Unable to find uri

[jianqin-mok]

I was trying out the TurtleBot3 Gazebo simulation in a VirtualBox, Ubuntu 16.04.
Installations following emanual for PC setup + simulation on https://emanual.robotis.com/docs/en/platform/turtlebot3/simulation/

When I launch Gazebo my TurtleBot burger seems to fall to underground, then I checked my terminal and I think the root cause might be from these two errors.

Error [parser.cc:581] Unable to find uri[model://sun]
Error [parser.cc:581] Unable to find uri[model://ground_plane]

I am not bothered by the sun but I think I atleast need the ground plane since the gravity in physics properties is not 0, and to move the robot around.

[jianqin-mok]

seems like the ~/.gazebo/models folder that suppose to have all the default gazebo model is empty. I solved mine by manual adding the gound_plane folder into ~/.gazebo/models.

[brean]

The Ubuntu 16.04 version is quite outdated, I suggest you switch to a newer version (we teached robotics with ROS melodic on Ubuntu 18.04 and noetic/Ubuntu 20.04 using the turtlebot3-simulation in gazebo in a virtual machine and it loaded the empty-world with the sun and the ground plane correctly)