Artificial Landmarks Research Articles

Tactile Landmarks: the Relative Landmark Location Alters Spatial Distortions.

The influence of landmarks, that is, nearby non-target stimuli, on spatial perception has been shown in multiple ways. These include altered target localization variability near landmarks and systematic spatial distortions of target localizations. Previous studies have mostly been conducted in the visual modality using temporary, artificial landmarks or the tactile modality with persistent landmarks on the body. Thus, it is unclear whether both landmark types produce the same spatial distortions as they were never investigated in the same modality. Addressing this, we used a novel tactile setup to present temporary, artificial landmarks on the forearm and systematically manipulated their location to either be close to a persistent landmark (wrist or elbow) or in between both persistent landmarks at the middle of the forearm. Initial data (Exp. 1 and Exp. 2) suggested systematic differences of temporary landmarks based on their distance from the persistent landmark, possibly indicating different distortions of temporary and persistent landmarks. Subsequent control studies (Exp. 3 and Exp. 4) showed this effect was driven by the relative landmark location within the target distribution. Specifically, landmarks in the middle of the target distribution led to systematic distortions of target localizations toward the landmark, whereas landmarks at the side led to distortions away from the landmark for nearby targets, and toward the landmark with wider distances. Our results indicate that experimental results with temporary landmarks can be generalized to more natural settings with persistent landmarks, and further reveal that the relative landmark location leads to different effects of the pattern of spatial distortions.

An Improved Trilateral Localization Technique Fusing Extended Kalman Filter for Mobile Construction Robot

Semi-open and chaotic environments of building sites are considered primary challenges for the localization of mobile construction robots. To mitigate environmental limitations, an improved trilateral localization technique based on artificial landmarks fusing the extended Kalman filters (EKFs) is proposed in this paper. The reflective intensity of the onboard laser is employed to identify artificial landmarks arranged in the ongoing construction environment. A trilateral positioning algorithm is then adopted and evaluated based on artificial landmarks. Multi-sensor fusion, combined with the EKF, is included to improve the positioning accuracy and reliability of the robot in complex conditions. We constructed validation scenarios in the Gazebo simulation environment to verify the required localization functionality. Concurrently, we established simulated testing environments in real-world settings, where the practicality of the proposed technique was validated through the fitting of ideal and actual localization trajectories. The effectiveness of the proposed technique was corroborated through comparative experimental results.

An Indoor 2-D LiDAR SLAM and Localization Method Based on Artificial Landmark Assistance

An Indoor 2-D LiDAR SLAM and Localization Method Based on Artificial Landmark Assistance

DSIL4IMR: A dual step-based initial localization method for industrial mobile robot

This paper introduces a dual-step based initial localization method for industrial mobile robots (DSIL4IMR) that operates without user intervention at start-up. Utilizing a differential chassis equipped with a radar sensor, the method combines feature extraction and spatial information matching steps to locate the robot’s initial position. A unique metric, degree of stability, is developed to identify a feature map whether it is a dynamic or erroneous feature. DSIL4IMR does not require artificial landmarks and outperforms existing WiFi fingerprinting and map filter methods in both accuracy and efficiency. DSIL4IMR triples the localization efficiency compared to traditional approaches while achieving centimetre-level precision.

Effect of artificial landmarks of the prefabricated auxiliary devices located at different arch positions on the accuracy of complete-arch edentulous digital implant scanning: An in-vitro study

