Accurate Distance Measurements Research Articles

Real-time Estimation of Road Surfaces using Fast Monocular Depth Estimation and Normal Vector Clustering

Estimating a road surface or planes for applying AR(Augmented Reality) or an autonomous vehicle using a camera requires significant computation. Vision sensors have lower accuracy in distance measurement than other types of sensor, and have the difficulty that additional algorithms for estimating data must be included. However, using a camera has the advantage of being able to extract various information such as weather conditions, sign information, and road markings that are difficult to measure with other sensors. Various methods differing in sensor type and configuration have been applied. Many of the existing studies had generally researched by performing the depth estimation after the feature extraction. However, recent studies have suggested using deep learning to skip multiple processes and use a single DNN(Deep Neural Network). Also, a method using a limited single camera instead of a method using a plurality of sensors has been proposed. This paper presents a single-camera method that performs quickly and efficiently by employing a DNN to extract distance information using a single camera, and proposes a modified method for using a depth map to obtain real-time surface characteristics. First, a DNN is used to estimate the depth map, and then for quick operation, normal vector that can connect similar planes to depth is calculated, and a clustering method that can be connected is provided. An experiment is used to show the validity of our method, and to evaluate the calculation time.

The Fornax3D project: Planetary nebulae catalogue and independent distance measurements to Fornax cluster galaxies

Extragalactic planetary nebulae (PNe) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (PNLF). Accurate PNe distance measurements rely on obtaining well-sampled PNLFs and the number of observed PNe scales with the encompassed stellar mass. This means either disposing of wide-field observations or focusing on the bright central regions of galaxies. In this work we take this second approach and conduct a census of the PNe population in the central regions of galaxies in the Fornax cluster, using VLT/MUSE data for the early-type galaxies observed over the course of the Fornax3D survey. Using such integral-field spectroscopic observations to carefully separate the nebular emission from the stellar continuum, we isolated [O III] 5007 Å sources of interest, filtered out unresolved impostor sources or kinematic outliers, and present a catalogue of 1350 unique PNe sources across 21 early-type galaxies, which includes their positions, [O III] 5007 Å line magnitudes, and line-of-sight velocities. Using the PNe catalogued within each galaxy, we present independently derived distance estimates based on the fit to the entire observed PNLF observed while carefully accounting for the PNe detection incompleteness. With these individual measurements, we arrive at an average distance to the Fornax cluster itself of 19.86 ± 0.32 Mpc (μPNLF = 31.49 ± 0.04 mag). Our PNLF distance measurements agree well with previous distances based on surface brightness fluctuations, finding no significant systematic offsets between the two methods as otherwise reported in previous studies.

Learning How to Surf: Reconstructing the Propagation and Origin of Gravitational Waves with Gaussian Processes

Abstract Soon, the combination of electromagnetic and gravitational signals will open the door to a new era of gravitational-wave (GW) cosmology. It will allow us to test the propagation of tensor perturbations across cosmic time and study the distribution of their sources over large scales. In this work, we show how machine-learning techniques can be used to reconstruct new physics by leveraging the spatial correlation between GW mergers and galaxies. We explore the possibility of jointly reconstructing the modified GW propagation law and the linear bias of GW sources, as well as breaking the slight degeneracy between them by combining multiple techniques. We show predictions roughly based on a network of Einstein Telescopes combined with a high-redshift galaxy survey (z ≲ 3). Moreover, we investigate how these results can be rescaled to other instrumental configurations. In the long run, we find that obtaining accurate and precise luminosity distance measurements (extracted directly from the individual GW signals) will be the most important factor to consider when maximizing the constraining power.

