2018 Abstracts


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Email: Peter Collier


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Survey Review 50, No 363. November/December 2018

1. Investigation of the success of monitoring slow motion landslides using Persistent Scatterer Interferometry and GNSS methods
K.O. Hastaoglu, F. Poyraz, T. Turk, I. Yılmaz, F. Kocbulut, M. Demirel, U. Sanli, H. Duman & F. Balik Sanli

The purpose of this study is to determine deformations in landslide areas with two methods, Persistent Scatterer Interferometry (PSI) and GNSS (Global Navigation Satellite System). In the Koyulhisar landslide area, 53 GNSS points were established throughout the region. Velocity values for these points are three-dimensional. In addition, TerraSAR-X SAR (Synthetic Aperture Radar) images were processed with Stanford Method for Persistent Scatterers software. Slip surfaces of the landslide region in the direction of the line of sight were calculated from PSI in addition to one-dimensional velocity values. These values were compared to GNSS data converted to the same format. GNSS was found more effective for tracking local deformations based on point data while PSI was better at areal movements. Using both methods together is the most effective in this region because there are small local movements independent of regional movements.

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2. Geographical data model for cultural immovable properties
Yakup Emre Coruhlu & Okan Yildiz

There are more than hundred thousand immovable cultural assets/heritages in Turkey such as inns, bathhouses, covered bazaars and mosques. It is known that there are some slums and illegal structures in the covered areas which are regulated with Conservation Development Plans. According to the plans, constructions are not allowed or limited generally. For the better management of these areas, some data such as ownership data of the immovable assets in these areas and other information such as real estate tax values, market values and building types should be known. For example, an object-oriented geographical database was developed for 40 immovable cultural assets selected in Trabzon city of Turkey. By this way, a model was established in accordance with Land Administration Domain Model. Costs of acquisition are analysed thanks to the GIS database. It is predicted that the study may be improved on a web basis for all immovable cultural assets.

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3. The potential of Web-GIS and geovisual analytics in the context of marine cadastre
Agnieszka Dawidowicz & Marcin Kulawiak

The importance of the marine environment to human existence makes it imperative that information models represent the multidimensional nature of reality as closely as possible in order to facilitate good governance. Information regarding jurisdiction, as well as the effects of formal law and community interests on the marine environment should be stored in a marine cadastre. The aim of the presented research is to present a concept marine cadastre structure for the EU Member State of Poland as well as show the potential of the application of open standards and Geovisual Analytics for the purpose of marine cadastre data integration, dissemination and analysis with the use of a Geographic Information System (GIS). The paper also presents a sample implementation of the proposed concept in the form of a Web-GIS for analysis and visualisation of risk assessment results in the context of a marine cadastre for the country of Poland.

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4. The geocentre inversion based on the global climate models and GPS site displacements
Nan Yu, Pengfei Cheng, Yingyan Cheng, Hanjiang Wen, Kaifa Kuang & Xinyun Cao

The geocentre is not static, reflecting the relative motion between CM and the ITRF origin. The degree-1 deformation of the earth surface involves the horizontal transport of the earth’s fluid envelope including mass transport of the non-tidal ocean, dynamics of atmosphere, and hydrological mass redistribution in the continents, which can be estimated through the global climate models and the global GNSS-based deformation monitoring. We use climate models of ECCO, NCEP and GLDAS to calculate the geocentre motion caused by the non-tidal ocean, atmosphere, and ground water, respectively. We calculate the ‘surface load moment’ using the displacement of 132 sites of IGS05, and then inverse geocentre by GPS. We find that the higher-degree terms would be induced in the degree-1 computing process and they will result in unmodelled errors. The number of GPS sites for inversion is not the more the better, while the even distribution is much more critical.

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5. The 2015 Mw 6.4 Pishan earthquake, China: geodetic modelling inferred from Sentinel-1A TOPS interferometry
Yongsheng Li, Yi Luo, Jingfa Zhang & Wenliang Jiang

This study investigates the 3 July 2015 (Mw=6.4) earthquake that affected Pishan County in Xinjiang, China. Using Synthetic Aperture Radar interferometry (InSAR), we mapped the near-field surface displacement of this event to better characterize the seismic source parameters. The inverted results suggest that a conjugate fault system could produce very similar deformation patterns as those observed in both ascending and descending InSAR observations, and the south-dipping fault is selected as the optimal fault responsible for the event. The selected fault was concentrated on a thrust fault with a strike of 112°, a dip of 25° and an average rake angle of 89°. The InSAR analysis reveals a fragmentation of the Western Kunlun north margin fault, and the overall deformation of the seismogenic fault is characterized by thrust motion, which is consistent with the transpressional tectonic characteristics of the major faults in this region.

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6. Application of PPP with ambiguity resolution in earth surface deformation studies: a case study in eastern Canada
Mohammad Ali Goudarzi & Simon Banville

Earth surface deformations are commonly studied by processing observations of continuously operating GPS (CGPS) stations located in the deformation area using differential methods. In this study, we assessed the performance of precise point positioning (PPP) with and without ambiguity resolution (AR) to recover station velocities. Using 37 CGPS stations mostly located in eastern Canada over a 10-year period, the PPP-derived velocities were compared with the official velocities of Natural Resources Canada obtained from differential processing using the Bernese GNSS Software. The estimated horizontal and vertical velocities of the three solutions (PPP, PPP-AR and differential) were in good agreement, and show the overall rotation and vertical uplift/subsidence of the study region. The same consistency was observed by comparing intraplate horizontal velocities. Ambiguity fixing abilities in PPP showed substantial improvement in the east component compared to the float solution. PPP was also found to considerably reduce computational load by processing each station independently, taking approximately 2.2 seconds per station on a desktop computer. The results of this study confirmed that PPP-AR can provide position and velocity accuracy comparable to a global differential solution, and can be used for identifying intraplate velocities.

