Absolute Orientation Research Articles

Quasi-Globally Optimal and Real-Time Visual Compass in Manhattan Structured Environments

We present a drift-free visual compass for estimating the three degrees of freedom (DoF) rotational motion of a camera by recognizing structural regularities in a Manhattan world (MW), which posits that the major structures conform to three orthogonal principal directions. Existing Manhattan frame estimation approaches are based on either data sampling or a parameter search, and fail to guarantee accuracy and efficiency simultaneously. To overcome these limitations, we propose a novel approach to hybridize these two strategies, achieving quasi-global optimality and high efficiency. We first compute the two DoF of the camera orientation by detecting and tracking a vertical dominant direction from a depth camera or an IMU, and then search for the optimal third DoF with the image lines through the proposed Manhattan Mine-and-Stab (MnS) approach. Once we find the initial rotation estimate of the camera, we refine the absolute camera orientation by minimizing the average orthogonal distance from the endpoints of the lines to the MW axes. We compare the proposed algorithm with other state-of-the-art approaches on a variety of real-world datasets including data from a drone flying in an urban environment, and demonstrate that the proposed method outperforms them in terms of accuracy, efficiency, and stability. The code is available on the project page: <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/PyojinKim/MWMS</uri>

Singularity-Free Lie Group Integration and Geometrically Consistent Evaluation of Multibody System Models Described in Terms of Standard Absolute Coordinates

Abstract A classical approach to the multibody systems (MBS) modeling is to use absolute coordinates, i.e., a set of (possibly redundant) coordinates that describe the absolute position and orientation of the individual bodies with respect to an inertial frame (IFR). A well-known problem for the time integration of the equations of motion (EOM) is the lack of a singularity-free parameterization of spatial motions, which is usually tackled by using unit quaternions. Lie group integration methods were proposed as an alternative approach to the singularity-free time integration. At the same time, Lie group formulations of EOM naturally respect the geometry of spatial motions during integration. Lie group integration methods, operating directly on the configuration space Lie group, are incompatible with standard formulations of the EOM, and cannot be implemented in existing MBS simulation codes without a major restructuring. The contribution of this paper is twofold: (1) A framework for interfacing Lie group integrators to standard EOM formulations is presented. It allows describing MBS in terms of various absolute coordinates and at the same using Lie group integration schemes. (2) A method for consistently incorporating the geometry of rigid body motions into the evaluation of EOM in absolute coordinates integrated with standard vector space integration schemes. The direct product group SO(3)×ℝ3 and the semidirect product group SE(3) are used for representing rigid body motions. The key element is the local-global transitions (LGT) transition map, which facilitates the update of (global) absolute coordinates in terms of the (local) coordinates on the Lie group. This LGT map is specific to the absolute coordinates, the local coordinates on the Lie group, and the Lie group used to represent rigid body configurations.

Systematic Odometry Error Evaluation and Correction in a Human-Sized Three-Wheeled Omnidirectional Mobile Robot Using Flower-Shaped Calibration Trajectories

Odometry is a simple and practical method that provides a periodic real-time estimation of the relative displacement of a mobile robot based on the measurement of the angular rotational speed of its wheels. The main disadvantage of odometry is its unbounded accumulation of errors, a factor that reduces the accuracy of the estimation of the absolute position and orientation of a mobile robot. This paper proposes a general procedure to evaluate and correct the systematic odometry errors of a human-sized three-wheeled omnidirectional mobile robot designed as a versatile personal assistant tool. The correction procedure is based on the definition of 36 individual calibration trajectories which together depict a flower-shaped figure, on the measurement of the odometry and ground truth trajectory of each calibration trajectory, and on the application of several strategies to iteratively adjust the effective value of the kinematic parameters of the mobile robot in order to match the estimated final position from these two trajectories. The results have shown an average improvement of 82.14% in the estimation of the final position and orientation of the mobile robot. Therefore, these results can be used for odometry calibration during the manufacturing of human-sized three-wheeled omnidirectional mobile robots.

