Scanning Errors Research Articles

A Method Based on Improved iForest for Trunk Extraction and Denoising of Individual Street Trees

Currently, the street tree resource survey using Mobile laser scanning (MLS) represents a hot spot around the world. Refined trunk extraction is an essential step for 3D reconstruction of street trees. However, due to scanning errors and the effects of occlusion by various types of features in the urban environment, street tree point cloud data processing has the problem of excessive noise. For the noise points that are difficult to remove using statistical methods in close proximity to the tree trunk, we propose an adaptive trunk extraction and denoising method for street trees based on an improved iForest (Isolation Forest) algorithm. Firstly, to extract the individual tree trunk points, the trunk and the crown are distinguished from the individual tree point cloud through point cloud slicing. Next, the iForest algorithm is improved by conducting automatic calculation of the contamination and further used to denoise the tree trunk point cloud. Finally, the method is validated with five datasets of different scenes. The results indicate that our method is robust and effective in extracting and denoising tree trunks. Compared with the traditional Statistical Outlier Removal (SOR) filter and Radius filter denoising methods, the denoising accuracy of the proposed method can be improved by approximately 30% for noise points close to tree trunks. Compared to iForest, the proposed method automatically calculates the contamination, improving the automation of the algorithm. Our method can provide more precise trunk point clouds for 3D reconstruction of street trees.

Online geometry calibration for retrofit computed tomography from a mouse rotation system and a small-animal imager.

Computed tomography (CT) generates a three-dimensional rendering that can be used to interrogate a given region or desired structure from any orientation. However, in preclinical research, its deployment remains limited due to relatively high upfront costs. Existing integrated imaging systems that provide merged planar X-ray also dwarfs CT popularity in small laboratories due to their addedversatility. In this paper, we sought to generate CT-like data using an existing small-animal X-ray imager with a specialized specimen rotation system, or MiSpinner. This setup conforms to the cone-beam CT (CBCT) geometry, which demands high spatial calibration accuracy. Therefore, a simple but robust geometry calibration algorithm is necessary to ensure that the entire imaging system works properly andaccurately. Because the rotation system is not permanently affixed, we propose a structure tensor-based two-step online (ST-TSO) geometry calibration algorithm. Specifically, two datasets are needed, namely, calibration and actual measurements. A calibration measurement detects the background of the system forward X-ray projections. A study on the background image reveals the characteristics of the X-ray photon distribution, and thus, provides a reliable estimate of the imaging geometry origin. Actual measurements consisted of an X-ray of the intended object, including possible geometry errors. A comprehensive image processing technique helps to detect spatial misalignment information. Accordingly, the first processing step employs a modified projection matrix-based calibration algorithm to estimate the relevant geometric parameters. Predicted parameters are then fine-tuned in a second processing step by an iterative strategy based on the symmetry property of the sum of projections. Virtual projections calculated from the parameters after two-step processing compensate for the scanning errors and are used for CT reconstruction. Experiments on phantom and mouse imaging data were performed to validate the calibrationalgorithm. Once system correction was conducted, CBCT of a CT bar phantom and a cohort of euthanized mice were analyzed. No obvious structure error or spatial artifacts were observed, validating the accuracy of the proposed geometry calibration method. Digital phantom simulation indicated that compared withthe preset spatial values, errors in the final estimated parameters could be reduced to 0.05° difference in dominant angle and 0.5-pixel difference in dominant axis bias. The in-plane resolution view of the CT-bar phantom revealed that the resolution approaches 150 m. A constrained two-step online geometry calibration algorithm has been developed to calibrate an integrated X-ray imaging system, defined by a first-step analytical estimation and a second-step iterative fine-tuning. Test results have validated its accuracy in system correction, thus demonstrating the potential of the described system to be modified and adapted for preclinicalresearch.

