Absolute Reference Research Articles

A novel method to create long capture volumes for video tracking

This study examined a novel method to create a long and narrow calibrated capture volume for tracking objects. The methodology relies on the reflection of parallel distance-measuring lasers. Images of a board, blocking the lasers as it is moved through the field of interest, were assembled into a virtual calibration fixture. The method accommodates large calibration volumes and can be used with multiple cameras, providing a consistent absolute positional reference that is difficult to achieve with large mechanical calibration boards. This study considered a 17.4 m long tracking volume. A 0.9 m long rod was tracked throughout the calibrated volume where its average tracked length was within 0.2% of its measured length. The speed of balls traveling through the calibrated volume were within 0.1% of independent speed sensors. The average residual error of a ball’s tracked trajectory and a polynomial fit was within 1.5 mm. The method shows promise as an efficient means of calibrating large calibration volumes with multiple camera pairs.

Analysis of Pacific Hotspot Chains

AbstractSeamount trails created by mantle plumes are often used to establish absolute reference frames for plate motion. When plume drift is considered, changes in seamount trail direction and age progression cannot be attributed to plate motion change alone. Here, improvements to age‐progressive models of eleven Pacific hotspot chains are made independently of plate motion models. Our approach involves bathymetry processing to robustly predict a smooth, continuous hotspot path by connecting maxima in filtered seamount bathymetry, with across‐track uncertainties from seamount trail width and amplitude. Published ages from seamount samples are projected orthogonally onto these paths. We determine best‐fit models of age as functions of along‐track distance, giving continuous age‐progression models for each seamount chain with uncertainties in age and geometry. Different sources of paleolatitudes are examined by incorporating data from the magnetization of seamount drill‐core samples, paleo‐poles from marine magnetic anomaly skewness inversions, and paleo‐spin‐axes inferred from shifts of equatorial sediments. Improved paleolatitude models for the Hawaiian‐Emperor and Louisville chains are determined by combining these different types of data. Paleolatitude models are predicted for other chains during periods when sufficient amounts of paleo‐pole or paleo‐spin‐axis data are available. Analysis of the eleven Pacific seamount chains provide constraints for future plate and plume motion models. We analyze the temporal change in distance between coeval seamounts, reflecting relative drifts between the hotspots at different times in the past. The observed changes imply systematic relative hotspot drifts compatible with paleolatitude trends.

Proof of Einstein’s postulates

Based on the assumption that the experiment confirms the STR, it is shown that the value of the speed of light is a very slowly decreasing function of its frequency, so that at a frequency of 2.2989.10-18 S-1, the speed of light becomes zero. Such light represents resting particles – photonics that could serve as the Absolute Reference System, but due to their negligible mass, do not have a noticeable effect on the processes taking place. This explains Einstein’s principle of relativity. The formulas for the change in the speed and frequency of light during the transition from one IRS to another, within the measurement error, remain unchanged, which proves the postulate of the constancy of the speed of light in any IRS. It is shown that all STR formulas include not the speed of light, but the fundamental constant C, equal to the speed of light with a frequency ν = ∞. The proposed explanation of the correctness of Einstein’s postulates is logically, apparently, the only possible one.

Absolute frequency referencing in the long wave infrared using a quantum cascade laser frequency comb.

Optical frequency combs (OFCs) based on quantum cascade lasers (QCLs) have transformed mid-infrared spectroscopy. However, QCL-OFCs have not yet been exploited to provide a broadband absolute frequency reference. We demonstrate this possibility by performing comb-calibrated spectroscopy at 7.7 µm (1305 cm-1) using a QCL-OFC referenced to a molecular transition. We obtain 1.5·10-10 relative frequency stability (100-s integration time) and 3·10-9 relative frequency accuracy, comparable with state-of-the-art solutions relying on nonlinear frequency conversion. We show that QCL-OFCs can be locked with sub-Hz-level stability to a reference for hours, thus promising their use as metrological tools for the mid-infrared.

Precise 3D Indoor Localization and Trajectory Optimization Based on Sparse Wi-Fi FTM Anchors and Built-In Sensors

Indoor location-based services have become more and more important due to their potential applications in a wide range of personalized services in recent years. The accuracy of smartphone based 3D indoor localization is subjected to the poor performance of low-cost sensors and limited coverage of location sources. In order to solve these problems, this paper proposes a precise 3D indoor localization and trajectory optimization framework that uses the combination of sparse Wi-Fi Fine Time Measurement (FTM) anchors and built-in sensors (3D-LOWS). The inertial navigation system (INS) mechanization, multi-level constraints and observed values are integrated by the adaptive unscented Kalman filter to eliminate effects of cumulative error, indoor magnetic interference, and diversity of handheld modes. The Wi-Fi based ranging and landmark detection information is used to provide an accurate absolute reference to the built-in sensors based method. In addition, this paper proposes and evaluates two different trajectory optimization algorithms and compares the improved localization performance. The comprehensive experiments indicate that the proposed 3D-LOWS is proved to achieve accurate and stable 3D indoor positioning and trajectory optimization performance under complex indoor environments using sparse wireless stations.

