steps im trying to follow are the below:

1)roslaunch laser_to_pcl kaser_assembler.launch 2)roslaunch loam_livox rosbag.launch 3)rosbag play bag.bag

The error happening when im try to play rosbag (step 3). I found some other posts here about different msgs versions, but i need help to fix it.

My launch file is :

image description

and my .py file is :

image description

Thanks in advance.

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i tried point_cloud_assembler instead of laser_scan_assembler.

my launch is now

<launch> <node type="point_cloud_assembler" pkg="laser_assembler" name="my_assembler"> <remap from="cloud" to="/livox/lidar"/> </node> <node type="laser2pcl.py" pkg="laser_to_pcl" name="laser2pcl"/> </launch>

when im running the launch file i have new error

Client [/my_assembler] wants topic /livox/lidar to have datatype/md5sum [sensor_msgs/PointCloud/d8e9c3f5afbdd8a130fd1d2763945fca], but our version has [sensor_msgs/PointCloud2/1158d486dd51d683ce2f1be655c3c181]. Dropping connection.

so i have to change PointCloud to Pointclkoud2. How can i do this ? i have to change inside the launch file the string remap from ="cloud" to remap from:cloud2" ? Is this the change or i have to do something more?

ManChrys gravatar image ManChrys  ( 2021-07-24 07:41:00 -0600 )edit

Please don't upload images of screen captures of text. You should copy/paste the actual text and format it using control-k.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-24 10:08:47 -0600 )edit

What are you trying to accomplish? Your bag file appears to already have PointCloud2 messages.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-24 10:43:46 -0600 )edit

i am using livox mid 40 lidar. So i record bag file or convert .lvx file to bag and i want to create a single pointcloud through this bag file. I tried rosrun pcl_ros bag_to_pcd <input_file.bag> <topic> <output_directory> but it creates multiple pcd files (one for each frame). As i said i want a single pointcloud (ply, las, las) which i can use it in cloudcompare meshlab or something like that. I saw that cloud assembler its the solution thats why im trying to solve this . I dont know if there is a better way.

ManChrys gravatar image ManChrys  ( 2021-07-24 10:48:12 -0600 )edit

I have no knowledge about pcd files. It seems like this topic now is quite far from your original question up above. Consider posting a new question asking for a methodology to get PointCloud2 into cloudcompare (or whatever tool you want to specify.)

Mike Scheutzow gravatar image Mike Scheutzow  ( 2021-07-24 11:40:49 -0600 )edit

ok thank you my friend.

ManChrys gravatar image ManChrys  ( 2021-07-24 11:43:08 -0600 )edit

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answered 2021-07-24 10:11:40 -0600

Mike Scheutzow gravatar image

updated 2021-07-24 10:20:24 -0600

I'm responding to the original question: the error indicates your launch file has not correctly hooked up the topic names recorded in the bag file. You can use rosbag info to see the topics & message types inside the bag file.

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im using the right topic and msgs i think

    types:       sensor_msgs/PointCloud2 [1158d486dd51d683ce2f1be655c3c181]
    topics:      /livox/lidar   6500 msgs    : sensor_msgs/PointCloud2
ManChrys gravatar image ManChrys  ( 2021-07-24 10:22:42 -0600 )edit

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Asked: 2021-07-23 20:15:39 -0600

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Last updated: Jul 24 '21