Making a 2D costmap from a .world

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I have a .world file with some walls and other simple obstacles in it. I need a 2D costmap in order to use move_base and plan paths for my quadrotors. In the past I have been able to do this by using a SLAM package (gmapping) and flying my quadrotor all around the world to generate a good map. This is incredibly time consuming. I was wondering if there are any people out there much smarter than me who have developed a way of going straight from a .world file, giving it a specific height (eg. if there are mountains, only count them as obstacles if they are above 10 ft since I only fly above 10 ft), and generating a 2D costmap. A 3D would be pretty sweet as well. If anyone has any ideas please let me know. Thanks!