Datum System Research Articles

Assessing the impacts of ice penetration on monitoring water levels of high-latitude and -altitude lakes from CryoSat-2 altimetry

The CryoSat-2 satellite provides high-precision and long-term monitoring of global lake levels, offering advantages for water resource management, ecological protection, and disaster warning. However, the lake ice penetration by radar electromagnetic waves of CryoSat-2 altimetry tends to result in underestimation of water levels for lakes in high latitudes and altitudes. By contrast, the laser altimetry of ICESat-2 enables us to obtain the height measurements from lake ice surface and the ice penetration impacts on lake levels can be nearly ignored in the ICESat-2 elevation product. After converting the CryoSat-2 and ICESat-2 altimetry data to the same datum and height reference system, the water level difference of (near-) synchronous observations between the two satellites could be mainly attributed to the influences by the lake ice penetration from CryoSat-2 data. In this study, totally 257 lakes in high-latitude (north of 50°N) and high-altitude (the Tibetan Plateau, TP) regions that are covered by both CryoSat-2 and ICESat-2 satellite tracks are examined to explore the characteristics of ice penetration impacts on water level measurements. The altimetry data during unfreezing seasons (June to October) are used to correct the systematic height biases of these two satellite measurements, thus their water level differences during freezing seasons (November to May of the following year) are deemed as the influences of ice penetration on lake level measurements by CryoSat-2 radar altimetry. The results show that the maximum underestimation depth of water level for each lake varies within the range of 0.01–3.47 m, with an average of 0.90 m. Particularly in North America with a dense distribution of lakes, the underestimation of lake levels by CryoSat-2 gradually ascends with increasing latitude. CryoSat-2 underestimates lake levels in Europe and the TP less than in North America. Among different months, the lake ice leads to the maximum underestimation on the water level by CryoSat-2 altimetry in March. The spatial and temporal characteristics of lake ice impacts on the water level measurements by CryoSat-2 altimetry would be an essential reference for quantifying and reducing the uncertainties of satellite radar altimetry for monitoring inland water dynamics.

Determination of uncertainty of coordinate measurements on the basis of the formula for EL,MPE

A technique of estimating the uncertainty of coordinate measurements, called the sensitivity analysis method according to ISO/TS 15530-1, developed at University of Bielsko-Biała, is presented. Measurement uncertainty is estimated on the basis of information contained in the formula for the maximum permissible error (EL,MPE) of the applied coordinate measuring system (CMS) and on the basis of its acceptance or reverification test results. Measurement models are of the nature of close mathematical dependencies expressing the measured characteristic in the form of a distance which is a function of coordinates differences of a low number of essential points, properly selected on the workpiece. Measurement models for dimensions and various geometrical deviations were developed. Thanks to the applied vector notation the models are in the form of cross and dot products and they are easily programmable in software such as Matlab, Maple or Python. Detailed examples of the uncertainty analysis for two characteristics (position deviations of the axes of the holes in relation to the datum system) of a car steering knuckle are provided.

Estimation of Geopotential Value W0 for the Geoid and Local Vertical Datum Parameters

Unification of the global vertical datum has been a key problem to be solved for geodesy over a long period, and the main challenge for unifying the global vertical datum system is to determine the geopotential value W0 of the geoid and to calculate the vertical offset between the local vertical datum and the global vertical datum W0. The geopotential value W0 can be calculated using the grid mean sea surface (GMSS) data and the global geopotential model (GGM). In this study, this GMSS data was measured with adjustment methods and 24 years of merged multi-satellite altimetry data. The data of HaiYang-2A (HY-2A) and Jason-3 were first used to calculate W0. The geopotential value W0 was determined to be 62,636,856.82 m2s−2 by combining the EIGEN-6C4 (European Improved Gravity Model of the Earth by New Techniques) and the GMSS data. Then, the geopotential difference approach and geodetic boundary value problem (GBVP) approach were used to determine the vertical datum parameters in this study. To compensate for the omission error of the GGM, this study utilized the remove–compute–restore (RCR) technique and the residual terrain model (RTM)-recovered high-frequency gravity signals. Finally, as a result of the GBVP solution, the geopotential value of the Australian Height Datum (AHD) was 62,636,851.935 m2s−2, and the vertical offset of the AHD relative to the global vertical datum W0 was 0.4885 m. As a result of the geopotential difference approach, the geopotential value of the Chinese Height datum was 62636861.412 m2s−2, and the vertical offset of the Chinese Height datum was −0.4592 m.

