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Survey Review 52, No 375. November/December 2020

1. Cadastral development in Norway: the need for improvement
Leiv Bjarte Mjøs

Cadastral systems provide important information for the public and private sectors. To understand the functions and impacts of a cadastral system one needs to understand its development. The Norwegian cadastral system has its origins in the 1600s and is defined as a German-style cadastral system. In the early 1800s, an economic survey was initiated in the kingdom of Denmark-Norway to modernise the tax cadastres. After the defeat in the Napoleonic wars, Norway entered into a union with Sweden in 1814 and the survey was stopped. Consequently, cadastral mapping would not be introduced in Norway until 1960, and at that time photogrammetric methods with poor quality control were used. Land subdivisions were undertaken by laymen until 1980. The paper describes cadastral development in Norway, challenges that have arisen and how they can be addressed. Measures to improve the system are proposed.

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2. Displacement monitoring of upper Atbara dam based on time series InSAR
Q. Q. Wang, Q. H. Huang, N. He, B. He, Z. C. Wang & Y. A. Wang

Dam is an important part of engineering structure, in the process of dam construction, the dam monitoring is crucial since water erosion and time-dependent motion may cause deformation. Traditional monitoring methods are time-consuming and labour-intensive. However, Interferometric Synthetic Aperture Radar (InSAR) can provide precise and spatially dense information on slow deformations. This research investigated the longest earth-rock-fill dam in Sudan to determine the spatial and temporal deformations Sentinel-1A descending SAR images were further used to analyse the issues mentioned above. The results suggested that the dam existed the maximum displacement with a value up to 190 mm on the dam crest. Besides, the selected sections along the riverbed of the dam were analysed and the RMSE was approximately 2 mm/year. The results were in good agreement with the in situ measurements, indicating the advancement of time series InSAR in dam deformation monitoring.

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3. Acquisition of weak GPS signals using wavelet-based de-noising methods
Mohaddeseh Sharie, Mohammad-Reza Mosavi & Narjes Rahemi

Various factors cause GPS signals to be weakened in their path from satellites to receiver. This phenomenon leads to some problems in the normal stages of the positioning process, including acquisition stage. The wavelet transform is one of the tools that have been employed in several methods to improve receiver’s sensitivity in confronting weak GPS signals. Choosing an appropriate threshold plays a key role in the performance of this de-noising method. This study presents two methods for selecting an appropriate threshold. In the first method, the threshold is determined based on the statistical information extracted from the signal. On the other hand, the threshold in the second method is determined by type II fuzzy sets. The results show that employment of these two methods increases SNR gain as well as the range of acquirable SNR which makes signals acquisition with minimum post-correlation SNR of −6.5dB in a GPS receiver possible.

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4. A claim to territory: hybrid solutions to securing land rights in the continuum between socially based and individualised tenure
David Goodwin

Rights to land situated in the continuum between socially based (or communal) and individualised (or formal or western) tenure are often weak, and right holders may derive security both from traditional ceremonies and from mimicking elements of individualised tenure. This research investigates the way that entries Zimbabwe’s development levy register – which was never intended as a title register – can help to secure land rights. A nuanced understanding is sought of issues involved in paying (or not paying) development levies at district and village level, and of how parts of the system are used by right holders as a first-stage cadastre capable of delivering a degree of land right security.

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5. OPUS versus Russian online GNSS data processing service
M. Dorsey & M. Berber

In the recent past, the information and analysis centre of Russia began providing GNSS static data processing operating in experimental mode. Since this service processes data in static mode only, the service is compared with the OPUS static service. OPUS produces better results for the points in the USA. OPUS produced slightly better results for the point with nearby ITRF reference stations than for a point far away from the ITRF reference stations. The Russian system did not differentiate between the point with nearby ITRF reference stations and the point which is far away from ITRF reference stations. In addition, for both services, having a longer observation period did not substantially improve the quality of the solutions for all coordinates. Additionally, coordinate differences between OPUS results and the Russian system results are in the order of decimetres.

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6. Metro gauge inspection system based on mobile laser scanning technology
L. Yao, S. Zhang, Z. Wang, H. Sun, Q. Chen & K. M. Gilbert

Detecting metro gauge is very important for the safe operation of the subway. In this study, we design a low-cost metro tunnel mobile scanning system (MDS-TJ-1), which integrates a laser profile scanner with an inertial measure unit and an odometer to provide positioning and attitude parameters of the trajectory. The Lagrange interpolation is used to accomplish the time unification of different sensors. A dynamic alignment scheme for profile scanner is proposed based on the designed plane reflector target with high reflectivity. The error accumulation of the odometer is corrected by recognising the tunnel longitudinal joints, and finish the multi-source data fusion. The horizontal ray method is developed to process the metro gauge inspection. The experiment results show that the alignment accuracy of scanner is within 8 mm, the inner coincidence of the point cloud is within 3 cm, and the average error of the gauge inspection is 7.8 mm.

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7. Optimizing Local Geoid Undulation Model using GPS/Levelling Measurements and Heuristic Regression Approaches
Mosbeh R. Kaloop, Ahmed Zaki, Hamad Al-Ajami & Mostafa Rabah

This study investigates to use GPS/Levelling measurements of Kuwait and four heuristic regression methods including Least Square Support Vector Regression (LSSVR), Gaussian Process Regression (GPR), Kernel Ridge Regression (KRR), and Multivariate Adaptive Regression Splines (MARS) for modelling local geoid undulation. The accuracy of the models was compared by geoid undulation of gravitational observations and Global Geopotential Models (GGMs). The results show that the KRR model is suitable for Kuwait geoid model, its error of percentage is 0.018 and 0.124% relative to gravity and GPS/Levelling geoid undulation models, respectively. Furthermore, the comparison of KRR model with GGMs models signifies its accuracy.

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8. Strategy for Cadastre development in Poland in 1989–2019
Monika Mika, Paweł Kotlarz & Magdalena Jurkiewicz

The modernisation of the Land and Property Register (Poland Cadastre), going on for many years, yields no intended results, and cadastral data are occasionally of a poor quality. The cadastral model being developed in Poland should make use of information from the existing land surveying, legal, and planning databases. This model should be consistent with the current technical norms and standards applied worldwide. This paper summarises, in chronological order, the most important cadastre modernisation projects undertaken in recent years in Poland, the latest of which is the Integrated System of Real Estate Information, still under development.

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Survey Review 52, No 374. September/October 2020

1. A comparative study of large karst cave point cloud registration in various scanning modes
Yu Guo , Yonghua Xia , Xiangying Yang , Minglong Yang , Hongqiang Bai & Ming Feng

With the development of 3D laser scanning technology, terrestrial 3D laser scanning technology has been applied in the field of underground space exploration. In this study, three different scanning modes were applied to collect data. Data collection was carried out in a branch hole of a karst cave in Yiliang County, Yunnan Province, China. After filtering, denoising and registration of the acquired cloud data. We analysed the registration effect and accuracy of the two adjacent stations under different scanning modes. Finally, the accuracy report of point cloud data obtained under different scanning modes was generated, and the application conditions of different scanning methods and the efficiency of scanning operation were discussed and analysed. The study would provide certain significant guidance for actual production.

