Is there any way to get the positions of all cells containing an obstacle from a costmap? It used to be you could just subscribe to the "obstacles" topic of either the local or global costmap, but that has since changed. It looks like you now need to subscribe to both the costmap (OccupancyGrid) and costmap_updates (OccupancyGridUpdate) topics, but there is very little documentation on what each actually does, or how to get useful data out of it.