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Survey Review 49, No 354. May/June 2017

1. An improved regional ionospheric model for single-frequency GNSS users
M. Abdelazeem, R. N. Çelik & A. El-Rabbany

In this study, we develop a regional ionospheric model for single-frequency precise point positioning (PPP) users in Europe. GNSS observations from 60 IGS and EUREF reference stations are processed using the PPP module in the Bernese software to estimate the vertical total electron contents. The developed model has spatial and temporal resolutions of 1° × 1° and 15 minutes, respectively. The resulting model is validated for PPP applications using GNSS observations from another set of stations in three different days. The single-frequency PPP accuracy and convergence time obtained through the developed model are assessed and compared with those obtained through the international GNSS service global ionospheric maps (IGS-GIM). The dual-frequency ionosphere-free PPP is used as a reference. It is shown that the model improves the PPP accuracy and convergence time by about 20, 45 and 45% for the 2D, height and 3D components, respectively, in comparison with the IGS-GIM model.

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2. A novel approach to design measurement models of single-frequency GPS receivers for cost-effective structural monitoring networks
H. Lee, J.-O. Lee, T. A. Musa & H.-Y. Chen

The global positioning system (GPS) has become an effective tool for measuring the dynamics of engineering structures from their absolute displacements. Although dual-frequency GPS receivers are widely adopted for structural monitoring applications to guarantee coordinate accuracy of the order of a few centimetres, the associated cost is too high to place larger number of these sensors. It has been recently recognised that single-frequency GPS receivers have great potential to be the smart sensors for measuring structural displacement due to their low-cost, small form-factor and low power consumption. Hence, the structural monitoring using single-frequency GPS receivers provides a much more cost-effective and compact tool for these applications; however, it remains a challenge to resolve the ambiguities rapidly and reliably. To address such a technical issue, this research focuses on design of GPS measurement models that can be effectively implemented in the structural monitoring networks. The main feature of these models is that they simultaneously model all available observables within the network, including not only GPS satellite ranging signals but also some dynamic constraints of structural monitoring networks, such as nominal coordinates and baselines of the target antennas. A series of tests has been carried out, using simulated satellite geometries and measurements, to assess impact of the proposed models on kinematic positioning performance. The results indicate that overall performance of the models that employ the single-frequency GPS observables and the dynamic constraints can be significantly improved by employing the redundant measurements.

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3. Solution for rank-defect EIV model based on TLS estimation
J. Yang, Y.-J. Wang, Q.-X. Wang & Y.-Q. Tao

Coefficient matrix of mathematical model is rank defect because of lacking essential observation data, traditional method of solving this kind of problem is to supplement constraint condition and compute parameters of model under least squares estimation. However, when elements of coefficient matrix are also made up of observation data as observation vector, error in variables model (EIV model) exists while the model is rank defect. In the contribution, EIV model with rank defect problem is talked about. After proposing this problem, the character of rank defect model is analysed under total least squares estimation. Solution for rank defect model based on TLS is presented, and iterative algorithm is established based on Lagrange function in the contribution. Coordinate transformation model with big rotation angle is taken as an example to prove the feasibility and performance of the presented solution. Based on numerical results of the instance, some conclusions are drawn at last of the contribution.

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4. A robust weighted total least-squares solution with Lagrange multipliers
X. Gong & Z. Li