Similarity-evaluation-based evolving of flexible neural trees for imbalanced classification

A flexible neural tree (FNT) is a special and effective kind of artificial neural network that can search optimal network structures using tree structure evolving algorithms, leading to its high performance in many real classification and prediction problems. However, the standard FNT model does not take into account tree structure similarities in its evolving process. This may result to a rapid and significant decrease of its tree structure population. Standard FNT also suffers from imbalanced data. In this study, we propose a new similarity evaluation method for FNT (SEFNT) to keep the population diversity and deal with the imbalanced data. The main idea of SEFNT is twofold. First, the difference between two nodes is introduced for similarity measurement. Second, the node position and height of trees are also taken into account for accurate tree structure distance measurement. SEFNT uses imbalanced fitness function to control its evolving procedure to deal with imbalanced problems. We compare SEFNT with 10 imbalanced methods on 46 KEEL datasets and 10 UCI datasets. The experimental results show that our approach can significantly improve the classification performance of FNT. In the comparisons with other algorithms, SEFNT shows significantly better performance. We also apply the proposed method to a practical imbalanced classification problem, that is, Internet video traffic identification. The results imply that our method is effective in dealing with practical problems.

Tropospheric and range biases in Satellite Laser Ranging

The Satellite Laser Ranging (SLR) technique provides very accurate distance measurements to artificial Earth satellites. SLR is employed for the realization of the origin and the scale of the terrestrial reference frame. Despite the high precision, SLR observations can be affected by various systematic errors. So far, range biases were used to account for systematic measurement errors and mismodeling effects in SLR. Range biases are constant for all elevation angles and independent of the measured distance to a satellite. Recently, intensity-dependent biases for single-photon SLR detectors and offsets of barometer readings and meteorological devices were reported for some SLR stations. In this paper, we study the possibility of the direct estimation of tropospheric biases from SLR observations to LAGEOS satellites. We discuss the correlations between the station heights, range biases, tropospheric biases, and their impact on the repeatability of station coordinates, geocenter motion, and the global scale of the reference frame. We found that the solution with the estimation of tropospheric biases provides more stable station coordinates than the solution with the estimation of range biases. From the common estimation of range and tropospheric biases, we found that most of the systematic effects at SLR stations are better absorbed by elevation-dependent tropospheric biases than range biases which overestimate the total bias effect. The estimation of tropospheric biases changes the SLR-derived global scale by 0.3 mm and the geocenter coordinates by 1 mm for the Z component, causing thus an offset in the realization of the reference frame origin. Estimation of range biases introduces an offset in some SLR-derived low-degree spherical harmonics of the Earth’s gravity field. Therefore, considering elevation-dependent tropospheric and intensity biases is essential for deriving high-accuracy geodetic parameters.

Tracing the local volume galaxy halo‐to‐stellar mass ratio with satellite kinematics

AbstractRapid advance has been made recently in accurate distance measurements for nearby ( Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way‐like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass‐to‐K‐band luminosity ratio is for the luminous galaxies, increasing up to toward dwarfs. The bulge‐dominated luminous galaxies are characterized with , while the disk‐dominated spirals have . We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km s−1 and a poor dark matter halo with . We note that a fraction of quenched (dSph, dE) companions around Milky Way‐like galaxies decreases with their linear projected separation as .

Implications for cardiac arrest coverage using straight-line versus route distance to nearest automated external defibrillator

AimQuantifying the ratio describing the difference between “true route” and “straight-line” distances from out-of-hospital cardiac arrests (OHCAs) to the closest accessible automated external defibrillator (AED) can help correct likely overestimations in AED coverage. Furthermore, we aimed to examine to what extent the closest AED based on true route distance differed from the closest AED using “straight-line”. MethodsOHCAs (1994–2016) and AEDs (2016) in Copenhagen, Denmark and in Toronto, Canada (2007–2015 and 2015, respectively) were identified. Three distances were calculated between OHCA and target AED: 1) the straight-line distance (“straight-line”) to the closest AED, 2) the corresponding true route distance to the same AED (“true route”), and 3) the closest AED based only on true route distance (“shortest true route”). The ratio between “true route” and “straight-line” distance was calculated and differences in AED coverage (an OHCA ≤ 100 m of an accessible AED) were examined. ResultsThe “straight-line” AED coverage of 100 m was 24.2% (n = 2008/8295) in Copenhagen and 6.9% (n = 964/13916) in Toronto. The corresponding “true route” distance reduced coverage to 9.5% (n = 786) and 3.8% (n = 529), respectively. The median ratio between “true route” and “straight-line” distance was 1.6 in Copenhagen and 1.4 in Toronto. In 26.1% (n = 2167) and 22.9% (n = 3181) of all Copenhagen and Toronto OHCAs respectively, the closest AED in “shortest true route” was different than the closest AED initially found by “straight-line”. ConclusionsStraight-line distance is not an accurate measure of distance and overestimates the actual AED coverage compared to a more realistic true route distance by a factor 1.4–1.6.