Perpendicularity Detection of Multistage Rotor Considering Compensation of Datum Error

Perpendicularity is an orientation tolerance, and the perpendicularity of end face can be utilized to assess the axial assembly precision of multistage rotor. The aim of this article is to detect the perpendicularity and parallelism of rotor using turntable-rotating approach. The misalignment between datum system of rotor and measurement datum of turntable will introduce the datum error, which is difficult to be thoroughly eliminated by the mechanical device of centering and leveling. To ensure that each measurement is carried out in the same datum system of rotor, the residual error of tilt and eccentricity between two datum systems is studied and compensated. The direction of assessment datum axis of rotor perpendicularity is determined by rotor axis rather than extrinsic measurement datum e.g. turntable axis. The experiment of rotor is performed to verify the effectiveness of the presented detection approach. The difference and relationship between rotor perpendicularity and parallelism are investigated and discussed. It is recommended that parallelism and perpendicularity should be considered together to fully reflect the axial geometric tolerance of rotor. The presented approach is general, which can also be conveniently utilized to detect axial geometric tolerances of other rotating components. For example, compressor rotor, motor rotor, gas turbine rotor, etc.

Estimation of Vertical Datum Parameters Using the GBVP Approach Based on the Combined Global Geopotential Models

Unification of the global vertical datum has been a key problem to be solved for geodesy over a long period, and the main challenge for a unified vertical datum system is to determine the vertical offset between the local vertical datum and the global vertical datum. For this purpose, the geodetic boundary value problem (GBVP) approach based on the remove-compute-restore (RCR) technique is used to determine the vertical datum parameters in this paper. In the RCR technique, a global geopotential model (GGM) is required to remove and restore the long wavelengths of the gravity field. The satellite missions of the GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity field and steady-state Ocean Circulation Exploration) offer high accuracy medium–long gravity filed information, but GRACE/GOCE-based GGMs are restricted to medium–long wavelengths because the maximum degree of their spherical harmonic representation is limited, which is known as an omission error. To compensate for the omission error of GRACE/GOCE-based GGM, a weighting method is used to determine the combined GGM by combining the high-resolution EGM2008 model (Earth Gravitational Model 2008) and GRACE/GOCE-based GGM to effectively bridge the spectral gap between satellite and terrestrial data. An additional consideration for the high-frequency gravity signals is induced by the topography, and the residual terrain model (RTM) is used to recover the omission errors effect of the combined GGM. In addition, to facilitate practical implementation of the GBVP approach, the effects of the indirect bias term, the spectral accuracy of the GGM, and the systematic levelling errors and distortions in estimations of the vertical datum parameters are investigated in this study. Finally, as a result of the GBVP solution based on the combined DIR_R6/EGM2008 model, RTM, and residual gravity, the geopotential values of the North American Vertical Datum of 1988 (NAVD88), the Australian Height Datum (AHD), and the Hong Kong Principal Datum (HKPD) are estimated to be equal to 62636861.31 ± 0.96, 62653852.60 ± 0.95 and 62636860.55 ± 0.29 m2s−2, respectively. The vertical offsets of NAVD88, AHD, and HKPD with respect to the global geoid are estimated as −0.809 ± 0.090, 0.082 ± 0.093, and −0.731 ± 0.030 m, respectively.

Effect of datum system and datum hierarchy on the design of functional components produced by additive manufacturing: a systematic review and analysis