Weighted total least-squares (WTLS) is becoming popular for parameter estimations in geodesy and surveying. However, it does not take into consideration the possible gross errors in observations, which may lead to a reduction in the robustness and reliability of parameter estimations. In order to solve this problem, in this study, Lagrange multipliers (LM) are employed to make WTLS solution rigorous and the IGG (Institute of Geodesy and Geophysics) weight function is employed to make WTLS solution more robust and reliable, resulting in a new robust WTLS solution (RWTLS-LM-IGG). A comparison with existing WTLS and robust WTLS solutions is conducted for linear regression and coordinate transformation, through experimental evaluation with simulation data sets (with different numbers and magnitudes of gross errors) and two sets of real-life data. The results of simulation experiments show that the variance component and the mean square error of estimated parameter vector obtained by using the existing methods increase almost linearly with an increase in the numbers and magnitudes of gross errors, but these values obtained by using the proposed method are almost stable, which means an effective reduction of the influence of the gross errors by the proposed method as compared with the existing methods. It is also found that the larger the numbers and magnitudes of gross errors, the more obvious such a reduction. Furthermore, the experiment results with two sets of real-life data are consistent with the results of simulation experiments.

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5. Assessing the performance of multi-GNSS precise point positioning in Asia-Pacific region
X. Zhao, S. Wang, C. Liu, J. Ou & X. Yu

Multi-Global Navigation Satellite System (GNSS) integration can effectively improve the satellite geometry strength, and certain effect on the precise point positioning (PPP) accuracy and convergence speed. Taking the system difference into account, this paper deduces the unified GNSS observation model, which is extended to the multi-GNSS PPP functional model. Meanwhile, the stochastic model used in Kalman filter parameter estimation is presented in the paper. Furthermore, to evaluate the performance of the multi-GNSS PPP in Asia-Pacific region, observed data from the International GNSS Service reference stations are analysed using the self-developed software. In detail, the results from Global Positioning System (GPS)-, GLObal NAvigation Satellite System (GLONASS)- and BeiDou Navigation Satellite System (BDS)-only PPP, double combined PPP and GPS/GLONASS/BDS combined PPP under the different observation duration and cut-off elevation angles are analysed. Results demonstrate: (1) compared with the single system PPP, the convergence speed of the multi-GNSS PPP is improved while the accuracy is not significantly improved after processing the 24-h data set; (2) when the observation duration is short, such as 0.5 h, the mean convergence percentage of the BDS combined with GPS and GLONASS PPP increases by an average of 49.6% compared with the single individual systems except for BDS, respectively, under the cut-off angle of 5° and (3) when PPP positioning with high cut-off elevation angles, and at the point of centimetre-level positioning, the GPS/GLONASS/BDS combined PPP has a better performance on the convergence percentage and convergence speed. For example, the percentages of the position biases within 0–5 cm for GPS/GLONASS/BDS are increased by 7.2 and 4.5% in North and East direction compared with GPS/GLONASS under the cut-off angle of 35°, more than any other. And the mean convergence time is only 14.5 min.

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6. Performance evaluation of single-frequency point positioning with GPS, GLONASS, BeiDou and Galileo
L. Pan, C. Cai, R. Santerre & X. Zhang

The single point positioning (SPP) mode has been widely used in many fields such as vehicle navigation, Geographic Information System and land surveying. For a long period, the SPP technology mainly relies on GPS system. With the recent revitalisation of the GLONASS constellation and two newly emerging constellations of BeiDou and Galileo, it is now feasible to investigate the performance of quad-constellation integrated SPP (QISPP) with GPS, GLONASS, BeiDou and Galileo measurements. As a satellite-based positioning technology, the QISPP is expected to improve the accuracy and availability of positioning solutions due to the increased number of visible satellites and the improved satellite sky distribution. In this study, a QISPP model is presented to simultaneously process observations from all four Global Navigation Satellite System (GNSS) constellations. Datasets collected at 47 globally distributed Multi-GNSS Experiment (MGEX) stations on two consecutive days and a kinematic experimental dataset are employed to fully assess the QISPP performance in terms of positioning accuracy and availability. Given that most navigation users are using single-frequency receivers, only the observations on a single frequency are utilised. The results indicate that the QISPP improves the positioning accuracy by an average of 16, 13 and 12% using the MGEX datasets, and 43, 31 and 51% using the kinematic experimental dataset over the GPS-only case in the east, north and up components, respectively. The availability of the QISPP solutions remains 100% even for a mask elevation angle of 40°, whereas it is only 37% for the GPS-only case. All these results are achieved using geodetic-type receivers and they are possibly optimistic for users who use navigation-type receivers.

