Average Misalignment Research Articles

Does Condylar Morphology Affect Maxillary Repositioning in Bimaxillary Orthognathic Surgery?

This study aimed to measure the association between condylar morphology and a measure of the maxillary centroid following bimaxillary surgery using mandibular-dependent splints. The study included skeletal Class III and Class II malocclusion patients, excluding those with facial asymmetry. Based on computed tomography imaging patients were characterized into normal or abnormal temporomandibular joint (TMJ) groups. A computer-aided design/computer-aided manufacturing splints were fabricated to reposition the maxilla in Le Fort I osteotomy. The primary outcome measure was the absolute differences between the maxillary centroid's the planned and actual postoperative positions calculated by superimposing computed tomography scans. The secondary outcome was the measure of other variations in linear and angular maxilla discrepancies. The demographic covariates included the age and sex of the patients. The operative covariates consisted of the dentofacial deformity and the planned movement of the maxilla. Seventy patients with skeletal maxillofacial deformities were included for analysis: 44 patients in the normal and 26 in the abnormal TMJ group. The average maxillary misalignment was 1.04±0.48mm in the normal and 1.53±0.63mm in the abnormal TMJ group (P<0.001). A statistically significant relationship existed between the discrepancies of the maxillary centroid and dentofacial deformity (η=0.656, P<0.001). These findings suggest an increased propensity for maxillary malposition in skeletal Class II patients. Furthermore, condylar morphology is a significant prognostic factor influencing maxillary repositioning errors in bimaxillary surgery with mandibular-dependent splints.

Left atrium surface mesh reconstruction from cardiac MRI

Abstract Funding Acknowledgements Type of funding sources: None. Background The strive towards personalised medicine is universal across all aspects of healthcare. In the management of atrial fibrillation (AF), this can take the form of shape analysis tools to predict an individual’s outcome from catheter ablation (1–3), or electrophysiological simulations to plan an ablation strategy (4–6). Fundamental to their application is our ability to derive accurate three-dimensional (3D) anatomical models of a patient’s left atrial geometry from cross-sectional imaging. MRI is widely utilised in this regard due to its excellent tissue characterisation. However, constructing surface meshes can be challenging given its relatively sparse two-dimensional (2D) image planes. A particular challenge exists in producing a mesh that balances concordance with left atrium segmentation and smoothing terms to eliminate sharp edges and artifact from the contouring process. Objective Here, we describe a novel method for left atrium surface mesh reconstruction from MRI contours. Methods Cardiac MRI was performed on ten patients with paroxysmal or persistent AF, on a 3T clinical MR scanner using phased-array receiver coils. Image sequences included respiratory and ECG-gated 15-minute post contrast late gadolinium enhancement, with a 1.3mm slice thickness and in-plane resolution of 0.66×0.66mm2. Seven individuals were in sinus rhythm, and three in AF at the time of MRI. A single, custom, graphical interface tool implemented in Matlab R2014a enabled 3D mesh reconstruction from 2D MRI slices (7,8). Endocardial surfaces of the left atrium were manually segmented by an experienced clinician, with the pulmonary veins and left atrial appendage excluded at their ostia (Figure 1A). Our tool produced an initial sparse representation with vertices equally spaced along the contours (Figure 1B). Attractor points were defined along the contours, with subdivision and Laplacian smoothing applied to the mesh. This was balanced with a deformation step, which iteratively pulled the mesh towards the attractor points (Figure 1C), resulting in its final shape (Figure 1D). Results Reconstruction performance was evaluated by measuring the distance between heart contours and the reconstructed 3D surface for each case, producing the value for average misalignment 0.71 ± 0.58mm, which compares favourably to the in-plane resolution. Conclusions Our approach offers a highly accurate method for producing 3D anatomical models of the left atrium from MRI, which is fully automated following segmentation through an interactive graphical interface. The iterative optimisation between attractor-based deformation towards the original contours and the Laplacian smoothing enables us to create smooth geometries which remain true to their segmentations. Furthermore, our approach does not require the use of a template mesh, which can result in final geometries being biased towards the template.

