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Survey Review 53, No 381. November/December 2021

1. Accuracy assessment of RTK-GNSS equipped UAV conducted as-built surveys for construction site modelling
Sander Varbla, Raido Puust & Artu Ellmann

Regular as-built surveys have become a necessary input for building information modelling. Such large-scale 3D data capturing can be conducted effectively by combining structure-from-motion and unmanned aerial vehicles (UAV). Using a RTK-GNSS equipped UAV, 22 repeated weekly campaigns were conducted at two altitudes in various conditions. The photogrammetric approach yielded 3D models, which were compared to the terrestrial laser scanning based ground truth. Better than 2.8 cm geometry RMSE was consistently achieved using integrated georeferencing. It is concluded that the RTK-GNSS based georeferencing enables reaching better than 5 cm geometry accuracy by utilising at least one ground control point.

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2. Determining locations of corners of building structures in real time using harmonisation of various surveying methods – case study
Robert Krzyżek

Determination of Cartesian coordinates of building can be performed using various surveying methods. One of these methods is real-time measurement in RTN GNSS mode. Therefore, tests were carried out that led to surveying contractors being presented with an alternative of using RTN GNSS surveys to determine the location of a building with high reliability and accuracy. This solution involves the harmonisation of various surveying methods hereinafter referred to as the HMM algorithm. After using the HMM algorithm, linear deviations dL were obtained for the determined X, Y coordinates at the level of 0.03 m and the mean location errors of the corners of the building at the level of 0.02 m, which were not significantly different from the reference values. Test tests and their verification allowed to state that the HMM algorithm was very useful for determining the location of a building structure in real time.

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3. Geoid determination through the combined least-squares adjustment of GNSS/levelling/gravity networks – a case study in Linyi, China
Dongmei Guo & Zhixin Xue

A detailed discussion of the adjustment problems used to combine GNSS/levelling/gravity network data is provided in this paper. The two primary problems inherent to heterogeneous data networks, namely, parametric models that describe the datums and systematic distortions among the available data sets and stochastic models that describe the observational residuals, are described. For parametric models, a relationship between the transformation parameters and the effects of datums and systematic distortions inherent among different height data types is established based on a least squares criterion. For stochastic models, the stochastic errors in GNSS/levelling/gravity data are evaluated, and a Helmert variance component estimation approach is introduced to refine weighting models. Finally, the proposed model is applied to determine the hybrid geoid in Linyi, China. The numerical results validate the capability and effectiveness of the proposed combined adjustment technique for hybrid geoid computations, revealing an achievable external accuracy of ±1.22 cm compared with GNSS/levelling measurements, which can be increased by 0.44 cm compared with classic adjustments of GNSS/levelling/geoid height data.

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4. Intelligent vectorised architecture for performance enhancement of GNSS receivers in signal blocking situations
A. Tabatabaei, Z. Koohi, M. R. Mosavi & Z. Tabatabaei

Navigation in harsh environments mostly encounters many problems such as signal blocking due to a variety of obstacles around the receiver. Vectorised receiver has an architecture in which the channels can share the information. As a result, the strong channels aid the blocked one to reacquire the signal immediately after returning. However, if the output of a channel is undesirable, it may disrupt the operation of the system especially for the weak blocked channels. In this paper, an intelligent vectorised architecture is proposed to solve this problem. Three popular architectures including federated, adaptive, and vectorised are combined and then evidence theory is utilised to select the result with higher certainty. The experimental results in urban canyons show the improvements in signal availability and thermal noise performance.

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5. Real-time GNSS precise point positioning using improved robust adaptive Kalman filter
Abdelsatar Elmezayen & Ahmed El-Rabbany

Multi-constellation GNSS precise point positioning (PPP) typically uses the extended Kalman filter (EKF) for kinematic applications. Unfortunately, the obtained positioning accuracy in this approach is prone to errors caused by measurement outliers and the system’s dynamic model. An adaptive robust Kalman filter (RKF) was recently developed to mitigate these errors. However, RKF uses empirical values as detection thresholds for the outliers, which requires the measurements to be from the same constellation and of equal precision to obtain an optimal PPP solution. The classification robust adaptive Kalman filter (CAKF) has subsequently been developed to deal with measurements of different precisions, namely pseudorange and carrier-phase measurements. This paper proposes a real-time GPS/Galileo PPP system, which employs a modified version of CAKF called the Improved Robust adaptive Kalman Filter (IRKF). The positioning performance of GPS/Galileo PPP through the IRKF is initially verified in comparison with those obtained through the EKF, RKF, and CAKF using the Centre for Orbit Determination in Europe (CODE) final orbit and clock products in both of static and kinematic modes. The real-time GPS/Galileo PPP solution through the IRKF is then assessed in comparison with its near-real-time counterpart. The results indicate that when the IRKF approach is utilised, the positioning accuracy is significantly improved and the convergence behaviour is enhanced compared with results from EKF, conventional RKF, and CAKF. In the real-time mode, centimeter-level horizontal positioning accuracy is achieved under an open sky environment, while decimeter-level horizontal positioning accuracy is achieved under a challenging environment. On the other hand, decimeter-level accuracy is achieved for the vertical positioning component under all environmental scenarios. Moreover, the positioning accuracy of the real-time solution is comparable to the near-real-time counterpart.