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2. A local projection for integrating geodetic and terrestrial coordinate systems
Mike Bremner & Marcelo Santos

This paper develops a system for projecting coordinates from a geocentric coordinate system to a topocentric coordinate system defined by terrestrial measurements. The proposed system uses an extension of the Stereographic Double Map Projection and a parametric least squares estimation to calculate the parameters for the map projection. The Extended Stereographic Double Projection and the projection parameter estimation are implemented and tested. Tests are performed to determine rate that discrepancies occur and the maximum extents of the Extended Stereographic Double Projection. This maximum area is determined to be ∼10 km2 with RMS values of residuals of 0.0029 m in northing and 0.0020 m in easting. Tests are also performed to determine the factor that limits the effective area of the Projection.

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3. Data model development for ‘buying and selling’ transactions as a real estate acquisition method
Yakup Emre Coruhlu & Tugay Toludan

There are many ways to acquire real estate in Turkey. The most common of them is ‘buying and selling’. The real estate/immovable property ‘buying and selling’ is a legal transaction carried out by rural Land Registry Offices in the General Directorate of Land Registry and Cadastre (GDLRC). The transactions are conducted through Land Registry and Cadastre Information Systems (LRCIS). LRCIS in e-Turkey is going to enable the transactions to be carried out efficiently. Turkish National Geographical Information Systems (TNGIS) studies and many academic studies based on e-Turkey and LRCIS have been developed in harmony with UML diagrams based on the Land Administration Domain Model (LADM) to the ISO standard. Within this context, possible situations that may be encountered in an immovable ‘buying and selling’ have been evaluated and modelled. One of the most important findings is that all immovable ‘buying and selling’ transactions are still not conducted entirely via e-Turkey. The model designed will contribute to the inclusion of elements not managed through e-Turkey. Thus, the trading process may proceed faster and more accurately thanks to the study. Before the process, it is additionally recommended that the application, which is defined as staking out a plot of the land/independent unit from a map/layout plan, and the valuation report showing the market value of the real estate should be made obligatory. Thanks to this obligation, rights of the buyer and seller according to the Confidence Principle and State's Responsibility Principle of the land register can be secured. In addition, the real estate tax values can be collected on the basis of these values. It is recommended to all those involved that they work on the model proposed by the study which guarantees the geometric and legal boundaries and the market value of the real estate with the necessary documents and institutions. In this way interoperability among all institutions can be provided quickly, data duplication can be avoided, correct data access can be ensured, data security can be kept at a high level, and transactions can be completed in a shorter time than the classical method.

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4. Performance of BDS triple-frequency positioning based on the modified TCAR method
Yijun Tian , Lifen Sui , Dongqing Zhao , Yuan Tian , Xu Feng & Mengya Qu

A modified TCAR method to improve the NL ambiguity resolution over medium-long baseline is presented. The estimated DD ionospheric delay derived from the Kalman-filter floating solution is adopted to modify the floating NL ambiguities. Modified by the smooth DD ionospheric delay, the NL ambiguity residuals are mostly within 0.5 cycles over medium-long baselines, showing a significant improvement in contrast to the classical TCAR method. The positioning performances of the modified method are even better than the LAMBDA method over 72 and 634 km baselines. As the ambiguity can be correctly fixed just after several epochs, high-precision positioning can be achieved in a very short time.

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5. On general constrained extended Kalman filter formulated by condition equations: three algorithms
V. Mahboub , N. Fatholahi & H. A. Aghaei

Three constrained extended Kalman filters (CEKF) are developed by making use of condition equations which equations allows one to predict directly the residuals of all variables. The first one is a general CEKF algorithm in which it is supposed that all of the observation equations, system equations and constraints of a dynamic problem are non-linear functions. Although the constrained Kalman filter was already investigated by a few contributions, they assumed some restrictive conditions such as linearity of constraints and/or equations. Moreover, this generalization helps one to deal with problems which encounter with raw GPS data. In some problems, constrains can be expressed by a quadratic form. Hence, the second algorithm proposes a CEKF solution with quadratic constraints. In this algorithm, the constraints are not linearized. Eventually, in case of using refined GPS data in which quadratic constraints must be imposed to the state vector, the third algorithm is developed. In this algorithm one does not require to linearize any part of the dynamic model. Rigorous prediction of posterior dispersion (variance-covariance) matrix of the unknown parameters is the other attainment of this contribution. A numerical example demonstrates the efficiency of the proposed algorithm.

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6. An alternative approach to generate temporal geopotential models similar to GRACE
Hussein A. Abd-Elmotaal

Time-dependent global gravity field models are available nowadays. The paper introduces an approach to generate geopotential earth models similar to GRACE models using such time-dependent global gravity field models. Such GRACE-similar models can then be used to estimate, for example, the Terrestrial Water Storage (TWS) for the months where GRACE data are not available. The paper gives the necessary derivation of such GRACE-similar models from the time-dependent global gravity field models. GRACE-similar models, created by using the time-dependent global gravity field models at the same months where GRACE data are available, are compared to the original GRACE models both in the frequency and the space domains. The results proved that the GRACE-similar models give comparable values to the original GRACE models and no loss of spectrum power occurs.

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7. An assessment of wide-lane ambiguity resolution methods for multi-frequency multi-GNSS precise point positioning
V. Duong , K. Harima , S. Choy , D. Laurichesse & C. Rizos

We assess the time-to-first-fix (TTFF) and the ambiguity fixing rate of two PPP wide-lane ambiguity resolution (WL-AR) methods, namely the geometry-based and ionospheric-free (GB-IF) method, and the geometry-free and ionospheric-free (GF-IF) method. First, an optimal GF-IF WL linear combination is selected based on the ratio between the code and carrier phase measurement noise (RT). Then, the relation between ambiguity variance and satellite geometry in the GB-IF WL-AR is investigated. Both simulated and real data from 31 GNSS stations over 37 consecutive days in 2017 were used. Numerical results show that the GF-IF WL-AR method has shorter TTFF and higher ambiguity fixing rate compared to the GB-IF method when RT≤150. However, when RT≥150, the GB-IF method outperforms the GF-IF method. Depending on RT values used, 2–10 min would be required to resolve the WL ambiguities when using GNSS measurements with one second sampling rate.

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8. Evaluation of single-frequency receivers for studying crustal deformation at the longitudinal Valley fault, eastern Taiwan
Horng-Yue Chen , Hsin Tung , Ya-Ju Hsu & HungKyu Lee

Applications of low-cost single-frequency continuous GPS receivers for monitoring volcano and landslide activities as well as to complement dual-frequency receivers have been demonstrated to produce stable and accurate positioning. In studies of crustal deformation, the relative distance between monitoring stations may vary from several kilometers to tens of kilometers, hence the differential single-frequency observations cannot model the ionospheric delay or other distance dependent errors. The 55 low-cost single-frequency continuous stations have been deployed together with 52 continuous dual-frequency stations in southeastern Taiwan since 2008. All of the single-frequency stations have applied corrections using dual-frequency stations to eliminate the distance dependent errors. Comparing velocity estimates from 8 co-located, the differences in horizontal and vertical components are less than 3 mm/yr and 6 mm/yr, respectively. Our study shows that the combination of single- and dual-frequency GPS data can provide robust results to study the fault slip behavior on the Longitudinal Valley fault.

