sim time stops when echo laserscan/data

[ronnic4280]

Hi, we are using the Robtnik Summit XL for the competition. While testing in the virtual maize field an trying to subscribe to rostopic echo /robot/front_laser/scan , we'll get the message: "WARNING: no messages received and simulated time is active. Is /clock being published?" and the simulation time in Gazebo pauses. I won't get the issue while testing on plain ground or in different worlds.
I don't know where to seach for a solution, it seems like this is a issue relating to the virtual maize field.
Has anybody an idea how to solve ist?

I'm using ros melodic on ubuntu 18.04

[Rick-v-E]

Hi, the topic for the laser scanner is different. You can try rostopic list to see which topics are available. I think the correct topic is something like /front_laser/scan instead of /robot/front_laser/scan.

[ronnic4280]

Hi, I'm subscribing to the right topic for the Summit-XL and it is working in different worlds, but not in the virtual maize field.

[Rick-v-E]

A few ideas:

• Did you start Gazebo in the paused mode? Because that results in the described error and can be solved by pressing the play button in Gazebo.
• Can you see the lidar data in RVIZ?
• Is the robot spawned correctly in Gazebo? And is there no error in the terminal that you used to start the Gazebo (roslaunch virtual_maize_field simulation.launch)?

[ronnic4280]

• Gazebo starts un-paused and the Button won't change to pause when trying to subscribe to the laserscan topic, but the time is stopping.
• I can't see the lidar data in Rviz. When trying to show them in Rviz, same thing happens and sim_time stops.
• while launching the maize field, I get following errors:
  

[Rick-v-E]

It looks like if Gazebo is not able to find the dandelion models. Did you add these models to the 'models' folder of the 'virtual_maize_field' package? I have sent these models by mail to the email address that the teams used for registration. If adding the dandelion models does not work, please upload the complete log from the terminal that you used to start Gazebo.

[ronnic4280]

The dandelions are at the right folder as suggested and the package is up to date.

[Rick-v-E]

It looks like you put the dandelions in the folder 'models/dandelions/dandelion_01', 'models/dandelions/dandelion_02' etc. However, this should be 'models/dandelion_01' and 'models/dandelion_02', without the subfolder. The reason for this is that Gazebo expects in every subfolder of the 'models' folder a 'model.config' file. So, move every single dandelion model in the 'models' folder and remove the (then empty) 'dandelions' folder.

[ronnic4280]

I fixed it and the Error for the dandelion won't occur anymore, but the sim time problem is still the same.

[Rick-v-E]

Does the example robot work on your computer?

[ronnic4280]

Yes, its working and I’m able to echo the /front/scan while driving.

[Rick-v-E]

What happens if you use your URDF files (and meshes) in the example robot workspace?

[Rick-v-E]

@ronnic4280, were you able to solve this problem?

[ronnic4280]

Unfortunally not, but we decided to not use the laserscan anyway. I might try to solve this problem later.

[g-pranav]

Unfortunally not, but we decided to not use the laserscan anyway. I might try to solve this problem later.

I am having the same issue, Lidar is not publishing anything when I use virtual_maize_field world but it works with other worlds.

[Darkproduct]

If you don't get laserscan data, this could be due to the type of ray plugin used in Gazebo. Altough, I would suspect, that there should be at least some data with the normal plugin as long as the scanner has something in its few.

It is however recommended to use the GPU ray plugin from Gazebo, because this plugin intersects with the mesh and not with the collision box of the plants. If you don't have a GPU available you can try to set ths environment variable export LIBGL_ALWAYS_SOFTWARE=1 to enable rendering on the CPU. But this will slow down the fps of Gazebo as well.