Wedge-Based Design for Phase Stable and Phase Accurate Heterodyne-Detected Sum-Frequency Generation Spectroscopy.

Phase sensitive and heterodyne-detected (HD) sum-frequency generation (SFG) spectroscopy offers the ability to separate the nonlinear susceptibility into its real and imaginary components. This provides information about the absolute orientation of molecules at interfaces while also producing an absorptive spectrum that is linear in spectral composition and can easily be decomposed into different spectral components. However, simultaneously obtaining phase accuracy and phase stability remains a challenge in SFG. Here we present a new experimental design for HD-SFG spectroscopy that incorporates a wedge pair to accurately control the timing between the local oscillator and the sample signal. This experimental approach provides high phase accuracy and long-time phase stability in a compact and flexible configuration.

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.

Conditional transport of geometrical flamelet statistics in planar freely propagating turbulent premixed flames

The geometrical flamelet statistics in a turbulent premixed flame are represented by c ¯ , Σ f , 〈 n 〉 f , 〈 ∇ · n 〉 f and 〈 | ∇ · n | 〉 f which are respectively mean reaction progress variable, flame surface density, mean orientation vector, mean curvature and mean absolute curvature. New conditional transport equations are derived for the listed geometrical statistics of successively higher orders in terms of net normal flame motion from the equation of the reaction progress variable. They are simpler and allow easier closure than the unconditionally averaged formulations involving the tangential velocity component and the turbulent flux term involving countergradient diffusion. Balance is checked for all component terms of those transport equations in two freely propagating, constant density DNS flames in statistical steadiness. Results show that the mean orientation vector and the mean absolute curvature remain approximately uniform in local equilibrium with negligible spatial transport except near the edges of a flame brush . A simple closure strategy is suggested with the flame surface density given in terms of uniform mean absolute curvature and mean orientation vectors, 〈 n x 〉 f and 〈 n x 〉 K , given as the conditional averages weighted by Σ f ′ ( = ∂ c / ∂ n ) and ∂ 2 c / ∂ n 2 respectively. The governing equations and closure models are expected to be valid in planar freely propagating turbulent premixed flames of either constant or variable density with heat release. The suggested closure requires prior knowledge on the magnitude of the mean orientation vector and the mean absolute curvature given as the ratio of laminar and turbulent flame speeds and the inverse characteristic wrinkling scale through a flame brush. Good agreement is shown against DNS results of two constant density flames for closure models of the conditional velocities, 〈 u 〉 f and 〈 S d 〉 f , and for the predicted profiles of c ¯ and Σ f except for minor deviation near the edges. The suggested closure scheme may be extended to general turbulent premixed flames, while further work may be required for proper closure relationships under the given circumstances.

Error compensation of industrial robot based on deep belief network and error similarity

• A error estimate model is established and verified by testing to predict the pose error of the robot. • Combines the advantages of deep nerual network and error similarity, the statistical feature of robot error similarity can improve the robustness and prediction accuracy of the error estimate model. • Cross contrast training can extract the contrast information and enlarged the sample size. • The proposed scheme doesn't depend on the kinematic parameters of the robot and needs neither retrofitting with the robot's control system and massive measurements. • The proposed scheme can effectively reduce the maximum positional errors and orientation errors of the robot. Abstract With the advantages of the high degree of freedom and large action space, industrial robots are gradually widely used in high-end large-scale equipment automatic assembly fields such as aerospace. It is very important to improve the absolute pose accuracy of the robot. This paper presents a deep learning scheme for the compensation of absolute pose errors for industrial robots. A mapping model of the robot's theoretical pose coordinates and actual pose errors is established based on the deep belief networks and error similarity, the pose error prediction is realized. Combined with the offline feedforward compensation method, the scheme has been verified on a 6-DOF serial industrial robot KUKA KR500-3 of robot automatic assembly system. The proposed scheme combines the feature expression of deep learning with statistical interpretability of error similarity, does not depend on the specific kinematic model of the robot, and without retrofitting with high-end encoder. After compensation, that the maximum absolute positional error and orientation error of the robot end-effector was reduced by 83.99% from 1.524 mm to 0.244 mm and reduced by 54.88% from 0.082 deg to 0.037 deg respectively, which can meet the accuracy requirement of the robotic automatic assembly system.