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9. Influence of the setback of backgrounds behind semi-transparent synthetic targets on the accuracy of reflectorless distance measurements
Grzegorz Lenda & Michał Buczek

Reflectorless distance measurements to synthetic materials are subjected to errors result from their partial transparency. The final reflection of the beam is from the background behind the synthetic. This paper examines the influence of the background setback on the accuracy of the measured distances for synthetics of various properties. The tests demonstrated a variable dependence of the measured distances on the setback of the background. For materials with a lower transparency, the errors were systematically decreasing as the background was being moved away. For the materials with a higher transparency, the errors initially increased and then they got systematically smaller.

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Survey Review 52, No 373. July/August 2020

1. Embedding the sustainability development goals in Survey Review’s remit
Peter Collier

In September 2015, the United Nations General Assembly adopted the sustainable development goals (SDGs). Seventeen SDGs were adopted, incorporating numerous targets and indicators, to set a global sustainable development agenda up to 2030 (United Nations 2018). The principles underlying the various SDGs were the aim of enhancing the livelihoods and dignity of people. Some SDGs were aimed specifically at basic issues, such as access to clean water and sanitation, alleviating poverty and hunger, giving improved access to health care and education, and promoting gender equality while safeguarding the planet. Other SDGs covered responsible production, consumption, action on climate, and protecting life on land and in water. Others dealt with engendering prosperity by providing decent work, promoting economic growth, industry, infrastructure, and innovation.

These SDGs developed on the Millennium Development Goals, but the emphasis was on a more bottom-up approach and not having just a focus on the global South. Clearly, many of the SDGs are very broad in scope and, at first sight, it may seem that a journal like Survey Review can only play a very marginal role in promoting the SDG agenda. In practice, areas of the work reported in Survey Review have an important role to play in helping to promote a number of goals through improved data collection and management or measuring and monitoring.

Areas with an obvious role to play are land administration and cadastre. In many countries, the operation of an efficient market in the land is still inhibited by the lack of security of ownership that only properly functioning cadastral system can provide. Without the security of ownership landowners cannot raise capital to invest in their land or use the land as security for loans invested in other ventures. Survey Review regularly publishes papers which discuss ways in which cadastre and land administration can be improved. In July 2018, we published a Survey Review Prize-winning paper by Asiama et al. (2018) on ‘Land valuation in support of responsible land consolidation on Ghana's customary lands’. It is widely recognised that land consolidation has played an important role in enhancing the sustainability of agriculture by reducing fragmentation and increasing agricultural production in much of Europe and a number of Asian countries. As Asiama et al. note, in sub-Saharan Africa attempts at land consolidation have been much less successful due to the transfer of European practices to societies with very different cultural and political contexts, among them long-standing customary land use. In March 2019, Hull and Whittal in their paper ‘Human rights in tension: guiding cadastral systems development in customary land rights contexts’ drew on their work in South Africa to suggest how the problems posed may be tackled when attempting to develop a cadastral system where customary land rights are the norm.

The July 2018 issue also included a paper by Divithure and Tang, ‘Scenario-based strategy selection for a sustainable cadastral system development program – a case study of Sri Lanka’. This paper addresses the poor progress made in the cadastral system development programme since it was introduced in 1998 and makes recommendations regarding improvements for future-proofing the system to enhance its sustainability.

In addition to the papers focussed on the global South, Survey Review has regularly published papers discussing the various cadastral and land administration needs countries which, for a variety of reasons, either lacked a proper cadastral system or in which the existing cadastral data was out of date. Examples include Turkey (for example, Aksu and Iban 2019, Baser and Biyik 2019, Saralioğlu et al. 2019), Serbia (Pržulj et al. 2019), India (Sengupta et al. 2016), Poland (Janus et al. 2018, Mika et al. 2018, Dawidowicz et al. 2019), Greece (Apostolopoulos et al. 2018, Kitsakis et al. 2018), and Russia (Ilyushina et al. 2018).

On a more general note, Unger et al. (2017) published a paper ‘On the need for pro-poor land administration in disaster risk management’, and in September 2018, Survey Review also published a Guest Editorial by Michael Barry ‘Fit-for-purpose land administration – administration that suits local circumstances or management bumper sticker’. In this, Barry (2018) argues that certain aspects of fit-for-purpose guidelines are overly prescriptive and do not take adequate account of local circumstances and do not involve the local community in such a way that it ensures successful implementation.

Survey Review has also published a number of papers concerned with the recording of culturally important structures, which fall under Target 11.4, such as Coruhlu and Yoldiz 2018 paper ‘Geographical data model for cultural immovable properties’ in which they discuss the recording of historic structures, such as mosques, bazaars, inns and bathhouses, and Georgopoulos et al. 2016 paper ‘The contribution of laser scanning technology in the estimation of ancient Greek monuments’ deformations’. Mulahusić et al. 2020 paper takes this work future by comparing different types of laser scanners for 3D modelling of complex cultural and historical objects.

In support of SDG 9A (sustainable and resilient infrastructure), the surveying and monitoring of more recent structures, such as dams and bridges, have also been a recurrent theme in papers in Survey Review as new technologies and methods have been applied. Examples include Núñez-Andrés et al. (2018) paper ‘The use of geomatic techniques to improve the management of metro infrastructure’, Chen et al. (2019) paper ‘Experimental research on daily deformation monitoring of bridge using BDS/GPS’ where the use of data from more than one Global Navigation Satellite System (GNSS) is compared with data captured using total stations to determine whether GNSS could provide a reliable and cost-effective way of continuously monitoring structure subject to external stresses. Similarly, Kaloop et al. (2020) paper evaluates the use of GNSS for monitoring vertical structure motion and Zhao et al. (2018) paper on the monitoring of subsidence of highways.

Many of the papers in Survey Review, which do not seem to have an overt role to play in support of the SDGs, still play a more tangential role through the development of more efficient and cost-effective ways in which high precision data can be captured for control surveys, the creation of digital terrain models and the construction of infrastructure.

Survey Review will continue to encourage submissions which help towards the attaining SDGs.

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2. Constrained and network multi-receiver single-epoch RTK positioning
Mieczysław Bakuła

This work presents the concept of RTK positioning based on two or three rover GNSS receivers from two or three different reference stations. Additionally, detailed mathematical models of constrained least squares adjustments of RTK positioning based on two or three different RTK/GNSS receivers are presented. The models were tested on real RTK data using three rover Trimble RTK receivers and three reference stations of the ASG-EUPOS system. Practical calculations obtained from the adjustments showed improved accuracy over traditional RTK positioning when reference GNSS stations were located far away (about 30 km from the mobile RTK receivers). The maximum average absolute error for horizontal and vertical coordinates in constrained RTK positioning was over two times lower than in the single baseline RTK positioning, and reached 0.021 and 0.046 m, respectively. Since the concept of constrained and redundant, single-epoch RTK adjustment can be used for static or kinematic applications in real-time positioning, it can also be widely used in geoscience surveying and remote sensing.

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3. The impact of terrestrial gravity data density on geoid accuracy: case study Bilogora in Croatia
Olga Bjelotomić Oršulić , Danko Markovinović , Matej Varga & Tomislav Bašić

One of the main challenges in physical geodesy today is achieving the 1-centimetre gravimetric quasi-geoid model, since a model of such accuracy could be used in the definition and realisation of the height reference frame. One of the main obstacles in this challenge is the lack of terrestrial gravity data or its uneven distribution. Therefore, the main question arises: what density of gravity points is necessary in order to obtain a gravimetric quasi-geoid model with an accuracy of 1 centimetre or even better? In this simulated study, the results show a trend of decreasing RMS related to the sparser dataset used in computation, leading to the conclusion that the determination of the sub-centimetre quasi-geoid model is no longer a theory, but can be achieved with the exact density of terrestrial gravity data: gravity observation stations have to be distributed no farther than 500 m from one another. When dealing with a very rough topography, the distance should be even shorter.