Solutions and limitations of the geomatic survey of an archaeological site in hard to access areas with a latest generation smartphone: the example of the Intihuatana stone in Machu Picchu (Peru)

<p class="Abstract"><span lang="EN-US">Archaeological remains need to be geometrically surveyed and set in absolute reference systems in order to allow a "virtual visit" and to create "digital twins" useful in case of deterioration for proper restoration. Some countries (e.g., Peru) have a vast archaeological heritage whose survey requires optimized procedures that allow high productivity while maintaining high standards of geometric accuracy. A large part of Peru's cultural heritage is located in remote areas, at high altitudes and not easily accessible. For this reason, it is of great interest to study the possible applications of easily transportable instruments. In this study it was verified how the capabilities of the latest smartphones in terms of absolute differential positioning and photogrammetric acquisition can allow the acquisition of a geometrically correct and georeferenced three-dimensional model. The experimentation concerned a new survey of the Intihuatana stones at Machu Picchu and its comparison with a previous survey carried out with a much more complex laser scanning instrumentation. It is important to note that both the photogrammetric survey and the GPS/GNSS survey were carried out with the same smartphone taking full advantage of both features of the same mobile phone. Relative comparison to an existing point cloud provided differences of 2 millimeters in mean with an RMSE of 2 cm. The absolute positioning accuracy compared to a very large-scale cartography appears to be of the order of one metre as was expected mainly due to the high distance of the GPS/GNSS permanent stations.</span></p>

Gonioreflectometer for measuring 3D spectral BRDF of horizontally aligned samples with traceability to SI

Present article describes a 3D gonioreflectometer developed at Aalto University for the measurement of spectral bidirectional reflectance distribution function (sBRDF) of horizontally aligned samples, needed to study sBRDF of sand from satellite calibration test sites. The new set-up incorporates three motorized arms that allow to measure in- and out-of-plane sBRDF. Illumination of the sample is provided by a supercontinuum laser coupled with laser line tunable filters and detection is performed with two types of photodiodes (Si and InGaAs) enabling collection of sBRDF in the spectral range from 450 nm to 1700 nm. The instrument is operated in the relative mode and its traceability to SI is achieved with the help of a 2D absolute reference gonioreflectometer available at Aalto University. The calibration procedure as well as system’s uncertainty estimation are described. The performance of the 3D gonioreflectometer is validated by measurements of a ceramic diffuse reflectance sample.

The pattern speed of the Milky Way bar/bulge from VIRAC andGaia

ABSTRACTWe compare distance resolved, absolute proper motions in the Milky Way bar/bulge region to a grid of made-to-measure dynamical models with well-defined pattern speeds. The data are obtained by combining the relative VVV InfraRed Astrometric Catalogue (VIRAC) v1 proper motions with the Gaia Data Release 2 absolute reference frame. We undertake a comprehensive analysis of the various errors in our comparison, from both the data and the models, and allow for additional, unknown, contributions by using an outlier-tolerant likelihood function to evaluate the best-fitting model. We quantify systematic effects such as the region of data included in the comparison, the possible overlap from spiral arms, and the choice of synthetic luminosity function and bar angle used to predict the data from the models. Resulting variations in the best-fitting parameters are included in their final errors. We thus measure the bar pattern speed to be $\Omega _{\mathrm{b}}=33.29 \pm 1.81\, \mathrm{km\, s^{-1}\, kpc^{-1}}$ and the azimuthal solar velocity to be $V_{\phi ,\odot }=251.31 \pm 1.95\,\mathrm{km\, s}^{-1}$. These values, when combined with recent measurements of the Galactic rotation curve, yield the distance of corotation, $6.5 \lt R_\mathrm{CR}\, (\mathrm{kpc})\lt 7.5$, the outer Lindblad resonance (OLR), $10.7 \lt R_\mathrm{OLR}\, (\mathrm{kpc})\lt 12.4$, and the higher order, m = 4, OLR, $8.7 \lt R_\mathrm{OLR_4}\, (\mathrm{kpc})\lt 10.0$. The measured pattern speed provides strong evidence for the ‘long-slow’ bar scenario.