MIXED REALITY VISUALIZATION OF POINT CLOUDS FOR SUPPORTING TERRESTRIAL LASER SCANNING

Abstract. 3D point clouds from terrestrial laser scanners (TLS) are used in a variety of fields and applications. To acquire high-quality point clouds that have enough point density, small scanning errors, and no lack of points in important regions, appropriate scan planning, including determination of scanner positions and scan conditions, is required. Currently, planning is supported by knowledge and experience of skilled workers, and it is difficult to ensure the quality of acquired point clouds. In this study, we propose a system for visualization of point clouds to support the acquisition of high-quality point clouds using TLS. The system allows the user to see and check the quality of scanned TLS point clouds and unscanned regions intuitively by superimposing the point clouds onto the real world using a mixed reality (MR) device. In addition, the system supports finding the next best scanner position for additional laser scans based on predicted scan quality visualization to acquire higher-quality points or fill the unscanned regions.

Digital Pathology Implementation in Private Practice: Specific Challenges and Opportunities.

Digital pathology (DP) is being deployed in many pathology laboratories, but most reported experiences refer to public health facilities. In this paper, we report our experience in DP transition at a high-volume private laboratory, addressing the main challenges in DP implementation in a private practice setting and how to overcome these issues. We started our implementation in 2020 and we are currently scanning 100% of our histology cases. Pre-existing sample tracking infrastructure facilitated this process. We are currently using two high-capacity scanners (Aperio GT450DX) to digitize all histology slides at 40×. Aperio eSlide Manager WebViewer viewing software is bidirectionally linked with the laboratory information system. Scanning error rate, during the test phase, was 2.1% (errors detected by the scanners) and 3.5% (manual quality control). Pre-scanning phase optimizations and vendor feedback and collaboration were crucial to improve WSI quality and are ongoing processes. Regarding pathologists’ validation, we followed the Royal College of Pathologists recommendations for DP implementation (adapted to our practice). Although private sector implementation of DP is not without its challenges, it will ultimately benefit from DP safety and quality-associated features. Furthermore, DP deployment lays the foundation for artificial intelligence tools integration, which will ultimately contribute to improving patient care.

Frequency response data-based peak filter design applied to MIMO large-scale high-precision scan stage

A large-scale high-precision scan stage is important equipment in the industrial productions of micro-fabrication such as flat panel display (FPD) lithography systems. Designing controllers for multi-input multi-output (MIMO) systems is time-consuming and needs experience because of the interaction between each axis and many controller tuning parameters. The aim of this study is to develop a peak filter design method based on frequency response data to reduce repetitive disturbance. This data-based approach does not use the model and only uses the frequency response data of the controlled system and the disturbance spectrum calculated from the scanning error data (Contribution 1). The peak filter is designed by convex optimization and satisfies robust stability conditions for six-degree-of-freedom systems (Contribution 2). The control performance of the designed peak filter is experimentally demonstrated with an industrial MIMO large-scale high-precision scan stage in reducing the scanning error of the main stroke of the translation along the x-axis (Contribution 3).

Analysis of photostimulable phosphor image plate artifacts and their prevalence.

BACKGROUND Digital radiography has recently been used in dentistry as a substitute for conventional film radiography worldwide. Digital imaging has many advantages and provides new possibilities for recording and interpreting radiographic data. This system uses different types of digital receptors.AIMTo detect the frequency, type, and reasons behind the appearance of intraoral image artifacts acquired by photostimulable phosphor plates (PSP).METHODSThis retrospective descriptive study was conducted in the oral and maxillofacial radiology unit of the dental clinics of the College of Dentistry, Princess Nourah University (PNU). All intraoral digital radiographs were acquired using (Gendex Expert DC., United States) an intraoral X-ray machine with 7 -mA, 65-kVP using a PSP system (Soredex DIGORA Optime imaging plate) and laser scanners (Soredex DIGORA Optime), which can house all sizes of reusable intraoral PSP sensor plates with image acquisition software (MIPACS Dental Enterprise viewer 3.2.2). A total of 50000 intraoral radiographs were retrieved from the clinical database from April 2018 to April 2020 to evaluate the reason, type, and solutions to these image artifacts.RESULTSOverall, 50000 intraoral digital radiographs were acquired in a two-year-period; that is, from April 2018 to April 2020. Of these, 3550 (7.1%) retakes were performed due to the presence of image artifacts. Periapical radiographs were the most common image type of intraoral retakes (80.8%). Imaging artifacts were divided into three categories: operator, plate and scanning errors. Out of 3550 retakes, 5%, 1.37%, and 0.73% were related to operator, plate, and scanning errors, respectively. The cone cut was the most common operator error (988 images), Bite marks were the most common plate error (276 images), and delayed scanning artifacts were the most common scanning errors (145 images). The calculated kappa value for interobserver reliability was 0.99, indicating almost perfect interobserver agreement. CONCLUSIONOur study discussed intraoral image artifacts that were characteristic of PSP, where the most common artifacts were bitemarks, image size reduction, scratches, and delayed scanning.