Real-time needle guidance for venipuncture based on optical coherence tomography

ABSTRACT An algorithm for real–time venipuncture needle guidance is described, using an optical coherence tomography (OCT) probe that emits light pulses at fixed angular intervals along a cone, giving accurate distance measurements to points on the blood vessel. Using this data, a method is developed to visually display the blood vessel for needle guidance. A least–squares fit to a general quadric surface, specified by a symmetric matrix, is performed. For a cylindrical blood vessel, this provides an estimate for its orientation, from which its location and radius can be determined. The algorithm is compatible, in efficiency and robustness, with real–time implementation.

Separation and Analysis of Nanoscale Zero-Valent Iron from Soil.

Nanoscale zero-valent iron (nZVI) has become one of the most used engineered nanoparticles for soil remediation. However, isolating nZVI particles from a complex soil matrix for their accurate particle characterizations and transport distance measurements is still challenging. Here, this study established a new analysis approach combining ultrasound-assisted solvent extraction, magnetic separation, and single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) analysis to isolate nZVI particles from soils and quantify their concentration and size. The interference from natural Fe-containing substances on nZVI analysis could be efficiently minimized by magnetic separation and dilution. After the optimization of extraction solvent type/concentration (i.e., 2.5 mM tetrasodium pyrophosphate) and ultrasonication time (i.e., 30 min), acceptable recoveries in both particle number (62.0 ± 10.8%-96.1 ± 4.8%) and Fe mass (70.6 ± 12.0%-119 ± 18%) could be achieved for different sizes (50 and 100 nm) and concentrations (50, 100, and 500 μg g-1) of spiked nZVI from six soils. The detection limits of particle size and concentration were approximately 43.1 nm and 50 μg nZVI per gram soil, respectively. These results provide a feasible approach to quantify the nZVI concentration and size in complex soil matrices, which will allow the improvements to characterize and track the nZVI particles in the field, promote the use of nZVI particles for soil remediation, and better assess their environmental implications.

Making Precise and Accurate Single-Molecule FRET Measurements using the Open-Source smfBox.

The smfBox is a recently developed cost-effective, open-source instrument for single-molecule Förster Resonance Energy Transfer (smFRET), which makes measurements on freely diffusing biomolecules more accessible. This overview includes a step-by-step protocol for using this instrument to make measurements of precise FRET efficiencies in duplex DNA samples, including details of the sample preparation, instrument setup and alignment, data acquisition, and complete analysis routines. The presented approach, which includes how to determine all the correction factors required for accurate FRET-derived distance measurements, builds on a large body of recent collaborative work across the FRET Community, which aims to establish standard protocols and analysis approaches. This protocol, which is easily adaptable to a range of biomolecular systems, adds to the growing efforts in democratising smFRET for the wider scientific community.