Polarized light-aided visual-inertial navigation system: global heading measurements and graph optimization-based multi-sensor fusion

Polarized skylight is as fundamental a constituent of passive navigation as the geomagnetic field. With regard to its applicability to outdoor robot localization, a polarized light-aided visual-inertial navigation system (VINS) modelization dedicated to globally optimized pose estimation and heading correction is constructed. The combined system follows typical visual simultaneous localization and mapping (SLAM) frameworks, and we propose a methodology to fuse global heading measurements with visual and inertial information in a graph optimization-based estimator. With ideas of‘adding new attributes of graph vertices and creating heading error-encoded constraint edges’, the heading, as the absolute orientation reference, is estimated by the Berry polarization model and continuously updated in a graph structure. The formulized graph optimization process for multi-sensor fusion is simultaneously provided. In terms of campus road experiments on the Bulldog-CX robot platform, the results are compared against purely stereo camera-dependent and VINS Fusion frameworks, revealing that our design is substantially more accurate than others with both locally and globally consistent position and attitude estimates. As a passive and tightly coupled navigation mode, the polarized light-aided VINS can therefore be considered as a tool candidate for a class of visual SLAM-based multi-sensor fusion.

Association between the saphenous vein diameter and venous reflux on computed tomography venography in patients with varicose veins.

Three-dimensional computed tomography venography is a useful tool to identify increased saphenous vein diameter and provides a complementary road map for surgery in patients with varicose veins. In this study, we investigated the correlation between saphenous vein diameter on computed tomography venography and venous reflux detected on duplex ultraonography. We enrolled 152 patients (213 extremities) who underwent endovenous laser ablation therapy, following high ligation of the saphenofemoral junction between January 2014 and December 2019. All patients underwent preoperative computed tomography venography evaluation. The saphenous vein diameter was measured on computed tomography venography, and venous reflux was evaluated in the operating room using Doppler ultrasonography. Among the 152 patients included in the study, 61 showed varicose veins affecting the bilateral extremities. Among the 213 extremities investigated, 165 (77.5%) and 48 (22.5%) extremities showed varicosities involving the greater and lesser saphenous veins, respectively. Among all extremities, venous reflux was detected in 172 (80.8%). The mean diameter of the greater saphenous vein measured 5 cm distal to the saphenofemoral junction was 8.07±1.82 mm in patients with reflux and 5.11±1.20 mm in patients without reflux (p < .05). The small saphenous vein diameter measured 5 cm distal to the saphenopopliteal junction was 7.65±1.74 mm in patients with reflux and 5.04±1.80 mm in patients without reflux (p < .05). Based on the receiver operating characteristic curve, the greater saphenous vein threshold diameter of 5.880 mm measured 5 cm distal to the saphenofemoral junction was the optimal cut-off value to predict reflux (sensitivity 91.4%, specificity 81.8%). The lesser saphenous vein diameter of 5.285 mm measured 5 cm distal to the saphenopopliteal junction was the optimal cut-off value to predict reflux (sensitivity 94.9%, specificity 75.0%). Vein diameter cannot be used as an absolute reference for venous reflux; however, it may have predictive value in patients with varicose veins. Computed tomography venography based measurements of vein diameter may serve as a useful diagnostic tool to predict venous reflux and recommend treatment.

TOOTHFIR: Presenting a dataset and a preliminary meta-analysis of Fourier Transform Infra-red Spectroscopy indices from archaeological and palaeontological tooth enamel

The assessment of the preservation status of archaeological and palaeontological tooth enamel is of vital importance in the interpretation of isotopic and elemental analyses that underpin chronological, dietary, and mobility studies. Transmission and ATR Fourier Transform Infra-red Spectroscopy (FTIR) have provided an important means of studying the presence and crystallographic context of key structural groups in tooth enamel. However, differences in sample preparation and measurement methods prevent the setting of absolute references to assess tooth enamel preservation. Here, we present TOOTHFIR, a dataset of FTIR indices developed to study the crystal-chemical properties of enamel bioapatite, from Miocene, Pliocene, Pleistocene, Holocene, and modern samples. Using collected data, we conducted a preliminary statistical meta-analysis to assess inter-lab measurement variability (relying on modern samples) and the extent to which the mixed data remains useful in revealing diagenetic patterns. Our results confirmed significant variations with measurement methodology although it remained possible to observe broad relationships between the values for FTIR indices and environmental parameters. In this respect, we introduced the use of principal component analysis to summarize FTIR data. To improve data comparability and interpretation of preservation status, we suggest several measures.