Lie Group Modelling for an EKF-Based Monocular SLAM Algorithm

This paper addresses the problem of monocular Simultaneous Localization And Mapping on Lie groups using fiducial patterns. For that purpose, we propose a reformulation of the classical camera model as a model on matrix Lie groups. Thus, we define an original-state vector containing the camera pose and the set of transformations from the world frame to each pattern, which constitutes the map’s state. Each element of the map’s state, as well as the camera pose, are intrinsically constrained to evolve on the matrix Lie group SE(3). Filtering is then performed by an extended Kalman filter dedicated to matrix Lie groups to solve the visual SLAM process (LG-EKF-VSLAM). This algorithm has been evaluated in different scenarios based on simulated data as well as real data. The results show that the LG-EKF-VSLAM can improve the absolute position and orientation accuracy, compared to a classical EKF visual SLAM (EKF-VSLAM).

Cooperative Control of Fixed-wing Drones Using Relative Jacobian with Obstacle Avoidance

This paper implements a new strategy to perform cooperative control for fixed-wing drones by the use of a relative Jacobian, with a subsequent method of avoiding obstacles while flying cooperatively. We present a derivation of the corresponding relative Jacobian for two fixed-wing drones that is expressed in modular form. We perform two experiments: using absolute pitch movement and another using absolute yaw movement in order to avoid obstacles, while simultaneously controlling the relative position with respect to each other. Experimental results are shown and analysed. Simulation experiments were perform in Gazebo and ROSflight to show relative position and orientation with respect to each other, absolute orientation with respect to the world, and obstacle avoidance.

Algorithms to solve absolute orientation problem for GL(3), O(3), and SO(3) groups

Algorithms to solve absolute orientation problem for GL(3), O(3), and SO(3) groups

The geoPebble System: Design and Implementation of a Wireless Sensor Network of GPS-Enabled Seismic Sensors for the Study of Glaciers and Ice Sheets

The geoPebble system is a network of wirelessly interconnected seismic and GPS sensor nodes with geophysical sensing capabilities for the study of ice sheets in Antarctica and Greenland, as well as mountain glaciers. We describe our design methodology, which has enabled us to develop these state-of-the art units using commercial-off-the-shelf hardware combined with custom-designed hardware and software. Each geoPebble node is a self-contained, wirelessly connected sensor for collecting seismic activity and position information. Each node is built around a three-component seismic recorder, which includes an amplifier, filter, and 24-bit analog-to-digital converter that can sample incoming seismic signals up to 10 kHz. The timing for each node is available from GPS measurements and a local precision oscillator that is conditioned by the GPS timing pulses. In addition, we record the carrier-phase measurement of the L1 GPS signal in order to determine location at sub-decimeter accuracy (relative to other geoPebble nodes within a radius of a few kilometers). Each geoPebble includes 32 GB of solid-state storage, wireless communications capability to a central supervisory unit, and auxiliary measurements capability (including tilt from accelerometers, absolute orientation from magnetometers, and temperature). The geoPebble system has been successfully validated in the field in Antarctica and Greenland.