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6. Towards standardisation of Turkish cadastral system using LADM with 3D cadastre
Hicret Gürsoy Sürmeneli & Mehmet Alkan

Cadastre in Turkey is executed as two-dimensional (2D) and parcel-based. The third dimension (3D) on land and real estate is shown in 2D on the map with permanent rights. The use of underground spaces cannot be registered. There are various problems in the registration and mapping of real estates that are under or above these excluded places. The research was motivated by some problems that have taken place in the Turkey 3D cadastre due to the inadequate spatial information systems. For this purpose, it is aimed to design a 3D cadastre country profile that takes into account the Turkish National Spatial Data Infrastructure (TUCBS in Turkish) land registry and cadastral data model and is compatible with the Land Administration Domain Model (LADM), which is defined within ISO 19152. In this study presents a detailed overview of the Turkish legal cadastre system and a proposal for realisation based on international standards.

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7. Maximum Tolerable Biases (MTBs) and hardly detectable points in least-squares adjustment
Jianfeng Guo

It is of vital importance to search for an objective quality metric which can provide insights into the geometric strength of the underlying adjustment model. The Minimal Detectable Bias (MDB) measure has been extensively used in geodesy and photogrammetry. However, MDB is a hypothetical quality measure. To this end, the Maximum Tolerable Bias (MTB) metric is introduced in this contribution. The definition of MTB measure is independent of the distribution of observables, the test statistics, the specified significance level and the given detection power for the one-sided hypothesis test. Consequently, MTB is an objective quality measure for least-squares adjustment models. Examination of the scaled version of MTB can reveal the hardly detectable data points. All the hardly detectable points should be removed before performing conventional outlier detection procedures.

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8. Book Review: Cadastre: principles and practice, by Roger Fisher and Jennifer Whittal with contributions, by Neil Guy, South African Geomatics Institute, 2020, pp. xxii and 840, ISBN 978-0-620-82878-9 R660, Cape Town
Richard Grover

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Survey Review 53, No 380. September/October 2021

1. Land reallocation model with simulated annealing algorithm
Ela Ertunç, Mevlüt Uyan & Vahit Tongur

Land consolidation project has many stages. Land reallocation is the most considerable stage in which many factors play a role and forms the basis of this project. In this study, a new optimisation-based reallocation model has been developed to realise block reallocation by evaluating the requests of landowners. The reallocation according to the developed method also reset the block spaces automatically. The most powerful aspect of the method is that while the reallocation phase in land consolidation projects takes weeks and months, this method can be done in minutes. This method contributes to projects in terms of time and cost.

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2. Horizontal coordinates transformation and residuals modelling on the territory of the Republic of Srpska
Slavko Vasiljević, Dejan D. Vasić, Oleg Odalović, Dragan Blagojević & Branko Milovanović

The paper describes the model for coordinate transformation between ETRS89 and old reference system in the Republic of Srpska. The Helmert’s parameters were estimated, based on a set of 1741 points. The average magnitude of residuals was 0.3 m per coordinate and they were homogeneous at the local level. The basic model was complemented by a corrections grid that uses bilinear interpolation. The accuracy of the transformed horizontal positions obtained by this model is about 10 cm. In this way, a link between the two reference systems has been established on the overall territory of the Republic of Srpska.

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3. Validation of GNSS baseline observation models using information criteria
Krzysztof Nowel, Sławomir Cellmer & Artur Fischer

This paper adapts and discusses the information criterion (IC) approach for the validation of baseline GNSS observation models in the context of outliers. Three IC methods are compared with the conventional procedure of iterative data snooping (IDS). To verify the reliability of the two considered approaches, several scenarios differing in: the magnitude and number of outliers, and the interval between measurement epochs were investigated. Generally, the IDS procedure achieved the highest rates of correct model specification when no outlier existed. However, as the number of outliers was increasing one of the IC methods was starting to achieve the highest rates.

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4. Optimising 2-parameter Lambert Conformal Conic projections for ground-to-grid distortions
Sergio Baselga

A Lambert Conformal Conic (LCC) projection with two true-scale parallels of latitudes ϕl and ϕu can be recast in a LCC projection with one standard parallel of latitude ϕ0 and scale k0, having the practical advantage that the same type of definition can be used for the two conformal projections universally used: LCC and Transverse Mercator (TM). While equations giving ϕ0 and k0 in terms ϕl and ϕu can be found in the literature, inverse relationships are not readily found. They are derived in the present paper. These may be necessary in views of the planned future definition of the United States State Plane Coordinate System (SPCS) 2022 for the users of particular mapping software requiring to specify the two latitude values instead of the central latitude and central scale. While map projection parameters are customary selected to minimise ellipsoid-to-grid distortions for a region, in some cases it could be more convenient to study and minimise ground-to-grid distortions. Also bearing in mind the design of SPCS 2022, we discuss the advantages and disadvantages of working with each type of distortion definition.