APPARILLO: a fully operational and autonomous staring system for LEO debris detection

For safe operation of active space crafts, the space debris population needs to be continuously scanned, to avoid collisions of active satellites with space debris. Especially the low Earth orbit (LEO) shows higher risks of collisions due to the highest density of orbital debris. Laser ranging stations can deliver highly accurate distance measurements of debris objects allowing precise orbit determination and more effective collision avoidance. However, a laser ranging station needs accurate a priori orbit information to track an orbital object. To detect and track unknown orbital objects in LEO, here, a passive optical staring system is developed for autonomous 24/7 operation. The system is weather-sealed and does not require any service to perform observations. To detect objects, a wide-angle imaging system with 10° field of view equipped with an astronomical CCD camera was designed and set up to continuously observe the sky for LEO objects. The system can monitor and process several passing objects simultaneously without limitations. It automatically starts an observation, processes the images and saves the 2D angular measurements of each object as equatorial coordinates in the TDM standard. This allows subsequent initial orbit determination and handover to a laser tracking system. During campaigns at twilight the system detected up to 36 objects per hour, with high detection efficiencies of LEO objects larger than 1 m3. It is shown that objects as small as 0.1 m3 can be detected and that the estimated precision of the measurements is about 0.05° or 7 × the pixel scale.

Comparative analysis of the accuracy requirements of the equipment for determining the mean integral refractive index of air using different realizations of the gradient method

The speed of propagation of electromagnetic waves in the Earth’s atmosphere differs from the speed of their propagation in a vacuum, which is one of the main factors that have a significant impact on the accuracy of long distance measurement. This influence is taken into account in long distance measurement with the correction for the mean integral group refractive index of air, which depends on such meteorological parameters as temperature, atmospheric pressure and relative air humidity. The purpose of this work is to compare the accuracy requirements for equipment designed to measure temperature, pressure, and relative humidity required to determine the above correction by the gradient method using the Euler-Maclaurin quadrature formula (hereafter, the Euler-Maclaurin method) and the formula based on Hermite interpolation polynomials (hereafter, the Hermite method). The requirements for the uncertainty of measurements carried out with the sensors of meteorological parameters, allowing to find the mean integral group refractive index of air, providing length measurements of the baselines of up to 5 km with an expanded uncertainty of not more than 1 mm, are established. Keywords: atmosphere; mean integral group refractive index of air; laser long distance measurement

Effect of dual aircraft formation spacing on target position tracking on measurement conversion by monopulse radar

Aimed at the current problem of insufficient analysis of the influence of the diversified formation of dual aircraft on monopulse radar position tracking, the dual aircraft echo equivalent two point source jamming model is built. We designed the dual aircraft formation penetration movement scenario and three different formation spacings of 150, 250, and 350 m and extracted the dynamic radar cross section sequences of dual aircraft under different formation spacings. We established the dual aircraft formation equivalent scenario and calculated the dynamic signal-to-noise ratio and distance measurement accuracy of the radar received echo signals with different formation spacings. We fully considered the randomness characteristics of the phase difference of the actual dual aircraft echo and built the random angle error model of dual aircraft echo equivalent jamming. The distribution and random numerical characteristics of the random angular error are simulated and analyzed, and we combined the radar measurement conversion target position tracking algorithm to analyze the influence of different formation spacings on the monopulse radar tracking target position and position tracking accuracy. The simulation results show that a formation spacing of 350 m produces a greater randomness of angular error for dual targets, resulting in a greater dispersion of radar measurement traces, and the final average position mean square error is 132.8 m, which improves the position error by 15.6% compared with 150 m spacing.

Lost in Space? Relativistic Interstellar Navigation using an Astrometric Star Catalog

The exploration of interstellar space will require autonomous navigation systems that do not rely on tracking from the Earth. Here I develop a method to determine the 3D position and 3D velocity of a spacecraft in deep space using a star catalog. As a spacecraft moves away from the Sun, the observed positions and velocities of the stars will change relative to those in a Earth-based catalog due to parallax and aberration. By measuring just the angular distances between pairs of stars, and comparing these to the catalog, we can infer the coordinates of the spacecraft via an iterative forward-modeling process. I perform simulations with existing star catalogs to demonstrate the method and to compute its performance. Using the 20 nearest stars and a modest angular distance measurement accuracy of 1″, the position and velocity of a spacecraft light years from the Sun moving at relativistic speeds can be determined to within 3 and 2 respectively. These accuracies improve linearly with the measurement accuracy, e.g., with angles measured to 1 the navigation accuracy is 1000 times better. Performance can also be improved using more stars, or by including onboard measurements of the stars’ radial velocities, as these too are affected by the spacecraft’s position and motion.