Absolute Absorption Cross Section and Orientation of Dangling OH Bonds in Water Ice

Abstract The absolute absorption cross section of dangling OH bonds in water ice, a free OH stretch mode by three-coordinated surface water molecules, is derived experimentally as 1.0 ± 0.2 × 10−18 cm2 at 3696 cm−1 for amorphous water at 90 K using infrared multiple-angle incidence resolution spectrometry (IR–MAIRS). The integrated absorption cross section (band strength) of the dangling OH bond at 90 K (1.4 ± 0.3 × 10−17 cm molecule−1 at 3710–3680 cm−1) is found to be more than 1 order of magnitude smaller than those in bulk ice or liquid water. This indicates that a lack of hydrogen-bonding significantly decreases the band strength of dangling OH bonds. The present study also provides average molecular orientations of dangling OH bonds at 10 K and 90 K, because both the surface-parallel (in-plane) and surface-perpendicular (out-of-plane) vibration spectra of dangling OH bonds are quantitatively measured by IR–MAIRS. The intensity ratio of the dangling-OH peaks between in-plane to out-of-plane spectra shows the isotropic nature (random orientation) of the two- and three-coordinated dangling OH bonds in microporous amorphous water prepared at 10 K; however, the three-coordinated dangling OH bonds in nonporous amorphous water prepared at 90 K are dominantly located at the top ice surface and oriented perpendicular to it. These findings provide fundamental insights into the relationship between the structure and optical properties of ice surfaces, and aid quantitative understanding of the surface structure of interstellar ices and their laboratory analogs.

Optical Probing of Crystal Lattice Configurations in Single CsPbBr3 Nanoplatelets.

Quantum-confined nanostructures of CsPbBr3 with luminescence quantum efficiencies approaching unity have shown tremendous potential for lighting and quantum light applications. In contrast to CsPbBr3 quantum dots, where the fine structure of the emissive exciton state has been intensely discussed, the relationship among lattice orientation, shape anisotropy, and exciton fine structure in lead halide nanoplatelets has not yet been established. In this work, we investigate the fine structure of the bright triplet exciton of individual CsPbBr3 nanoplatelets by polarization-resolved micro- and magnetophotoluminescence spectroscopy at liquid helium temperature and find a large zero-field splitting of up to 2.5 meV. A unique relation between the crystal structure and the photoluminescence emission confirms the existence of two distinct crystal configurations in such nanoplatelets with different alignments of the crystal axes with respect to the nanoplatelet facets. Polarization-resolved experiments eventually allow us to determine the absolute orientation of an individual nanoplatelet on the substrate purely by optical means.

A new inertial navigation system for guiding implant placement. An in-vitro proof-of-concept study.

The aim of this study was to assess the potential use of a new advanced inertial navigation system for guiding dental implant placement and to compare this approach with standard stereolithographic template guiding. A movement processing unit with a 9-axis absolute orientation sensor was adapted to a surgical handpiece and wired to a computer navigation interface. Sixty implants were placed by 10 operators in 20 jaw models. The 30 implants of the test group were placed in 10 models guided by the new inertial navigation prototype. The 30 implants of the control group were placed in another 10 models using a CAD-CAM template. Both groups were subdivided into experienced and non-experienced operators. Pre- and postoperative computer tomography images were obtained and matched to compare the planned and final implant positions. Four deviation parameters (global, angular, depth, and lateral deviation) were defined and calculated. The primary outcome was the angular deviation between the standard stereolithographic approach and the new inertial navigation system. Results showed no significant differences between both groups, suggesting that surgical navigation based on inertial measurement units (IMUs) could potentially be useful for guiding dental implant placement. However, more studies are still needed to translate this new approach into clinical practice.

