Merge multiple maps in kinetic

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How do you merge multiple maps (generated by map_server map_saver) to form a single map?

I want to generate a single map of a building with high accuracy. Then I will use the map in AMCL for localization

1. Place the LIDAR in a known position
2. Generate the scan map using gmapping with the known position
3. Move to a new known position by moving the LIDAR manually
4. Repeat 2 until the entire building is mapped
5. Merge the maps to a single map