ObjectivesTo examine the effect of artificial landmarks of prefabricated auxiliary devices (PAD) located at different arch positions on the accuracy of complete-arch edentulous digital implant scanning. MethodsA reference model containing four analogs and PAD were fabricated by a 3D printer (AccuFab-C1s, 3DShining). 10 digital scans were performed using an intraoral scanner (Aoralscan 3, 3DShining), sv 1.0.0.3115, with artificial landmarks located at different arch positions: group I, without any artificial landmarks; group II, with artificial landmarks at the anterior region; group III, with artificial landmarks at the posterior region. group IV: with artificial landmarks at both anterior and posterior regions. For group V: Conventional open-tray splinted impressions. The reference file and conventional stone casts were digitalized by using a dental laboratory scanner. The related files were imported into inspection software for trueness and precision assessment. Statistical analysis was performed with One-way ANOVA and Kruskal-Wallis test. The level of significance was set at α=0.05. ResultsFor the global accuracy assessment, significantly higher global trueness was seen in group II (p < 0.01), III (p < 0.001), IV (p < 0.001) and V (p < 0.001) than group I. Significantly higher global precision was seen in group III (p < 0.001), IV (p < 0.001) and V (p < 0.001) than group I. For the local accuracy assessment, the PAD primarily improved accuracy on the linear deviations. ConclusionsArtificial landmarks of PAD at different arch positions significantly influenced the scanning accuracy. Applying the PAD in group IV could achieve comparable outcomes to conventional open-tray splinted impressions. Artificial landmarks on the posterior region may be more pivotal than those on the anterior region. Clinical significanceGroup IV could achieve comparable accuracy to conventional open-tray splinted impressions.

A novel post-processing strategy to improve the accuracy of complete-arch intraoral scanning for implants: an in vitro study

ObjectivesTo develop a new post-processing strategy that utilizes an auxiliary device to adjust intraoral scans and improve the accuracy of 3D models of complete-arch dental implants. Materials and methodsAn edentulous resin model with 6 dental implants was prepared. An auxiliary device, consisting of an opaque base and artificial landmarks, was fabricated and mounted onto the resin model. Twenty intraoral scans (raw scans) were taken using this setup. A new post-processing strategy was proposed to adjust the raw scans using reverse engineering software (verified group). Additionally, ten conventional gypsum casts were duplicated and digitized using a laboratory scanner. The linear and angular trueness and precision of the models were evaluated and compared. The effect of the proposed strategy on the accuracy of complete-arch intraoral scans was analyzed using one-way ANOVA. ResultsThe linear trueness (29.7 µm) and precision (24.8 µm) of the verified group were significantly better than the raw scans (46.6 µm, 44.7 µm) and conventional casts (51.3 µm, 36.5 µm), particularly in cross-arch sites. However, the angular trueness (0.114°) and precision (0.085°) of the conventional casts were significantly better than both the verified models (0.298°, 0.168°) and the raw scans (0.288°, 0.202°). ConclusionsThe novel post-processing strategy is effective in enhancing the linear accuracy of complete-arch implant IO scans, especially in cross-arch sites. However, further improvement is needed to eliminate the angular deviations. Clinical significanceErrors generated from intraoral scanning in complete edentulous arches exceed the clinical threshold. The elimination of stitching errors in the raw scans particularly in the cross-arch sites, through the proposed post-processing strategy would enhance the accuracy of complete-arch implant prostheses.

Position correction of mobile robot by detecting line landmark using Hough line transform

Mobile robots are used in a laboratory automation system to transport specimens or experiments to their destinations. When moving, the robot has some error positions because of the wheels skid on the floor and the inaccuracy direction of the robot. The robot needs to correct its position and return to the track. By reading the landmarks in the environment, the robot can correct its position. This research proposes to do the position correction of the robot using a camera by reading the orange lines as an artificial landmark on the laboratory environment floor. The camera detects the orange lines as two parallel edges. And by Hough line transform (HLT) it produces Δρ value between line edges. The robot calculates the error position using the Δρ value and the biggest ρ (ρMAX) as the distance prediction robot to the line. Compared to the original robot movement on the Webots simulator application, this method can help the robot keep its position on the track. On the goal position, the robot can reduce 90% the error position. This error improvement makes the error position of the robot becomes around 5 mm from the target position.

Effect of novel prefabricated auxiliary devices attaching to scan bodies on the accuracy of intraoral scanning of complete-arch with multiple implants: An in-vitro study

