Map-centric SLAM utilizes elasticity as a means of loop closure. This approach reduces the cost of loop closure while still providing large-scale fusion-based dense maps, when compared to trajectory-centric SLAM approaches. In this article, we present a novel framework, namedElasticLiDAR++, for multimodal map-centric SLAM. Having the advantages of a map-centric approach, our method exhibits new features to overcome the shortcomings of existing systems associated with multimodal (LiDAR-inertial-visual) sensor fusion and LiDAR motion distortion. This is accomplished through the use of a local continuous-time trajectory representation. Also, our surface resolution preserving matching algorithm and normal-inverse-Wishart-based surfel fusion model enables nonredundant yet dense mapping. Furthermore, we present a robust metric loop closure model to make the approach stable regardless of where the loop closure occurs. Finally, we demonstrate our approach through both simulation and real data experiments using multiple sensor payload configurations and environments to illustrate its utility and robustness.

As Information and Communication Technology (ICT) literacy education has recently shifted to fostering computing thinking ability as well as ICT use, many countries are conducting research on national curriculum and evaluation. In this study, we measured Korean students’ ICT literacy levels by using the national measurement tool that assesses abilities of the IT (Information Technology) area and the CT (Computational Thinking) area. A research team revised an existing ICT literacy assessment tool for the IT test and developed a new CT test environment in which students could perform actual coding through a web-based programming tool such as Scratch. Additionally, after assessing ICT literacy levels, differences in ICT literacy levels by gender and grade were analyzed to provide evidence for national education policies. Approximately 23,000 elementary and middle school students participated in the 2018 national assessment of ICT literacy, accounting for 1% of the national population of students. The findings demonstrated that female students had higher literacy levels in most sub-factors of IT and CT areas. Additionally, in the areas of strengths and weaknesses, the ratio of below-basic achievement among male students was at least two times greater than that of female students. Nonetheless, male students scored higher on CT automation, a coding item that involved problem solving using Scratch. Looking at the difference according to grade level, the level improved as the school year increased in elementary school, but there was no difference in middle school. When analyzing the detailed elements of middle school students, the automation factor of seventh grade students was found to be higher than eighth and ninth grade students. Based on these results, this study discussed some implications for ICT and computing education in elementary and middle schools.

In this paper, we present a novel method to detect and resolve motion conflicts in visual-inertial odometry. Recently, it has been common to integrate an IMU sensor with visual odometry in order to improve localization accuracy and robustness. However, when a disagreement between the two sensor modalities occurs, the localization accuracy reduces drastically and leads to irreversible errors. In such conditions, multiple motion estimates based on the set of observations used are possible. This creates a conflict (motion conflict) in determining which observations to use for accurate ego-motion estimation. Therefore, we present a method to detect motion conflicts based on per-frame positional estimate discrepancy and per-landmark reprojection errors. Additionally, we also present a method to resolve motion conflicts by eliminating inconsistent IMU and landmark measurements. Finally, we implement Motion Conflict aware Visual Inertial Odometry (MC-VIO) by combining both detection and resolution of motion conflicts. We perform quantitative and qualitative evaluation of MC-VIO on visually and inertially challenging datasets. Experimental results indicate that the MC-VIO algorithm reduces the increase in absolute trajectory error by 80% and the relative pose error by 60% for scenes with motion conflict, in comparison to the state-of-the-art reference VIO algorithm.

The concept of continuous-time trajectory representation has brought increased accuracy and efficiency to multi-modal sensor fusion in modern SLAM. However, regardless of these advantages, its offline property caused by the requirement of global batch optimization is critically hindering its relevance for real-time and life-long applications. In this paper, we present a dense map-centric SLAM method based on a continuous-time trajectory to cope with this problem. The proposed system locally functions in a similar fashion to conventional Continuous-Time SLAM (CT-SLAM). However, it removes the need for global trajectory optimization by introducing map deformation. The computational complexity of the proposed approach for loop closure does not depend on the operation time, but only on the size of the space it explored before the loop closure. It is therefore more suitable for long term operation compared to the conventional CT-SLAM. Furthermore, the proposed method reduces uncertainty in the reconstructed dense map by using probabilistic surface element (surfel) fusion. We demonstrate that the proposed method produces globally consistent maps without global batch trajectory optimization, and effectively reduces LiDAR noise by surfel fusion.

In this paper we propose a novel method called s-DVO for dense visual odometry using a probabilistic sensor noise model. In contrast to sparse visual odometry, where camera poses are estimated based on matched visual features, we apply dense visual odometry which makes full use of all pixel information from an RGB-D camera. Previously, t-distribution was used to model photometric and geometric errors in order to reduce the impacts of outliers in the optimization. However, this approach has the limitation that it only uses the error value to determine outliers without considering the physical process. Therefore, we propose to apply a probabilistic sensor noise model to weigh each pixel by propagating linearized uncertainty. Furthermore, we find that the geometric errors are well represented with the sensor noise model, while the photometric errors are not. Finally we propose a hybrid approach which combines t-distribution for photometric errors and a probabilistic sensor noise model for geometric errors. We extend the dense visual odometry and develop a visual SLAM system that incorporates keyframe generation, loop constraint detection and graph optimization. Experimental results with standard benchmark datasets show that our algorithm outperforms previous methods by about a 25% reduction in the absolute trajectory error.

