Coordinate System Alignment Research Articles

Validation of an IMU Suit for Military-Based Tasks.

Investigating the effects of load carriage on military soldiers using optical motion capture is challenging. However, inertial measurement units (IMUs) provide a promising alternative. Our purpose was to compare optical motion capture with an Xsens IMU system in terms of movement reconstruction using principal component analysis (PCA) using correlation coefficients and joint kinematics using root mean squared error (RMSE). Eighteen civilians performed military-type movements while their motion was recorded using both optical and IMU-based systems. Tasks included walking, running, and transitioning between running, kneeling, and prone positions. PCA was applied to both the optical and virtual IMU markers, and the correlations between the principal component (PC) scores were assessed. Full-body joint angles were calculated and compared using RMSE between optical markers, IMU data, and virtual markers generated from IMU data with and without coordinate system alignment. There was good agreement in movement reconstruction using PCA; the average correlation coefficient was 0.81 ± 0.14. RMSE values between the optical markers and IMU data for flexion-extension were less than 9°, and 15° for the lower and upper limbs, respectively, across all tasks. The underlying biomechanical model and associated coordinate systems appear to influence RMSE values the most. The IMU system appears appropriate for capturing and reconstructing full-body motion variability for military-based movements.

Iterative alignment of reflector panels for large-scale compact test range in non-metrology environment based on laser tracker

The reflector panel used for a large-scale compact test range (CTR) is usually divided into several sub-panels with appropriate size to be fabricated separately, and then these sub-panels are assembled and aligned for a long period to form a high-precision reflective surface. Toward that end, an iterative alignment system is established to accomplish alignment of reflector panels based on commercial laser tracker and 6-degree-of-freedom adjustment mechanism. The alignment is a very challenging task involving two aspects: coordinate system alignment and measurement uncertainty evaluation, especially in a non-metrology environment. For the former, an alignment method is developed to unify the measurement coordinate system of the system based on iteratively adding and modifying reference points. For the latter, the actual uncertainty model of laser tracker based on a large amount of field measurement data is analyzed and established using statistical analysis. Based on the uncertainty model, the measurement and alignment error is evaluated and verified by Monte Carlo simulations. As verification, 15 sub-panels of the CTR reflector with 12 m width and 7 m height are opportunely assembled and aligned using the iterative alignment system and algorithm. The final root-mean-square error of the deviation between the actual and theoretical profiles is achieved at 0.041 mm, where the accuracy loss caused by alignment is only 7.9% of the theoretical value. Results show that the alignment system and method proposed in this paper is effective and efficient to align the reflector panels for large-scale CTR in a non-metrology environment.

Current Problems of Improving the Coordinate-Time Support of GLONASS and Promising Methods for Their Solution: II. Alignment of Coordinate Systems Used by Various Information Technologies to Refine the Universal Time

Current Problems of Improving the Coordinate-Time Support of GLONASS and Promising Methods for Their Solution: II. Alignment of Coordinate Systems Used by Various Information Technologies to Refine the Universal Time

Current Problems of Improving the Coordinate-Time Support of GLONASS and Promising Methods for Their Solution. 1. Alignment of Coordinate Systems Used by Various Information Technologies to Refine the Geocenter’s Position

The article considers the problem of improving the coordinate-time support of GLONASS, which implies refining the models of a wide range of stochastic error components caused by inaccurate knowledge of geodetic and geodynamic parameters, such as the position and displacement rate of the geocenter, Universal Time, pole shift, irregularities of the Earth’s rotation, precession, and nutation. It is shown that the problem can be solved only using a comprehensive measurement technique that includes the use of various information measurement “techniques,” namely, global navigation satellite systems, quantum-optical communication stations, Doppler velocity sensors, and very-long-baseline radio interferometers. The problem of aligning coordinate systems on which the application of a particular information technology is based that arises from using this approach is discussed. Mathematical models, algorithms, and the results of their development in the experiments on the alignment of coordinate systems used in global navigation satellite systems and quantum-optical communication stations are given. The presented results contain estimates of the misalignment between different coordinate systems, including misalignment by center position and misalignment due to difference in the scale factor and orientation with respect to the inertial coordinate system.