ObjectivesTo examine the effect of novel prefabricated auxiliary devices with different geometric features called Scan Body Clasp (SBC) at different levels on the accuracy of intraoral scanning of complete-arch with multiple implants. MethodsAn edentulous maxilla 4-implant model and SBCs with different geometric features (flat or curved) were fabricated by a 3D printer (AccuFab-C1s, 3DShining, Hangzhou, China). Test scans were performed using an intraoral scanner (Aoralscan 3, 3DShining, Hangzhou, China) software version 1.0.0.3104 under different scenarios: group A (CO), without any SBCs; group B&C (LC&HC), with curved SBCs adjacent to and away from the mucosa; group D&E (LF&HF), with flat SBCs adjacent to and away from the mucosa. 20 scans were done for each group (CO, LC, HC, LF and HF). Reference Scans were obtained by digitizing the model in group A using a dental laboratory scanner (D2000, 3Shape, Copenhagen, Denmark). The related files were imported into inspection software for trueness and precision assessment. Statistical analysis was performed with One-way ANOVA, Independent-Sample T test for trueness values. Kruskal-Wallis test and Mann-Whitney test were used to assess the precision values. The level of significance was set at α=0.05. ResultsGroups with SBCs demonstrated trueness enhancement, among which LF revealed the best trueness. Significant differences were also found between LF and HC (p < .01), LF and HF (p < .001), LC and HF (p < .01). LF and HF showed precision enhancement. The best precision was LF, which was found to be more precise than LC (p < .001) and HC (p < .001). HF was more precise than LC (p < .001) and HC (p < .001). ConclusionsAttaching the scan bodies with SBCs at different levels significantly influenced the scanning accuracy. The SBCs near the mucosa result in superior trueness, while the flat morphology benefits the precision. Clinical significanceThe results demonstrated the feasibility of the SBCs in enhancing intraoral complete-arch implant scanning accuracy. Among the configurations tested in the present study, low-level and flat surfaces of the artificial landmarks may be the potential pivotal elements to optimizing long-span scanning accuracy.

Effect of splinting scan bodies on the trueness of complete arch digital implant scans with 5 different intraoral scanners

Statement of problemThe absence of fixed reference points can affect the trueness of complete arch intraoral digital implant scans. The effect of splinting intraoral scan bodies (ISBs) or the inclusion of artificial landmarks (AL) on the trueness of complete arch digital implant scans is still unclear. PurposeThe purpose of this study was to analyze the effect of splinting ISBs or the inclusion of AL on the trueness of complete arch digital implant scans with 5 intraoral scanners (IOSs). Material and methodsSix tissue-level dental implants (Straumann Tissue Level) were placed in an edentulous patient, and the correspondent definitive cast was digitized with a desktop scanner (IScan4D LS3i) to obtain the reference digital cast. Digital scans (n=10) were performed with 5 IOSs: TRIOS 4, Virtuo Vivo, Medit i700, iTero Element 5D, and Cerec Primescan. Three different scanning techniques were evaluated: conventional (cIOSs), splinted (sIOSs), and AL (AL-IOSs). The scan data obtained were imported into a metrology software program and superimposed to the reference digital cast by using a best-fit algorithm. The overall deviations of the positions of the ISBs were evaluated by using the root-mean-square (RMS) error (α=.05). ResultsThe mean ±standard deviation trueness values for the cIOSs, sIOSs, and AL-IOSs groups were 48 ±8 µm, 53 ±7 µm, and 49 ±11 µm, respectively, with no statistically significant differences (P=.06). Significant differences were found for the IOSs used with each technique (P<.001). Primescan (27 ±4 µm cIOSs; 28 ±3 µm sIOSs; 31 ±3 µm AL-IOSs) showed significantly higher trueness than iTero 5D (47 ±5 µm cIOSs; 47 ±4 µm sIOSs; 50 ±6 µm AL-IOSs) (P=.002) and TRIOS 4 (93 ±18 µm cIOSs; 76 ±18 µm sIOSs; 107 ±13 µm AL-IOSs) (P=.001) for all techniques. In addition, no significant differences were found between the techniques by using iTero 5D or Primescan (P=.348 and P=.059, respectively). ConclusionsThe cIOSs, sIOSs, and AL-IOSs techniques showed similar trueness. The IOS used influenced the trueness of complete arch digital implant scans.

