# Set global_frame and robot_base_frame parameters for costmap_2d::Costmap2DROS object

I am trying to use a costmap_2d::Costmap2DROS object to read the occupacy grid being published on the /map topic. How do I modify the values of the global_frame and the robot_base_frame parameters for the costmap_2d::Costmap2DROS object? I tried to go through the documentation. But, I didn't really get it.