Design and optimisation of the Compact Linear Collider main LINAC module for micron-level stability and alignment

The Compact Linear Collider (CLIC) study is developing a Multi-TeV e+e− linear collider. An acceleration gradient of 100MVm−1 will be achieved in the Main LINACs using 11.994GHz Super Accelerating Structures (SAS). To achieve the required luminosity, the SAS will be prealigned within modules to less than 14µm and maintain their position to within 1.4µm when exposed to local sources of mechanical noise. A module design is presented and Finite Element Analysis (FEA) is used to optimise the harmonic frequencies of this module and thereby minimise the potential impact of unknown sources of vibration. A module with a fundamental frequency of 60Hz is presented. Historical ground noise data from the LHC at CERN is used to statistically quantify the magnitude of SAS misalignments unavoidably induced by local ground noise. The one-standard-deviation average vertical misalignment due to ground noise is less than 0.044µm above 0.1Hz for all SAS.

Phantom study of SPECT/CT augmented reality for intraoperative localization of sentinel lymph nodes in head and neck melanoma

ObjectiveTo show that augmented reality (AR) visualization of single-photon emission computed tomography (SPECT)/computed tomography (CT) data in 3D can be used to accurately localize targets in the head and neck region. Materials and methodsEight head and neck styrofoam phantoms were painted with a mixture of radioactive solution (Tc-99m) detectable with a handheld gamma probe and fluorescent ink visible only under ultraviolet (UV) light to create 10–20 simulated lymph nodes on their surface. After obtaining SPECT/CT images of these phantoms, virtual renderings of the nodes were generated from the SPECT/CT data and displayed using a commercially available AR headset. For each of three physician evaluators, the time required to localize lymph node targets was recorded (1) using the gamma probe alone and (2) using the gamma probe while wearing the AR headset. In addition, the surface localization accuracy when using the AR headset was evaluated by measuring the misalignment between the locations visually marked by the evaluators and the ground truth locations identified using UV stimulation of the ink at the site of the nodes. ResultsFor all three evaluators, using the AR headset significantly reduced the time to detect targets (P = 0.012, respectively) compared to using the gamma probe alone. The average misalignment between the location marked by the evaluators and the ground truth location was 8.6 mm. ConclusionAR visualization of SPECT/CT data in 3D allows for accurate localization of targets in the head and neck region, and may reduce the localization time of targets.

Influence of misalignment and spacing on the pressure drop through wire mesh Stirling engine regenerators

In order to obtain high Stirling engine efficiencies, pressure losses in the regenerator must be minimized. In this study, numerical methods are used to determine the influence of misalignment and spacing on the pressure drop through stainless steel wire mesh regenerators. Microscope images were taken to discover the average wire misalignment found in wire mesh regenerators, and it was found that regardless of the intended stacking arrangement, the average misalignment was 44%–49%. A 3-dimensional CFD model was validated against previous empirical results, and used to determine the effect of wire mesh misalignment on the pressure drop for steady flow through a regenerator. A new friction factor correlation equation was developed to include the effect of wire misalignment in the form of tortuosity. It was found that if a perfectly aligned regenerator was manufactured, Stirling engine designers could expect a 38%–45% decrease in pressure losses. The numerical model was also used to determine the influence of axial spacing on the pressure drop, and it was found to be dependent on the misalignment, with pressure loss reductions only being realized in highly misaligned cases. As a result of this study, Stirling engine designers can confidently disregard alignment and spacing when assembling wire mesh regenerators, and can more accurately calculate the expected pressure losses.

On the MLC leaves alignment in the direction orthogonal to movement.

