Robust and Efficient Multirobot 3-D Mapping Merging With Octree-Based Occupancy Grids

Recent robotics applications require 3-D representations of the environments. In many cases, it is not feasible for a single robot to map the entire environment. In these cases, it is necessary for a team of robots to build maps independently and merge them into a single global map. In this paper, octree-based occupancy grids, which are currently the state-of-the-art 3-D map representation, are applied to the problem of multirobot mapping. Octrees allow large environments to be mapped efficiently, in terms of memory usage, while still providing sufficiently fine resolution where required. The main contribution of this work lies in the definition and validation of a system, which use map data from commonly mapped portions of the environment with registration techniques, such that maps are merged coherently despite measurement noise and error in the relative transformations between maps for experimental data sets. The system defined can then be used in a complete solution that is ported to mobile robots. The results demonstrate that octree occupancy grids are a suitable representation for multirobot 3-D mapping, but that the proposed techniques for improving erroneous transformation estimates between map frames allow multiple maps to be merged efficiently and robustly.