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7. Agricultural land values using Geographic Information Systems: design location model and tools for information available by geoportal. Application to a Spanish Agricultural Area
Inmaculada Marques-Perez, Gaspar Mora-Navarro, Jose-Luis Perez-Salas, Joan Velilla-Torres & Carmen Femenia-Ribera

Quantifying the effect of location on land values can be done by designing a location factor which considers the most relevant aspects that may influence this value such as proximity to large cities, the population living around the parcel or land to be valued, the distance from it to markets or logistic centres, or the existence of places of environmental or landscape interest. Considering these variables can be complicated by having to process large amounts of distinct data (distances, no. of inhabitants or population size, protected areas, etc.), which have to be processed and interpreted to be able to define the factor that summarises them, and can affect the land value from income, such as productive assets, to correct its value. The main proposal put forward in this research is to study the various location aspects that affect land values, and the possibilities that Geographic Information Systems (GIS) offer to design with free software tools that allow simple calculations of a location correction factor and, consequently, land values. Calculations were made for all the rural cadastral parcels (2.3 million) in the Valencian Region. Results can be integrated into a new online GIS portal and make these available to users in soil valuation studies.

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Survey Review 50, No 362. September/October 2018

1. Guest Editorial
Michael Barry

Fit-for-purpose land administration – administration that suits local circumstances or management bumper sticker?

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2. Accurate coupled lines fitting in an errors-in-variables framework
Yongjun Zhou, Jinghai Gong & Xing Fang

For the purpose of accurate measurement of regular polygons, the boundary lines with parallel, perpendicular or given angles are defined as coupled lines. Provided that the noisy data points are measured from each line without outliers, an accurate and numerical reliable weighted total least squares (WTLS) method is proposed for two dimensional coupled lines fitting task. The underlying problem is modelled within an errors-in-variables framework by assuming all the coordinates are subject to random errors. In order to overcome the possible ill-posedness, the lines are parameterised as constrained Hessian normal form instead of the intercept and slope one. A generic WTLS algorithm is derived in case of the random columns are corrupted by fully correlated errors. Special case that the data are corrupted by homocedastic errors are considered and solved with less computational expenses. A single line fitting and a simulated regular hexagon fitting examples are performed with comparisons and discussions. The proposed methods can be used for accurate regular polygon measurement in vision metrology or reverse engineering.

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3. Algorithm of land cover spatial data processing for the local flood risk mapping
Monika Siejka, Monika Mika, Tomasz Salata & Przemysław Leń

Floods are a natural phenomenon that has always been and will pose a threat to people’s life and health, their property and the environment. Total elimination of the flood is impossible, but the current state of knowledge enables the use of the available tools in order to reduce the scale of these threats. The aim of the study is to develop a methodology of identification of the areas of hindered flow of water, located in the immediate vicinity of rivers. The proposed methodology is based on a study of the land cover. The developed algorithm of land cover spatial data processing for the local flood risk mapping implements GIS tools. Verification of the developed method was carried out on the example of selected rivers in Poland, only one of which is covered by the plans of flood risk management and causes periodic floodings.

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4. An investigation of different Wi-Fi signal behaviours and their effects on indoor positioning accuracy
V. İlçi, E. Gülal & R. M. Alkan

In recent years, in addition to 2.4 GHz Wi-Fi signals, 5 GHz signals have been introduced making it possible to transmit data at both IEEE 802.11n and 802.11ac standards. Therefore, researchers have increasingly focused on developing indoor positioning applications based on Wi-Fi dual band. This study was conducted in two stages. In the first stage, we investigated the behaviours of 2.4 and 5 GHz Wi-Fi signals by collecting received signal strength (RSS) values from access points and determined the relationship between RSS and distance for each signal frequency using a curve fitting technique. Furthermore, we comparatively analysed signal fluctuations and their effects on positioning accuracy. In the second part of the study, we compared the positioning accuracy of four algorithms; namely, bilateration, trilateration, weighted iterative non-linear least square and extended Kalman filter using 2.4 and 5 GHz Wi-Fi signals. The experimental results revealed that the 5 GHz signals were more stable and had better positioning accuracy than the 2.4 GHz signals. Concerning the positioning algorithms, bilateration had the best positioning accuracy at both frequencies.

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5. The triangulated affine transformation parameters and barycentric coordinates of Turkish Permanent GPS Network
K. Ansari, O. Corumluoglu & P. Verma

There are several computational approaches and methods to produce the complete solutions of geometry problems and they give sufficient computational strength for geodetic networks. Every approach and method has their advantages and drawbacks. Barycentric coordinates, also called areal coordinates, provide a new knock approach for geometry problems of such networks. This coordinate system offers triangular finite elements which are quite different from the usual Cartesian coordinate system. Actually, barycentric coordinates are a natural system of coordinates for the affine geometry. The modified approach for the affine transformation and barycentric coordinate system has been introduced and discussed, respectively in the study whether the affine transformation improves the results deteriorated by geometry of a GPS network. For this aim, general affine transformation of six-parameters between Eurasia Fixed Reference Frame (EUREF) and International Terrestrial Reference Frame (ITRF) for Turkish Permanent Global Positioning System Network (TPGN) has been computed. The affine transformation results show that the effects of the first and second translation parameters are in negative and positive directions, respectively. The third and sixth parameters are almost constant, on the other hand the fourth and fifth have a very small positive effect. Additionally, three triangular networks of GPS stations, at different locations in Turkey as a numerical example of barycentric coordinates, have also been presented. In the numerical example, the coordinate values of EUREF and ITRF have some differences after the decimal point, but the barycentric coordinates have very small amount of differences (sixth digit after decimal) which proves that the modified approach is meaningful.