Research on the Monocular Ranging Method of the Leading Vehicle in Multi-weather

In order to improve the accuracy of the monocular distance measurement of the vehicle in front under sunny, cloudy, rainy, snowy, and foggy weather, an improved pixel-mapping monocular distance measurement method is proposed. This method is based on eight-connected domains to detect the front vehicle, obtain the line pixels of the target vehicle in the image, and fit the image line pixels to the corresponding real longitudinal distance function, and combine the fitted function with the internal and external parameters of the camera. An improved pixel-mapping monocular ranging model is obtained. Set up a test environment under different weather to verify the feasibility of the algorithm. The results show that in the four environments, the detectable distances are within 70m, 60m, 30m, and 40m respectively; the error of the improved pixel-mapping monocular ranging method is reduced by 0.6% on average compared with before the improvement, up to 0.92% ; The improved algorithm ranging errors under the four weathers are 1.8513%, 2.6987%, 4.0137%, and 2.5795% respectively, which achieves the purpose of improving the accuracy of the monocular distance measurement of the vehicle in front under multiple weather conditions.

A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging

Abstract The large and diffuse galaxies NGC 1052–DF2 and NGC 1052–DF4 have been found to have very low dark matter content and a population of luminous globular clusters (GCs). Accurate distance measurements are key to interpreting these observations. Recently, the distance to NGC 1052–DF4 was found to be 20.0 ± 1.6 Mpc by identifying the tip of the red giant branch (TRGB) in 12 orbits of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. Here we present 40 orbits of HST ACS data for NGC 1052–DF2 and use these data to measure its TRGB. The TRGB is readily apparent in the color–magnitude diagram. Using a forward model that incorporates photometric uncertainties, we find a TRGB magnitude of m F814W,TRGB = 27.67 ± 0.10 mag. The inferred distance is D TRGB = 22.1 ± 1.2 Mpc, consistent with the previous surface brightness fluctuation distances to the bright elliptical galaxy NGC 1052. The new HST distance rules out the idea that some of NGC 1052–DF2's unusual properties can be explained if it were at ∼13 Mpc; instead, it implies that the galaxy’s GCs are even more luminous than had been derived using the previous distance of 20 Mpc. The distance from NGC 1052–DF2 to NGC 1052–DF4 is well-determined at 2.1 ± 0.5 Mpc, significantly larger than the virial diameter of NGC 1052. We discuss the implications for formation scenarios of the galaxies and for the external field effect, which has been invoked to explain the intrinsic dynamics of these objects in the context of modified Newtonian dynamics.

Cortical Thickness Estimation: A Comparison of FreeSurfer and Three Voxel-Based Methods in a Test-Retest Analysis and a Clinical Application.

