Point clouds derived using structure from motion (SfM) algorithms from unmanned aerial vehicles (UAVs) are increasingly used in civil engineering practice. This includes areas such as (vegetated) rock outcrops or faces above linear constructions (e.g., railways) where accurate terrain identification, i.e., ground filtering, is highly difficult but, at the same time, important for safety management. In this paper, we evaluated the performance of standard geometrical ground filtering algorithms (a progressive morphological filter (PMF), a simple morphological filter (SMRF) or a cloth simulation filter (CSF)) and a structural filter, CANUPO (CAracterisation de NUages de POints), for ground identification in a point cloud derived by SfM from UAV imagery in such an area (a railway ledge and the adjacent rock face). The performance was evaluated both in the original position and after levelling the point cloud (its transformation into the horizontal plane). The poor results of geometrical filters (total errors of approximately 6–60% with PMF performing the worst) and a mediocre result of CANUPO (approximately 4%) led us to combine these complementary approaches, yielding total errors of 1.2% (CANUPO+SMRF) and 0.9% (CANUPO+CSF). This new technique could represent an excellent solution for ground filtering of high-density point clouds of such steep vegetated areas that can be well-used, for example, in civil engineering practice.

Vegetation Filtering of a Steep Rugged Terrain: The Performance of Standard Algorithms and a Newly Proposed Workflow on an Example of a Railway Ledge

Abstract “A Craftsman Must Sharpen His Tools to Do His Job,” said Confucius. Nuclear detection and readout techniques are the foundation of particle physics, nuclear physics, and particle astrophysics to reveal the nature of the universe. Also, they are being increasingly used in other disciplines like nuclear power generation, life sciences, environmental sciences, medical sciences, etc. The article reviews the short history, recent development, and trend of nuclear detection and readout techniques, covering Semiconductor Detector, Gaseous Detector, Scintillation Detector, Cherenkov Detector, Transition Radiation Detector, and Readout Techniques. By explaining the principle and using examples, we hope to help the interested reader underst and this research field and bring exciting information to the community. 

Advances in nuclear detection and readout techniques

Due to the complexity of surrounding environments, lidar point cloud data (PCD) are often degraded by plane noise In order to eliminate noise, this paper proposes a filtering scheme based on the grid principal component analysis (PCA) technique and the ground splicing method The 3D PCD is first projected onto a desired 2D plane, within which the ground and wall data are well separated from the PCD via a prescribed index based on the statistics of points in all 2D mesh grids Then, a KD-tree is constructed for the ground data, and rough segmentation in an unsupervised method is conducted to obtain the true ground data by using the normal vector as a distinctive feature To improve the performance of noise removal, we propose an elaborate K nearest neighbor (KNN)-based segmentation method via an optimization strategy Finally, the denoised data of the wall and ground are spliced for further 3D reconstruction The experimental results show that the proposed method is efficient at noise removal and is superior to several traditional methods in terms of both denoising performance and run speed

https://www.mdpi.com/1424-8220/21/11/3703/pdf

PCA-Based Denoising Algorithm for Outdoor Lidar Point Cloud Data

Separating point clouds into ground and nonground points is an essential step in the processing of airborne laser scanning (ALS) data for various applications. Interpolation-based filtering algorithms have been commonly used for filtering ALS point cloud data. However, most conventional interpolation-based algorithms have exhibited a drawback in terms of retaining abrupt terrain characteristics, resulting in poor algorithmic precision in these regions. To overcome this drawback, this paper proposes an improved adaptive surface interpolation filter with a multilevel hierarchy by using a cloth simulation and relief amplitude. This method uses three hierarchy levels of provisional digital elevation model (DEM) raster surfaces with thin plate spline (TPS) interpolation to separate ground points from unclassified points based on adaptive residual thresholds. A cloth simulation algorithm is adopted to generate sufficient effective initial ground seeds for constructing topographic surfaces with high quality. Residual thresholds are adaptively constructed by the relief amplitude of the examined area to capture complex landscape characteristics during the classification process. Fifteen samples from the International Society for Photogrammetry and Remote Sensing (ISPRS) commission are used to assess the performance of the proposed algorithm. The experimental results indicate that the proposed method can produce satisfying results in both flat areas and steep areas. In a comparison with other approaches, this method demonstrates its superior performance in terms of filtering results with the lowest omission error rate; in particular, the proposed approach retains discontinuous terrain features with steep slopes and terraces.

An Adaptive Surface Interpolation Filter Using Cloth Simulation and Relief Amplitude for Airborne Laser Scanning Data


 Observations of gravitational waves (GW) provide us with a new probe to study the Universe. GW events can be used as standard sirens if their redshifts are measured. Normally, standard sirens can be divided into bright/dark sirens according to whether the redshifts are measured by electromagnetic (EM) counterpart observations. First, we investigate the capability of the 2.5 m Wide-Field Survey Telescope (WFST) to take follow-up observations of kilonova counterparts. For binary neutron star (BNS) bright sirens, WFST is expected to observe 10–20 kilonovae per year in the second-generation GW detection era. As for neutron star–black hole (NSBH) mergers, when a BH spin is extremely high and the neutron star (NS) is stiff, the observation rate is ∼10 per year. Combining optical and GW observations, the bright sirens are expected to constrain the Hubble constant H
 0 to ∼2.8% in five years of observations. As for dark sirens, the tidal effects of NSs during merging provide us with a cosmological model-independent approach to measure the redshifts of GW sources. Then we investigate the applications of tidal effects in redshift measurements. We find in the third generation era, the host galaxy groups of around 45% BNS mergers at z < 0.1 can be identified through this method, if the equation of state is ms1, which is roughly equivalent to the results from luminosity distant constraints. Therefore, tidal effect observations provide a reliable and cosmological model-independent method of identifying BNS mergers’ host galaxy groups. Using this method, the BNS/NSBH dark sirens can constrain H
 0 to 0.2%/0.3% over a five-year observation period.