Techniques to Improve the Accuracy of Intraoral Digital Impression in Complete Edentulous Arches: A Narrative Review

Complete edentulous arches have been considered as one of the main limitations of intraoral scanners (IOSs). In these clinical scenarios, the accuracy of IOSs can be reduced because of several anatomical factors. To overcome these limitations, some studies have proposed several techniques to increase the accuracy of the impressions by means of various materials and instruments. The aim of this narrative review was to describe these techniques and to compare the obtained results to understand if it is currently feasible to increase the accuracy of the digital impressions of complete edentulous arches. An accurate analysis of the literature was performed using PubMed (National Library of Medicine) as well as manual searching without time and language restrictions. The results showed that there are few articles in the indexed literature on this topic, and that all are in vitro studies. Although the results of the analyzed studies were encouraging and reported useful in vitro results for artificial landmarks as well as for the use of an auxiliary geometry part related to the splinting of intraoral scan bodies (ISBs), clinical trials are needed to confirm that these techniques are feasible in daily clinical practice.

Absence of visual cues motivates desert ants to build their own landmarks

The desert ants Cataglyphis fortis inhabit the harsh salt pans of Tunisia. The individually foraging ants rely on path integration to navigate back to their nest.1,2,3,4 However, as path integration accumulates errors5 at a rate that increases with distance traveled,6,7 it is supplemented by visual and olfactory cues.8,9,10,11,12,13 We show that despite their impressive homing accuracy, ants returning from long foraging journeys face a mortality rate of up to 20%. To facilitate homing, colonies inhabiting the featureless center of the salt pan build tall nest hills as visual cues. Removing these hills triggers rebuilding, but visual artificial landmarks placed near the nest entrance are sufficient to suppress the ants' rebuilding activity. Our data suggest that the desert ant builds its own landmark on purpose in a featureless environment to increase its chances of successful homing and survival. VIDEO ABSTRACT.

Vision-Based Global Localization of Points of Gaze in Sport Climbing

Investigating realistic visual exploration is quite challenging in sport climbing, but it promises a deeper understanding of how performers adjust their perception-action couplings during task completion. However, the samples of participants and the number of trials analyzed in such experiments are often reduced to a minimum because of the time-consuming treatments of the eye-tracking data. Notably, mapping successive points of gaze from local views to the global scene is generally performed manually by watching eye-tracking video data frame by frame. This manual procedure is not suitable for processing a large number of datasets. Consequently, this study developed an automatic method for solving this global point of gaze localization in indoor sport climbing. Particularly, an eye-tracking device was used for acquiring local image frames and points of gaze from a climber’s local views. Artificial landmarks, designed as four-color-disk groups, were distributed on the wall to facilitate localization. Global points of gaze were computed based on planar homography transforms between the local and global positions of the detected landmarks. Thirty climbing trials were recorded and processed by the proposed methods. The success rates (Mean[Formula: see text]±[Formula: see text]SD) were up to 85.72%[Formula: see text]±[Formula: see text]13.90%, and the errors (Mean[Formula: see text]±[Formula: see text]SD) were up to [Formula: see text][Formula: see text]m. The proposed method will be employed for computing global points of gaze in our current climbing dataset for understanding the dynamics intertwining of gaze and motor behaviors during the climbs.

Research on underwater target measurement technology based on sonar image and artificial landmark

Research on underwater target measurement technology based on sonar image and artificial landmark

A Robust Planar Marker-Based Visual SLAM

Many visual SLAM systems are generally solved using natural landmarks or optical flow. However, due to textureless areas, illumination change or motion blur, they often acquire poor camera poses or even fail to track. Additionally, they cannot obtain camera poses with a metric scale in the monocular case. In some cases (such as when calibrating the extrinsic parameters of camera-IMU), we prefer to sacrifice the flexibility of such methods to improve accuracy and robustness by using artificial landmarks. This paper proposes enhancements to the traditional SPM-SLAM, which is a system that aims to build a map of markers and simultaneously localize the camera pose. By placing the markers in the surrounding environment, the system can run stably and obtain accurate camera poses. To improve robustness and accuracy in the case of rotational movements, we improve the initialization, keyframes insertion and relocalization. Additionally, we propose a novel method to estimate marker poses from a set of images to solve the problem of planar-marker pose ambiguity. Compared with the state-of-art, the experiments show that our system achieves better accuracy in most public sequences and is more robust than SPM-SLAM under rotational movements. Finally, the open-source code is publicly available and can be found at GitHub.