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5. A constrained extended Kalman filter based on LS-VCE formulated by condition equations with prediction of cross-covariances
Vahid Mahboub & Narges Fatholahi

A constrained extended Kalman filter (CEKF) based on least-squares variance component estimation (LS-VCE) is generally developed by condition equations since the proper prediction of dispersion matrices is one of the main bottlenecks in the KF algorithms. Here we investigate four problems which have not been simultaneously considered yet. These problems are examination of non-linearty of dynamic model, VCE, general non-linear state constraints and fairly general stochastic model. Although a few contributions proposed some adaptive KF in particular based on Helmert’s VCE method, they developed their filters for special problems with some restrictive conditions such as independence of all variables and/or linearity of the dynamic model. Also some of these filters did not apply VCE methods to all parts of the dynamic model. In this contribution, we try to overcome all of these restrictions. Moreover, LS-VCE method gives some added advantages over other VCE methods. First the new formulation of CEKF is developed by condition equations with prediction of all possible cross-covariances as algorithm 1. Then the LS-VCE method is applied to it after some modifications which results in an adaptive constrained extended Kalman filter (ACEKF) as the second algorithm.

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6. A copula approach for sea level anomaly prediction: a case study for the Black Sea
Ahmet Yavuzdoğan & Emine Tanır Kayıkçı

Forecasting future sea levels is of great importance in terms of the conservation of coastal areas, monitoring and forecasting coastal ecosystems, and the maintenance and planning of coastal structures. In addition, highly accurate sea level forecasts allow adequate water management policies and coastal infrastructures to be developed. Today, many methods, such as harmonic analyses, artificial neural networks and support vector machines, are used to predict sea level anomalies. In this study, a novel approach based on Copula functions is presented for the prediction of sea level anomalies. The primary purpose of this study is to examine the applicability and capability of Copula-based prediction models in predicting short-term variations in the sea level. The minimum 95% correlations and minimum 22 mm RMSE values in sea level anomaly predictions during the testing period indicate that the Copula approach can be a powerful tool in the prediction of sea level anomalies.

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7. Results from the first strapdown airborne gravimetry campaign over the Lake District of Turkey
Mehmet Simav

The first production-oriented strapdown airborne gravimetry in Turkey was carried out during fall 2019 over the Turkish Lake District. Comparisons at the large amounts of crossover points yield RMSE values below 1 mGal level, and the external comparison with the latest high-resolution global geopotential model (GGM) shows a mean bias of around 1.1 mGal where the largest deviations are observed on the areas that could not be resolved by the GGM. The incorporation of new airborne data into the gravity field computations is supposed to reduce the errors stem from the data voids and enhance the maps for better interpretations.

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8. An iterated reweighting total least squares algorithm formulated by standard least-squares theory
Wuyong Tao, Xianghong Hua, Peng Li, Fei Wu, Shaoquan Feng & Dong Xu

If both the coefficient matrix and the observation vector are affected by noise, a total least-squares algorithm should be applied to obtain the solution. However, if they are also contaminated by outliers, the solution of the algorithm will seriously deviate from the true values. Therefore, the effect of outliers needs to be eliminated. For this purpose, the robust estimation is introduced into the total least-squares algorithm, developing a new robust weighted total least-squares algorithm. Simultaneously, considering the robustness of structure space, the standardized residuals are utilized to construct the weight function. Finally, the robustness and efficiency of this algorithm are verified by three experiments involving line-fitting and 2D affine transformation.

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9. Indoor space as the basis for modelling of buildings in a 3D Cadastre
Jernej Tekavec, Marjan Čeh & Anka Lisec

This paper presents a 3D cadastral data model for buildings. A review of the relevant research shows that a common concept in the 3D cadastre domain is using the legal building unit, i.e. real property unit, as the core modelling unit. Alternatively, this study proposes using indoor space as a core modelling unit. The main reason is to enable the efficient integration of cadastral data with the data from other domains. On the conceptual level, the model is linked to the Land Administration Domain Model (LADM). The integration options are studied for three international standards: IFC, CityGML and IndoorGML.

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Survey Review 53, No 379. July/August 2021

1. A correlational inference-based unscented total Kalman filter for integrated navigation
Hang Yu, Jian Wang & Bin Wang

An unscented total Kalman filter (UTKF) estimator with nonlinear dynamic errors-in-variables (DEIV) model is derived based on correlational inference. The proposed UTKF considers all random errors in both system and observation equations and is a Jacobian matrix free alternative to the existing TKF estimators. In particular, this estimator is applied to the inertial navigation system (INS)/ultra-wideband (UWB) integration, in which the marginalised unscented transformation (MUT) as well as the use of generalised Rodrigues parameter (GRP) for attitude updates are embedded into the UTKF to improve the computational efficiency and deal with the dimensional mismatching problems. Furthermore, a theoretical analysis to the effects of DEIV model on total Kalman filter is given. Simulation test has been conducted to compare the performance of UTKF and standard unscented Kalman filter (UKF) in terms of attitude, velocity and position errors. The results demonstrate the feasibility and effectiveness of the proposed estimator.

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2. An adaptive filtering algorithm of multilevel resolution point cloud
Youyuan Li, Jian Wang, Bin Li, Wenxiao Sun & Yanyi Li

The existing filtering methods for airborne LiDAR point cloud have low accuracy. An adaptive filtering algorithm is proposed which is improved based on multilevel resolution algorithm. First double index structure of Octree and KDtree is established. Then the initial reference surface is constructed by ground seed points. According to the slope fluctuation situation, the grid resolution of the ground referential surface is adjusted in an adaptive way. Finally, the refined surface is formed gradually by multilevel renewing resolution to provide filtered point cloud with high accuracy. Experimental results show that the error of Type II can be effectively reduced, the average Kappa coefficient increases by 0.53% and the average total error decreases by 0.44% compared with multiresolution hierarchical classification algorithm. The result tested by practically measured data shows that Kappa coefficient can reach 90%. Especially, it maintains advantages of high accuracy under complex topographic environment.