Lower jaw virtual reposition accuracy research

The aim is to study of the accuracy of the virtual reposition of the mandible (LF) by comparing the virtual and real position of the LF heads, as well as the analysis of factors contributing to the occurrence of errors. An experimental model of a human skull with a movable LF was made of radiopaque material. The resulting computed tomogram (CT) of the upper and lower jaws and temporomandibular joint (TMJ) was combined with dental scans of dental rows and CT scans and a report on the position of the heads of the LF was obtained. Then the LF was shifted to another position and this position was fixed. Optical bite recorders were obtained using an intraoral scanner. An experimental model with a fixed new position of the LF was placed in a tomograph and repeated CT was obtained. In the program, according to optical registers, a virtual reposition of the LF was carried out. The correspondence of the virtual and real position of the mandibular heads was compared. The absolute difference of glenoid fossa space between the actual and virtual reconstruction was 0.542±0.3354 mm in the anterior joint section (M±δ, M - average mean, δ - standard deviation); for the upper joint section - 0.309±0.2246 mm; and 0.260±0.1862 mm for the posterior section. The integral indicator of surface coincidence (q) when the virtual and actual position are directly compared was 0.296±0.1254 (s.u.). The total margin of error depends on the following factors: repeated scanning error (teeth arches and bite scans), repeated CBCT error, a combination of scan and CBCT error, a combination of teeth arch scan and bite scan error, error of TMJ separation. The latter two factors were the most significant.

Types and frequency of whole slide imaging scan failures in a clinical high throughput digital pathology scanning laboratory

Digital workflow transformation continues to sweep throughout a diversity of pathology departments spanning the globe following catalyzation of whole slide imaging (WSI) adoption by the SARS-CoV-2 (COVID-19) pandemic. The utility of WSI for a litany of use cases including primary diagnosis has been emphasized during this period, with WSI scanning devices gaining the approval of healthcare regulatory bodies and practitioners alike for clinical applications following extensive validatory efforts. As successful validation for WSI is predicated upon pathologist diagnostic interpretability of digital images with high glass slide concordance, departmental adoption of WSI is tantamount to the reliability of such images often predicated upon quality assessment notwithstanding image interpretability but extending to quality of practice following WSI adoption. Metrics of importance within this context include failure rates inclusive of different scanning errors that result in poor image quality and the potential such errors may incur upon departmental turnaround time (TAT). We sought to evaluate the impact of WSI implementation through retrospective evaluation of scan failure frequency in archival versus newly prepared slides, types of scanning error, and impact upon TAT following commencement of live WSI operation in May 2017 until the present period within a fully digitized high-volume academic institution. A 1.19% scan failure incidence rate was recorded during this period, with re-scanning requested and successfully executed for 1.19% of cases during the reported period of January 2019 until present. No significant impact upon TAT was deduced, suggesting an outcome which may be encouraging for departments considering digital workflow adoption.