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6. Tight integration of kinematic precise point positioning and digital map for land vehicle localisation
Yashar Balazadegan Sarvrood, Fei Liu & Yang Gao

This paper proposes a method for tight integration of kinematic precise point positioning (PPP) and digital map. The proposed method starts with PPP to estimate the vehicle position. PPP uses Global Positioning System observables, and precise orbit and clock products and additional error modelling to estimate the navigation solution. The estimated navigation solution is used as the input to the fuzzy logic based map matching (MM) algorithm. The proposed MM improves the kinematic PPP by constraining the vehicle location on the road, which provides the map-matched position and the road link azimuth as the feedback to the Kalman filter of PPP. The results indicate that a tight integration of digital map and kinematic PPP outperforms a stand-alone PPP and improves the horizontal root-mean-square error (RMSE) by 56.5% and 60.7% for the open sky and the harsh environment, respectively. Moreover, the float ambiguities can converge faster using this method.

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7. The use of geomatic techniques to improve the management of metro infrastructure
Mª Amparo Núñez-Andrés, Felipe Buill, Saturio Delgado-Medina & Carlos Plancho-Milian

The management of large infrastructures requires comprehensive knowledge of their characteristics and the elements that constitute them. It is essential to know which elements are involved and where they are located. At the same time also, it is vital to understand the overall geometry. However, it is difficult to obtain this information about underground infrastructures due to their lighting characteristics, hazards, lack of GNSS (Global Navigation Satellite System) signals and time available. In this case, to achieve the required quality in both tasks, the mobile mapping systems that are widely used in large surveys and urban inventories have to be adapted to obtain data in underground conditions. To achieve this, geodesic support is necessary. Therefore, a laser scanning and kinematic photogrammetry survey was carried out to obtain the centimetric precision and complete information that is still used today. This paper presents an adaptation of these systems for use in the Ferrocarril Metropolità de Barcelona.

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8. Cadastral system in the Russian Federation after the modern transformation
Tatiana V. Ilyushina, Tomasz Noszczyk & Józef Hernik

The paper presents the notion and procedure of cadastral registration of land and real property objects in the Russian Federation. Russia has gone through significant changes in cadastre over the last dozen years. Introduction of the State Real Property Cadastre Act in 2007 was a corner stone in this regard. Today, the cadastre encompasses all types of real property. The goal of this paper is to present the modern cadastre in the Russian Federation, which has been introduced to keep record of real property. Additionally, the cadastre collects information on the number, surface area, quality and use of land and other real property objects. Data in the state register are used to carry out administrative tasks, protect and use land in an effective manner, plan agricultural management and also to ensure proper location and specialisation of production. The study has shown that the cadastre implemented in Russia essentially achieves its goals and completes the tasks it was given, but its organisation requires further development and improvement.

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9. Geostatistical determination of recent vertical movements of the Earth’s crust on the territory of the Republic of Srpska
Dejan D. Vasić, Gorana Z. Todorić & Radenko I. Višnjić

The aim of this paper is the geodetic determination of vertical movements of the Earth’s crust using the methods of geostatistics. A practical research is conducted for the territory of the Republic of Srpska and most of Bosnia and Herzegovina. A free kinematic levelling network is constructed based on the data of high accuracy levelling, and vertical velocities of levelling points (benchmarks) are determined by applying the least squares adjustment method. Spatial vertical velocities and their horizontal gradients are evaluated using geostatistical methods. These results are compared with the existing geodetic solutions and other geo-data, and areas with significant values of vertical movements of the Earth’s crust are marked.

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10. A simplification method for grid-based DEM using topological hierarchies
W. Sun, H. Wang & X. Zhao

Terrain simplification is the basis of constructing multi-scale digital elevation models. However, a definite corresponding relationship between the scales and the hierarchy of terrain skeleton lines cannot be established easily. In this paper, a novel method is designed based on multi-resolution Morse complex. First, a universal improved algorithm for the original terrain Morse complex is proposed to prevent artificial intersections. Second, significant points are adaptively selected in the hierarchical skeleton lines through topological simplification. Finally, an experimental companion is created. Results indicate that the proposed simplification method can not only retain the main terrain structural characteristics, but also offer better simplification precision.

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11. Research into the impact of systemic errors on the index values of strains
Ruta Puziene, Arminas Stanionis & Jurate Suziedelyte-Visockiene

The article analyses the impact of systemic errors in coordinates on the strain tensors and on internal deformation measures (dilatation and elongation) calculated applying the finite element method to the position changes of stations inferred from GPS measurements. The paper presents the formulas obtained for calculating the impact of errors under different linear models for accumulating systemic errors. Theoretical decisions have been verified conducting computational experiments. The computational experiment carried out on the basis of GPS measurements, using data of six stations established around the Ignalina Nuclear Power Plant, demonstrates that constant errors in coordinates do not affect the tensors and indexes of strains. Any systemic errors in coordinates linearly dependent on the position of geodetic control points have an impact on the values of tensor elements and the indexes of strains; however, variations in deformations across the examined territory remain similar to those without systemic errors.

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Survey Review 50, No 361. July/August 2018

1. Editorial
Peter Collier

Survey Review Biennial Prize.

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2. Land valuation in support of responsible land consolidation on Ghana’s rural customary lands
Kwabena Obeng Asiama, Rohan Bennett, Jaap Zevenbergen & Seth Opuni Asiama

In this paper, we develop a framework for an approach that assigns values to customary rural farmland parcels based on the local people’s view of land value to support land consolidation. In a case study of Nanton, Ghana, key land value factors were identified and weighted by the local community. The weights were integrated into the framework that produced a Land Value Index for each farmland parcel. Though the strength of the approach is found in scenario and sensitivity analyses. However, the prime weakness of this framework is that it is more expensive to use than automatic valuation models.

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3. Scenario-based strategy selection for a sustainable cadastral system development program – a case study of Sri Lanka
Homindra Divithure & Conrad Tang

Scenario-based strategy selection, widely applied to organisational strategic planning and business prognostication, is highly appropriate for cadastral system development exercises. This study elaborately discussed such an example with a case study of Sri Lanka. The aims of this paper are; (1) develop a framework that can be used to formulate strategies for long-term cadastral system development, (2) build scenarios framing the future of a cadastral system development in Sri Lanka in the year 2020, and (3) derive strategies for sustainable cadastral system development in Sri Lanka. It is not a static process and needs dynamic monitoring and adjustment for establishing a valid approach.