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4. A robust total Kalman filter algorithm with numerical evaluation
Sida Li , Lintao Liu , Zhiping Liu & Guocheng Wang

In this study, the observation model of Kalman Filter (KF) is extended to an errors-in-variables (EIV) model because the observations may exist in the design matrix of the observation model. Then, a robust total least squares method (RTLS) is introduced into the KF, and a robust total Kalman filter (RTKF) algorithm is derived. The RTKF is a simple, flexible and effective algorithm. It is simple because its computational formulae are similar to the computational formulae of a standard KF; it is flexible because it can be used in a wide range of applications; it is effective because the influence of outliers on estimated results is weakened. Finally, the simulated example of the indoor location and the empirical example of pseudorange differential positioning are used to demonstrate the performance of the RTKF algorithm. The results prove the validity, robustness, and reliability of the RTKF in dealing with the outliers that exist in both observation vector and design matrix of the EIV model. Furthermore, the results of the empirical example show that the RTKF improves the precision of a pseudorange differential positioning compared with KF and robust Kalman filter (RKF) algorithms regardless the observation model has outliers or not in this empirical example.

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5. Triangulation network of 1929–1944 of the first 1:500 urban map of València
Miriam Villar-Cano , Ángel Marqués-Mateu & María Jesús Jiménez-Martínez

Triangulation is a surveying method on which earlier maps made were based. Although the origins of the method can be traced back to the 16th century, it is still used today, with minor changes, to adjust networks observed with modern geodetic techniques. In this paper we present the geodetic survey work that was carried out for the primary triangulation network of the first 1:500 urban map of the city of València (Spain). It spanned from 1929 to 1944 and resulted in 421 maps covering about 174 square kilometres. We focus on four key elements to define the geometric framework of a map: (1) the geodetic network, (2) the cartographic projection, (3) the baseline measurements, and (4) the primary triangulation. The paper is based on the interpretation of original documents and field books recovered from the archives of the València City Council. In order to check the accuracy and consistency of the survey work, we recomputed all calculations directly from the field data, following the mathematical procedures of the time. We obtained a set of transformation parameters to convert the coordinates of 1929 to current coordinates based on the European Terrestrial Reference System of 1989 (ETRS89). Results showed that the 1929 primary triangulation angles and coordinates are accurate to 8 s of arc and 35 cm respectively, and that the coordinates transform well into the current reference system with average residuals of 26 cm across nine control points, demonstrating the high quality of the 1929 work.

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6. A new recursive satellite selection method for multi-constellation GNSS
A. A. Abedi , M. R. Mosavi & K. Mohammadi

Development of navigation satellites systems as GPS, GLONASS, Galileo and Beidou has increased the accuracy and reliability. On the other hand, by employing more satellites, the receivers’ computational load increases, and their power consumption rises. Therefore, the selection of optimum satellites from the visible satellites can provide good accuracy. At the same time, the computational burden does not increase significantly. A new algorithm for optimal satellite selection is proposed in this paper. This algorithm is based on a down-top recursive that initial combination of satellites is obtained in a simple method, and then a satellite from the remaining satellites with a special GDOP-based metric is added to this subset. In the next step, a satellite is removed from this new combination with another specific criterion. The process of increasing and decreasing the number of satellites will continue for a certain number of repetitions, and eventually the optimal combination of satellites is achieved. The computational load of this method has been decreased by two factors. One is the reduction of the number of repetitive loops to achieve an optimal subset, and the other is the selection of initial combination with fewer satellites. This method in some cases improves accuracy compared to previous methods. This new approach is evaluated via collected data from four stations. The results indicate that this new algorithm can reduce the number of multiplication and addition operations more than Top-Down recursive method by 20% and 56%, respectively.

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7. Sub-hourly precise point positioning accuracy analysis – case study for selected ASG-EUPOS stations
Karol Dawidowicz

Precise Point Positioning (PPP) is still considered a new technique of GNSS measurements intensively developed in recent years. One of the main advantages of this method is the autonomous mode of measurement, requiring only one receiver, which ensures the high accuracy of the measured position. The accuracy, in some modes of measurement and processing, is similar to the results obtained with the use of Relative GNSS technique (RGNSS). The main disadvantages of PPP include the need to introduce a set of corrections, which in the RGNSS are reduced using differential equations and a relatively long time (about 20 min or more) needed for ambiguity resolution. The analysis conducted so far concerning the determination of the PPP accuracy focused mainly on the results obtained from long (daily) static observation. The results obtained from the sub-daily observation, less often analysed, involved longer time intervals (1–8 h). In this paper, time series of position components derived from sub-hourly (30 min) PPP solutions were analysed. The analysis was based on 30 days of observations performed at 8 ASG-EUPOS system stations. For processing the collected GNSS observations (in different variants) the NAvigation Package for Earth Orbiting Satellites (NAPEOS) software was chosen. If it will be assumed that standard deviation (SD) can be a good measure of the accuracy of the obtained results, the conducted analyzes prove that the sub-hourly PPP technique can provide accuracy in the order of 0.5 cm (SD below 0.5 cm) for the horizontal position components and 1 cm (SD below 1 cm) for the vertical position component. The above accuracy was obtained in the multi-station PPP approach (fixed ambiguity solution). In float ambiguity solution scenarios the standard deviation increases up to 1 cm for horizontal components and up to 2 cm for the vertical component. The periodicity, in the obtained position components time series, were analysed using the Lomb-Scargle periodogram. Spectral analysis showed clear periodicity in the obtained results (especially for GPS-only fixed and float solutions). For GPS or GPS/GLONASS processing strategies 73% of detected periodic signals correspond to a multiple of the orbital periods of the satellites.

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8. The 5 mm geoid model for Estonia computed by the least squares modified Stokes’s formula
Artu Ellmann , Silja Märdla & Tõnis Oja

Computational stages of a new high-resolution 5 mm quasigeoid model for Estonia are explained. Certain requirements for the quality and coverage of gravity data in the context of 5 mm geoid modelling were fulfilled. The present gravity data coverage over the target area is 1 point per 10 km2, less dense in adjacent land and marine areas. The average uncertainty estimate of gravity data within the target area is about 0.5 … 0.75 mGal. The gravity data were merged, cleaned, analysed, reduced and gridded to yield a seamless gravity anomaly field. A least squares modified Stokes formula (Sjöberg, L.E., 1991. Refined Least Squares Modification of Stokes Formula”. Manuscripta Geodaetica, 16, 367–375.) that combines local terrestrial gravity anomalies and the global geopotential model derived long-wavelength component in a truncated Stokes’s integral yielded the best gravimetric geoid modelling results. The combined uncertainty for most of the Estonian GNSS-levelling points is not exceeding 5 mm, allowing an adequate verification of the geoid modelling quality. Inter-comparison of the geoid model, GNSS-derived and spirit-levelled heights at discrete points was conducted for geoid modelling assessment. A two stage stochastic spatial prediction was applied to obtain an optimal fit between precise GNSS-levelling data and the geoid model. The location-specific post-fitting uncertainties of the resulting model EST-GEOID2017 revealed standard deviation of 4.2 mm, i.e. the same level as the accuracy of the used GNSS-levelling control points.