Anterior superior iliac spine is not always reliable as a pelvic reference axis. -3D study of pelvic axis-

BackgroundThis study aims to evaluate the accuracy of the axis connecting both anterior superior iliac spines (ASIS axis) as the absolute pelvic axis. No study has ever verified the accuracy of ASIS axis particularly on the AP pelvic radiograph, which cannot be specified on it. MethodsSixty patients who underwent total knee arthroplasty and fifty patients with femoral neck fracture were recruited as subjects without hip deformities and their CT scan data were collected. We defined the line through both center of femoral heads as absolute reference axis of pelvis three-dimensionally. On the coronal plane, the errors between the femoral head axis and the axes through six pelvic landmarks in total, including ASIS were analyzed. On the axial plane, the errors of the lines through four landmarks were analyzed in the same way. Finally, on the coronal images, the mediolateral diameter of the obturator foramen and the mediolateral distance between the midline of the sacrum and the pelvic cavity were measured to evaluate bilateral symmetry of the pelvis. ResultsThe errors tended to be smaller as the axes were closer to the femoral head axis (axes connecting bilateral superior aspects of the acetabulum and the teardrops) and the ASIS axis errors were moderate. The obturator foramen based on the ASIS axis was more asymmetrical than the femoral head axis. ConclusionAdjusting the pelvic tilt and rotation, surgeons should not always rely on the ASIS and refer to appropriate, close to the hip joint references in each case.

Conflation of spatial reference frames in deaf community sign languages

AbstractLinguistic spatial descriptions are not purely arbitrary, but are to some extent motivated by many interactive factors. For example, whether the language community is predominantly urban or rural may motivate its reliance on relative or absolute reference frame (Dasen and Mishra 2010; Pederson 1993, 2006). This review paper contributes to Sociotopography in two ways: first, by showing that the distribution of reference frames reported in the literature corresponds to deaf community sign languages and village sign languages (thus the urban-rural differences generalize across modalities), and second, that deaf community sign languages all allow their users to employ a conflated intrinsic-relative frame, which is possibly due to affordances of the visual-manual modality (a modality-specific feature). Comparing the visual-manual and the aural-oral modalities therefore shows that some variation in spatial descriptions correlates with the environment regardless of the modality used, but also highlights modality-specific properties.

Tracking an occluded visual target with sequences of saccades.

Gaze behavior during visual tracking consists of a combination of pursuit and saccadic movements. When the tracked object is intermittently occluded, the role of smooth pursuit is reduced, with a corresponding increase in the role of saccades. However, studies of visual tracking during occlusion have focused only on the first few saccades, usually with occlusion periods of less than 1 second in duration. We investigated tracking on a circular trajectory with random occlusions and found that an occluded object can be tracked reliably for up to several seconds with mainly anticipatory saccades and very little smooth pursuit. Furthermore, we investigated the accumulation of uncertainty in prediction and found that prediction errors seem to accumulate faster when an absolute reference frame is not available during tracking. We suggest that the observed saccadic tracking reflects the use of a time-based internal estimate of object position that is anchored to the environment via fixations.

Individual-based Creatine Kinase Reference Values in Response to Soccer Match-play.

The aim of the present study was to determine the creatine kinase reference limits for professional soccer players based on their own normal post-match response. The creatine kinase concentration was analyzed in response to official matches in 25 players throughout a 3-year period. Samples were obtained between 36-43 hours following 70 professional soccer matches and corresponded to 19.1±12.1 [range: 6-49] samples per player. Absolute reference limits were calculated as 2.5th and 97.5th percentile of the samples collected. Creatine kinase values were also represented as a percentage change from the individual's season mean and represented by 90th, 95th and 97.5th percentiles. The absolute reference limits for creatine kinase concentration calculated as 97.5th and 2.5th percentiles were 1480 U.L-1 and 115.8 U.L-1, respectively. The percentage change from the individual's season mean was 97.45±35.92% and players were in the 90th, 95th and 97.5th percentiles when the percentages of these differences were 50.01, 66.7, and 71.34% higher than player's season mean response, respectively. The data allowed us to determine whether the creatine kinase response is typical or if it is indicative of a higher than normal creatine kinase elevation and could be used as a practical guide for detection of muscle overload, following professional soccer match-play.

Relative Binding Free Energy Calculations for Ligands with Diverse Scaffolds with the Alchemical Transfer Method.