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4. Using UAVs for map creation and updating. A case study in Rwanda
M. Koeva, M. Muneza, C. Gevaert, M. Gerke & F. Nex

Aerial or satellite images are conventionally used for geospatial data collection. However, unmanned aerial vehicles (UAVs) are emerging as a suitable technology for providing very high spatial and temporal resolution data at a low cost. This paper aims to show the potential of using UAVs for map creation and updating. The whole workflow is introduced in the paper, using a case study in Rwanda, where 954 images were collected with a DJI Phantom 2 Vision Plus quadcopter. An orthophoto covering 0.095 km2 with a spatial resolution of 3.3 cm was produced and used to extract features with a sub-decimetre accuracy. Quantitative and qualitative control of the UAV data products were performed, indicating that the obtained accuracies comply to international standards. Moreover, possible problems and further perspectives were also discussed. The results demonstrate that UAVs provide promising opportunities to create high-resolution and highly accurate orthophotos, thus facilitating map creation and updating.

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5. Real-time relative mobile target positioning using GPS-assisted stereo videogrammetry
B. Ergun, I. Sayim, C. Sahin & N. Tok

Positioning of a GPS-equipped (Global Positioning System) moving target was determined by stereo-videogrammetry from two images of cameras where they were placed on another GPS-equipped moving platform. The computed position outputs of target were compared with the relative positions obtained from two GPS receivers. The target, a small square-like pattern, was tracked from a certain distance depending on the base distance between the cameras. The video files were created from acquired images data. These video files were used in real-time computation to get the target image position for every film frame. First, the location of target was computed within video film frames. Since the target cannot be searched on the whole picture, maximum pixel length, which the target can travel on the consecutive film frames was considered as offset. Therefore, the search was made over a small area rather than whole picture. That was improved the performance of positioning. Finally, videogrammetrically computed coordinates for all epochs were compared with GPS-based relative distances to justify performance of relative target positioning results.

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6. A Landmark-based cognition strength grid model for indoor guidance
Lin Li, Kai Mao, Guozhong Li & Ya Wen

Indoor guidance has captured the attention of location-based services researchers due to different features between indoor and outdoor spaces. The recognition of indoor landmarks serves a vital role for pedestrian navigation to destinations. To provide better indoor path planning and path guidance, this paper proposes a landmark-based cognition strength grid (CSG) model that caters to a wide spectrum of individualised wayfinding services. In the CSG model, each grid cell that is embedded with these salient characteristics can be oriented to surrounding landmarks to ensure the use of the CSG model to plan various paths, such as the most reliable path, the path with the most identifiable landmarks or specific patrol paths for individuals. Using a large shopping mall as a test site, the model is validated by two scenarios that illustrate the diverse applications of the CSG model in the field of indoor wayfinding.

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7. A regression approach for mitigating periodic errors in 1 Hz GPS kinematic solutions
Xingsheng Deng, Zhiran Zhao & Meiqing Ding

There are wide ranges of errors that degrade the accuracy of high-rate GPS double-difference solutions. The high-rate random noises are eliminated by a median filtering method. Observing data from four base stations are selected from HNCORS for experiments. Experiments show that the random error is ±4 – ±4.5 mm in the horizontal direction and ±9 mm in the vertical direction. The periods of system errors are determined by maximising correlation coefficient between different sidereal days. The recurrence period ranges from 86 153 to 86 165 seconds. Repetition cycles of the north, east and up direction are not consistent, while there is a slight difference ranging from 3 to 12 seconds. An algorithm is proposed to model the periodic system error accurately. Examples show that the algorithm can get a higher precision than that of the wavelet analysis or direct removal. The root mean square of model residual error is only 0.6 – 0.8 mm. The model can be used to improve the accuracy of GPS epoch by epoch data processing.

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8. The impact of solid Earth-tide model error on tropospheric zenith delay estimates and GPS coordinate time series
Fei Li, Jintao Lei, Shengkai Zhang, Chao Ma, Weifeng Hao, Dongchen E & Qingchuan Zhang

Any unmodelled or mismodelled subdaily signals left in the model may not only affect the instantaneous site positions and the associated estimates, but also propagate into spurious seasonal signals, contaminating the daily coordinate time series. To demonstrate how subdaily ‘error’ in the modelling of the solid Earth-tide affects the estimates of tropospheric zenith total delay (ZTD) and how it propagates into long-period signal in the daily GPS time series, we analyse GPS observations collected between 2009 and 2013 for 13 sites in the coastal regions of Antarctica using the GAMIT/GLOBK 10.6 software. We find that ZTD differenced time series, with amplitude at 2 mm level, have inverse correlation with the input K1 correction, and the corresponding admittances range from 6% to 14%; Propagated spurious annual signals are evident in the vertical component of coordinate differenced time series, with amplitudes at the mm level and admittances of around 2–11%.

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9. A universal and robust computation procedure for geometric observations
R. Lehmann

This contribution describes an automatic and robust method, which can be applied to all classical geodetic computation problems. Starting from given input quantities (e.g. coordinates of known points, observations), computation opportunities for all other relevant quantities are found. For redundant input quantities, there exist a multitude of different computation opportunities from different minimal subsets of input quantities, which are all found automatically, and their results are computed and compared. If the computation is non-unique, but only a finite number of solutions exist, then all solutions are found and computed. By comparison of the different computation results, we may detect outliers in the input quantities and produce a robust final result. The method does not work stochastically, such that no stochastic model of the observations is required. The description of the algorithm is illustrated for a practical case. It is implemented on a webserver and is available for free via internet.

