EnviRe’s Multi-Level Surface Maps are based on [Schwendner, 2013, §2.1.2] which itself is based on work by [Triebel et al., 2006]. The idea is to represent 3D structure by a grid where each grid cell contains a list of surface patches. This can be thought of as a generalization of an elevation map that allows representing multiple levels.

MLSMap are a specialization of Multi-Level Grid Maps MLGrid which are GridMaps of LevelLists. In an MLSMap each LevelList contains SurfacePatches of a specific type. At the moment we provide classical MLS maps where each patch is represented by a z-coordinate with uncertainty and an optional height, which we call MLSMapKalman. Furthermore, we provide an MLS map where each surface patch accumulates the momenta of all measured points in that cell which can be used to calculate a sloped plane fitting best to the given measurement. We call the latter MLSMapSloped.

MLGrids are also used to represent 3d traversability maps.