The main focus of the recommended spatial accuracy tests for the multi‐leaf collimators (MLC) is calibration of the leaf position along the movement direction and overall alignment to the radiation isocenter. No explicit attention was typically paid to the alignment of the leaves from the opposing banks in the direction orthogonal to movement. This paper is a case study demonstrating that verification of such alignment at the time of acceptance testing is prudent. The original standard MLC (SMLC) on an MRIdian MRI‐guided linac (ViewRay Inc., Mountain View, CA, USA) was upgraded to a high‐speed MLC (HSMLC), which is supposed to be mechanically identical to the SMLC except for the higher drive screw pitch. The results of the end‐to‐end IMRT tests demonstrated unacceptable dosimetric results exemplified by an average and maximum ion chamber (IC) point dose error in the high‐dose low‐gradient region of 2.5 ± 1.4% and 4.6%, respectively. Before the upgrade, those values were 0.3 ± 0.7% and 0.9%, respectively. An exhaustive analysis of possible failure modes eventually zeroed in on the average misalignment of about 1 mm in the Y (along the couch) direction between the right and left upper MLC banks. The MLC was replaced, reducing the Y‐direction misalignment to 0.4 mm. As a result, the average and maximum IC dose‐errors became acceptable 1.0 ± 0.7% and 1.6%, respectively. Simple film and/or chamber array tests during acceptance testing can easily detect Y‐direction misalignments between opposing leaves banks measuring a fraction of a mm at isocenter. Left undetected, such misalignment can cause nontrivial dosimetric consequences.

Acute Toxicity in Hypofractionated/Stereotactic Prostate Radiotherapy of Elderly Patients: Use of the Image-guided Radio Therapy (IGRT) Clarity System.

The use of intra-fractional monitoring and correction of prostate position with the Image Guided Radio Therapy (IGRT) system can increase the spatial accuracy of dose delivery. Clarity is a system used for intrafraction prostate-motion management, it provides a real-time visualization of prostate with a transperineal ultrasound. The aim of this study was to evaluate the use of Clarity-IGRT on proper intrafraction alignment and monitoring, its impact on Planning Tumor Volume margin and on urinary and rectal toxicity in elderly patients not eligible for surgery. Twenty-five elderly prostate cancer patients, median age=75 years (range=75-90 years) were treated with Volumetric Radiotherapy and Clarity-IGRT using 3 different schemes: A) 64.5/72 Gray (Gy) in 30 fractions on prostate and seminal vesicles (6 patients); B) 35 Gy in 5 fractions on prostate and seminal vesicles (12 patients); C): 35 Gy in 5 fractions on prostate (7 patients). Ultrasound identification of the overlapped structures to the detected ones during simulation has been used in each session. A specific software calculates direction and entity of necessary shift to obtain the perfect match. The average misalignment in the three-dimensional space has been determined and shown in a box-plot. All patients completed treatment with mild-moderate toxicity. During treatment, genitourinary toxicity was 32% Grade 1; 4% Grade 2, rectal was 4% Grade 1. At follow-up of 3 months, genitourinary toxicity was 20% Grade 1; 4% Grade 2, rectal toxicity was 4% Grade 2. At follow-up of 6 months, genitourinary toxicity was 4% Grade 1; 4% Grade 2. Rectal toxicity was 4% Grade 2. Radiotherapy with the Clarity System allows a reduction of PTV margins, the amount of fractions can be reduced increasing the total dose, not exacerbating urinary and rectal toxicity with greater patient's compliance.

ValveTech: A Novel Robotic Approach for Minimally Invasive Aortic Valve Replacement.

Aortic valve disease is the most common heart disease in the elderly calling for replacement with an artificial valve. The presented surgical robot aims to provide a highly controllable instrument for efficient delivery of an artificial valve by the help of integrated endoscopic vision. A robot (called ValveTech), intended for minimally invasive surgery (MIS) and consisting of a flexible cable driven manipulator, a passive arm, and a control unit has been designed and prototyped. The flexible manipulator has several features (e.g., stabilizing flaps, tiny cameras, dexterous introducer and custom cartridge) to help the proper valve placement. It provides 5 degrees of freedom for reaching the operative site via mini-thoracotomy; it adjusts the valve and expands it at the optimal position. The robot was evaluated by ten cardiac surgeons following a real surgical scenario in artificial chest simulator with an aortic mockup. Moreover, after each delivery, the expanded valve was evaluated objectively in comparison with the ideal position. The robot performances were evaluated positively by surgeons. The trials resulted in faster delivery and an average misalignment distance of 3.8 mm along the aorta axis; 16.3 degrees rotational angle around aorta axis and 8.8 degrees misalignment of the valve commissure plane to the ideal plane were measured. The trials successfully proved the proposed system for valve delivery under endoscopic vision. The ValveTech robot can be an alternative solution for minimally invasive aortic valve surgery and improve the quality of the operation both for surgeons and patients.

