turtlebot playgronud does not launch correctly

edit

Hello. I want to try "Make a map and navigate with it" in Tutorials, but I compiled,

$ source /opt/ros/hydro/setup.bash

$ roslaunch turtlebot_gazebo turtlebot_playground.launch

gazebo displayed only a bookshelf, a column and a turtlebot.

Errors are

Error [ModelDatabase.cc:408] Unable to download model[model://dumpster/meshes/dumpster.dae]

Error [SystemPaths.cc:371] File or path does not exist[""]

Error [Visual.cc:2072] No mesh specified

...etc

What do I have to do?