GNSS-Free End-of-Row Detection and Headland Maneuvering for Orchard Navigation Using a Depth Camera

GPS-based navigation in orchards can be unstable because trees may block the GPS signal or introduce multipath errors. Most research on robot navigation without GPS has focused on guidance inside orchard rows; end-of-row detection has not received enough attention. Additionally, navigation between rows relies on reference maps or artificial landmarks. In this work, a novel row-end detection method is presented, which detects drastic changes in the statistical distribution of the sensed point cloud as the robot gets closer to the row’s end. A row-entry method was also implemented that builds a local map that is used by a reactive path tracker. The system was evaluated in a 24-row block in a vineyard. Once the robot was closer than 7 m from the end of a row, the algorithm detected it with a 100% success rate and calculated the distance from it with a mean error of 0.54 m. The system was also evaluated in vineyard configurations with parallel and slanted vine rows in consecutive blocks. The system worked well in all configurations, except where the next block had rows aligned to the rows of the current block and the headland width was closer than 5 m.

SLAM for Indoor Parking: A Comprehensive Benchmark Dataset and a Tightly Coupled Semantic Framework

For the task of autonomous indoor parking, various Visual-Inertial Simultaneous Localization And Mapping (SLAM) systems are expected to achieve comparable results with the benefit of complementary effects of visual cameras and the Inertial Measurement Units. To compare these competing SLAM systems, it is necessary to have publicly available datasets, offering an objective way to demonstrate the pros/cons of each SLAM system. However, the availability of such high-quality datasets is surprisingly limited due to the profound challenge of the groundtruth trajectory acquisition in the Global Positioning Satellite denied indoor parking environments. In this article, we establish BeVIS, a large-scale Be nchmark dataset with V isual (front-view), I nertial and S urround-view sensors for evaluating the performance of SLAM systems developed for autonomous indoor parking, which is the first of its kind where both the raw data and the groundtruth trajectories are available. In BeVIS, the groundtruth trajectories are obtained by tracking artificial landmarks scattered in the indoor parking environments, whose coordinates are recorded in a surveying manner with a high-precision Electronic Total Station. Moreover, the groundtruth trajectories are comprehensively evaluated in terms of two respects, the reprojection error and the pose volatility, respectively. Apart from BeVIS, we propose a novel tightly coupled semantic SLAM framework, namely VIS SLAM -2, leveraging V isual (front-view), I nertial, and S urround-view sensor modalities, specially for the task of autonomous indoor parking. It is the first work attempting to provide a general form to model various semantic objects on the ground. Experiments on BeVIS demonstrate the effectiveness of the proposed VIS SLAM -2. Our benchmark dataset BeVIS is publicly available at https://shaoxuan92.github.io/BeVIS .

Effect of scanning strategies on the accuracy of digital intraoral scanners: a meta-analysis of in vitro studies.

This study aimed to investigate whether the accuracy of intraoral scanners is influenced by different scanning strategies in an in vitro setting, through a systematic review and meta-analysis. This review was conducted in accordance with the PRISMA 2020 standard. The following PICOS approach was used: population, tooth impressions; intervention, the use of intraoral scanners with scanning strategies different from the manufacturer's instructions; control, the use of intraoral scanners following the manufacturers' requirements; outcome, accuracy of intraoral scanners; type of studies, in vitro. A comprehensive literature search was conducted across various databases including Embase, SciELO, PubMed, Scopus, and Web of Science. The inclusion criteria were based on in vitro studies that reported the accuracy of digital impressions using intraoral scanners. Analysis was performed using Review Manager software (version 5.3.5; Cochrane Collaboration, Copenhagen, Denmark). Global comparisons were made using a standardized mean difference based on random-effect models, with a significance level of α = 0.05. The meta-analysis included 15 articles. Digital impression accuracy significantly improved under dry conditions (P < 0.001). Moreover, trueness and precision were enhanced when artificial landmarks were used (P ≤ 0.02) and when an S-shaped pattern was followed (P ≤ 0.01). However, the type of light used did not have a significant impact on the accuracy of the digital intraoral scanners (P ≥ 0.16). The accuracy of digital intraoral scanners can be enhanced by employing scanning processes using artificial landmarks and digital impressions under dry conditions.