The evolving technology of additive manufacturing (AM) is posing novel challenges in manufacturing practice since nowadays functional, end-use components, and assemblies are produced by commercially available AM equipment. In order to safeguard the functionality and the interchangeability of a part, the designer must clearly denote a set of Geometrical Product Specifications (GPS) in the 3D model or in the engineering drawing by using the existing standards, e.g., ISO 1101, ISO 5459, and ISO 1660. Apparently, the family of ISO GPS standards that are currently used in design, manufacture, and verification has been developed so as to address the needs of traditional manufacturing processes rather than AM. Supported by numerous recent publications, the argument that current standardization does not sufficiently support the geometrical specification and verification of AM parts is getting more and more popular. The paper investigates and questions the need for the development of AM process-specific standards, related to the tolerancing and verification of mechanical components, as encountered with castings, forgings, and composites. Focusing on the most critical issue of datum establishment and datum hierarchy, the capability of existing tolerancing tools, as provided by the ISO GPS standards, to serve the process-specific AM needs is systematically examined. Moreover, major AM process-specific parameters such as build direction, layer thickness, support structure, and hatching plan are linked with the datum system designation and datum hierarchy tasks through a design case study and analysis. The major findings of this research pointing towards the establishment of AM-specific design-for-accuracy good practices are presented and discussed.

Computed tomography enabling virtual assembly

Computed tomography (CT) is the only dimensional measurement technology that captures holistic geometric information of the complete object. The availability of equally and densely distributed measurement data gathered by CT enables the consideration of local form deviations of the object's surface for the definition of a datum system. A datum system describes a coordinate system that is used for referencing geometrical tolerances. Therefore, the datum definition by an approximation of datum features is replaced by a fitting method called virtual assembly (VA), where the datum surfaces are registered in order to simulate the real, physical workpiece contact. Besides describing the theory, in this paper the method is evaluated using a linear guide assembly as an example that is compared to the real assembly of the object.

Formulation of Determining the Gravity Potential Difference Using Ultra-High Precise Clocks via Optical Fiber Frequency Transfer Technique

Based on gravity frequency shift effect predicted by general relativity theory, this study discusses an approach for determining the gravity potential (geopotential) difference between arbitrary two points P and Q by remote comparison of two precise optical clocks via optical fiber frequency transfer. After synchronization, by measuring the signal’s frequency shift based upon the comparison of bidirectional frequency signals from P and Q oscillators connected with two optical atomic clocks via remote optical fiber frequency transfer technique, the geopotential difference between the two points could be determined, and its accuracy depends on the stabilities of the optical clocks and the frequency transfer comparison technique. Due to the fact that the present stability of optical clocks achieves 1.6×10−18 and the present frequency transfer comparison via optical fiber provides stabilities as high as 10−19 level, this approach is prospective to determine geopotential difference with an equivalent accuracy of 1.5 cm. In addition, since points P and Q are quite arbitrary, this approach may provide an alternative way to determine the geopotential over a continent, and prospective potential to unify a regional height datum system.

Independence of metrological operations: the relevance of datum systems in GD&T

Nowadays most of the technical drawings, to be complete, must contain information that allows a correct reading about its functionality, and simultaneously the correct interpretation for manufacturing and assembly operations: It is desirable that information allow a definition of manufacturing and assembly sequences to create conditions that lead to more probabilities to avoid production errors. With the increase of the use of geometrical tolerances, the inspection operations are essentially coordinate metrology. So, as to manufacturing and assembly, also to inspection is imperative the definition of a correct sequence of operations, which are dependent of adequate datum systems, to avoid “circular” references that may be a source of coupled operations. An important condition to produce parts with quality is using the same reference systems (datum system) to all operations in manufacturing, in assembly and in inspection. This is obtained in the design phase and this is possible with GD&T - which is a true engineering language – using the independence concept of Axiomatic Design. In this paper is presented a case that illustrates the application of the independence axiom as a contribute to an adequate application of GD&T, which points to a correct sequence of inspection operations.

Definition of edges in correlation to abrasive flow machining as a finishing process

The transition of two geometrical features, like a radius or edge, is one part of the geometrical properties of a workpiece. For abrasive flow machining as a surface finishing process the characterization of the edge is important. Different processing parameters of the abrasive flow machining process are compared to geometrical properties within a test series. Based on 3D measurements and a datum system first results of an edge definition are derived. A histogram of radii provides a simplified method to separate the geometrical features to define the start and end of the edge.

