Hardware/software integration of a GNSS receiver in RTX with an iMMS slam based system for the insertion of geometric constraints in mixed indoor-outdoor mapping applications

Abstract. Indoor Mobile Mapping Systems (iMMS) are based on trajectory estimation through the implementation of the SLAM (Simultaneous Localization and Mapping) algorithm. The algorithm has the limitation of requiring the environment being surveyed to have well-varied geometry. Indeed, the SLAM algorithm, by assuming a stable environment, tracks changes in the device’s position relative to a landscape of fixed elements and geometries surrounding it. iMMS can operate in outdoor environments and in mixed indoor/outdoor situations. It has been established that SLAM systems are affected by significant geometric drift effects in trajectory estimation. One commonly adopted strategy is to enforce that the surveyed trajectories are closed. Another approach involves introducing constraints in the form of control scans or control points. In particular, control vertices are typically constituted of coordinate points physically measured in the field by the operator, by placing the tip of a measuring pole on them. If in indoor applications, control vertices are generally measured with a total station, in outdoor applications they can also be measured with GNSS measurement campaign. For this reason, it is increasingly necessary to develop easy and accurate integration between iMMS and GNSS receivers to enhance the efficiency of SLAM-based mobile systems in outdoor environments, allowing high-throughput surveys. This article presents the results of such integration, providing guidelines on the most efficient operational methods for introducing these constraints. The contribution details the procedures for hardware design, electronic integration and the development of an application that applies a rigorous cartographic approach, within the compatible limits of the available technologies.