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3. Design and development 3D RRR model for Turkish cadastral system using international standards
Mehmet Alkan, Hicret Gürsoy Sürmeneli & Zeynel Abidin Polat

The concepts of three-dimensional cadastre (3D) and property ownership led to increased interest in land use management and research towards the end of the 90s. Within the scope of these studies, international standards and definitions have been realised. In Turkey, there are some academic studies available. However, there are not many studies conducted on an institutional basis. Turkey cadastre carried out by the General Directorate of Land Registry, and Cadastre (GDLRC) are kept. In this context, a 3D RRR (Right, Restriction and Responsibility) for Turkey-based cadastral data model design and development is essential in terms of not constitute a base for the study. The fact that these studies are in the context of LADM and ISO standards and OGC is very important in terms of the fact that the cadastral system is related to international standards.

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4. Improved wavelet neural network based on change rate to predict satellite clock bias
Xu Wang, Hongzhou Chai, Chang Wang, Guorui Xiao, Yang Chong & Xiaoguo Guan

To develop a high-accuracy method for predicting SCB based on the analysis of the shortcomings of the wavelet neural network (WNN) model, an improved WNN model to predict SCB is proposed herein. The activation function of the WNN is constructed by combining the advantages of Shannon and Gauss ‘window’ functions to improve the WNN. Finally, the improved WNN model is used to predict SCB. The results show that the proposed model has the highest prediction accuracy, stability, and robustness. Moreover, it effectively predicts long-time SCB data. Therefore, the proposed model can predict SCB with high accuracy.

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5. Cadastral updating: the case of Turkey
Okan Yildiz & Çağrı Erden

Turkey has produced cadastral data using different methods until today. Therefore, not all the data are the same standard in quality. Three different methods (correction, digitisation and updating) have been applying for update. Choosing the right method will save significant time and cost. Also, surveying the fixed boundaries will give the most accurate results. However, this is not always possible. The distribution of fixed boundaries is only 46.39% in the application area. So, fixed boundaries should be measured as far as possible. The places where the digitisation and updating methods will be applied should be determined very well.

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6. Implementing a mass valuation application on interoperable land valuation data model designed as an extension of the national GDI
Arif Cagdas Aydinoglu, Rabia Bovkir & Ismail Colkesen

The main purpose of this study is to propose an interoperable land valuation data model for residential properties as an extension of the national geographic data infrastructure (GDI) and to make mass valuation process applicable with the use of machine learning approach. As an example, random forest (RF) ensemble algorithm was implemented in Pendik district of Istanbul to evaluate the prediction performance by using thematic datasets compatible with the data model. This study provides a methodology for various urban applications and robustness of the algorithm increases the prediction of the real estate values with the use of qualified datasets.

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7. Estimation of parameters of probability integral method model based on improved fireworks algorithm
Lei Wang, Kegui Jiang, Tao Wei, Chuang Jiang, Jianfeng Zha & Shenshen Chi

How to accurately estimate the probability integral parameters based on the measured data has always been a difficult point in the application of the probability integral method. This paper introduced FWA into the solution of the probability integral method for the first time. Based on the analysis of strengths and weaknesses of FWA, IFWA (improved fireworks algorithm) was proposed. Then, the IFWA-based inversion model for probability integral parameters (MIFWA) was constructed by the fusion the mining subsidence law and probability integral method. Experiments show that MIFWA has better performance in anti-errors of the observation and the geological mining generalization.

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Survey Review 53, No 378. May/June 2021

1. Increasing efficiency of the robust deformation analysis methods using genetic algorithm and generalised particle swarm optimisation
Mehmed Batilović, Zoran Sušić, Željko Kanović, Marko Z. Marković, Dejan Vasić & Vladimir Bulatović

The paper analyses the possibility of increasing efficiency of the Iterative Weighted Similarity Transformation (IWST) method, which is a prototype of classic robust methods, using global optimisation approach instead of classical one, available in the literature. For the purpose of solving the optimisation problem of the IWST method, in addition to the Iterative Reweighted Least Squares (IRLS) method, the Genetic algorithm (GA) and Generalised Particle Swarm Optimisation (GPSO) algorithm were applied, in order to overcome some flaws of IRLS method. Experimental research was performed based on the Monte Carlo simulation using the mean success rate (MSR) on the example of the geodetic control network for monitoring the Šelevrenac dam in the Republic of Serbia. By using the GA and GPSO algorithms, the overall efficiency of the IWST method has been increased by about 18% compared to the IRLS method. Also, it has been determined that the efficiency of the IRLS method significantly reduces with the increase in the number of displaced potential reference points (PRPs), while the GA and GPSO algorithms’ efficiency does not change significantly. The values of overall absolute true errors due to the increased number of displaced PRPs in the GA and GPSO algorithms did not change notably while with the IRLS method their values increased significantly.