The cortical thickness has been used as a biomarker to assess different cerebral conditions and to detect alterations in the cortical mantle. In this work, we compare methods from the FreeSurfer software, the Computational Anatomy Toolbox (CAT12), a Laplacian approach and a new method here proposed, based on the Euclidean Distance Transform (EDT), and its corresponding computational phantom designed to validate the calculation algorithm. At region of interest (ROI) level, within- and inter-method comparisons were carried out with a test-retest analysis, in a subset comprising 21 healthy subjects taken from the Multi-Modal MRI Reproducibility Resource (MMRR) dataset. From the Minimal Interval Resonance Imaging in Alzheimer's Disease (MIRIAD) data, classification methods were compared in their performance to detect cortical thickness differences between 23 healthy controls (HC) and 45 subjects with Alzheimer's disease (AD). The validation of the proposed EDT-based method showed a more accurate and precise distance measurement as voxel resolution increased. For the within-method comparisons, mean test-retest measures (percentages differences/intraclass correlation/Pearson correlation) were similar for FreeSurfer (1.80%/0.90/0.95), CAT12 (1.91%/0.83/0.91), Laplacian (1.27%/0.89/0.95) and EDT (2.20%/0.88/0.94). Inter-method correlations showed moderate to strong values (R > 0.77) and, in the AD comparison study, all methods were able to detect cortical alterations between groups. Surface- and voxel-based methods have advantages and drawbacks regarding computational demands and measurement precision, while thickness definition was mainly associated to the cortical thickness absolute differences among methods. However, for each method, measurements were reliable, followed similar trends along the cortex and allowed detection of cortical atrophies between HC and patients with AD.

Nanophotonics for light detection and ranging technology.

Light detection and ranging (LiDAR) technology, a laser-based imaging technique for accurate distance measurement, is considered one of the most crucial sensor technologies for autonomous vehicles, artificially intelligent robots and unmanned aerial vehicle reconnaissance. Until recently, LiDAR has relied on light sources and detectors mounted on multiple mechanically rotating optical transmitters and receivers to cover an entire scene. Such an architecture gives rise to limitations in terms of the imaging frame rate and resolution. In this Review, we examine how novel nanophotonic platforms could overcome the hardware restrictions of existing LiDAR technologies. After briefly introducing the basic principles of LiDAR, we present the device specifications required by the industrial sector. We then review a variety of LiDAR-relevant nanophotonic approaches such as integrated photonic circuits, optical phased antenna arrays and flat optical devices based on metasurfaces. The latter have already demonstrated exceptional functional beam manipulation properties, such as active beam deflection, point-cloud generation and device integration using scalable manufacturing methods, and are expected to disrupt modern optical technologies. In the outlook, we address the upcoming physics and engineering challenges that must be overcome from the viewpoint of incorporating nanophotonic technologies into commercially viable, fast, ultrathin and lightweight LiDAR systems.

Documenting carved stones from 3D models. Part II — Ambient occlusion to reveal carved parts

Revealing carved parts in rock art is of primary importance and remains a major challenge for archaeological documentation. Computational geometry applied to 3D imaging provides a unique opportunity to document rock art. This study evaluates five algorithms and derivatives used to compute ambient occlusion and sky visibility on 3D models of Mongolian stelae, also known as deer stones. By contrast with the previous companion work, models are processed directly in 3D, without preliminary projection. Volumetric obscurance gives the best results for the identification of carved figures. The effects of model resolution and parameters specific to ambient occlusion are then evaluated. Keeping tridimensional information intact allows accurate measurement of distance, volume, and depth. Objects augmented by ambient occlusion can easily be manipulated in 3D viewers, for seamless and effortless access to the overall organization of the figures, at the scale of the entire object. Qualitatively speaking, the 2D projected outputs are equivalent to, or even better than, existing archaeological documentation. The proposed workflow should be easily applicable in many situations, particularly as the functions provided for the free R programming software are fully configurable.

Пассивный дальномер Ковалева

The authors present the results of longtime research on the development and improvement of a passive geodetic rangefinder based on the inbasis method of distance measurement. Actually, active laser range finders are not always effective at field works. An original compact optical scheme of a passive rangefinder based on a theodolite telescope and a mould photo receiver with application of digital methods for coordinate calculation is proposed. The distance and dimensions of the object are defined. The former is identified by the shift between the images on the horizontal axis. The merit of such a system is the absence of mechanical displacements. Its main advantage is an extremely simple optical path. The technical result is reduction in overall dimensions and weight, while maintaining an acceptable error in the passive range measurement. The use of Kovalev passive rangefinder is promising at performing geodetic measurements with total stations. There is also a description of the rangefinder sample as well as the calculations results according to the distance measurement accuracy.