Basic ROS package for who need map transform or robot pose message with covariance.
git clone https://github.com/huseyintutan/pose-and-map-tf-publisher-for-gazebo.git
rosrun map_publisher map_publisher_node
You can add this to your URDF file.
<gazebo>
<plugin name="p3d_base_controller" filename="libgazebo_ros_p3d.so">
<alwaysOn>true</alwaysOn>
<updateRate>200.0</updateRate>
<bodyName>base_link</bodyName>
<topicName>odom_plugin</topicName>
<gaussianNoise>0.01</gaussianNoise>
<frameName>world</frameName>
<xyzOffsets>0 0 0</xyzOffsets>
<rpyOffsets>0 0 0</rpyOffsets>
</plugin>
</gazebo>