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2. Impact of observation sampling rate on Multi-GNSS static PPP performance
Berkay Bahadur & Metin Nohutcu

The main objective of this study is to investigate the impact of observation sampling rate on the PPP performance, in terms of positioning accuracy and convergence time, under different multi-GNSS combinations. For this purpose, daily observation datasets collected at ten IGS-MGEX (International GNSS Service-Multi-GNSS Experiment) stations during the 1-week period of January 6-12, 2019 with 1-s, 5-s,15-s, and 30-s sampling rates were processed under three different PPP processing modes, namely GPS-only, GPS/GLONASS and multi-GNSS. The results indicate that the use of high-rate observation sampling improves the PPP performance for all processing modes significantly. The contribution of increasing sampling rate, both for positioning error and convergence time, is more prominent in shorter periods, especially within the first 30 min for all processing modes. Finally, the multi-GNSS processing mode with the 1-s observation sampling rate has the best PPP performance and offers a considerable prospect for the GNSS applications.

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3. Quality evaluation of linear inequality constrained estimation by Monte Carlo sampling in parameter space
Songlin Zhang, Jingchang Li, Kun Zhang & Jie Han

Existing approaches that describe the quality of inequality constrained estimates are not sufficient to meet the demands of inequality constrained least-square problems. We reconstruct the existing Monte Carlo method by converting the sampling space from observation space to parameter space, and propose a workflow to improve the computational efficiency. The proposed method is verified by a straight-line fitting example with independent and dependent inequality constraints, and the constraints have different intensities. The results show that the proposed workflow has higher computational efficiency than the existing workflow and that the saved time is almost linearly related to the intensity of the inequality constraints.

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4. Bias in least-squares adjustment of implicit functional models
Michael Lösler, Rüdiger Lehmann, Frank Neitzel & Cornelia Eschelbach

To evaluate the benefit of a measurement procedure onto the estimated parameters, the dispersion of the parameters is usually used. To draw objective conclusions, unbiased or at least almost unbiased estimates are required. In geodesy, most of the functional relations are nonlinear but the statistical properties of the estimates are usually obtained by a linearised substitute-problem. Since the statistical properties of linear models cannot be passed to the nonlinear case, the estimates are biased. In this contribution, the bias of the parameters as well as the bias of the dispersion in nonlinear implicit models is investigated, using a second-order Taylor expansion. Nonlinear implicit models are general models and are used, for instance, in the framework of surface-fitting or coordinate transformation, which considers errors for the coordinates in source and target system. The bias is introduced as a further indicator to validate the benefit of an adapted measurement process using more precise measuring instruments. Since some parametrisations yield an ill-posed problem, also the case of a singular equation system is investigated. To demonstrate the second-order effect onto the estimates, a best-fitting plane is adjusted under varying configurations. Such a configuration is recommended in evaluating uncertainties of optical 3D measuring systems, e.g. in the framework of the VDI/VDE 2634 guideline. The estimated bias is used as an indicator whether a large number of poor observations provides better results than a small but precise sample.

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5. Efficient point cloud corrections for mobile monitoring applications using road/rail-side infrastructure
Hao Jing, Xiaolin Meng, Neil Slatcher & Graham Hunter

Light Detection and Ranging (LiDAR) systems are known to capture high density and accuracy data much more efficiently than other surveying methods. Therefore they are used for many applications, e.g. mobile mapping and surveying, 3D modelling, hazard detection, etc. However, while the accuracy of the laser measurements is very high, the accuracy of the resulting 3D point cloud is greatly affected by the geo-referencing accuracy. This is especially problematic for mobile laser scanning systems, where the LiDAR is installed on a moving platform, e.g. a vehicle, and the point cloud is geo-referenced by the data provided by a navigation system. Owing to the complexity of the surrounding environments and external conditions, the accuracy of the navigation system varies and thereby changes the quality of the point cloud. Conventional methods for correcting the point cloud accuracy either rely heavily on manual work or semi-automatic registration methods. While they can provide geo-referencing under different conditions, each has their own problems. This paper presents a semi-automated geo-referencing trajectory correction method by extracting features from the pre-processed point cloud and integrating this information to reprocess the navigation trajectory which is then able to produce better quality point clouds. The method deals with the changing errors within a point cloud dataset, and reducing the trajectory error from metre level to decimetre level, improving the accuracy by at least 56%. The accuracy of the regenerated point cloud then becomes suitable for many accuracy-demanding monitoring and change detection applications.

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6. An institutional analysis of land readjustment in Turkey
Volkan Çağdaş & Hans Joachim Linke

Land readjustment is a property formation process which rearranges the geometries of cadastral parcels and immovable property rights thereof in accordance with land use plans. The literature presents several studies which analyze the effectiveness of land readjustment in various countries. This article aims to contribute to the existing work by presenting an analysis for the Turkish case study based on the Institutional Analysis and Development Framework developed by Elinor Ostrom. For this purpose, the organizational procedures and institutional arrangements that frame land readjustment in Turkey are examined. This analysis reveals the areas of possible reform that may facilitate a transparent and accountable, participatory and inclusive, fair and cost-effective development of land.