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10. Comparative analysis of multi-constellation GNSS single-frequency precise point positioning
Mahmoud Abd Rabbou, Adel El-Shazly & Kamal Ahmed

We develop new single-frequency PPP models, which combine the observations of the current GNSS constellations, including GPS, GLONASS, Galileo and BeiDou. Four single-frequency GNSS PPP models are developed, namely, the undifferenced single-frequency GNSS PPP model, the undifferenced ionosphere-free (IF) code and phase model known as quasi-phase model, the between-satellite-single-difference model (BSSD) and the between-satellite-single-difference ionosphere-free (BSSDIF) model. The IGS final precise products are used to account for the orbital and clock errors. For both undifferenced and BSSD models, the IGS final global ionospheric maps (GIM) model is used to correct the ionospheric delay. The GNSS inter-system biases are treated as additional unknowns in the estimation process for the undifferenced models, while a loosely coupled technique is used for the BSSD models. Various GNSS combinations are considered in the assessment for each PPP model, including GPS/GLONASS, GPS/Galileo, GPS/BeiDou and quad-constellation GNSS observations. It is shown that the multi-GNSS observations enhance the PPP solution accuracy in comparison with the GPS-only solution. Furthermore, the use of IF-PPP technique enhances the positioning accuracy by 25, 20, 24, 20 and 19% compared with the GIM-based PPP model for the GPS-only, GPS/GLONASS, GPS/Galileo, GPS/BeiDou and quad-GNSS combinations, respectively, for 1 h of GNSS data processing. In addition, an average of 15% positioning accuracy improvement can be obtained when the BSSD techniques are used compared with the undifferenced techniques. However, for 6 h of processing, comparable positioning accuracy can be obtained from all four single-frequency models.

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Survey Review 50, No 360. May/June 2018

1. Reviewing the status of national spatial data infrastructures in Africa
Collins Mwange, Galcano Canny Mulaku & David N Siriba

The paper reviews the status of National Spatial Data Infrastructure (NSDI) in Africa, based on a survey conducted between April and October 2014. Web searches and data from the United Nations Department of Economic and Social Affairs E-Government survey of year 2014 were used to supplement the survey data. Using the SDI-Readiness methodology, the SDI-Readiness index is computed. Of the twelve countries reviewed, Senegal (0.69), Rwanda (0.65), South Africa (0.64) and Ghana (0.61) have higher indices; while Tanzania (0.33), Zimbabwe (0.33), Botswana (0.35) and Malawi (0.38) have lower indices. Countries with higher SDI-Readiness indices, which is a proxy for the capacity and willingness to develop an SDI, have a better chance of success in developing their NSDI. Lower indices implies that a lot more effort is required by the respective countries. Although all SDI components should be given equal prominence, the study suggests that more emphasis should be placed on improving the human and financial resources if Africa is to succeed in NSDI development.

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2. The concept of using the water cadastre databases components for the construction of multi-dimensional cadastre in Poland
M. Mika, M. Siejka, P. Leń & Ż. Król

The article has analytical and conceptual character. It contains a detailed analysis of the scope of cadastral information on waters based on actual data from the regional databases, which are established in four logistically major cities in Poland: Warsaw, Krakow, Wroclaw and Szczecin. The authors examine the contents of water cadastre databases in Poland and possibilities of using them in building the 3D cadastre. The concept of using water cadastre as a subsystem of the 3D cadastre presented in the work was carried out using graphical methods of the object-oriented analysis. The authors present a Real Estate Cadastre (REC) model based on synchronisation of the Land Register databases with the water cadastre databases carried out in District Water Management Boards. Modernisation and thematic expansion of Land Register databases, which act in Poland as cadastre, consistent with the presented REC model is a chance to improve the real estate market in Poland.

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3. From point cloud to BIM: an integrated workflow for documentation, research and modelling of architectural heritage
C. Rodríguez-Moreno, J. F. Reinoso-Gordo, E. Rivas-López, A. Gómez-Blanco, F. J. Ariza-López & I. Ariza-López

Heritage buildings traditionally have been tackled from several points of view: architectonic features, architectural style, archaeology, history, etc. Documents derived from those studies were classified and put together to form the documentation for consultation, taking decisions about its conservation, and restoration. Such a document organisation has some inconveniences: objects composing the building were treated as isolated objects not related to its adjacent objects. Nowadays technology may help to discover the relationship between architectural objects forming heritage buildings. The tool that makes it possible to include functionality in architectural objects is BIM (Building Information Modelling). In this paper the historical evolution of Saint Jeromés Church in Baza will be analysed and stored in a functional model which includes geometry and its current state. We propose a procedure for building the BIM through its historical roots and evolution to be included in each remarkable object modelled from the point cloud surveyed.

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4. Terrestrial laser scanner error quantification for the purpose of monitoring
Hasan Abdulhussein Jaafar, Xiaolin Meng & Andrew Sowter

In this paper, TLS error sources are discussed and the types and magnitudes of these errors are observed. Furthermore, a procedure for eliminating laser scanner outliers and reducing noise is introduced. For this purpose, two TLS instruments have been examined: Leica Scanstation P20 and P40. The results of the tests reveal the average noise level (mean errors) between two scans can be improved by using a surface model rather than direct point to point differencing, with improvements from 2.8 mm to 1.7 mm and from 0.7 mm to 0.2 mm for P20 and P40 respectively. In addition, the best fit local planes technique can remove outliers without reducing point density. Therefore, the maximum errors decreased from 50 mm (due to outliers) to 11 mm and from 13 mm (due to outliers) to 1 mm for P20 and P40 respectively.

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5. Triple-frequency GNSS models for PPP with float ambiguity estimation: performance comparison using GPS
M. Deo & A. El-Mowafy

This contribution proposes two new precise point positioning (PPP) models that use triple-frequency data, designed to accelerate convergence of carrier-phase float ambiguities. The first model uses a triple-frequency ionosphere-free linear combination that has minimum noise propagation and geometry-preserving properties. The second model uses a mixed code and carrier-phase linear combination with the same properties. A third model was also implemented, which uses individual uncombined triple-frequency measurements. The three models were validated using triple-frequency GPS data and their performance was compared to the traditional dual-frequency model in terms of the convergence time taken to achieve and maintain a uniform three-dimensional accuracy of 5 cm. Testing includes PPP processing of 1-h measurement blocks using 1–8 days of data from three locations in Australia. It was shown that all the three triple-frequency models had improved solution convergence time compared to the traditional PPP dual-frequency model although they gave almost similar accuracy and precision. The convergence time, when using the triple-frequency ionosphere-free model improved, by 10%, the improvement was 9% when using the mixed code-phase model, whereas the individual uncombined model resulted in 8% improvement.