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9. Study on the selection of optimal global geopotential models for geoid determination in Kuwait
Mohamed El-Ashquer , Hamad Al-Ajami , Ahmed Zaki & Mostafa Rabah

In this study, a thorough validation of the recently released Global Geopotential Models (GGMs) has been carried out by comparing all models with both the free-air (FA) gravity anomaly observations and GPS/Levelling data in Kuwait. First, the gravity functional in terms of FA gravity anomalies and geoid heights that derived from GGMs and compared with the ground-based data before applying the Spectral Enhancement Method (SEM). The findings indicate that the combined GGMs, generally, fit the ground data better than the satellite-only GGMs due to the existing spectral gaps. Second, the FA gravity anomalies and geoid heights, obtained from GGMs at maximum Spherical Harmonics (SH) degree/order (d/o) for the combined models and from spherical harmonics d/o ranging from 100 to their maximum d/o, with a step of 10 d/o for the satellite only GGMs, were compared with the corresponding ones from terrestrial data using the SEM. For the FA gravity signal, the EIGEN-6C4 manifested the best results of combined GGMs with differences characterised with a mean of 0.967 mGal and a Standard Deviation (STD) of 2.845 mGal, while TIM_R5 at SH (d/o) 200 showed the best results with a mean of satellite only GGMs with a mean if 1.008 mGal and a STD of 2.657 mGal. In the case of the evaluation of the geoidal height with GPS/levelling, XGM2016 manifested the best results of combined GGMs with differences characterised with a STD of 0.234 m. For the satellite only GGMs, the best results have been obtained from SPW_R5 at SH d/o 250 with a STD 0.207 m.

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Survey Review 52, No 372. May/June 2020

1. Study of usability of aerial images and high-resolution satellite images in cadastre renewal works in Turkey
Fazıl Nacar, Hakan Karabörk & Tayfun Çay

If the usability of orthophotos of aerial images and high-resolution satellite images in cadastre renewal works is ensured, the state cadastre can be maintained and constantly updated. For this purpose, three pilot fields in Konya, Adana and Şanlıurfa were selected. In these fields, land surveys were made with a CORS method by using GPS. The coordinates were obtained by using orthophotos in Konya (1/2000 scale) and in Adana (1/5000 scale) and orthophotos with 1/5000 scale obtained from WorldView-2 high-resolution satellite images in Şanlıurfa. One aim was to establish the positional accuracy of the data obtained from digital orthophotos and area accuracy in comparison with cadastral areas by presuming that the land surveys were accurate. In light of the discovered results, comments on the usability of orthophotos obtained from aerial images and high-resolution satellite images in renewal cadastre were made.

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2. Applicability of knowledge innovation value chain model for the land administration system of municipality of Maputo in Mozambique
Tarun Ghawana, Raul Cumbe, Joao Paulo Hespanha, Silvane Paixao & Andrea f. T. Carneiro

The knowledge innovation value chain (KIVC) model and land administration domain model (LADM) are applied for Mozambique. The study focus moving forward along the value chain using the conceptual components of LADM as the starting point to meet the societal and market demands by relevant ministry and Municipality of Maputo. The Municipality is developing an Integrated Municipal Management System (SIGEM). With rapid urban development, Municipality needs to innovate. Three innovation value chains are presented: (1) national-level portal for Urban Land Development integrating services; (2) municipal-level public access portal supporting several land administration functions such as Plots/Building purchase; (3) local infrastructural level concerning water and sanitation services, through an integrated, single-window online system supporting client-driven services. International standards, ICT and Geo-ICT must be considered to modernize the land administration arrangements. To make a successful application of the KIVC model, municipalities have to go for PPP mode projects.

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3. Delineating minor landslide displacements using GPS and terrestrial laser scanning-derived terrain surfaces and trees: a case study of the Slumgullion landslide, Lake City, Colorado
Jin Wang, Duo Wang, Shengqi Liu & Boyu Jia

Multi-temporal high-density terrestrial laser scanning (TLS) datasets are processed to delineating possible movements from terrain surfaces and trees. Terrain surface movements are estimated with the help of segmentation and random sample consensus (RANSAC) algorithm. Tree movements are interpreted by iterative closest point (ICP) solved translations and rotations of tree point clouds. The capabilities of the proposed methodology were tested using a case study of the Slumgullion landslide, where the trees without clear trunks cover the terrain surfaces. The displacements from the terrain surfaces and trees are similar with the results observed using our global positioning system (GPS) and historic results.

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4. Modernisation of the Cadastre in Poland as a tool to improve the land management and administration process
Monika Mika

The article describes a detailed analysis of the modernisation procedure for cadastral data in Poland in both theoretical and practical aspects. Modernisation of the cadastral system is an essential tool to ensure both the continuity in time and the timeliness of cadastral data. In Poland, the function of the Cadastre is served by a public register known as the Land and Building Cadastre which records the actual data on the ground, resulting from the current state of ownership or use. Legal data are stored in a separate register known as the Land and Mortgage Register. The Cadastre in Poland has numerous disadvantages; however, its advantage is that no construction of the system anew is required. The existing cadastral data need to be skilfully used, and the quality of cadastral data needs to be adjusted to international requirements through the use of technical and legal guidelines in the field of modernisation. The research material consisted of source texts of existing legal provisions equivalent to an act of legislature and implementing regulations as well as technical documentation for modernisation works performed in southern Poland (Małopolskie Voivodeship). The method of comparative analysis of the compliance of modernisation work results with national requirements was applied. An analysis of the adopted indicators for cadastral data evaluation, using the selected example, showed that the properly performed modernisation of the Land and Building Cadastre may become a tool for improving the land management and administration process.

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5. Customary Land Rents Administration in Ghana: Emerging Discourse on Family Lands in the Upper West Region
Samuel B. Biitir & E. D. Kuusaana

In Ghana, the constitution recognises stool land revenues as a principal source of funding local economic development. However, there has been a lacuna on the collection and disbursement of family land revenues. The study examines ground rent collection and disbursement on family land, revenue losses and the capacity of family landowners to assess and collect ground rents. The analyses show ground rent collection is for infrastructure development and the sharing formula is similar to the Constitutional formula. Also, ground rent losses is significant and family landowners do not have the human and technical capacity to assess ground rents on their own lands.

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6. Assessment of the accuracy of DTM river bed model using classical surveying measurement and LiDAR: a case study in Poland
Paweł Kotlarz, Monika Siejka & Monika Mika

The aim of this paper is to show that natural watercourses surveying gives the best results using integrated measurement methods (classical surveying and LiDAR). The paper contains comparison of the riverbed DTM results obtained using LiDAR data in relation to data derived from direct measurements. The paper involved the performance of appropriate tests on selected structures using integrated measurement techniques – GNSS, tachymetry and LiDAR. The conducted studies showed some limitations method for acquiring data from LiDAR. This is because the method does not enable the determination of measuring points coordinates which describe the topography in places inaccessible for a laser beam.