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7. Estimators of covariance matrices in Msplit(q) estimation
Z. Wiśniewski & M.H. Zienkiewicz

This paper proposes methods for the determination of covariance matrices of Msplit(q) estimators. The solutions presented here allow Msplit(q) estimation to be supplemented by the operations from the domain of accuracy analysis (especially that concerning estimators of parameters). Theoretical forms of covariance matrices of Msplit(q) estimators were established using the empirical influence functions and the equivalent covariance matrices of observation errors. The estimators of covariance matrices of Msplit(q) estimators were determined based on the adopted statistical observation models and their random errors. The unknown variance coefficients of these models were estimated employing the principles of square estimation.

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8. Velocity estimation performance of GNSS online services (APPS and AUSPOS)
Ömer Gökdaş & M. Tevfik Özlüdemir

Before now, the various studies that have been undertaken to investigate the positioning performance of GNSS Online Services have been limited with regard to both time and number of sessions. Within the scope of this study, the accuracy of the velocity models estimated by APPS and AUSPOS are analysed using a wider period. Local ISKI CORS Network stations are used as the subject. To generate true values for an accurate comparison, 129 sessions with BERNESE (v5.2) software were conducted between 2008 and 2019. A linear trend was determined by using least-squares adjustment to obtain true velocity values. To test the reliability of the true velocity values, seasonal, semi-annual and annual oscillation movements have been examined. Additionally, the coherence of the velocity model with the sample data and compliance with the tectonic plate has been investigated. For GNSS Online Services, 34 sessions were carried out over the same timescale, and the velocity model was estimated. A Z-test with a 0.05 significance level was used to examine the performance of APPS and AUSPOS velocity values. As a result, the estimated true velocity model shows high compliance with sample data and the tectonic plate; no seasonal, semi-annual or annual oscillation movements were identified. According to the study’s statistical test, the velocity model of APPS solutions performs slightly better than that of AUSPOS. However, both services show high performance in the velocity determination. In summary, the usability of GNSS Online Services in determining velocity has been shown with this study.

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Survey Review 53, No 377. March/April 2021

1. A practical method for calculating reliable integer float estimator in GNSS precise positioning
Xianwen Yu, Siqi Xia & Wang Gao

To overcome the problem that a fixed estimator is contaminated by a system error for the ambiguity be misjudged in the GNSS precise positioning, a reliable integer float estimator is recommended. Accordingly, the method for determining a finite number of integer vectors based on a given reliability probability is proposed, the formula for calculating the variance matrix of the recommended estimator is derived, and the judgment method of the estimator’s availability is proposed. The detailed process and the effect of the method are also demonstrated using examples to facilitate user application.

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2. Object-based geographical data model for determination of the cemetery sites using SWOT and AHP integration
Yakup Emre Coruhlu, Volkan Baser & Okan Yildiz

While in the times of feudalism the land was a source of wealth, having only a financial value, today it has become valuable as a limited resource. It should not be forgotten land is becoming scarce, so it must be very well planned and managed. In order for cemeteries to be sustainable and effectively manageable, it is essential to collect, store and examine information related to these sites like other types of areas. A geographic database design was developed in order to identify and resolve existing problems related to cemetery management nationwide in accordance with the ISO 19152 standard.

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3. Receiver DCB analysis and calibration in geomagnetic storm-time using IGS products
Jianfeng Li, Dingfa Huang, Yinghao Zhao & Abubakr Hassan

Solar activity and geomagnetic storm cause ionospheric disturbance and affect the GNSS positioning accuracy, which this effect cannot be ignored. The reliability depends mainly on differential code bias (DCB), when estimating the total electron content (TEC) with GNSS pseudorange observations. This study analyzes the variation characteristics of receiver DCB (RDCB) during a strong geomagnetic storm to determine whether the RDCB estimation is affected by space weather. Results show that the RDCB dispersion of low-latitude stations is larger than that of other areas. On the storm day, the RDCB standard deviation (STD) exhibits a peak characteristic and the number of RDCB abnormal stations is significantly more than that on quiet day. Analysis shows that the RDCB abnormality is caused by the ionospheric model misalignment during the ionospheric disturbance. By correcting the RDCB, the RDCB STD is reduced by 43.10%. Thus, the model correction can improve the estimation accuracy of RDCB during geomagnetic storm.

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4. Calibration of CCD sensors mounted on geodetic measuring systems
Lajos Völgyesi & Gyula Tóth

If the eyepiece of a total station is replaced with a CCD sensor, the most important task is to calibrate the instrument. Calibration establishes a connection between the readings on the horizontal and vertical circles of the total station and the readings in the coordinate system of the CCD sensor. Our calibration method uses a collimator in a few meters distance, which serves as a target at infinity during the calibration. We tested the calibration using a QDaedalus astrogeodetic measuring system. The optimal number of calibration measurements, the optimal raster size, and the temperature dependence of the measurements were investigated.

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5. A feature-preserving point cloud denoising algorithm for LiDAR-derived DEM construction
Chuanfa Chen, Yuan Gao & Yanyan Li

To attenuate positional errors of LiDAR-derived datasets for constructing digital elevation models (DEMs), a feature-preserving point denoising algorithm (F-PDA) is developed in this paper. F-PDA includes three main steps: surface normal estimation, normal filtering and point position update. Numerical tests with two simulated surfaces indicate that F-PDA is always more accurate than kriging and natural neighbour. Furthermore, F-PDA has a high effectiveness of preserving feature lines. Real-world examples of interpolating LiDAR samples demonstrate that F-PDA can best retain both prominent and subtle terrain features, while faithfully removing errors in mountainous and flat regions. Moreover, it outperforms some well-known interpolation methods.