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6. High performance filtering for big datasets from Airborne Laser Scanning with CUDA technology
Wioleta Błaszczak-Bąk, Artur Janowski & Piotr Srokosz

There are many studies on the problems of processing big datasets provided by Airborne Laser Scanning (ALS). The processing of point clouds is often executed in stages or on the fragments of the measurement set. Therefore, solutions that enable the processing of the entire cloud at the same time in a simple, fast, efficient way are the subject of many researches. In this paper, authors propose to use General-Purpose computation on Graphics Processing Units (GPGPUs) to process the big datasets obtained from ALS. GPGPU handles computation for computer graphics using GPUs (Graphic Processing Units). This study was based on programming model Compute Unified Device Architecture (CUDA), which facilitates the development of applications in GPUs. CUDA programming was used to carry out the filtration based on adaptive TIN model method in the initial stage of the processing of big ALS dataset. Results of the analysis showed that GPGPU can be used for the filtration of ALS point clouds and significantly speeds up calculations for big dataset.

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7. Terrestrial laser scanning for the monitoring of bridge load tests – two case studies
H. Lõhmus, A. Ellmann, S. Märdla & S. Idnurm

Terrestrial laser scanning (TLS) technology has various applications due to its capability of acquiring detailed 3D information about objects within a limited time-period. Yet, it is not widely used for the deformation monitoring of structures. To investigate the suitability of TLS for such tasks, a time-of-flight type Leica ScanStation C10 was used to determine the vertical deformations for two bridge load tests in Estonia, namely for the Loobu highway bridge and the Tartu railway overpass. The TLS results were verified with precise levelling, reflectorless tacheometry and dial gauges. Generally, deformation estimates obtained from TLS and other measurement techniques show sub-millimetre agreements (in terms of standard deviations). The maximum differences between the TLS and precise levelling results were 3.4 and 0.8 mm for the Loobu and the Tartu study, respectively. Since TLS has not yet reached the same accuracy as conventional geodetic high-precision techniques, it cannot fully replace them in high accuracy applications. However, TLS can be considered a complementary survey method for load tests as it provides valuable entire surface covering 3D information.

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8. Obituary: Clifford Dann MBE, FRICS
Dr Peter Collier

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Survey Review 50, No 359. March/April 2018

The following articles were presented at the Joint 2015 Malta FIG Commission 3 and Commission 7 Workshop

1. A comparison of address geocoding techniques – case study of the city of Zagreb, Croatia
V. Cetl, T. Kliment & T. Jogun

In the last years a lot of online geocoding services have become available online. Some of them are based on VGI as input data. Such services are very useful in the case of big amounts of objects that need to be geocoded. However, the quality of such services has still not been adequately explored. In this paper we tried to answer several questions regarding the quality of online geocoding services using the city of Zagreb in Croatia as a research area. The results of research showed that the currently available services need improvements to provide accurate sources for geocoding.

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2. Three-dimensional cadastre modelling of customary real property rights
D. Kitsakis, C. Apostolou & E. Dimopoulou

Although repealed from legislation, customary rights, restrictions and responsibilities (RRRs) deriving, inter alia, from religious, cultural and historical background still impact real estate property. Such RRRs may constitute complex, overlapping properties not easily accommodated within contemporary cadastral infrastructure. Peculiarities regarding customary law-derived properties’ geometry and contradictions to statutory legislation result in difficulties integrating them to national cadastral systems. This paper investigates the status of customary law-derived RRRs, presenting a three-dimensional modelling and recording application for the Hellenic Cadastre, adjusting Land Administration Domain Model, examined through implementation on two cases of special real property objects in Greece.

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3. A new model for cadastral surveying using crowdsourcing
K. Apostolopoulos, M. Geli, P. Petrelli, C. Potsiou & C. Ioannidis

A ‘fit-for-purpose’ approach is developed, tested and presented for cadastral surveys through increased owners’ participation using new technology and m-government services. Three case studies are reported, for urban, suburban and rural areas, with a combined use of two mobile applications: a commercial software package (ESRI’s Collector for ArcGIS) and an opensource self-developed application named BoundGeometry. The parameters of time, quality and accuracy are assessed and the identified difficulties are classified. It is concluded that the method is applicable both in developed and developing countries, and each time adjustable to the available infrastructure.

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4. 3D visibility analysis indicating quantitative and qualitative aspects of the visible space
D. Golub, Y. Doytsher & D. Fisher-Gewirtzman

This paper presents the development of a 3D visibility analysis model that consist a combination of objective calculations and a subjective evaluation, representing the value of the view and its possible impact on the perception of a viewer. The model, developed in Matlab, has default weightings for different elements of the view, which can be changed in accordance to future users. A bounding box, defined as working area consisting buildings and topography, is divided into equal-size voxels and sub-voxels for higher accuracy. This model may be further developed for use in practice to support a sustainable future urban environment.