Limitations in Primary Datum Plane Establishment Imposed by ISO Standard and a Proposal for an Improved Methodology

According to the ISO Geometrical Product Specification (GPS), a primary common datum plane of a part with two parallel offset planes is established by two datum targets on one plane and one datum target on another parallel plane. This process cannot function theoretically, because the primary common datum plane is the bisector plane of these two parallel planes which cannot be established by only 3 datum targets on different planes. This deficit causes ambiguous datum establishing process for a part and leads an irreproducible measurement results in practice. This paper suggests a new approach for a function-oriented, explicitly defined primary datum plane establishing process and offers a corresponding clarified and simplified notation system of datums and datum system. This research is based on the analysis of physical behavior and theoretical alignment of a part during the alignment process by measuring. As a result, an improved methodology for a stable and reliable primary datum plane establishment was developed.

Variation propagation modeling for locating datum system design in multi-station assembly processes

The locating datum system is an important content to uniform positioning throughout the design, manufacture, assembly, and inspection in dimensional management of sheet metal product. This paper develops a more accurate variation propagation model in multi-station assembly processes using a discrete time nonlinear state-space model to provide a mathematical representation for process-oriented locating datum system design. The proposed model which includes detail design parameters of locating datum system establishes the quantitative relation between Key Control Characteristics (KCCs) and Key Product Characteristics (KPCs) using the motion vector of the component-oriented reference system as a state variable. In addition, the nonlinear accumulated deviation of locating datum (holes and slots) on parts caused by the fixture deviation is considered in the process of modeling for the first time. And the effectiveness of the model is verified through comparison with widely used software, Variation System Analysis (VSA) in a four-station assembly process of a body side inner panel.

Requirements for Datum Systems in Computer Aided Tolerancing and the Verification Process

The recent attempt in Geometrical Product Specification to change from dimensional to geometrical tolerancing leads to a stronger focus on datum systems. Two aspects on the requirements for these and their effects on each other will therefore be discussed in this paper. A new approach to develop a functional datum system in the early stages of the methodical design process that is derived from the functional interaction of the indeterminate workpiece geometry within the outlined assembly group will be explained. It will also show current research results to overcome the gaps in ISO 5459 about extraction and association requirements for the verification process.

Quantifying the Contribution of Post-Processing in Computed Tomography Measurement Uncertainty

This paper evaluates and quantifies the repeatability of post-processing settings, such as surface determination, data fitting, and the definition of the datum system, on the uncertainties of Computed Tomography (CT) measurements. The influence of post-processing contributions was determined by calculating the standard deviation of 10 repeated measurement evaluations on the same data set. The evaluations were performed on an industrial assembly. Each evaluation includes several dimensional and geometrical measurands that were expected to have different responses to the various post-processing settings. It was found that the definition of the datum system had the largest impact on the uncertainty with a standard deviation of a few microns. The surface determination and data fitting had smaller contributions with sub-micron repeatability.

The Composition Principle of the Datum Reference Frame

The datum reference frame (DRF) is an orthogonal coordinate system used to locate the geometric features in tolerance technology and is a fundamental tool for tolerance analysis, tolerance validation and tolerance inspection. Additionally, establishment of the composition principle for DRF is an essential process for automation of tolerance technology. This paper presents the concept of a construction element of the DRF and the composition principle of DRF using the construction element. In this approach, the DRF is decomposed into three construction elements, i.e., a point, a line passing through the point, and a plane containing the line, and DRF is established by determining these three construction elements. The rules and algorithms used to determine the construction elements are established and the construction elements can be automatically established from the datum feature according to the rules and algorithm. The composition rules of the DRF are defined with the construction elements, and the DRF can be constructed automatically. The notion of and the establishment method for the construction elements can be used to validate the datum validity and the completeness of the datum system.

