**6. Discussion**

In this chapter, we presented a system for continuous mapping and exploration of underground sites. Most of this work has been developed as part of the project "Underground 4D+ Positioning, Navigation and Mapping System for Highly Selective, Efficient and Highly-secure Exploitation of Important Resources" (UPNS4D+) which was funded by the German Federal Ministry of Education and Research within the programme of "R4–Innovative Technologies for Resource Efficiency – Research for the Provision of Raw Materials of Strategic Economic Importance".

We first reported on the hardware platform that was built to acquire comparably densely populated 3D point clouds of the (underground) environment using a rotating LiDAR device. Afterwards, we reported on the framework mapit which is used to track and execute post-processing operations on the data acquired by the robot. Namely, it allows for registering a (large) set of individual maps to one global map. The important aspect is that mapit does not store the resulting map and discards the original data, but instead it keeps track of the operations that were performed on the data and logs these operations. This allows for reapplying all postprocessing in case an algorithm has been improved or a misalignment in the calibration of the sensor setup has been detected. Finally, we presented the options for visualizing the resulting maps in different contexts.

The system described in this chapter provides diverse support for (first) responders in search and rescue applications. For one, the resulting maps can be used to conduct further missions with rescue robots. Also, analysis tools can be run on the maps. For example, the mapit framework supports running algorithms to compare maps from different points in time to see which changes have occurred. The versatile visualization capabilities allow for planning rescue missions and training first responders before sending them into the field.