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7. On robust constrained Kalman filter for dynamic errors-in-variables mode
Vahid Mahboub, Somayeh Ebrahimzadeh, Mohammad Saadatseresht & Mehran Faramarzi

A robust Kalman filter algorithm is proposed to solve nonlinear errors-in-variables dynamic problems in the presence of outliers. This algorithm is robust constrained integrated total Kalman filter (RCITKF). The method iteratively reweights the predicted solution when the observable quantities are contaminated by gross errors (outliers). It can impose the quadratic constrains which may appear in some problems. Moreover, the RCITKF algorithm can consider the neglected random unknowns of the functional model of the dynamic problem which gives an added advantage over the previous Kalman filters. In two geodetic applications, the efficiency of these algorithms is demonstrated in contrast to the extended Kalman filter (EKF) and unscented Kalman filter (UKF) algorithms.

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8. A half-century of Baarda’s concept of reliability: a review, new perspectives, and applications
Vinicius Francisco Rofatto, M. T. Matsuoka, I. Klein, M. R. Veronez, M. L. Bonimani & R. Lehmann

Over the 50 years of its existence, Baarda’s concept of reliability has been used as a standard practice for the quality control in geodesy and surveying. In this study, we analysed the pioneering work of Baarda (Publ Geod New Ser 2(4) 1967; Publ Geod New Ser 2(5) 1968) and recent studies on the subject. We highlighted that the advent of personal computers with powerful processors has rendered Monte Carlo method as an attractive and cost-effective approach for quality control purposes. We also provided an overview of the latest advances in the reliability theory for geodesy, with particular emphasis on Monte Carlo method.

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9. Efficacy of the conventional deformation analysis based on different strategies on the design stage of the network
Bahattin Erdogan, Utkan Mustafa Durdag & Serif Hekimoglu

In different Geodetic networks the observations are measured repetitively. These observations, called original observations, are independent. At the design stage of the deformation monitoring network, either the mean value of the original observations or the original observations may be considered. Conventional Deformation Analysis (CDA) is based on the ordinary Least Square Estimation (LSE) that uses the mean value of the original observations. In this paper, the efficacies of results of CDA were investigated for the three different strategies 1o ordinary LSE, 2o LSE with original observations and 3o both LSE with original observations and subnetwork design. To perform the investigation of reliability, leveling network and GPS network were designed, and the mean success rate (MSR) of the methods were computed. The MSRs of the third strategy gets improvements on MSR about 34% for leveling network and 38% for GPS network according to ordinary LSE when three of eight points displaced.

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Survey Review 52, No 371. March/April 2020

1. BDS four frequency carrier phase combination models and their characteristics
Xinshuai Zhang & Wei Cai

The fourth signal of BDS (BeiDou Navigation System) allows for measurements on frequency S. To take advantage of this new signal, an investigation has been carried out on the models and characteristics of four frequency carrier phase combinations. Four categories of combinations are studied: ionosphere delay reduced combinations, troposphere delay reduced combinations, minimum noise combinations and optimal combinations for ambiguity resolution. Among them, the optimal combinations for ambiguity resolution are mainly focused. In four frequency case, we have proved that the low noise axis used for searching optimal combinations also exists. Besides, the sum of combination coefficients also proves to be an important indicator which systematically classifies combinations. Moreover, an efficient method for searching four frequency combinations is also proposed and used. Finally, based on the search results and analysis we give some sets of four frequency combinations which are suitable for cycle slip detection, short baseline and long baseline ambiguity resolution.

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2. Comparison and analysis of results of 3D modelling of complex cultural and historical objects using different types of terrestrial laser scanner
Admir Mulahusić, Nedim Tuno, Dubravko Gajski & Jusuf Topoljak

Laser scanning does not provide unlimited geometrical accuracy and integrity when scanning complex objects. Scanning systems have a minimum and maximum range in which they operate, depending on the technical characteristics. Scanning below or above these limits results in gross errors and registering of incorrect data. Laser scanners can have difficulties with certain materials such as marble and reflective surfaces. This paper presents the results of laser scanning of a complex monument of cultural and historical heritage using two different types of terrestrial laser scanners. Afterwards, the comparison and analysis of the results are shown. The scanners used were terrestrial laser scanners Faro Focus 3D (phase mode distance measurements) and STONEX X300 (pulse mode distance measurements).

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3. Generation of digital terrain model for forest areas using a new particle swarm optimization on LiDAR data
Behnaz Bigdeli, Masoomeh Gomroki & Parham Pahlavani

Since Light Detection and Ranging (LiDAR) data are capable of distinguishing vegetation from bare earth, these data are used nowadays to produce digital terrain models (DTMs) for forest regions. In this research, raw LiDAR data were filtered using hybrid and slope-based filtering methods and the filtered data were then interpolated using the new modified particle swarm optimisation (PSO) and accordingly the results were compared with those achieved by the other intelligent and conventional interpolation methods. The new modified PSO optimized the polynomial degree for interpolation and found suitable parameters for optimisation. Two data sets from two forest regions in some northern regions of Iran located in Golestan province were selected to compare these methods. Region 1 with dense vegetation and region 2 with grass vegetation. The results indicated that the hybrid filter performed lower RMSE than the slope-based filter. Finally, the DTM with lowest RMSE was obtained using the hybrid filter and the modified PSO interpolation method with RMSE of 6 mm for region 1 (Tavar-kuh) and 61 mm for region 2 (Shastkola River Basin).

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4. A general partial errors-in-variables model and a corresponding weighted total least-squares algorithm
Jie Han, Songlin Zhang, Yali Li & Xin Zhang

The partial errors-in-variables (PEIV) model is an structured errors-in-variables (SEIV) model reformulated by collecting all the random elements of the coefficient matrix into an auxiliary random error vector to better treat the case where the coefficient matrix (or ‘data matrix’) A and observation vector y share common elements. In the usual PEIV model, the case of A and y sharing common elements has not been treated explicitly. However, in some cases, A and y do have common elements, taking the autoregressive problem as an example. To apply the PEIV model to SEIV problems with correlated matrix A and vector y, we propose an extended model named general PEIV (GPEIV). We also provide a corresponding algorithm for the total least-squares solution within the GPEIV model. A weight-matrix construction method, which is suitable for PEIV and GPEIV models, is also presented. The GPEIV model, the algorithm and the weight-matrix construction method are tested using two groups of numerical examples. The results show that the proposed model and corresponding algorithm can solve both uncorrelated and correlated SEIV problems, and the weight-matrix construction method is simple and efficient.

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5. Geodetic investigation of landslides and land subsidence: case study of the Bhurkunda coal mines and the Sirobagarh landslide
Ashutosh Tiwari, Avadh Bihari Narayan, Ramji Dwivedi, Ashutosh Swadeshi, Sumanta Pasari & Onkar Dikshit

This study presents a geodetic deformation monitoring approach and its application on two severely affected and uninvestigated study sites in India, namely the Bhurkunda coal mines in Jharkhand, and the Sirobagarh landslide in Rudraprayag, Uttarakhand. For the Bhurkunda site (characterized by underground coal mining related subsidence), a network of 56 GNSS points, densified by Total Station (TS) ground points, was set up during three field visits. GNSS derived deformation estimates reveal that the southern part of the investigated area underwent subsidence (maximum displacement 1.813 m). Furthermore, DEM differences of the three epochs generated using TS points detect a subsidence of 1.358±0.057 m with similar pattern and magnitude of movement as detected by GNSS stations. For the Sirobagarh landslide (witnessing recurring slides due to local geological conditions and rainfall), a GNSS network of six control points in an area of 500×600 m2 was established. Deformation estimates from GNSS show subsidence in the area with a horizontal trend of movement towards the Alaknanda river situated below the landslide (maximum horizontal and vertical displacement values are 0.1306 m and 2.1315 m respectively). Further, for the Sirobagarh landslide, multi-temporal interferometry using Sentinel-1 SAR images detect displacement vectors showing downward movement of the landslide, with displacement rates ranging from 0.008 to −0.115 m yr−1. It is evident that the landslide scarp encountered high magnitude subsidence, whereas the area containing and surrounding the landslide (~30 km2) underwent a moderate rate of subsidence. A set of surveying guidelines for monitoring deformation events of similar kind are discussed.