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7. TotalStation/GNSS/EGM integrated geocentric positioning method
E. Osada, M. Owczarek-Wesołowska, M. Ficner & G. Kurpiński

In this study, we have investigated the use of the plumb line direction from Global Gravity Earth Model EGM2008 in the 3D integrated TotalStation/GNSS positioning. Our study shows that measurements along a total station traverse provides more accurate positioning results if the vertical deflection of plumb line is retrieved from EGM2008, than positioning with unknown deflection. The use of EGM2008 model improves the 3D coordinates accuracy to the level of precise GNSS measurements, while lack of this data introduce spatial displacements of the measured points, up to 26 cm. Hence our method can be useful for building precise 3D models of terrestrial objects in the GRS80 geocentric coordinate system.

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8. A method of GPS/BDS/GLONASS combined RTK positioning for middle-long baseline with partial ambiguity resolution
W. Gao, C. Gao & S. Pan

As China's BeiDou Navigation Satellite System (BDS) has become operational in the Asia-Pacific region, it is important to demonstrate the capabilities that a combination of GPS, BDS and GLONASS to high-precision positioning. Multi-constellation combination increases the available satellites and thus improves the positioning reliability. However at the same time, it will bring some challenges to the high-dimension ambiguity resolution (AR). In this contribution, a GPS/BDS/GLONASS combined real time kinematic (RTK) positioning method for middle-long baseline is proposed. In order to reduce the influence of troposphere and ionosphere delays on AR, a two-step AR strategy is adopted, where wide-lane and ionosphere-free observation model are used respectively. In the integer ambiguity search process, a partial ambiguity resolution (PAR) method is proposed to improve the AR performance. In the PAR method, satellite cutoff elevation, satellite number, AR success rate and ratio are used together to determine the ambiguity subset, which can be fixed reliably. A set of baselines ranging from about 30 to 60 km, which all contain GPS/BDS/GLONASS observations, are used to test RTK positioning performance. Experiment results demonstrate that GPS/BDS/GLONASS combined RTK positioning with partial ambiguity resolution can get much improved performance for middle-long baseline both in positioning speed and accuracy, as within about 20 s and 5 cm, respectively.

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9. Theory and method of hypothetical test for nonparameters in linear semiparametric model
S. Ding, J. Shi & W. Jiang

The linear semiparametric regression model is a combination of the linear parametric model and nonparametric model. Based on the penalised least squares theory for the semiparametric model, this paper presents a detailed discussion on the theory and method of the hypothetical test for the non-parameter in the semiparametric model. The hypothetical statistics are derived and the corresponding property is proved. The proposed theory and method of the hypothesis test are confirmed by simulated experiments.

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10. Optimal conformal map projections in harmonic polynomials in terms of Gauss-Schreiber coordinates
S. Orihuela

The Gauss–Schreiber projection generates a kind of rectangular isometric coordinates that allow to represent, in a continuous form, a terrestrial sector in NS extension including the poles. When they are applied in harmonic polynomials, they enable the optimal mapping of regions that are impracticable for other variables commonly used, e.g. Mercator or stereographic. In this paper, we present the detailed development of the polynomial in Gauss–Schreiber coordinates and an algorithm for map projection optimisation according to the Chebyshev–Gravé's thesis. The result is practical and allows the use of stereographic polar coordinates to be replaced.

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11. Book Review
Martin Schaefer

GPS Satellite Surveying, fourth edition.