The alignment between reported profits and real activity in times of the BEPS Action Plan

Several empirical studies suggest that companies allocate profits regardless of the underlying real activity to avoid taxes. The Organisation for Economic Co-operation and Development (OECD) Base Erosion and Profit Shifting (BEPS) Action Plan, with its first formal document published in 2014, requires the taxation of profits where economic value is created. In this study, we investigate whether firms have improved the alignment between reported profits and real activity. We examine a large unconsolidated sample of European Union (EU) subsidiaries and find that earnings and economic activities are better aligned in the years after the BEPS Action Plan. Following the publication of the OECD’s recommendations, the average misalignment of 12.58 %–14.47 % of a corporate group’s reported profits decreased by more than 5%. This alignment is achieved by both the relocation of profits and real activity. Other measures by the EU probably contributed to this improvement. Our study informs politicians and researchers about firms’ reactions to the measures against BEPS.

Large-scale Quality Control of Cardiac Imaging in Population Studies: Application to UK Biobank

In large population studies such as the UK Biobank (UKBB), quality control of the acquired images by visual assessment is unfeasible. In this paper, we apply a recently developed fully-automated quality control pipeline for cardiac MR (CMR) images to the first 19,265 short-axis (SA) cine stacks from the UKBB. We present the results for the three estimated quality metrics (heart coverage, inter-slice motion and image contrast in the cardiac region) as well as their potential associations with factors including acquisition details and subject-related phenotypes. Up to 14.2% of the analysed SA stacks had sub-optimal coverage (i.e. missing basal and/or apical slices), however most of them were limited to the first year of acquisition. Up to 16% of the stacks were affected by noticeable inter-slice motion (i.e. average inter-slice misalignment greater than 3.4 mm). Inter-slice motion was positively correlated with weight and body surface area. Only 2.1% of the stacks had an average end-diastolic cardiac image contrast below 30% of the dynamic range. These findings will be highly valuable for both the scientists involved in UKBB CMR acquisition and for the ones who use the dataset for research purposes.

Alignment-Free Offline Calibration of Commercial Optical See-Through Head-Mounted Displays With Simplified Procedures

Despite the growing availability of self-contained augmented reality head-mounted displays (AR HMDs) based on optical see-through (OST) technology, their potential applications across highly challenging medical and industrial settings are still hampered by the complexity of the display calibration required to ensure the locational coherence between the real and virtual elements. The calibration of commercial OST displays remains an open challenge due to the inaccessibility of the user’s perspective and the limited hardware information available to the end-user. State-of-the-art calibrations usually comprise both offline and online stages. The offline calibration at a generic viewpoint provides a starting point for the subsequent refinements and it is crucial. Current offline calibration methods either heavily rely on the user-alignment or require complicated hardware calibrations, making the overall procedure subjective and/or tedious. To address this problem, in this work we propose two fully alignment-free calibration methods with less complicated hardware calibration procedures compared with state-of-the-art solutions. The first method employs an eye-replacement camera to compute the rendering camera’s projection matrix based on photogrammetry techniques. The second method controls the rendered object position in a tracked 3D space to compensate for the parallax-related misalignment for a generic viewpoint. Both methods have been tested on Microsoft HoloLens 1. Quantitative results show that the average overlay misalignment is fewer than 4 pixels (around 1.5 mm or 9 arcmin) when the target stays within arm’s reach. The achieved misalignment is much lower than the HoloLens default interpupillary distance (IPD)-based correction, and equivalent but with lower variance than the Single Point Active Alignment Method (SPAAM)-based calibration. The two proposed methods offer strengths in complementary aspects and can be chosen according to the user’s needs. We also provide several update schemes for the two methods that can be integrated for an on-line viewpoint-dependent refinement of the calibration parameters. Both methods have been integrated into a Unity3D-based framework and can be directly applied to Unity-assisted devices.

