ReviewMobile indoor mapping technologies: A review
Graphical abstract
Introduction
Building surveying and mapping have been traditionally tedious and time-consuming works, especially the task of elaborating plans and models from existing buildings. Recent year politics regarding heritage buildings conservation, where the gap of data and the complicated indoor environment are typical problems, as well as politics regarding massive building inspections, have been growing the interest in indoor mapping and surveying. Thus, it has been the driver to the development of the technology of mobile mapping systems and the increment of commercial devices. This kind of devices eases and speeds the survey process, in comparison with fixed devices, since it is not necessary to perform occlusion studies and take measurements from multiple points. The user can capture the environment just by walking across the building. There is no need for further training of the user. And, although the resolution against fixed devices is lower, the values are enough for building analysis purposes.
Commercial mobile indoor mapping systems can be classified based on their physical configuration as handheld, backpack and trolley. Their main components are, for all classes, the hardware for data processing and synchronization of sensors and the mapping sensor which is usually a LiDAR (Light Detection And Ranging) or an RGB-D (Red, Green, Blue – Distance) camera. These systems can also include complementary sensors like RGB cameras or thermographic sensors to expand de data acquired from the environment. In addition, indoor mapping systems have one important difference from outdoor devices. Outdoor devices usually use GNSS (Global Navigation Satellite Systems) signals (typically GPS) for the calculus of the position. But this cannot be used for indoor environments since radio signals cannot penetrate into the buildings [1]. The problem is solved by estimating the position with inertial methods such as odometers or IMUs (Inertial Measurement Units) [2] [3], beacons [4,5] along the mapped environment or one of the most extended methods, the use of SLAM (Simultaneous Localization and Mapping) algorithms, which were developed for autonomous robots but resulted very useful for scanning and mapping.
Regarding the output of the survey, which is a map either in 2D or 3D, different typologies are possible, like topological maps [[6], [7], [8]] and radio maps [9] but this article will focus on systems that generate point clouds, since these are the most widely used for indoor surveying with mobile devices. Point clouds are discrete models formed by a subset of points pi ∈ ℝ3, which correspond to positions in the surfaces of the environment surveyed.
Despite the numerous studies of indoor mapping systems in literature, they are usually restricted to a comparison between a few devices [[10], [11], [12], [13], [14]]. Thus, it is difficult for researchers to have a global vision of the state of the art of the technology. In this article, a wide selection of examples of commercial devices is reviewed, and their interesting characteristics for construction and architectural studies are analysed. The choice of the best system depends on a compromise between user requirements, environmental conditions and performance parameters from the device. This article aims to help potential users to select the best device for the required task and give an updated overview of the state-of-the-art on existing commercial mobile indoor mapping devices based on a double review: literature and platform specifications.
In the remainder of this paper, the commercial devices reviewed, classified by their physical configuration and subclassified by their mapping sensor, are presented in Section 2. Section 3 includes a comparison attending to the following criteria: physical configuration, weight, sensor weight, colouring possibilities and operating time. The paper closes with the conclusions.
Section snippets
Mobile indoor mappping systems
This section shows a selection of different commercial devices with a brief description classified by their physical configuration: handheld, backpack and trolley devices.
Discussion
In this section, the features of each of the 21 devices studied are compared in order to give the reader an overview of their capacities, with which being able to choose the best option for the expected requirements. The features to analyse are: physical configuration, weight, sensor type, colouring possibilities and operating time.
Conclusions
In this paper, a wide selection of examples of commercial devices and their characteristics of interest for construction and architectural studies are reviewed, based on both literature and specifications from the platforms, to establish the current state of the art of such a broad technological field. The study has focused on devices integrating geomatic sensors (LiDAR sensors or RGB-D cameras), leaving aside indoor mapping methodologies based on other types of measurements or equipment). The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 769255. This document reflects only the author's view and the European Commission is not responsible for any use that may be made of the information it contains. Authors would also like to thank the European Commission for the funding given through the program H2020-FTIPilot-2015-1 to the proposal 720661 – ENGINENCY. Special thanks are given to the Cátedra
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