Physical Design and Experimental Verification of a Huygens’ Metasurface Two-Lens System for Phased-Array Scan-Angle Enhancement

Over the past decades, many radome designs to extend the angular scan range of phased-array antennas have been devised by utilizing dielectric materials and metamaterials. More recently, metasurface technology such as planar lenses and beam deflectors have been applied to phased arrays, enabling scan-angle enhancers to have a low profile. In this work, a physical Huygens’ metasurface (HMS) two-lens system for scan-angle doubling of a phased array is presented. For the HMS unit cells, the wire-loop topology is deployed to achieve high transmission for the required phase-angle shift. The proposed two-lens system is analyzed by full-wave simulations and experiments. The simulation results demonstrate that the scan angle doubles when the incident angle is below 15° in accordance to the design specification. Furthermore, the directivity degradation of the refracted beams by the two-HMS lenses is in good agreement with theory. Finally, a fabricated two-lens system with two 15λ long by 15λ wide metasurface lenses and a 16 × 16-element patch antenna array as a source is experimentally verified at 10 GHz. The experimental results are in good agreement with the simulated results by showing angle-doubling performance with ±2° scan errors.

How the geometry of the scan body affects the accuracy of digital impressions in implant supported prosthesis. In vitro study.

To determine and compare how three-dimensionally accurate scan bodies of different geometric shapes are placed over 6 implants (platform or crestal module). A master plaster model was made with 6 INHEX STD implant analogs made by Mozo-Grau S.A and 4 scan body types were compared. Several groups were made: a control group using a DS101 85G20 contact scanner (Renishaw, Gavá, Spain) and 2 experimental groups using optical scanners: Cerec Omnicam (Sirona, Bensheim, Germany) and Trios 3 (3Shape, Copenhagen, Denmark). 3 parameters were measured on the implants: dis-tance between the axial axes, height difference and angulation difference. Two experienced op-erators scanned 10 times using each of the 2 scanners. The STL files were compared using the "Best-Fit" technique and the data was then extrapolated and processed statistically. The scan bodies PRMG (SB3) and TALL (SB4) lead to smaller errors in distance, projected height and angulation than ELOS (SB1) and MG (SB2). Despite the results obtained in PRMG (SB3) and TALL (SB4), the scanning errors may still be too large to achieve a good fit in large rehabilitations over implants. Any marginal discrepancy may lead to the failure of the rehabilitation or the implant due to the associated biomechanical problems. Key words:IOS, CAD/CAM, SCAN Bodies.

Optical Character Recognition and text cleaning in the indigenous South African languages

This article represents follow-up work on unpublished presentations by the authors of text and corpus cleaning strategies for the African languages. In this article we provide a comparative description of cleaning of web-sourced and text-sourced material to be used for the compilation of corpora with specific attention to cleaning of text-based material, since this is particularly relevant for the indigenous South African languages. For the purposes of this study, we use the term “web-sourced material” to refer to digital data sourced from the internet, whereas “text-based material” refers to hard copy textual material. We identify the different types of errors found in such texts, looking specifically at typical scanning errors in these languages, followed by an evaluation of three commercially available Optical Character Recognition (OCR) tools. We argue that the cleanness of texts is a matter of granularity, depending on the envisaged application of the corpus comprised by the texts. Text corpora which are to be utilized for e.g. lexicographic purposes can tolerate a higher level of ‘noise’ than those used for the compilation of e.g. spelling and grammar checkers. We conclude with some suggestions for text cleaning for the indigenous languages of South Africa.

Wide range retina-like scanning based on liquid crystal optical phased array

A retina-like scanning method based on liquid crystal optical phased array (LCOPA) is proposed to improve field of view and efficiency. The functions of human retina, lens and fovea gaze control are achieved with optimized designed scanning strategy. Beam splitting method and angular magnification system are used to meet the requirements of the efficient scanning and large FOV. The models are verified by several experiments and the results show that the scanning performance well with the flexible retina-like strategy, especially for eccentric fovea. The scanning FOV is magnified 2.2 times and the average scanning error is less than 5%.