Processing Chain for Estimation of Tree Diameter from GNSS-IMU-Based Mobile Laser Scanning Data

Mobile laser scanning (MLS) is a progressive technology that has already demonstrated its ability to provide highly accurate measurements of road networks. Mobile innovation of the laser scanning has also found its use in forest mapping over the last decade. In most cases, existing methods for forest data acquisition using MLS result in misaligned scenes of the forest, scanned from different views appearing in one point cloud. These difficulties are caused mainly by forest canopy blocking the global navigation satellite system (GNSS) signal and limited access to the forest. In this study, we propose an approach to the processing of MLS data of forest scanned from different views with two mobile laser scanners under heavy canopy. Data from two scanners, as part of the mobile mapping system (MMS) Riegl VMX-250, were acquired by scanning from five parallel skid trails that are connected to the forest road. Misaligned scenes of the forest acquired from different views were successfully extracted from the raw MLS point cloud using GNSS time based clustering. At first, point clouds with correctly aligned sets of ground points were generated using this method. The loss of points after the clustering amounted to 33.48%. Extracted point clouds were then reduced to 1.15 m thick horizontal slices, and tree stems were detected. Point clusters from individual stems were grouped based on the diameter and mean GNSS time of the cluster acquisition. Horizontal overlap was calculated for the clusters from individual stems, and sufficiently overlapping clusters were aligned using the OPALS ICP module. An average misalignment of 7.2 mm was observed for the aligned point clusters. A 5-cm thick horizontal slice of the aligned point cloud was used for estimation of the stem diameter at breast height (DBH). DBH was estimated using a simple circle-fitting method with a root-mean-square error of 3.06 cm. The methods presented in this study have the potential to process MLS data acquired under heavy forest canopy with any commercial MMS.

Improvement of optical and mechanical properties of self-written polymer waveguides attached to optical fibers

Polymer waveguide bridges with high reproducibility up to 750 μm in length were optically written between two single-mode optical fibers. Fiber ends were treated by adhesion promoter to covalently bond to both the silica fiber and the photopolymer waveguide, the mechanical properties of both long and short bridges were improved. The optical insertion loss was 0.5 dB for the longest waveguide. The mechanical properties and optical transmission of polymer waveguides were investigated under shear and tensile stress. Bi-directionally cured 500 μm polymer bridges showed average lateral misalignment of 175 μm before breakage. Fibers treatment also improved adhesion bonding at both polymer/fiber interfaces such that 300 μm polymer waveguide could endure average longitudinal strain of 23% for photobleached and 32% for unbleached polymer bridges.

Stability-controlled hybrid adaptive feedback cancellation scheme for hearing aids.

Adaptive feedback cancellation (AFC) techniques are common in modern hearing aid devices (HADs) since these techniques have been successful in increasing the stable gain. Accordingly, there has been a significant effort to improve AFC technology, especially for open-fitting and in-ear HADs, for which howling is more prevalent due to the large acoustic coupling between the loudspeaker and the microphone. In this paper, the authors propose a hybrid AFC (H-AFC) scheme that is able to shorten the time it takes to recover from howling. The proposed H-AFC scheme consists of a switched combination adaptive filter, which is controlled by a soft-clipping-based stability detector to select either the standard normalized least mean squares (NLMS) algorithm or the prediction-error-method (PEM) NLMS algorithm to update the adaptive filter. The standard NLMS algorithm is used to obtain fast convergence, while the PEM-NLMS algorithm is used to provide a low bias solution. This stability-controlled adaptation is hence the means to improve performance in terms of both convergence rate as well as misalignment, while only slightly increasing computational complexity. The proposed H-AFC scheme has been evaluated for both speech and music signals, resulting in a significantly improved convergence and re-convergence rate, i.e., a shorter howling period, as well as a lower average misalignment and a larger added stable gain compared to using either the NLMS or the PEM-NLMS algorithm alone. An objective evaluation using the perceptual evaluation of speech quality and the perceptual evaluation of audio quality measures shows that the proposed H-AFC scheme provides very high-quality speech and music signals. This has also been verified through a subjective listening experiment with N = 15 normal-hearing subjects using a multi-stimulus test with hidden reference and anchor, showing that the proposed H-AFC scheme results in a better perceptual quality than the state-of-the-art PEM-NLMS algorithm.