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6. Equivalence properties of 3D conformal transformations and their application to reverse transformations
A. C. Ruffhead

Seven-parameter conformal coordinate transformations, also known as Helmert transformations, can be constructed in more than one way. Two possible orderings of the rotations are in common use, giving rise to Helmert versions 1 and 2. It is demonstrated how the rotation parameters of either version can be converted into the rotation parameters of the other. This is useful when software is designed for the other version. It also enables computation of the same-formula inverse transformation by changing the sign of the equivalent ‘other version’ parameters. These results were primarily intended for conformal transformations between geodetic datums. They can, however, be extended to coordinate transformations in disciplines such as photogrammetry where rotations sometimes exceed 90 degrees.

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7. A highly adaptable method for GNSS cycle slip detection and repair based on Kalman filter
Xianwen Yu & Siqi Xia

The cycle slip detection and repair are crucial steps in the preprocessing of GNSS carrier phase observation. Currently, however, there are few cycle slip detection and repair methods that can meet the data processing needs for diverse situations. To solve this problem, a highly adaptable cycle slip detection and repair method is proposed. First, a cycle slip detection equation is established using the pseudo-range and carrier double-differenced (DD) observations; the state equation is developed based on the satellite-ground distance. Then, a Kalman filter estimation model is established by joining the two equations. Subsequently, the cycle slip can be detected and repaired. Finally, the state parameters are refined in accordance with the conditional distribution. According to the results of the example, all the simulated cycle slips are detected and repaired by the method proposed. It shows that the method can meet the data processing needs for multiple situations.

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8. A review of universal hydrographic data model
Jing Duan, Xiaoxia Wan & Jianan Luo

The Universal Hydrographic Data Model is a new generation of marine geographic information data model, referred to as S-100 standard. In addition to supporting Electronic Navigational Charts (ENC) production, S-100 can be used as a Geographic Information System standard to model all maritime objects. Therefore, it is necessary to carry out a comprehensive study on S-100. In this review, we begin with a succinct overview of the history and development of S-100. Then we discussed the problems of S-100 and the corresponding solutions. Finally, some research directions of S-100 are proposed to provide reference for future research and application.

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Survey Review 53, No 376. January/February 2021

1. Urban land speculation; failure of land market
B. S. Gemeda, B. Girma Abebe & F. Eckardt

This article is intended to examine the nature of urban expansion and development from a land speculation and urban sprawl perspective. Survey and case study approach were used to achieve this aim. As urban territory extends into adjacent periurban areas, speculators keep their land out of the current market so that developers of land and buildings must bypass it and home buyers should travel further distance to buy new lands and houses. This extra distance creates additional costs by increasing the cost of development, operation and travel. The finding of this article concludes that the speculators who held their land out off the market and received an average land value increase of about $230 per m2 each year generated extra social costs which they did not pay about $1,810 per m2 each year.

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2. Derivation of rigorously-conformal 7-parameter 3D geodetic datum transformations
A. C. Ruffhead

This paper proposes a new method of deriving rigorously-conformal 7-parameter 3D coordinate transformations between geodetic datums. The problem of linearisation is reduced by distance analysis which provides an estimate of scale-change. The resulting 6-parameter transformation is linearised to enable an initial least-squares estimate of the rotation parameters. The 6-parameter transformation is then re-linearised to obtain a least-squares estimate of the corrections to the rotations. The validity of the scale-change estimate can be tested and is verified in almost all cases. The exception is transformations covering very small areas where short distances maximise the impact of measurement errors in the control data. Even there, the method can be adapted to optimise the transformation. The method can also be used to obtain pseudo-optimal conformal transformations that provide a closest fit to published Bursa-Wolf transformations.

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3. GPS + Galileo + QZSS + BDS tightly combined single-epoch single-frequency RTK positioning
Shaolin Zhu, Dongjie Yue, Jian Chen & Zhiqiang Liu

The multi-GNSS fusion makes positioning more reliable and accurate. Considering the signal difference of different systems, GPS + Galileo + QZSS + BDS tightly combined double-difference model (TCDDM), including function and stochastic model, is proposed. The proposed model fully utilizes the overlapping frequency signals of various systems, and thus to enhance positioning model when DISBs are known beforehand. The observations of 3 ultra-short (1~10 m) and 3 short (4~10 km) baselines were processed by self-programming software, and the single-epoch single-frequency RTK performance using different system-combined models was evaluated by ambiguity-fixed correctness rate (ACR) and positioning accuracy. It demonstrated that three- and four-system TCDDM were superior to their corresponding loosely combined double-difference model (LCDDM) for ACR and positioning accuracy especially at high cut-off elevation. Moreover, four-system TCDDM had the best RTK performance obtaining average ACRs of 100% and 97.6% even at 25° cut-off elevation for ultra-short and short baseline, respectively.

