Autonomous mobile robots should be aware of their situation, understood as a comprehensive understanding of the environment along with the estimation of its own state, to successfully make decisions and execute tasks in natural environments. 3D scene graphs are an emerging field of research with great potential to represent these situations in a joint model comprising geometric, semantic and relational/topological dimensions. Although 3D scene graphs have already been utilized for this, further research is still required to effectively deploy them on-board mobile robots. To this end, we present in this paper a real-time online built Situational Graphs (S-Graphs), composed of a single graph representing the environment, while simultaneously improving the robot pose estimation. Our method utilizes odometry readings and planar surfaces extracted from 3D LiDAR scans, to construct and optimize in real-time a three layered S-Graph that includes a robot tracking layer where the robot poses are registered, a metric-semantic layer with features such as planar walls and our novel topological layer constraining higher-level features such as corridors and rooms. Our proposal does not only demonstrate state-of-the-art results for pose estimation of the robot, but also contributes with a metric-semantic-topological model of the environment
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