Packaging and Demonstration of Optical-Fiber-Coupled Photodiode Array for Operation at 4 K

An optoelectronic module for operation at 4 K is developed, intended for use in pulse-driven Josephson arbitrary waveform synthesizer. Multiple InP/InGaAs photodiodes with customized optical fiber assembly were assembled on a single silicon carrier. Photodiodes were flip-chip bonded on the carrier using Au stud bumps, and laser-cut silicon fixtures were aligned and adhesively bonded to the carrier in order to attach pigtailed borosilicate ferrules. Optical simulations were performed to estimate the tolerance for fiber-chip misalignment. The photodiodes were bonded with an average misalignment of $8~\mu \text{m}$ , while the misalignment between the silicon fixture and the photodiodes after bonding was $13~\mu \text{m}$ . The electrical response to continuous-wave laser inputs was measured at room temperature and at 4 K by direct immersion in liquid helium. The results show that the assembly technique could facilitate a stable and efficient optical coupling. The individual photodiodes were able to deliver currents up to 12 mA at room temperature and 7 mA at 4 K.

Burst Misalignment Evaluation for ALOS-2 PALSAR-2 ScanSAR-ScanSAR Interferometry

This paper reports the validation results of burst misalignment for ScanSAR-ScanSAR interferometry of the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard the Advanced Land Observing Satellite-2 (ALOS-2, “DAICHI-2”). After the internal software modification on 8 February 2015, ALOS-2 ScanSAR observation mode archives have been available for use in interferometric analysis, as it was planned. However, it has not been reported whether its burst misalignment satisfies the mission requirements: 90% or higher burst overlap ratio. The validation results in this paper confirm that the expected observation misalignment satisfies the required range, including minimal seasonal and orbital dependencies. The results in this paper are obtained directly from the azimuth offset of the single look complex (SLC) data and are not derived from the orbit records. Nine identical orbits and frame numbers are chosen and evaluated to investigate the average burst misalignment and orbital dependency.

A comparison of three different corneal marking methods used to determine cyclotorsion in the horizontal meridian.

During toric intraocular lens (IOL) implantation, surgeons must take particular care to ensure that inaccurate preoperative measurement and intraoperative misalignment do not cause unexpected postoperative residual astigmatism. This retrospective, comparative case series study aimed to analyze the rotational deviation, or cyclotorsion, of three corneal marking methods: VERION digital marker (VDM; reference), horizontal slit beam marking (HSBM), and subjective direct visual marking (SDVM) on the table (using a bevel knife tip). Subjects included 81 eyes of 61 patients (mean age: 65.70±13.14 years; range: 32–91 years) undergoing scheduled cataract surgery. A preoperative reference image was taken of each eye. Subsequently, a slit lamp with the light beam turned to the horizontal meridian was used to align the seated patient’s head, and two reference marks were placed at the 3- and 9-o’clock positions of the corneal limbus using a 27-gauge needle and marking pen (HSBM). Upon transfer to the surgical table, the VDM was used to display a real-time dial scale on the patient’s eye, with the entrance of the temporal clear corneal incision (CCI) at 0° (horizontal meridian). Simultaneously, a bevel knife tip was used to create a marker based on the surgeon’s visual determination of the temporal 0° point (SDVM). We used the VDM to quantitatively evaluate the accuracy of axis alignment via deviation from the horizontal reference meridian. Compared with the reference meridian, the SDVM (−3.46°±7.32°, range: −18° to 13°) exhibited greater average relative cyclotorsion versus the HSBM (0.41°±4.92°, range: −10° to 10°). Furthermore, the mean average misalignment was significantly less in the HSBM group versus the SDVM group (t=4.179, P<0.001). The VDM is likely a reliable marking method, similar to the HSBM. In contrast, the SDVM is not entirely reliable. The VDM usage may prevent inaccurate preoperative manual marking during toric IOL implantation.