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6. Unsupervised extraction of urban features from airborne lidar data by using self-organizing maps
Alper Sen, Baris Suleymanoglu & Metin Soycan

The extraction of artificial and natural features using light detection and ranging (Lidar) data is a fundamental task in many fields of research for environmental science. In this study, the possibility of using self-organising maps (SOM), which is an unsupervised artificial neural network classification method to extract the bare earth surface and features from airborne Lidar data, was investigated for two different urban areas. The effect of the enlargement of the study area was analysed using the proposed approach. The appropriate weights of SOM inputs, which are 3D coordinates and intensity, obtained from a Lidar point cloud were determined by using Pearson's chi-squared independence test. The weighted SOM feature extraction performance was better than that of the unweighted SOM. The filtering results of SOM to separate ground and non-ground data were also compared with those obtained by the adaptive TIN filtering algorithm. Most of the non-ground features could be removed by the weighted SOM.

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7. Evaluation of the high-rate GNSS-PPP method for vertical structural motion
Mosbeh R. Kaloop, Cemal Ozer Yigit, Ahmet Anil Dindar, Mohamed Elsharawy & Jong Wan Hu

This study aims at the investigation of GNSS-PP method to determine the dynamic characteristics of structures. Cantilever steel bars having lengths of 70, 100 and 120 cm were tested under dynamic excitation. The GNSS was used to measure the natural frequencies and damping values of all the tested cantilever structures. The GNSS data were processed using relative GNSS positioning and PPP methods. The results obtained using these two methods were also compared with the dynamic characteristics obtained by applying the theoretical and finite element (FE) methods. Furthermore, it is investigated the impact of the stable data length before oscillation events on kinematic PPP. The study showed that the maximum difference among the experimental results in terms of natural frequencies proceeded using PPP is 0.08 Hz when compared with the theoretical and FE results. Furthermore, there is no difference between the PPP and relative GNSS positioning in determining the dynamic behaviour of structures eventhough roving GNSS antenna remains motionless for short-time, such as a few-minutes, before an event occurred.

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8. BeiDou/GPS relative kinematic positioning in challenging environments including poor satellite visibility and high receiver velocity
Junbo Shi, Yongshuai Huang, Chenhao Ouyang, Xingning Lu & Chaoqian Xu

Global Positioning System (GPS) satellite tracking loss always occurs under challenging observation conditions such as poor satellite visibility, high receiver velocity and so on. The announcement of China’s BeiDou Navigation Satellite System (BDS) regional service in 2012 has, on one hand, provided a new standalone positioning system and, on the other hand, augmented GPS under challenging observation conditions. This paper carries out BDS/GPS relative kinematic positioning with poor satellite visibility and high receiver velocity including an under-foliage pedestrian positioning at the speed of ∼5 km h−1, a city urban vehicle positioning at the speed of ∼30 km h−1, and an open-sky air vehicle positioning at the speed of ∼130 km h−1. Numerical results reveal that the standalone system cannot always provide reliable kinematic positioning solution in challenging observation environments. Instead, BDS/GPS combined system can provide better kinematic performance, i.e. 94.2% solution with 0.251 m precision (1-sigma) for the under-foliage pedestrian scenario and 97.0% solution with 0.151 m precision (1-sigma) for the city-urban vehicle scenario. As for the high receiver velocity case, both BDS and GPS can provide cm-level kinematic positioning precisions from the perspective of aerial photogrammetry. The BDS/GPS combined system cannot further improve the positioning availability and precision too much.

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9. Quantitative quality measure for photorealistic three dimensional models
Ahmed Abdelhafiz & Yasser Mostafa

The demand for virtual photorealistic models has been recently increased especially in the field of documenting large archaeological sites. These models are commonly assessed qualitatively as no quantitative measure tool is available. In this work, a new approach is presented for a quantitative measure of models texture similarity. Deciding for the reference texture is crucial. Metrics that have been used to assess image stitching quality in panoramic images are employed in the presented approach. A proposed metric is also presented and employed to assess the overall quality of the whole model’s texture. The work is then extended to manage misalignments that might appear in textured models in case of using wide angle lenses. A function that fits a second order polynomial equation is derived experimentally. The approach has been validated by three real models. The quantitative measure approach and the visual inspection of subjects for the models show a consistent correlation between the results.

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Survey Review 52, No 370. January/February 2020

1. A LADM-based temporal cadastral information system for modelling of easement rights – A case study of Turkey
Z. A. Polat, M. Alkan, P. J. M. van Oosterom & C. H. J. Lemmen

Type people to land relations are dynamic and, as a consequence, the nature of land title and cadastral data is of a dynamic nature. Land title and cadastral data are core components for a lot of property applications (e.g. taxation, valuation, mortgage). Those applications require up to date, complete and reliable data – including temporal data as in use in application forms and transactions. In this paper, the modelling of Rights, Restrictions and Responsibilities (RRR) is discussed with a focus on the modelling of easement rights in a case study in Turkey. Functional requirements with respect to the characteristics of easement rights are investigated based upon interviews with professional experts in the public and private sector. Then a prototype model was built based on a simple implementation of the Land Administration Domain Model (LADM) RRR classes and by conforming to the national cadastral data management standards related to land registration systems. This new proposed model includes temporal cadastral attributes related to easements. This is materialised in the ‘Administrative Package’ and illustrated in the Turkey LADM country profile. We show that the LADM can be used to describe for the time dimension of cadastral information in Turkey, but that there are semantic differences, similarities and mismatches of classes and attributes between the LADM and the cadastral information system in Turkey. Proposed LADM-based model for the time dimension of cadastral information will be of immense advantage to land administrators, the governments and land users in Turkey.

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2. Determination of an adequate number of competitive functional models in the square Msplit(q) estimation with the use of a modified Baarda’s approach
Marek Hubert Zienkiewicz

The article presents the issue of determining a proper number of competitive functional models in the square Msplit(q) estimation. It is assumed in the theoretical fundamentals of the method of parameter estimation in a split functional model that the observation vector may constitute an unrecognised and unassigned mixture of realisations of several random variables. As such, the observation vector may contain the realisations of a greater number of random variables than the adopted q of the competitive functional models. Too small number q of competitive functional models may leads to breakdown of Msplit(q) estimation. In the theoretical part of the paper, a modified Baarda’s test was proposed to detect too small a number of competitive functional models. The idea of the proposed approach is about detection of the observations that should not be assigned to a specific functional model. The efficacy of the proposed strategy was illustrated by two numerical examples.

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3. Georeferenced measurements of building objects with their simultaneous shape detection
Edward Osada, Krzysztof Karsznia & Izabela Karsznia

The paper presents a new method of georeferenced measurements of building objects with their simultaneous shape detection. The method is based on a robust adjustment of a linear network localised on the measured object and connected to GNSS-surveyed points deployed near building corners. In the robust adjustment process, the angles of the object physically outlying from their theoretical design values are detected, the remaining angles retain the design values. The performed field surveying experiment underlined the effectiveness of the proposed method.

