unit_cylinder not a model in turtlebot3_world

edit

Hi guys, I am launching a gazebo world using:

export TURTLEBOT3_MODEL=waffle_pi

roslaunch turtlebot3_gazebo turtlebot3_world.launch

And, I see 9 tall cylindrical obstacles places in a gazebo world. But, I couldn't fetch or modify the locations of those obstacles.

When I do:

rosservice call /gazebo/get_world_properties

I get:

"

sim_time: 691.492

model_names: [ground_plane, ros_symbol, turtlebot3_burger, coke_can]

rendering_enabled: True

success: True

status_message: "GetWorldProperties: got properties"

"

But, none of those model_names seem to correspond to those 9 unit cylinders. So, How can I get the locations of those cylinders? and, how can I change those locations?

Thank you