Permanent Magnet Demagnetization Process Considering the Inclination of the Demag Field

Computer simulations of the magnetizing process have been carried out by applying a numerical model to the theory of magnetization and demagnetization for magnetic materials. The numerical model (written using the Python programming language) is able to calculate the magnetization/demagnetization of the permanent magnet material according to its $B$ – $H$ curves. This numerical model is combined with an existing finite-element method (FEM) model in which the result of computations is the approximated potential value in the FEM mesh. The aim of this paper was to develop a tool able to simulate the behavior of an anisotropic sintered permanent magnet during the demagnetization process. The permanent magnet material that has been studied in this paper is sintered Nd–Fe–B and it was modeled taking into account an average misalignment angle related to the magnet easy axis. This model also takes into account different demagnetizing field directions, such as a demagnetizing field perpendicular to the orientation direction, which is often ignored. It is shown that even a demagnetizing field perpendicular to the magnetization direction can produce visible demagnetization effects. A Gaussian distribution of the average misalignment angle in the permanent magnet material is also taken into account as well as its variation. Demag curves have been calculated varying the misalignment angle and the intensity and direction of the external magnetic field. The simulation results are in perfect agreement with the ${1}/{\cos \theta} $ law. The model can be applied in many magnetization and magnetic tuning applications.

QUALITY ANALYSIS AND CORRECTION OF MOBILE BACKPACK LASER SCANNING DATA

Abstract. Backpack laser scanning systems have emerged recently enabling fast data collection and flexibility to make measurements also in areas that cannot be reached with, for example, vehicle-based laser scanners. Backpack laser scanning systems have been developed both for indoor and outdoor use. We have developed a quality analysis process in which the quality of backpack laser scanning data is evaluated in the forest environment. The reference data was collected with an unmanned aerial vehicle (UAV) laser scanning system. The workflow included noise filtering, division of data into smaller patches, ground point extraction, ground data decimation, and ICP registration. As a result, we managed to observe the misalignments of backpack laser scanning data for 97 patches each including data from circa 10 seconds period of time. This evaluation revealed initial average misalignments of 0.227 m, 0.073 and -0.083 in the easting, northing and elevation directions, respectively. Furthermore, backpack data was corrected according to the ICP registration results. Our correction algorithm utilized the time-based linear transformation of backpack laser scanning point clouds. After the correction of data, the ICP registration was run again. This revealed remaining misalignments between the corrected backpack laser scanning data and the original UAV data. We found average misalignments of 0.084, 0.020 and -0.005 meters in the easting, northing and elevation directions, respectively.

QUALITY ANALYSIS AND CORRECTION OF MOBILE BACKPACK LASER SCANNING DATA

Backpack laser scanning systems have emerged recently enabling fast data collection and flexibility to make measurements also in areas that cannot be reached with, for example, vehicle-based laser scanners. Backpack laser scanning systems have been developed both for indoor and outdoor use. We have developed a quality analysis process in which the quality of backpack laser scanning data is evaluated in the forest environment. The reference data was collected with an unmanned aerial vehicle (UAV) laser scanning system. The workflow included noise filtering, division of data into smaller patches, ground point extraction, ground data decimation, and ICP registration. As a result, we managed to observe the misalignments of backpack laser scanning data for 97 patches each including data from circa 10 seconds period of time. This evaluation revealed initial average misalignments of 0.227 m, 0.073 and -0.083 in the easting, northing and elevation directions, respectively. Furthermore, backpack data was corrected according to the ICP registration results. Our correction algorithm utilized the time-based linear transformation of backpack laser scanning point clouds. After the correction of data, the ICP registration was run again. This revealed remaining misalignments between the corrected backpack laser scanning data and the original UAV data. We found average misalignments of 0.084, 0.020 and -0.005 meters in the easting, northing and elevation directions, respectively.