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4. Single point positioning using full and fractional pseudorange measurements from GPS and BDS
Sihao Zhao, Xiaowei Cui & Mingquan Lu

In conventional global navigation satellite system (GNSS) receivers, full pseudorange measurements are usually required to complete a single point position fix, which takes longer time than obtaining fractional pseudorange measurements. In order to shorten the time to first fix and improve the position accuracy during cold or warm start of a dual-constellation GNSS receiver, we propose a positioning algorithm using at least four full pseudorange measurements from one constellation and fractional measurements from either or both constellations. Theoretical rapid position results can be obtained with an identical accuracy to that of the conventional method using full measurements. Tests with simulated and real Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) data validate the performance of the proposed approach.

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5. Determination of the under water position of objects by reflectorless total stations
Štefan Rákay, Slavomír Labant & Karol Bartoš

When surveying through a water surface, a distortion of several centimetres caused by the refraction and the change in the velocity of the electromagnetic waves can be observed. Therefore, neither the position nor the height of an underwater point (object), which can be seen from above the water surface, is correctly measured. The authors want to point out the magnitude of geometric errors when measuring to points under water as well as the computation of correct under water positions of points from measurement through a water layer. A practical experiment was performed for a water depth of 0.16 m.

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6. Global gravity models and the Ghanaian Vertical Datum: challenges of a proper definition
C. I. Kelly, S. A. Andam-Akorful, C. M. Hancock, P. B. Laari & J. Ayer

This paper analyzes errors in satellite gravity and GPS/trigonometric benchmarks (BMs) in relation to defining the Ghanaian Vertical Datum (GhVD). Results indicate that synthesized gravity introduce approximately 5 mm of error to corrected heights. However, large errors in BMs render them unsuitable for applications, including properly defining the GhVD. Overall, normal-orthometric corrections were of the order of a few millimetres, with comparatively larger Helmert orthometric and normal corrections. Accordingly, the most suitable heights for the GhVD are the normal-orthometric heights, with the geopotential of the Helmert orthometric heights, 62636861.534±2.27 m2 s−2, suggested as the potential of the GhVD.

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7. Application of baseline constraint Kalman filter to BeiDou precise point positioning
Xiaoguo Guan, Hongzhou Chai, Guorui Xiao, Chunhe Liu & Mingchen Shi

This paper proposes a baseline constrained PPP method to enhance the performance. The approach is based on constrained Kalman filter, and applied to BeiDou PPP in static, pseudo-kinematic, real kinematic modes. Both zero baseline and short baseline constrained PPP are verified in static mode, while a marine geodesy environment is designed to evaluate the performance in kinematic mode. The experiment results show that, compared to the PPP without constraint, the baseline constrained PPP can significantly improve the positional accuracy. Furthermore, the accuracy of baseline constrained static PPP can reach centimetre level, while the kinematic PPP can reach decimetre level.

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8. Evaluating success factors in the land readjustment applications: a case study of Trabzon Province, Turkey
H. E. Colak & T. Memisoglu

Land Readjustment plans (LR) provide tools for taking control of land development and construction, while organising social, cultural and technical infrastructure. In Turkey, LR applications, Pursuant to Law No. 3194, enable the creation of regular planned urban developments. The success of LR applications involves a comprehensive knowledge about the rules and relationships of the legal and community aspects of society. In this context, LR applications must be addressed and analysed by considering the success factors. In this study, LR application process was analysed to determine a set of quantitative factors in the Trabzon Province in Turkey. Cadastral and LR plans were reviewed to determine the success factors. By determining the quantitative factors: the correct regulation limits, an appropriate change in position of the parcel, the accuracy of the Development Readjustment Share account, the correctness of Public Partnership Share interruptions and the construction of the appropriate parcels, the success of LR applications were tested for pilot sites and comparisons were made with graphics.

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9. The determination of the true geometrical form of Great Ephesus theater, Turkey by using field surveys
Ozan Arslan & Orhan Kurt

The current deals with the determination of the ‘true’ geometrical shape of the Great theatre of Ephesus, which is the largest theatre in Asia Minor. To detect the geometrical form of the theatre a precise point dataset was created using terrestrial measurements performed directly on the theatre site. The well-known ellipse and circle fitting algorithms were presented for detecting the precise geometrical shape of the amphitheatre rings. The study reveals that ellipse geometry fits well to the theatre arcs that is amphitheatre rings are generally elliptical in shape. The precise metric values of the parameters of the geometrical shape were computed to characterise theatre features.

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10. Variations of precipitable water vapor using GNSS CORS in Thailand
Chokchai Trakolkul & Chalermchon Satirapod

This research aims to analyze variation in a time series of Precipitable Water Vapor (PWV time series) using data at 11 widely-distributed Continuously Operating Reference Stations (CORS) in Thailand. In this paper, the PWV time series is estimated based on data from 2007 to 2015, used to monitor trends and seasonal variations. Significant annual variations of PWV are found at all GNSS stations, with amplitude from 6 to 19 kg/m2. The variations between the annual amplitudes of PWV in the South and near the ocean coasts are generally smaller than in the inland regions. The phase shift of annual PWV variation is about −0.43 (around July, rainy season). The comparison of PWV and 24-hour cumulative rainfall data showed that the rainy season (running from around mid-May to the end of October) exhibits the slightest swing, and the highest average amount of PWV. These results are consistent with the 24-hour cumulative rainfall data.

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