УМОВИ І МЕХАНІЗМИ ДІЄВОГО ЗАПОБІГАННЯ КОРУПЦІЇ В УКРАЇНІ

Розкрито зміст системно мережевого структурування корупції як інституту абсолютної антисуспільної спрямованості. Увагу приділено понятійній чистоті категоріального апарату, зокрема, розмежовано поняття «корупція» і «хабарництво». Наведено характеристику персоніфікованих і корпоративно-асоційованих суб’єктів корупції, розкрито зміст сучасних форм і характерних різновидів об’єкта корупційного підкупу. Наведено диференційований перелік і розкрито зміст специфічних ринків «корупційних послуг», що функціонують у межах загального «чорного» ринку України. Показано соціально-економічні витоки та розкрито характер особистих і корпоративних інтересів суб’єктів – носіїв корупційних відносин.Визначено реальний спектр руйнівних антисуспільних наслідків синергії бінарної злуки «інституту корупції» з «інститутом кримінальної «чорної» економіки». Виділено три базових блоки злочинної економічної діяльності: 1) кримінальний промисел; 2) надання послуг кримінального характеру; 3) кримінальне порушення норм господарсько-комерційної діяльності. На засадах узагальненого досвіду США визначено необхідні умови й надано пропозиції щодо формування організаційно-економічних та економіко-правових антикорупційних механізмів. Доведено, що подолання корупції неможливе без скасування правового принципу «презумпції невинуватості» у сфері підтвердження легітимності доходів платників податків, які зобов’язані надавати вичерпну інформацію, що доводить легітимність джерел походження особисто-сімейної нерухомості.Визначено умови забезпечення дієвого порядку у сфері обліку і контролю повноти виконання громадянами податкових зобов’язань на засадах удосконаленню механізму декларування доходів та державно-ринкового обліку нерухомості населення України. У контексті критичних зауважень щодо помилок, допущених за останні п’ять років, надано пропозиції стосовно вдосконалення організаційно-економічних засад декларування річних доходів, а також проведення соціально-справедливої і антикорупційної легалізації статків, майна і капіталів фізичних осіб шляхом забезпечення сплати до державної скарбниці компенсаційно-справедливих відшкодувань за завдані бюджету збитки за період незалежності України.

An Efficient Closed Form Solution to the Absolute Orientation Problem for Camera with Unknown Focal Length.

In this paper we propose an efficient closed form solution to the absolute orientation problem for cameras with an unknown focal length, from two 2D–3D point correspondences and the camera position. The problem can be decomposed into two simple sub-problems and can be solved with angle constraints. A polynomial equation of one variable is solved to determine the focal length, and then a geometric approach is used to determine the absolute orientation. The geometric derivations are easy to understand and significantly improve performance. Rewriting the camera model with the known camera position leads to a simpler and more efficient closed form solution, and this gives a single solution, without the multi-solution phenomena of perspective-three-point (P3P) solvers. Experimental results demonstrated that our proposed method has a better performance in terms of numerical stability, noise sensitivity, and computational speed, with synthetic data and real images.

Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide ice core site

Abstract. The crystal orientation fabric (COF) of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics. Though not widely implemented, coherent ice-penetrating radar is able to detect bulk anisotropic fabric patterns by exploiting the birefringence of ice crystals at radar frequencies, with the assumption that one of the crystallographic axes is aligned in the vertical direction. In this study, we conduct a suite of quad-polarimetric measurements consisting of four orthogonal antenna orientation combinations near the Western Antarctic Ice Sheet (WAIS) Divide ice core site. From these measurements, we are able to quantify the azimuthal fabric asymmetry at this site to a depth of 1400 m at a bulk-averaged resolution of up to 15 m. Our estimates of fabric asymmetry closely match corresponding fabric estimates directly measured from the WAIS Divide ice core. While ice core studies are often unable to determine the absolute fabric orientation due to core rotation during extraction, we are able to identify and conclude that the fabric orientation is depth-invariant to at least 1400 m, equivalent to 6700 years BP (years before 1950) and aligns closely with the modern surface strain direction at WAIS Divide. Our results support the claim that the deformation regime at WAIS Divide has not changed substantially through the majority of the Holocene. Rapid polarimetric determination of bulk fabric asymmetry and orientation compares well with much more laborious sample-based COF measurements from thin ice sections. Because it is the bulk-averaged fabric that ultimately influences ice flow, polarimetric radar methods provide an opportunity for its accurate and widespread mapping and its incorporation into ice flow models.