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Regular contributions to the journal

5. Bridge pier settlement prediction in high-speed railway via autoregressive model based on robust weighted total least-squares
X. Gong & Z. Li

The autoregressive model for time series prediction is a common method in settlement prediction. In the traditional parameter estimation of autoregressive model, least-squares (LS) is the method, which only considers the errors in the observation vector. However, the errors in the coefficient matrix have not been considered. To solve this issue, weighted total least-squares (WTLS) method is developed for parameter estimation. However, it does not consider the possible gross errors in observations, which may lead to a reduction in the robustness and reliability of parameter estimation. In order to solve this problem, in this study, robust WTLS (RWTLS) method is proposed to estimate parameters of autoregressive model for bridge pier settlement prediction in high-speed railway. A comparison with LS, robust LS (RLS) and WTLS methods is conducted for bridge pier settlement prediction and two sets of observed data are used in this evaluation. The results of experiments show that the variance components and the mean absolute values of predictive residuals obtained by WTLS and RWTLS methods are smaller than those by using LS and RLS methods in the case of modelling data without gross errors, and the variance component and the mean absolute value of predictive residuals obtained by RWTLS method is the smallest in the case of modelling data with gross errors. It shows that autoregressive model settlement prediction for bridge pier by using RWTLS method is more reliable and accurate than LS, RLS and WTLS methods in high-speed railway.

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6. Kriging and moving window kriging on a sphere in geometric (GNSS/levelling) geoid modelling
M. Ligas & M. Kulczycki

A comparison of kriging and moving window kriging (MWK) on a sphere is performed on GNSS/levelling data. The study was to give the answer on whether there is a significant gain in prediction accuracy when we apply an MWK instead of ‘classical’ kriging and also to what extent the use of global geopotential model EGM2008 improves prediction. The quality of prediction for all kriging and data variants has been investigated on three regions (being on the territory of the conterminous USA) characterised with a different spatial extent and density of sampling. Numerical tests revealed that in case of high-sampling density there was no accuracy gain when using MWK instead of classical kriging (cK). In contrast, for less numerous datasets and a much larger spatial extent (low-sampling density) MWK adapts itself to data much better than cK. Incorporation of EGM2008-based undulations as a long-wavelength trend for both cases (classical and moving window) significantly improved prediction quality.

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7. Chronology of the development of geodetic reference networks in Serbia
Oleg Odalović, Miljana Todorović Drakul, Sanja Grekulović, Jovan Popović & Danilo Joksimović

In this paper, the development of geodetic reference networks in Serbia is shown. This historical summary covers the time from the first organised work in 1855 until today. Special attention has been paid to the establishment of the modern network using Global Navigation Satellite Systems (GNSS). Within the networks established by GNSS, two last realised networks are especially distinguished. The first one is a classic spatial reference network SREF (Serbian Reference Frame) established in 2003, and the second one is a permanent stations network – AGROS (Active Geodetic Reference Network of Serbia) realised in 2006.

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8. Study on high-precision regional monitoring method of high-grade highways subsidence under the influence of underground mining
B. C. Zhao, H. Z. Li, G. L. Guo & L. Q. Mi

High-grade highways are the foundation of regional economic development. How to monitor the deformation of high-grade highways under the influence of underground mining and guarantee their safe operation is very important and is directly relevant to regional economic development. Considering that Differential interferometric synthetic aperture radar (D-InSAR) technology has low monitoring accuracy around the maximum subsidence and high-accuracy levelling can only monitor the deformation of finite number points, the method of assimilating the D-InSAR data and levelling monitoring data based on Kalman filtering theory is proposed to improve precision of regional monitoring. Research results indicate that data assimilation results based on ensemble Kalman filter are much better than the inversion results and D-InSAR data. When applied to Zouji Highway of Jining, the total RMS is 17.7 mm after assimilating the D-InSAR data and levelling monitoring data, which can meet accuracy requirements of deformation monitoring of high-grade highways. Research results are of theoretical and practical significance to guarantee safe operation of high-grade highways under the influence of mining activities.

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9. On the total least-squares estimation for autoregressive model
W. Zeng, X. Fang, Y. Lin, X. Huang & Y. Zhou

The classical Least-Squares (LS) adjustment has been widely used in processing and analysing observations from Global Satellite Navigation System (GNSS). However, in detecting temporal correlations of GNSS observations, which can be described by means of autoregressive (AR) process, the LS method may not provide reliable estimates of process coefficients, since the Yule-Walker (YW) equations refer to structured Errors-In-Variables (EIV) equations. In this contribution, we proposed a Total Least-Squares (TLS) solution with the singular cofactor matrix to solve the YW equations. The proposed TLS solution is obtained based on the fact that random errors belong to column space of its cofactor matrix. In addition the proposed solution does not need any substitution of the squared true parameter vector as done by the current publications. Finally, we simulate the AR process to prove that our solution is more reliable than the existing methods.

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Survey Review 50, No 358. January/February 2018

1. A new approach to calculate the land fragmentation indicators taking into account the adjacent plots
J. Janus, M. Mika, P. Leń, M. Siejka & J. Taszakowski

Land fragmentation is a phenomenon which constitutes one of the biggest obstacles to profitable agricultural production. Measurable estimation of this phenomenon is possible by a number of known indicators, based on the surface area of parcels in the given area, their location in space and belonging to individual farms. This method of calculation of the indicators is inaccurate due to the phenomenon of neighbourhood of plots which belong to the same owners. For the purposes of calculating the ratios of actual fragmentation of land, these parcels should be treated as one complex. The article presents a proposal for the adjustment of existing methods of determination of the fragmentation of land indicators, taking into account these phenomena. The object of the research covered area of the voivodeship of Malopolska located in the southern part of Poland. Developed by the authors, method of calculation of land fragmentation indicators, based on complexes of land belonging to the same owners (complexes of plots aggregation), gives very good results in the evaluation of the intensity of the land fragmentation. Obtained in this way, indicator’s land fragmentation represents the real situation on the ground.

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2. Surface area calculation for DEM-based terrain model
S. Xue, Y. Dang, J. Liu, J. Mi, C. Dong, Y. Cheng, X. Wang & J. Wan

The surface area calculation is meaningful for a variety of space-filling phenomena, for example the packing of plants or animals within an area of land. An integral method for calculating the landscape surface area is proposed by considering the curvature of terrain and the measurement errors in Digital Elevation Model (DEM) data. Applying the least squares method, with the DEM data we estimate the first-order and second-order derivatives of the terrain surface to reduce the influence from the DEM data errors. It shows that the first-order derivatives estimated are statistically independent to the second-order derivatives estimated when using a symmetrical configuration composed of a series of DEM points. The surface area within a polygonal region is obtained by partitioning the polygonal region into a series of squares, rectangles and triangles. The proposed method is compared with the triangle-based methods and the results show that the proposed method is more robust.