We present an extension of the alchemical transfer method (ATM) for the estimation of relative binding free energies of molecular complexes applicable to conventional, as well as scaffold-hopping, alchemical transformations. Named ATM-RBFE, the method is implemented in the free and open-source OpenMM molecular simulation package and aims to provide a simpler and more generally applicable route to the calculation of relative binding free energies than what is currently available. ATM-RBFE is based on sound statistical mechanics theory and a novel coordinate perturbation scheme designed to swap the positions of a pair of ligands such that one is transferred from the bulk solvent to the receptor binding site while the other moves simultaneously in the opposite direction. The calculation is conducted directly in a single solvent box with a system prepared with conventional setup tools, without splitting of electrostatic and nonelectrostatic transformations, and without pairwise soft-core potentials. ATM-RBFE is validated here against the absolute binding free energies of the SAMPL8 GDCC host-guest benchmark set and against protein-ligand benchmark sets that include complexes of the estrogen receptor ERα and those of the methyltransferase EZH2. In each case the method yields self-consistent and converged relative binding free energy estimates in agreement with absolute binding free energies and reference literature values, as well as experimental measurements.

Geometry-Constrained Scale Estimation for Monocular Visual Odometry

We propose a robust geometry-constrained scale estimation approach for monocular visual odometry, which takes the camera height as an absolute reference. Visual odometry is an essential module for robot self-localization and autonomous navigation in unexplored environments. Scale recovery is an indispensable requirement for monocular visual odometry, since it compensates for the metric information lost by a single camera and helps to reduce the scale drift. When the camera height is considered the absolute reference, the precision of scale recovery depends on the accuracy of the road point selection and road geometric model calculation. However, most of the previous approaches solve these two problems sequentially, and their road point selection is based on the color model of the road or prior-knowledge-based fixed region. In this paper, we propose combining and iteratively solving these two problems. We adopt the geometric model, instead of the color model, of the road to select the road points. Furthermore, the selected road feature points are used to estimate the road model, which limits the road point selection. In detail, we segment our feature points with Delaunay triangulation and select road points based on the depth consistency and road model consistency. The experiments on the KITTI dataset show that our method achieves the best performance among state-of-the-art monocular visual odometry methods.

Research on rapid surveying and mapping of outfield absolute gravity based on vehicle-mounted atomic gravimeter

The information about Earth’s gravity field is an important basic information necessarily for geodesy, geophysics, geodynamics and other disciplines. The mapping of gravity field is an effective mean to obtain the gravity field information. Compared with the surveying of gravity field based on satellite, ship, and airplane, vehicle-mounted gravity mapping has advantages of strong flexibility, high spatial resolution and high accuracy. A short baseline or a small-scale gravity field mapping can be realized based on the combination of relative gravimeters and the high-precision absolute gravity reference point. However, this method is not suitable for the situation of a long baseline or a large-scale gravity field surveying due to the drift of relative gravimeter. In this work, a vehicle-mounted system for rapid surveying of the absolute gravity field is built up based on a miniaturized atomic gravimeter. The inner precision of the instrument is evaluated to be 0.123 mGal, and the outer precision is 0.112 mGal in a field test which contains 12 points for 3 km distance. Furthermore, with this system, the absolute gravity data are obatined within 2 min for adjusting and 5 min for measuring in downtown for each measured point. A rapid surveying of absolute gravity field for 19 points is carried out and the route covers 24 km. The inner precision of the instrument is evaluated to be 0.162 mGal, and the outer precision is 0.169 mGal. Finally, the free-air gravity anomalies obtained from the measured data of atomic gravimeter and the fitting results of satellite gravity model are analyzed, and it is found that the trends of changing are basically consistent with each other. This paper provides a new proposal for the rapid surveying of the absolute gravity field.

Criteria for choosing an absolute reference system for relative motion

Criteria for choosing an absolute reference system for relative motion

Estimating Single-Epoch Integrated Atmospheric Refractivity From InSAR for Assimilation in Numerical Weather Models

Numerical weather prediction (NWP) models are used to predict the weather based on current observations in combination with physical and mathematical models. Yet, they are limited by the spatial density and the accuracy of the available observations. Satellite radar interferometry (InSAR) is known to be extremely sensitive to the 3D atmospheric refractivity distribution, and has a high spatial resolution, providing information that can be used for assimilation in NWP models. However, due to the inherent superposition of two or more atmospheric states, only biased and temporally differenced signals can be retrieved, that can also be contaminated by deformation signals and decorrelation. Here we present a method to estimate single-epoch absolute atmospheric delays by combining InSAR time series with prior NWP model prediction time series, using a constrained least-squares estimation. We show that this leads to a solution that reliably extracts the single-epoch relative delays from InSAR data and uses prior NWP model data to find the absolute reference for these delays, while mitigating long-term deformation and decorrelation signal. This approach leads to repetitive delay updates with a spatial resolution of 500 m, that can be directly assimilated into numerical weather models.