Research of daily activity recognition has been extensively conducted in the field of ubiquitous computing. However, previous daily activity recognition schemes are either obtrusive or inaccurate since they use just special-purpose devices. In this paper, we propose the collaborative classification for recognizing daily activities with a smartwatch. We exploit a single off-the-shelf smartwatch to distinguish 5 different daily activities such as eating, vacuuming, sleeping, showering, and TV watching. More precisely, we conduct experiments for collecting sensor data from accelerometer and acoustic sensor which are embedded in a smartwatch. However, the simple combination of the raw acceleration and acoustic data does not deliver accurate recognition accuracy. In order to achieve high accuracy, we propose a collaborative classification algorithm which integrates sensor data and ground-truth label for improving recognition accuracy by constructing a mapping table. We evaluate accuracies using single-sensor based approach, multi-sensor based approach, and our collaborative classification approach. The results from activity recognition for about 20 hours data collected by subjects show reliable accuracies for all 5 activities, and the overall accuracy of our collaborative approach is about 91.5%. Experimental results reveal that our approach improves the recall rate of each activity by up to 21.5% as compared to that of the simply combined multi-sensor based approach.

This paper presents an efficient method of building continuous occupancy maps using Gaussian processes for large-scale environments. Although Gaussian processes have been successfully applied to map building, the applications are limited to small-scale environments due to the high computational complexity. To improve the scalability, we adopt a divide and conquer strategy where data are partitioned into manageable size of clusters and local Gaussian processes are applied to each cluster. Particularly, we propose overlapping clusters to mitigate the discontinuity problem that predictions of local estimators do not match along the boundaries. The results are consistent and continuous occupancy voxel maps in a fully Bayesian framework. We evaluate our method with simulated data and compare map accuracy and computational time with previous work. We also demonstrate our method with real data acquired from a laser range finder.

Although RGB-D sensors have been successfully applied to visual SLAM and surface reconstruction, most of the applications aim at visualization. In this paper, we propose a noble method of building continuous occupancy maps and reconstructing surfaces in a single framework for both navigation and visualization. Particularly, we apply a Bayesian nonparametric approach, Gaussian process classification, to occupancy mapping. However, it suffers from high-computational complexity of O(n(3))+O(n(2)m), where n and m are the numbers of training and test data, respectively, limiting its use for large-scale mapping with huge training data, which is common with high-resolution RGB-D sensors. Therefore, we partition both training and test data with a coarse-to-fine clustering method and apply Gaussian processes to each local clusters. In addition, we consider Gaussian processes as implicit functions, and thus extract iso-surfaces from the scalar fields, continuous occupancy maps, using marching cubes. By doing that, we are able to build two types of map representations within a single framework of Gaussian processes. Experimental results with 2-D simulated data show that the accuracy of our approximated method is comparable to previous work, while the computational time is dramatically reduced. We also demonstrate our method with 3-D real data to show its feasibility in large-scale environments.

This paper proposes a new method for occupancy map building using a mixture of Gaussian processes. We consider occupancy maps as a binary classification problem of positions being occupied or not, and apply Gaussian processes. Particularly, since the computational complexity of Gaussian processes grows as O(n3), where n is the number of data points, we divide the training data into small subsets and apply a mixture of Gaussian processes. The procedure of our map building method consists of three steps. First, we cluster acquired data by grouping laser hit points on the same line into the same cluster. Then, we build local occupancy maps by using Gaussian processes with clustered data. Finally, local occupancy maps are merged into one by using a mixture of Gaussian processes. Simulation results will be compared with previous researches and provided demonstrating the benefits of the approach.

In this paper we propose a new method for on-line object segmentation through human-robot interaction. Particularly, we define three types of human gestures for object learning by the size of target objects; holding small objects, pointing at medium ones and contacting two corners of large ones. The regions of interest where objects are likely to be located are interpreted from those gestures and represented as rectangles in captured images. For object segmentation, we suggest a marker-based watershed segmentation method which segregates an object within a region of interest in real-time performance. Experimental results show that the segmentation quality of our method is as good as that of the GrabCut algorithm, but the computational time of ours is so much faster that it is appropriate for practical applications.

In this paper, we suggest a new method of human augmented mapping for indoor environments using only a stereo camera. Through user's help, a robot with a stereo camera can investigate the environment without failure and even more efficiently. Moreover, the user can share the information about the environment with the robot and add semantic information to the environmental map. We employ PCA features for visual landmarks and a hybrid map for map representation. Particularly, we define two types of nodes, U/R-nodes and divide the map building into three processes, User's Guidance, Robot's Map Revision, and Robot's Map Completion. We implemented a human augmented mapping system with a stereo camera and demonstrated it in rectangular-shaped corridors. From the comparison with a manually-built map, we showed the feasibility of the environmental map generated by our proposed method.