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3. Informal economies, state finances and surveyors
P. van der Molen

All countries host informal economies, sometimes even exceeding the size of the formal economy. Living in the informal economy means for citizens that they and their activities are invisible for the government. Governments miss information about which people live in their country and what economically happens. They miss relevant data to develop policies, to monitor implementation and to levy taxes for generating budget. This hampers good governance and state building. This paper analyses the problem, and argues that when surveyors would expand their capacity for administration of land to other recordable subjects and objects, they can contribute to a solution.

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4. Height biases of SRTM DEM related to EGM96: from a global perspective to regional practice
A. Üstün, R. A. Abbak & E. Zeray Öztürk

It is investigated to what extent EGM96 affects the accuracy of digital elevation model (DEM) produced from the shuttle radar topography mission (SRTM). Global and regional analysis of EGM96 compared with EGM2008 indicate that locally there are large differences distorting to the accuracy level of SRTM DEM. In the absolute sense, the overall geoid differences throughout 1x1 arc-degree tiles reach −5 m in the northeast and 2–3 m in the southern parts of Turkey. A numerical investigation over the test profiles of 200–700 km length running at various directions proves that a possible vertical datum change from EGM96 to EGM2008 yields systematically more accurate height information with an improvement of up to 2.5 m. A GPS-levelling traverse of about 900 km length points out some key patterns of this recovery. Consequently, a correction for the present version of SRTM DEM should be considered in critical implementations of Earth sciences like geoid or water flow modelling, especially for areas where EGM96 shows weak performance.

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5. Maintenance of the state survey in the Republic of Montenegro
R. Đurović, I. R. Aleksić & R. Mihajlović

The paper provides an overview of the maintenance of the state survey, as the foundation for the development of the geodetic infrastructure, real estate cadastre, mapping and the National Spatial Data Infrastructure (NSDI) in the Republic of Montenegro. A proper understanding of the problems that emerge in the maintenance of the real estate cadastre requires familiarity with its background, i.e. the conditions under which it emerged. Particular attention is focused on geodetic reference networks, as the foundation upon which the cadastral databases were established and have subsequently been maintained, with analysis of their occurrence and current state included.

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6. The use of low-cost, single-frequency GNSS receivers in mapping surveys
M. Tsakiri, A. Sioulis & G. Piniotis

The emergence of low-cost, navigation-type receivers capable to provide carrier-phase data (the so-called high-sensitivity carrier-phase positioning) has been steadily growing over the recent years. The aim of this study was to evaluate the positioning performance of a high-sensitivity receiver in a network real-time kinematic environment for mapping surveying applications. Specifically, using as rover receiver the u-blox NEO-7P module and the low-cost antenna Tallysman TW2410, sets of data were collected for the purpose of mapping surveying. The external accuracy of the obtained solutions is considered using different positioning techniques and the internal indicators of the system during real-time kinematic (RTK) positioning are assessed. The assessment indicates that in benign environments this type of receivers produce results that are comparable to RTK positioning using geodetic receivers and with a significantly lower cost.

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7. An effective QR-based reduction algorithm for the fast estimation of GNSS high-dimensional ambiguity resolution
L. Lu, W. Liu & X. Zhang

To fast estimate high-dimensional ambiguities, we propose a new lattice reduction algorithm based on QR decomposition, which achieves fast integer transformation through an iterative strategy of whole size reduction and the deep insertion of minimum basis vectors. It acquires better basis vectors for ambiguity resolution. The feasibility of the proposed algorithm is verified by comparing its performance with those of LAMBDA, LLL, the parallel Cholesky-based reduction algorithm with ascending sorting (ASCE), and a modified LLL algorithm with deep insertions (PotLLL) under three experimental scenarios. The Hermite defect and defined length ratio are used to measure the reduction quality. Both metrics verify that our proposed method acquires a good reduced basis for accelerating the ambiguity search. To evaluate the practical ambiguity resolution behaviour, we tracked the runtime of ambiguity resolution. The results show that the computational efficiency of the proposed algorithm is better than those of the comparative algorithms.

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8. Representation of the rotation parameter estimation errors in the Helmert transformation model
Q. Wang, G. Chang, T. Xu & Y. Zou

In the Helmert transformation model, the rotation is more difficult to be treated in terms of representation, estimation, and error analysis. First, two classes of representations of the rotation, i.e. the redundant class including the direction cosine matrix and the unit quaternion, and the minimum class including the rotation vector, the Gibbs vector, the modified Rodrigues parameters, and the Euler angles, are reviewed. It is concluded that in general the redundant class should be preferred as they are transcendental-function-free, singularity-free, and discontinuity-free. Second, two classes of estimation errors, i.e. the additive and the multiplicative errors, are defined and compared in detail. While the multiplicative errors are more convenient, the relationship among different representations and the relationship with their additive counterparts are also explored from first principle. It can be seen as a review paper; however, the content concerning the relationship between the additive and the multiplicative errors is believed new.

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9. Introduction to multiple regression equations in datum transformations and their reversibility
A. C. Ruffhead

This paper provides an introduction to multiple regression equations as a method of performing geodetic datum transformations. The formulae are particularly useful when there are non-linear distortions that need to be built into the transformation model. However, the equations take the form of a one-way transformation, usually a local geodetic datum to a global datum. The standard procedure for applying the equations to obtain the reverse transformation only gives approximate results relative to the original model. This paper quantifies the problem and describes three methods for computing the reverse transformation (or inverse transformation) more accurately.

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10. Comment on ‘The use of laser scanning as a method for measuring stairways following an accident’
R. Bowman, M. Roys & N. Davies

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11. Obituary: George Russell ‘Brim’ Brimacombe 5 June 1939–27 July 2017
Dr Peter Collier

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