RAMT

Recently a class of new in-vehicle technologies based on off-the-shelf mobile devices have been developed to improve driving safety and experience. For instance, wearables like the smartwatches are utilized to monitor the action of the driver and detect possible secondary tasks. Moreover, wearables can allow a driver to use gesture for in-vehicle controls, reducing distractions to driving. The accuracy of these systems can be significantly improved by tracking the real-time attitude of mobile devices. This paper proposes a novel system called Real-time Attitude and Motion Tracking (RAMT) that can enable a mobile device to accurately learn the coordinate system of a moving vehicle, and hence track its attitude and motion in real time. RAMT consists of a series of lightweight algorithms to sense the vehicle's movement and calculate the device's attitude. It provides a solution for trajectory-based gesture recognition. We have implemented RAMT on a smartphone and a smartwatch and evaluated the performance in 10 real driving trips. Our results show that the overall error of the coordinate system alignment is around 5° for the smartphone and 10° for the smartwatch, and over 84% of customized hand gestures can be accurately recognized with the result of RAMT. A video demo of RAMT is available at https://youtu.be/9rZp7HxyRts.

Optical probing for CNC machining of large parts made from fiber-reinforced polymer composite materials

In machining of large fiber-reinforced polymer (FRP) composite parts, the part must be precisely located before machining. The exact location and shape are usually determined by the probing systems employing a touch probe integrated with a CNC machine. When measuring a large number of points, touch probing consumes a significant amount of time and adversely affects the utilization of the CNC machine in serial production. In order to increase the probing speed and acquire additional details, a new optical probing operating on the laser triangulation measuring principle is developed. The paper describes the measuring principle, system integration, neural network as the measuring system transfer function, and the calibration process. When measuring polyester or epoxy resin-based materials, the laser light penetrates into the part and reflects back inside of the part. This interference is successfully neutralized by the calibration body made from the same FRP material as the measured part. Verification of the calibration body and the machine coordinate system alignment is demonstrated by comparison of corrections determined with the optical and touch probing.

Secure alignment of coordinate systems using quantum correlation

We show that two parties far apart can use shared entangled states and classical communication to align their coordinate systems with a very high fidelity. Moreover compared with previous methods proposed for such a task, i.e. sending parallel or anti-parallel pairs or groups of spin states, our method has the extra advantages of using single qubit measurements and also being secure, so that third parties do not extract any information about the aligned coordinate system established between the two parties. The latter property is important in many other quantum information protocols in which measurements inevitably play a significant role.

Coordinate System Alignment Algorithm of Advanced Remote Handling System for Decommissioning of Nuclear Facility

Coordinate System Alignment Algorithm of Advanced Remote Handling System for Decommissioning of Nuclear Facility

Integration of marker and force data to compute three-dimensional joint moments of the thumb and index finger digits during pinch

This study presents methodology to determine joint moments of the digits of the hand during pinch function. This methodology incorporates steps to identify marker-based kinematic data defining aligned coordinate systems for individual digit segments and joint centre locations. The kinematic data are then transformed to a common reference frame along with the force data collected at pinch contact of a customised apparatus in three dimensions. These methods were demonstrated with a pilot investigation to examine the static joint moments occurring during two-digit oppositional precision pinch at a particular end point force level applied at the digit pads. Notable abduction joint moments at the proximal joints of both digits were observed, which implicate the role of respective intrinsic and extrinsic muscles in maintaining pinch grasp. Examining differences in joint moment results when substituting selected steps of this methodological approach suggested greater relative importance for joint centre identification and segment coordinate system alignment.

Robust Identification of Three-Dimensional Thumb and Index Finger Kinematics With a Minimal Set of Markers

This study presents a methodology to determine thumb and index finger kinematics while utilizing a minimal set of markers. The motion capture of skin-surface markers presents inherent challenges for the accurate and comprehensive measurement of digit kinematics. As such, it is desirable to utilize robust methods for assessing digit kinematics with fewer markers. The approach presented in this study involved coordinate system alignment, locating joint centers of rotation, and a solution model to estimate three-dimensional (3-D) digit kinematics. The solution model for each digit was based on assumptions of rigid-body interactions, specific degrees of freedom (DOFs) at each located joint, and the aligned coordinate system definitions. Techniques of inverse kinematics and optimization were applied to calculate the 3-D position and orientation of digit segments during pinching between the thumb and index finger. The 3-D joint center locations were reliably fitted with mean coefficients of variation below 5%. A parameterized form of the solution model yielded feasible solutions that met specified tolerance and convergence criteria for over 85% of the test points. The solution results were intuitive to the pinching function. The thumb was measured to be rotated about the CMC joint to bring it into opposition to the index finger and larger rotational excursions (>10 deg) were observed in flexion/extension compared to abduction/adduction and axial rotation for all joints. While the solution model produced results similar to those computed from a full marker set, the model facilitated the usage of fewer markers, which inherently lessened the effects of passive motion error and reduced the post-experimental effort required for marker processing.