Measuring the Hubble Constant of Binary Neutron Star and Neutron Star–Black Hole Coalescences: Bright Sirens and Dark Sirens

The Wide Field Survey Telescope (WFST) is a dedicated photometric survey facility under construction jointly by the University of Science and Technology of China and Purple Mountain Observatory. It is equipped with a primary mirror of 2.5m in diameter, an active optical system, and a mosaic CCD camera of 0.73 Gpix on the main focus plane to achieve high-quality imaging over a field of view of 6.5 square degrees. The installation of WFST in the Lenghu observing site is planned to happen in the summer of 2023, and the operation is scheduled to commence within three months afterward. WFST will scan the northern sky in four optical bands (u, g, r, and i) at cadences from hourly/daily to semi-weekly in the deep high-cadence survey (DHS) and the wide field survey (WFS) programs, respectively. WFS reaches a depth of 22.27, 23.32, 22.84, and 22.31 in AB magnitudes in a nominal 30-second exposure in the four bands during a photometric night, respectively, enabling us to search tremendous amount of transients in the low-z universe and systematically investigate the variability of Galactic and extragalactic objects. Intranight 90s exposures as deep as 23 and 24 mag in u and g bands via DHS provide a unique opportunity to facilitate explorations of energetic transients in demand for high sensitivity, including the electromagnetic counterparts of gravitational-wave events detected by the second/third-generation GW detectors, supernovae within a few hours of their explosions, tidal disruption events and luminous fast optical transients even beyond a redshift of 1. Meanwhile, the final 6-year co-added images, anticipated to reach g about 25.5 mag in WFS or even deeper by 1.5 mag in DHS, will be of significant value to general Galactic and extragalactic sciences. The highly uniform legacy surveys of WFST will also serve as an indispensable complement to those of LSST which monitors the southern sky.

pdf/sciences-for-the-2-5-meter-wide-field-survey-telescope-wfst-2eam6prd.pdf

Sciences for The 2.5-meter Wide Field Survey Telescope (WFST)

Background: The correlation between myocardial strain and infraction size by cardiac magnetic resonance imaging in ST-segment elevation myocardial infarction (STEMI) with preserved left ventricular ejection fraction (LVEF) is not clear. Objective: To investigate the correlation between myocardial strain and myocardial infarction size in patients of acute STEMI with preserved LVEF. Materials and Methods: A retrospective study was conducted to assess 31 patients with acute ST-segment elevation myocardial infarction (STEMI)after primary percutaneous coronary intervention (PCI) who received cardiac magnetic resonance (CMR) imaging during hospitalization at the Central Hospital of Shandong First Medical University from 2019 to 2022 and whose echocardiography indicated preserved LVEF (LVEF≥50%). The control group consisted of 21 healthy adults who underwent CMR during the same period. We compared the CMR characteristics, global and segmental strain between the two groups. Furthermore, the correlation between the global strain and the segmental strain of the left ventricle and late gadolinium enhancement (LGE) were evaluated. Results: Compared with healthy controls, the left ventricular ejection fraction (LVEF) of STEMI patients with preserved LVEF was significantly decreased (p < 0.05). Moreover, the global radial strain (GRS) (24.09% [IQR:17.88–29.60%] vs. 39.56% [IQR:29.19–42.20%], p < 0.05), global circumferential strain (GCS) [−14.66% (IQR: 17.91–11.56%) vs. −19.26% (IQR: 21.03–17.73%), p < 0.05], and global longitudinal strains (GLS) (−8.88 ± 2.25% vs. −13.46 ± 2.63%, p < 0.05) were damaged in patients. Furthermore, GCS and GLS were associated with LGE size (%left ventricle) (GCS: r = 0.58, p < 0.05; GLS: r = 0.37, p < 0.05). In the multivariate model, we found that LGE size was significantly associated with GCS (β coefficient = 2.110, p = 0.016) but was not associated with GLS (β coefficient = −0.102, p = 0.900) and LVEF (β coefficient = 0.227, p = 0.354). The receiver operating characteristic (ROC) results showed that GCS emerged as the strongest LGE size (LGE >25%) prognosticator among strain parameters (AUC: 0.836 [95% CI, 0.692—0.981], sensitivity: 91%, specificity: 80%) and was significantly better (p = 0.001) than GLS [AUC: 0.761 (95% CI, 0.583—0.939), sensitivity: 64%, specificity: 85%] and LVEF [AUC: 0.673 (95% CI, 0.469—0.877), sensitivity: 73%, specificity: 70%]. Conclusion: Among STEMI patients with preserved LVEF after PCI, CMR-FT-derived GCS had superior diagnostic accuracy than GLS and LVEF in predicting myocardial infarction size.

Predictive value of myocardial strain on myocardial infarction size by cardiac magnetic resonance imaging in ST-segment elevation myocardial infarction with preserved left ventricular ejection fraction

The existing filtering methods for airborne LiDAR point cloud have low accuracy. An adaptive filtering algorithm is proposed which is improved based on multilevel resolution algorithm. First double...

An adaptive filtering algorithm of multilevel resolution point cloud

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Sciences for The 2.5-meter Wide Field Survey Telescope (WFST)

Predictive value of myocardial strain on myocardial infarction size by cardiac magnetic resonance imaging in ST-segment elevation myocardial infarction with preserved left ventricular ejection fraction

An adaptive filtering algorithm of multilevel resolution point cloud