다목적 및 고활용성을 위한 객체지향 모델링 기반의 전자 측량기준점 모니터링 S/W 구현

표시점의 위치 및 고도를 표시하기 위한 기준점은 각종 측량에 유용하게 활용되는 장점을 가지고 있다. 그러나 기상 변화 및 지각 변화 등의 이유로 손 망실되는 사례가 급증하고 있으며, 무의미하게 방치되는 기준점이 늘어나고 있는 실정이다. 이에 본 논문에서는 기존 측량기준점의 활용성을 극대화할 뿐만 아니라 기준점 주변의 각종 환경 데이터 수집과 주변 지역의 지각변동 감지 기능 등이 포함된 다목적 전자 측량기준점 시스템모니터링 S/W를 설계 및 구현한다. 제안하는 S/W는 S/W의 재사용성 및 확장성을 충분히 지원할 수 있도록 객체지향 모델링 기법을 이용하여 설계하고 구현한다. 본 S/W에서는 전자측량 기준점 관리자를 위한 GUI 뿐만 아니라, 웹 및 모바일 사용자를 위한 GUI를 지원한다. 제공하는 GUI에서는 전자 측량기준점의 손 망실 예방 및 지각 변동을 감지하기 위해 측위된 위치정보 및 각종 센싱 정보를 데이터베이스에 실시간으로 저장하고 분석할 수 있도록 각종 데이터를 위한 그래프 GUI 지원한다. 아울러 QR-Code 및 RFID 인식 기능도 포함되어 있다. 마지막으로, 자이로센서를 이용한 지각 변화 감지 및 GPS 위치 오차율을 확인하기 위해 성능평가 결과를 제시한다. Datum point for displaying location and altitude of point has being advantage usefully in various measurement parts. However, datum point has been increasing loss cases owing to weather changes and stratum changes and neglecting meaninglessly. In this paper, we design and implement a multi electronic measurement system monitoring software with functions such as include maximize utilization of existing measurement datum system as well as collected various environment data and detection stratum changes of surround area. Proposed software is implemented to support that reusability and extensibility of software using object oriented modeling method. Our software supports a GUI for electronic measurement datum point administrator as well as for web user and mobile user. Our system can support a graph GUI for various data analysis and reposition in realtime to database that measured location information and various sensing information to prevent loss of electronic measurement datum point and to detected stratum changes. In addition, we include a QR code and RFID recognition function. Finally, we suggest performance evaluation result to confirm stratum changes detection and GPS location error rate.

A Digital Application for Geometrical Tolerancing Concepts Understanding

The general concept and main capabilities of the application Geometrical Tolerancing that has been consequently developed by the authors for a couple of years to effectively present and disseminate the ISO GPS system rules in industry and technical universities are presented. The application structure is shortly shown and discussed through a few screen shoots. The paper is focused on the approach used to present differences between requirements defined by the position tolerance of the two hole pattern without and with maximum material requirement with respect to the datum system created by three datum planes. The other cases of the two hole pattern tolerancing covered by the application are also briefly discussed. It should be noticed that visualizations of deviation measurements by usage of the various measuring methods starting from classical techniques employing indicators and measuring plate or hard gauges up the modern ones like FMM or CMM are just implemented in the application for selected tolerances.

Evaluation of True Position Using Coordinate Measuring Machine

The article makes a contribution to the ever-important topic of evaluating geometric deviations of tolerated forms related to the datum system using coordinate measuring machines with a touch probe system. The datum system consists of the coordinate system and the coordinates planes. An integral part of the article is the quantification of the true position tolerated form related to the datum system and experimental evaluation of the deviation with calculation of measurement uncertainty, according to STN EN ISO 15530-3.

Spatial reference systems

Geospatial data gained from different sources have to be referenced to the same geodetic datum and coordinate system. Forming of joint reference system enables easier update and geometric harmonization, access, exchange and use of geospatial data. Horizontal and vertical positions of points are no longer independent components. Development of GPS technology enabled their integration into the unique 3D datum. Geodetic datum is a base for determination the spatial reference system. Reference system is a group of fundamental points on the Earth surface with defined coordinates. The International Terrestrial Reference System (ITRS) is the most accurate global reference system. ETRS89 is used as the standard accurate GPS coordinate system in Europe. This system is a spine of every geographic and geodynamic project on the European territory, both on a national and international level.

Animated visualization of the maximum material requirement

The usage of animation technique applied as a powerful tool to explain the complex concept of the maximum material requirement (MMR) is shown. The concepts of datum system and the maximum material virtual condition envelope, that is located by theoretically exact dimensions are highlighted. The maximum material virtual condition state, that limits the collective effect of the feature maximum material size and the maximum acceptable geometrical deviation for that size is examined. The tolerances of perpendicularity and position with the maximum material modifiers applied in the tolerance frames for the toleranced features or respectively for the datum features are explored. The simplicity of the verification of the conformance with the specification employing the MMR by the gauge that represents the matting counter part is emphasized.