Sensitivity analysis for plane orientation in three-dimensional cephalometric analysis based on superimposition of serial cone beam computed tomography images

The purpose of this study was to evaluate the potential errors associated with superimposition of serial cone beam CT (CBCT) images utilizing reference planes based on cranial base landmarks using a sensitivity analysis. CBCT images from 62 patients participating in a maxillary expansion clinical trial were analysed. The left and right auditory external meatus (AEM), dorsum foramen magnum (DFM) and the midpoint between the left and right foramen spinosum (ELSA) were used to define a three-dimensional (3D) anatomical reference co-ordinate system. Intraclass correlation coefficients for all four landmarks were obtained. Transformation of the reference system was carried out using the four landmarks and mathematical comparison of values. Excellent intrareliability values for each dimension were obtained for each landmark. Evaluation of the method to transform the co-ordinate system was first done by comparing interlandmark distances before and after transformations, giving errors in lengths in the order of 10-14% (software rounding error). A sensitivity evaluation was performed by adding 0.25 mm, 0.5 mm and 1 mm error in one axis of the ELSA. A positioning error of 0.25 mm in the ELSA can produce up to 1.0 mm error in other cranial base landmark co-ordinates. These errors could be magnified to distant landmarks where in some cases menton and infraorbital landmarks were displaced 4-6 mm. Minor variations in location of the ELSA, both the AEM and the DFM landmarks produce large and potentially clinically significant uncertainty in co-ordinate system alignment.

Mapping ligament insertion sites onto bone surfaces in knee by co-registration of CT and digitization data

This paper describes a new methodology that enables mapping of the ligament insertion sites onto bone surfaces in the knee joint by co-registration of the data acquired using digitization and computed tomography (CT). Local coordinate systems on the distal femur and proximal tibia were established by three spherical fiducial markers rigidly affixed to each bone. The fiducial marker centroid locations were identified by a least-squares sphere-fitting algorithm. An optimization correction procedure was proposed to mitigate the effect of the target registration error (TRE) on the alignment of coordinate systems for co-registration. A test with four cadaveric specimens demonstrated successful mapping of insertion sites for five ligaments. Fiducial registration error (FRE) as measured by the differences in inter-marker distances between the two modalities was smaller than 2%. The optimization procedure corrected the insertion site invisibility or partial visibility problem and improved the overall mapping quality, as indicated by substantial reduction of the mean and dispersion of distances from digitized insertion site points to the bone surfaces.

A vision-aided alignment datum system for coordinate measuring machines

This paper presents the development of a CAD-based and vision-aided precision measurement system. A new coordinate system alignment technique for coordinate measuring machines (CMMs) is described. This alignment technique involves a machine vision system with CAD-based planning and execution of inspection. The determination method for measuring datums for the coordinate measuring technique, using the AutoCAD development system, is described in more detail. To improve image quality in the machine vision system, a contrast enhancement technique is used on the image background to reduce image noise, and an on-line calibration technique is applied. Some systematic errors may be caused by imperfect geometric features in components during coordinate system alignment. This measurement system approach, with its new measuring coordinate alignment method, can be used for high-precision measurement to overcome such errors.

Helical motion analysis of the knee—I. Methodology for studying kinematics during locomotion

A technique for investigating the three-dimensional kinematics of knee motion during dynamic functional tasks has been developed. It involves the combined usage of a six degree of freedom goniometer and helical motion analysis. A detailed procedure for coordinate system alignment and calibration must be followed. Once established this entire procedure is routinely implementable. Ensemble averages from multiple walking strides reveal that this technique is sensitive enough to differentiate between the kinematics of an uninjured and injured knee.