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4. Estimation and evaluation of the triple-frequency GPS satellite inter-frequency clock bias
Haojun Li, Jingxin Xiao, Ling Yang & Jiexian Wang

A new estimation method is presented to detect and remove the potential outliers in the triple-frequency GPS inter-frequency clock bias (IFCB) estimating. The estimated results of the robust estimation (RE) can successfully mitigate the influence of outliers on IFCB estimation, IFCB modelling and IFCB application. The difference between the constant parts of IFCB estimated with observations and the differential code bias (DCB) (P1–P2) and DCB (P1–P5) products is computed and this difference shows that the DCB products cannot completely replace the constant parts of IFCB. The characteristic of the IFCB modeling is discussed based on the 5- year results. The estimated IFCB is evaluated and its impact on the precise point positioning (PPP) is analysed. The PPP results show that the influence of the IFCB on the static positioning is different with that of kinematic mode.

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5. Characteristics and modelling of BDS satellite inter-frequency clock bias for triple-frequency PPP
Yan Xia, Shuguo Pan, Qing Zhao, Denghui Wang & Wang Gao

Aiming at the problem of the inter-frequency clock bias (IFCB) in Beidou Navigation Satellite System (BDS) triple-frequency observations, the variation characteristics with time are analysed in detail. The IFCB models for all the three kinds of satellites, i.e. GEO, IGSO and MEO, are proposed. Then the attenuation and long-term forecasting performance of the models are evaluated. Finally, the validity and benefit of the model are verified by triple-frequency Precise Point Positioning (PPP) experiments. The IFCB results from consecutive two-month BDS triple-frequency observation data of 44 globally distributed Multi-GNSS Experiment (MGEX) stations show that the IFCBs of GEO satellites have prominent periodic variation in general. The correlation coefficient and the determination coefficient of predicted IFCB by the model for GEO satellites are up to 0.957 and 0.915 respectively, which shows the model has a high stability and is suitable for long-term prediction. The IFCBs of IGSO satellites have the same periodicity as those of GEO satellites. Although the model is not as good as that of GEO satellites, it still performs well overall and can be applied to long-term prediction in most instances. The model of MEO satellites performs worse than GEO and IGSO due to the numerical instability and less obvious periodicity of IFCBs. Moreover, the effect of the IFCB models is better than the substitution method of using the IFCB at the corresponding moment in the previous period as the IFCB forecast value of the current period. In the triple-frequency Precise Point Positioning (PPP) experiments, the modelled IFCB correction can improve the positioning accuracy by 21.1%, 9.0% and 9.9% in the north, east and up directions and also shorten the convergence time in these three directions by 26.8%, 10.4% and 24.4% respectively compared with the observation model without IFCB correction.

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6. Constrained homogeneous errors-in-variables modelling and extended weighted total least squares solutions
Yongjun Zhou & Yu Zhou

The homogeneous errors-in-variables (HEIV) model is extended from the regular EIV model for a more wide range of applications. Necessary constraints are imposed to avoid trivial solution or provide ancillary information of parameters. For the constrained HEIV (CHEIV) model with linearly structured data matrix, a generic constrained homogeneous weighted total least squares (CHWTLS) algorithm based on Newton method is derived by assuming the measurements are mutually correlated. An approximate accuracy assessment method is proposed with first order approximation by treating the CHEIV model as a constrained Gauss-Helmert problem. A quadratic constrained HEIV model frequently encountered in fitting and photogrammetry task is proposed as a specific CHEIV model, and a simpler WTLS method based on iterative singular value decomposition (SVD) is developed. A typical two dimensional rectangular building reconstruction problem is simulated to demonstrate the advantages of the homogeneous EIV model and the proposed WTLS algorithms in overcoming the possible ill-posedness and enhancing the numerical efficiency compared with the regular one.

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7. Coordinate transformation with variable number of parameters
Gilad Even-Tzur

Similarity transformation model does not provide a satisfactory solution for non-uniformly deformed systems because it allows only for a uniform scale and right angles. Instead, an affine model can be used, since it characterizes non-uniform dilatations and obliquity of the three axes. The general affine transformation contains 12 parameters. Nonetheless, it is not always necessary to use them all. The question of how many parameters should take part in the transformation and in what combinations is examined in the paper. In order to choose the proper transformation, a refined AIC is proposed. The paper also presents how to conduct the conversion of parameters between different coordinate systems with reference to the invariance property of coordinate transformation. To demonstrate the impact of using variable number of parameters and to observe the influence of coordinate systems on the transformation outcome, we use a network of 18 permanent GNSS stations in Israel as a case study.

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8. Validation and verification procedures for defining legal 3D boundaries using terrestrial laser scanners
Sam Rondeel, Michael Barry & Derek D. Lichti

A gap exists in law and practice with respect to calibrating terrestrial laser scanners (TLS) for legal boundary surveying. Laws, calibration infrastructure and calibration procedures have long existed for electronic distance measurement units used for boundary surveys, but laser scanners present new challenges. The aim of this paper is to present a practical, inexpensive procedure for validating laser scanner calibration and for verifying surface information extracted from terrestrial laser scanner data. The methodology verifies the TLS calibration parameters and extracted surfaces using total station measurements. The results indicate that total stations and TLS are complimentary tools and should both be used where complicated 3D boundaries exist.

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9. Precise local quasigeoid modelling using GNSS/levelling height anomalies and gravity data
Marek Trojanowicz, Edward Osada & Krzysztof Karsznia

This study compares four approaches of local quasigeoid modelling using GNSS/levelling height anomalies. The first two approaches utilise only a dense network of points with known GNSS/levelling height anomalies and the EGM2008 model. They are based on the interpolation of residual values of height anomalies by applying the least squares collocation (LSC) and the thin plate spline (TPS). The next two approaches use additional data in the form of surface gravity data and the digital elevation model. One of these approaches is based on the classical Molodensky method combined with LSC. The other approach utilises the method of geophysical gravity data inversion (GGI). During the research, the authors used a local network of points with precisely defined GNSS/levelling height anomalies located in South-Western Poland. They obtained comparable results for all tested approaches at the maximum analysed density of GNSS/levelling points (about 1point/30km2). The differences between the modelling results became apparent only with an increase in the distance between the GNSS/levelling data points and the reduced accuracy of the used global geopotential model.

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10. The need for re-engineering in the real estate appraisal system in Turkey
Nuri Erdem

Real estate appraisal in Turkey is one of the areas that need restructuring in the field of land administration. Although this requirement has been frequently expressed in recent years, systematic attempts to solve the problem do not seem to be available yet. At the solution stage, in addition to the creation of some of the work to be done, legal and institutional structures will be needed in real characteristics and precedent transaction price databases. In appraisal, performance and maintenance of databases will be achieved by utilising development of models to perform mass appraisal, and a presentation will be made to the user regarding the specified values that may be listed as the creation of mechanisms. In this context, it is argued that the Turkish real estate appraisal system needs to be re-engineered. Primarily for this, there must be an appropriate Law on Real Estate Appraisal and a governing institution for implementing this law. Under the leadership of the lead agency, real estate characteristics and market price databases should be built for usage in real estate appraisal.

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