An Efficient Visual SfM Framework Using Planar Markers

Structure-from-Motion (SfM) is a prevalent solution for vision measurement. Traditional SfM methods rely on sparse feature matching to establish visual associations between different views. However, both the incremental-based and global-based SfM show sensitiveness to outliers generated by existing hand-crafted features under challenging environments. Planar marker-assisted SfM is an alternative solution that employs artificial landmarks to help robust pose estimation. Nevertheless, using planar markers also exists the planar pose ambiguity problem, which means there may be more than one reasonable solution for pose estimation; it is a great challenge for camera pose estimation. This paper proposes an efficient planar marker-assisted global SfM method and resolves the planar pose ambiguity problem by examining the rotation consistency across multiple views. In particular, we construct two complementary graphs and present a graph filter method to filter out the views with pose ambiguity according to our designed rotation consistency checking. Afterward, we perform sparse feature matching following the proposed graph structure and make a pose-fixed bundle adjustment for high-quality 3D reconstruction. Extensive experiments have been conducted on synthetic and real datasets, and the results verify the effectiveness of the proposed method. Our method outperforms several state-of-the-art methods with encouraging efficiency, especially in challenging scenes.

Landmark-Based Scale Estimation and Correction of Visual Inertial Odometry for VTOL UAVs in a GPS-Denied Environment.

With the rapid development of technology, unmanned aerial vehicles (UAVs) have become more popular and are applied in many areas. However, there are some environments where the Global Positioning System (GPS) is unavailable or has the problem of GPS signal outages, such as indoor and bridge inspections. Visual inertial odometry (VIO) is a popular research solution for non-GPS navigation. However, VIO has problems of scale errors and long-term drift. This study proposes a method to correct the position errors of VIO without the help of GPS information for vertical takeoff and landing (VTOL) UAVs. In the initial process, artificial landmarks are utilized to improve the positioning results of VIO by the known landmark information. The position of the UAV is estimated by VIO. Then, the accurate position is estimated by the extended Kalman filter (EKF) with the known landmark, which is used to obtain the scale correction using the least squares method. The Inertial Measurement Unit (IMU) data are used for integration in the time-update process. The EKF can be updated with two measurements. One is the visual odometry (VO) estimated directly by a landmark. The other is the VIO with scale correction. When the landmark is detected during takeoff phase, or the UAV is returning to the takeoff location during landing phase, the trajectory estimated by the landmark is used to update the scale correction. At the beginning of the experiments, preliminary verification was conducted on the ground. A self-developed UAV equipped with a visual-inertial sensor to collect data and a high-precision real time kinematic (RTK) to verify trajectory are applied to flight tests. The experimental results show that the method proposed in this research effectively solves the problems of scale and the long-term drift of VIO.

Influence of artificial landmarks on the accuracy of complete arch scans in the partially edentulous maxilla: An in vitro study

Statement of problemScan path length and the presence of edentulous alveolar ridge sections have a negative influence on scanning accuracy. How different artificial landmarks combined with an adapted scanning method affect accuracy is unclear. PurposeThe purpose of this in vitro study was to determine the influence of 2 different artificial landmarks combined with an adapted scanning method on the scanning accuracy of a partially edentulous maxillary model. Material and methodsThe model simulated a maxilla with 6 prepared teeth to accommodate a complete arch fixed partial denture. Five ceramic precision balls (ball center P1–P5), distributed buccally to the dental arch, were used to detect the dimensional and angular changes between the reference model and the intraoral scans. One intraoral scanner (Primescan) was used to make 30 scans each with either the scanning strategy recommended by the manufacturer (M) or with an adapted scanning strategy and the use of a bar (B) or 4 plates (P) as artificial landmarks in the dorsal palate. Data were statistically analyzed using a generalized least squares regression model (α=.05). ResultsScanning with artificial landmarks reduced the maximum absolute distance deviations (M: 249 μm, B: 190 μm, P: 238 μm) and the maximum angle deviations (M: 0.31 degrees, B: 0.28 degrees, P: 0.26 degrees). Vertical distance deviations were improved by 10 to 50% with the use of artificial landmarks. Absolute mean distance deviations were significantly lower for group M (P<.001). In contrast, with artificial landmarks, mean angle (P<.001) and mean vertical distance deviations (P<.014) improved significantly. ConclusionsScanning with artificial landmarks in the dorsal palate combined with an adapted scanning method improved the scanning accuracy and reliability of vertical distance deviations.