Indexation of electron diffraction patterns at grain boundaries

Grain boundaries play a vital role in materials science, and they are extensively studied through experimental and numerical methods. Electron backscatter diffraction (EBSD) is commonly used to characterize crystalline materials, yet its performance is often compromised at grain boundaries. The key difficulty is to index the overlapped electron backscatter patterns, where Kikuchi bands from multiple crystal orientations coexist. Hough-indexation often fails in treating overlapped EBSP, while the recently proposed dictionary indexation and sphere indexation give only one triplet of Euler angles from overlapped patterns. For all these methods, the orientation indexing precision drops for overlapped EBSP. Here we propose an integrated Digital Image Correlation (DIC) procedure to determine simultaneously and precisely multiple crystal orientations by registering the overlapped EBSP and the master pattern. The contribution ratio of each crystal orientation to the overlapped pattern is also available. Through an experimental EBSD dataset around a triple point, multiple benefits of the rich results from the method are demonstrated, such as refining grain boundaries, revealing EBSD scan errors and quantifying spatial resolution of EBSD. At the grain boundaries, the crystal orientation measurement uncertainty is 0.03∘ for both indexed crystal orientations, the same order for grain interiors, while their contribution ratios of uncertainty around 0.02 are obtained.

The Effect of Ballot Characteristics on the Likelihood of Voting Errors

AbstractIn the United States, people are asked to vote on a myriad of candidates, offices, and ballot questions. The result is lengthy ballots that are time intensive and complicated to fill out. In this paper, we utilize a new analytical technique harnessing ballot scanner data from a statewide midterm election to estimate the effects of ballot complexity on voting errors. We find that increases in ballot length, increases in the number of local ballot questions, and increases in the number of candidates listed for single offices significantly increase the odds of encountering ballot marking and scanning errors. Our findings indicate that ballots’ characteristics can help election administrators make Election Day planning and resource allocation decisions that decrease ballot errors and associated wait times to vote while increasing the reliability of election results and voter confidence in the electoral process.

Correction of PZT scanner errors using a phase compensation method in white-light phase-shifting interferometry

White-light phase-shifting interferometry (WLPSI) is widely used for obtaining surface profiles of inspection targets in liquid-crystal displays (LCD) and semiconductor manufacturing processes. Phase errors caused by irregular and nonlinear scanner movement are inevitable in WLPSI. Moreover, these errors affect the measurement stability. It is difficult to eliminate the mechanical and electrical delay of scanner movement entirely. A novel method, to the best of our knowledge, is proposed that consists of a scanner position tracking system and a phase correction algorithm called compensated peak detection and modified bucket algorithm. The proposed method is experimentally verified and outperforms the conventional phase corrections in both the measurement accuracy and the repeatability.

Scanning error detection and compensation algorithm for white-light interferometry

As the primary error source in white-light interferometry (WLI), the error of scanning steps directly affects coherence peak sensing and greatly lowers the measurement accuracy. Based on the least-squares iterative algorithm, we present an algorithm to detect and compensate for scanning error in WLI. The actual scanning step is calculated from the continuous moving fringes with an iterative algorithm, and the surface is reconstructed with the calculated scanning steps to make compensation. Both simulations and experiments indicate that the high-accuracy measurements can be implemented under disturbance over a wide frequency band. The proposed algorithm could relax the environment requirement of white-light interferometer application.

Micrometre-scale strain mapping of transistor arrays extracted from undersampled atomic-resolution images

Strain maps extracted from atomic resolution images have the ultimate spatial resolution, but have a field of view limited by the sampling necessary to resolve atomic lattices. This has typically confined strain maps to dimensions less than ∼100 nanometers. To extend the field of view beyond this limit, we apply a modified geometric phase analysis to undersampled images of atomic lattices (i.e. with a pixel size too large to resolve atomic lattices). To reduce the effects of environmental and instrumental instabilities, the images were obtained by aligning series of rapid annular dark field scanning transmission electron microscopy acquisitions. We demonstrate that for undersampled images, a geometric phase analysis can still be performed on aliased frequencies and, as long as the appropriate scaling matrix is applied, provide accurate atomic displacement measurements at large scale. Experimental challenges related to the increased effects of scanning errors as the magnification is lowered are examined. Although such errors are found to significantly reduce geometric phase signals, it was still possible to produce strain maps for arrays of up to sixteen 20nm-technology transistors, corresponding to a field of view exceeding one micrometer.

Influence of Liquid on the Tooth Surface on the Accuracy of Intraoral Scanners: An In Vitro Study.