A Robot Mimicking Heart Motions: An Ex-Vivo Test Approach for Cardiac Devices

PurposeThe pre-clinical testing of cardiovascular implants gains increasing attention due to the complexity of novel implants and new medical device regulations. It often relies on large animal experiments that are afflicted with ethical and methodical challenges. Thus, a method for simulating physiological heart motions is desired but lacking so far.MethodsWe developed a robotic platform that allows simulating the trajectory of any point of the heart (one at a time) in six degrees of freedom. It uses heart motion trajectories acquired from cardiac magnetic resonance imaging or accelero-meter data. The rotations of the six motors are calculated based on the input trajectory. A closed-loop controller drives the platform and a graphical user interface monitors the functioning and accuracy of the robot using encoder data.ResultsThe robotic platform can mimic physiological heart motions from large animals and humans. It offers a spherical work envelope with a radius of 29 mm, maximum acceleration of 20 m/s2 and maximum deflection of ±19° along all axes. The absolute mean positioning error in x-, y- and z-direction is 0.21 ±0.06, 0.31 ±0.11 and 0.17 ±0.12 mm, respectively. The absolute mean orientation error around x-, y- and z-axis (roll, pitch and yaw) is 0.24 ±0.18°, 0.23 ±0.13° and 0.18 ±0.18°, respectively.ConclusionThe novel robotic approach allows reproducing heart motions with high accuracy and repeatability. This may benefit the device development process and allows re-using previously acquired heart motion data repeatedly, thus avoiding animal trials.

Precision of inertial measurement unit sensors in head-tracking systems used for binaural synthesis

Binaural synthesis is the most used sound system for diverse virtual and augmented reality systems nowadays, given its simplicity of implementation and the need of using only two audio channels. It is widely used in computer games, auralization and even audio production. To achieve the most natural sound field recreation, systems used for binaural synthesis must include a head-tracking sensor to dynamically calculate the binaural signal for the head orientation at any given moment. This is done by inertial measurement unit (IMU) sensors, specifically the triaxial accelerometers, gyroscopes, and magnetometers. Simpler systems, e.g., Arduino or other embedded systems, provide only raw sensor data, and the orientation is calculated by a processing unit. Other, more complex systems such as smartphones or VR headsets already calculate their position from the raw data using complex sensor integration algorithms. In this paper, a measurement procedure for measuring the precision of IMU sensors is presented. The need of absolute orientation calibration is addressed, and challenges of sensor data drift are discussed. Measurement results for simple embedded systems and complex systems found in smartphones are presented, and an estimation of IMU sensor quality for binaural synthesis is made.

IMAGE-BASED ORIENTATION DETERMINATION OF MOBILE SENSOR PLATFORMS

Abstract. Estimating the pose of a mobile robotic platform is a challenging task, especially when the pose needs to be estimated in a global or local reference frame and when the estimation has to be performed while the platform is moving. While the position of a platform can be measured directly via modern tachymetry or with the help of a global positioning service GNSS, the absolute platform orientation is harder to derive. Most often, only the relative orientation is estimated with the help of a sensor mounted on the robotic platform such as an IMU, with one or multiple cameras, with a laser scanner or with a combination of any of those. Then, a sensor fusion of the relative orientation and the absolute position is performed. In this work, an additional approach is presented: first, an image-based relative pose estimation with frames from a panoramic camera using a state-of-the-art visual odometry implementation is performed. Secondly, the position of the platform in a reference system is estimated using motorized tachymetry. Lastly, the absolute orientation is calculated using a visual marker, which is placed in the space, where the robotic platform is moving. The marker can be detected in the camera frame and since the position of this marker is known in the reference system, the absolute pose can be estimated. To improve the absolute pose estimation, a sensor fusion is conducted. Results with a Lego model train as a mobile platform show, that the trajectory of the absolute pose calculated independently with four different markers have a deviation &lt; 0.66 degrees 50% of the time and that the average difference is &lt; 1.17 degrees. The implementation is based on the popular Robotic Operating System ROS.