How to merge 2D and 3D maps in ROS ?

edit

My question is How to merge 2D and 3D maps of an environment. I did 2D mapping using gmapping and also hector mapping. The 3D maps are generated using octomap package. Now I want to integrate both 2D and 3D maps with automatic switching. Presently we are implementing these things in a rescue robot. We are presently focusing on a stair-case scenario in which we want 3D maps on stairs. When the steps are detected we want to swap the mapping process from 2D to 3D and rest it will be in 2D only. So we are using a LiDar and a kinect to map 2D and 3D maps respectively. At last we want to make both the maps into a single file format. We got struck at the merging process. How to achieve this? Thanks in Advance :)