To assess the influence of liquid attached on the tooth surfaces on the accuracy (trueness and precision) of intraoral scanners and the effectiveness of the drying method (using compression air) to exclude the influence of liquid on the scanning results. A mandibular jaw model was scanned using an industrial computed tomography scanner to obtain a reference model. A scanning platform was designed to simulate three specific tooth surface states (dry, wet, blow-dry). Two kinds of liquids (ultra-pure water and artificial saliva) were used for the test. Two intraoral scanners (Trios 3 and Primescan) were used to scan the mandibular jaw model 10 times under each condition. All scanning data were processed and analyzed using dedicated software (Geomagic Control 2015). Trueness and precision comparison were conducted within the 12 groups of 3D models divided based on different intraoral scanners and liquids used under each condition. The root mean square (RMS) value was used to indicate the difference between the aligned virtual models. The color maps were used to evaluate and observe the deviation distribution patterns. The 3-way ANOVA (condition, intraoral scanner, liquid) followed by the Tukey test were used to assess precision and trueness. The level of significance was set at 0.05. The mean RMS values obtained from wet condition were significantly higher than those of the dry and blow-dry condition (p < 0.001, F = 64.033 for trueness and F = 54.866 for precision), which indicates less accurate trueness and precision for wet condition. For two different types of liquids, the mean RMS value was not significantly different on trueness and precision. The deviations caused by liquid were positive and mainly distributed in the pits and fissures of the occlusal surface of posterior teeth, the interproximal area of the teeth, and the margin of the abutments. Liquid on the tooth surface could affect intraoral scanning accuracy. Blow-drying with a three-way syringe can reduce scanning errors.

Accuracy Improvement Method of a 3D Laser Scanner Based on the D-H Model

A three-dimensional (3D) laser scanner with characteristics such as acquiring huge point cloud data and noncontact measurement has revolutionized the surveying and mapping industry. Nonetheless, how to guarantee the 3D laser scanner precision remains the critical factor that determines the excellence of 3D laser scanners. Hence, this study proposes a 3D laser scanner error analysis and calibration-method-based D-H model, applies the D-H model method in the robot area to the 3D laser scanner coordinate for calculating the point cloud data and creatively derive the error model, comprehensively analyzes six external parameters and seven inner structure parameters that affect point cloud coordinator error, and designs two calibration platforms for inner structure parameters. To validate the proposed method, we used SOKKIA total station and BLSS-PE 3D laser scanner to attain the center coordinate of the testing target sphere and then evaluate the external parameters and modify the point coordinate. Based on modifying the point coordinate, comparing the point coordinate that considered the inner structure parameters with the point coordinate that did not consider the inner structure parameters, the experiment revealed that the BLSS-PE 3D laser scanner’s precision enhanced after considering the inner structure parameters, demonstrating that the error analysis and calibration method was correct and feasible.

Magnetic interference mapping of four types of unmanned aircraft systems intended for aeromagnetic surveying

Abstract. Magnetic interference source identification is a critical preparation step for magnetometer-mounted unmanned aircraft systems (UAS) used for high-sensitivity geomagnetic surveying. A magnetic field scanner was built for mapping the low-frequency interference that is produced by a UAS. It was used to compare four types of electric-powered UAS capable of carrying an alkali-vapour magnetometer: (1) a single-motor fixed-wing, (2) a single-rotor helicopter, (3) a quad-rotor helicopter, and (4) a hexa-rotor helicopter. The scanner's error was estimated by calculating the root-mean-square deviation of the background total magnetic intensity over the mapping duration; averaged values ranged between 3.1 and 7.4 nT. Each mapping was performed above the UAS with the motor(s) engaged and with the UAS facing in two orthogonal directions; peak interference intensities ranged between 21.4 and 574.2 nT. For each system, the interference is a combination of both ferromagnetic and electrical current sources. Major sources of interference were identified such as servo(s) and the cables carrying direct current between the motor battery and the electronic speed controller. Magnetic intensity profiles were measured at various motor current draws for each UAS, and a change in intensity was observed for currents as low as 1 A.