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Survey Review 49, No 353. March/April 2017

1. A fast positioning method with altitude hypothesis for BDS receivers
S. Jing, B. Li, W. Liu & G. Sun

A fast positioning method with altitude hypothesis is proposed and described for BeiDou Navigation Satellite System (BDS) receivers to reduce time to first fix (TTFF). First, a rough user position can be estimated using pseudorange measurements of Geostationary Earth Orbit (GEO) satellites and altitude hypothesis, which is called coarse positioning. The altitude aiding can improve the poor geometry of the GEO constellation. In addition, we use an altitude hypothesis instead of accurate altitude information to avoid increasing external assistance. Second, the full pseudoranges of non-GEO satellites are constructed using rough position and fractional code-phase measurements. Finally, the receiver position is determined with all full pseudoranges. Furthermore, the residuals test is used to check positioning convergence to the correct solution. In the end, the validity of the fast positioning method is checked with B1 observation data from the international GNSS Monitoring & Assessment System (iGMAS).

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2. The application of spatial analysis to cadastral zoning of urban areas: an example in the city of Madrid
M.C. Morillo, F. García Cepeda & S. Martínez-Cuevas

Spatial Analysis has been used since the 1990s for hedonic cadastral models of urban areas in large cities. This research aims to apply spatial analysis to zoning a district in Madrid located in the central part of the city in order to estimate urban housing prices. In doing so, the necessary data have been gathered, both vector and raster, as found on the official government website and private company websites. This was done firstly to analyse the characteristics and then for the objectives of the study because it is helpful to use these types of analyses based on vector and raster data along with interpolation methods that obtain regular structures and attempt to avoid the subjective component inherent to traditional procedures. The essence of the work consisted of studying the minimum parameters that influence housing appraisals to resolve the problem. Normally, cadastral appraisal work fulfils the Official Technical Regulations in each country considering a greater number of parameters and corrective coefficients. The importance of this work consisted of lowering and prioritising the number of basic parameters necessary to set urban housing prices. The conclusions section confirms a high likelihood of successfully reducing the number of parameters to achieve an appraisal value that is similar to the one obtained using official methods.

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3. 3D Indoor Surveying – A Low Cost Approach
M. Kalantari & M. Nechifor

Satisfying the accommodation needs of the world's urban population requires high-rise buildings. Accommodating some of 3.5 billion urban population in complex apartments has created challenges including the human scale understanding of complex 3D property rights, and engineering and architectural features relating to building interiors. Technological developments have brought about the prevalence of inexpensive systems such as gaming consoles and smartphones. This paper explores the use of Kinect for Windows (a consumer grade technology that was originally designed for computer gaming purposes) to survey indoors in 3D. This paper presents the result of an investigation into the utility of this widespread and economical technology for 3D surveying of interiors of buildings in relation to Surveying (Cadastral Survey) Regulation 2005, Victoria, Australia. Building on the results of the investigation, the paper argues that such a technology has the potential to be used in other application domains and crowdsourcing 3D indoor information.

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4. A review of the use of terrestrial laser scanning application for change detection and deformation monitoring of structures
W. Mukupa, G. W. Roberts, C. M. Hancock & K. Al-Manasir

Change detection and deformation monitoring is an active area of research within the field of engineering surveying and other overlapping areas such as structural and civil engineering. This paper reviews the application of terrestrial laser scanning in the monitoring of structures and discusses registration and georeferencing of scan data. Past terrestrial laser scanning research work has shown trends in addressing issues such as accurate registration and georeferencing of scans, error modelling, point cloud processing techniques for deformation analysis, scanner calibration and detection of millimetre deformations. However, several issues are still open to investigation such as robust methods of point cloud processing for detecting change and deformation, incorporation of measurement geometry in deformation measurements, design of data acquisition and quality assessment for precise measurements and modelling the environmental effects on the performance of laser scanning. A three-stage process model for deformation analysis is proposed as conceptualised from the material reviewed.

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5. Housing poverty in Ecuador: challenges to eradication
G. Alova & G. Burgess

Slum dwelling and housing poverty are not transitional phenomena. They often demonstrate significant resilience to government interventions and the overall economic development. The paper explores these challenges from the experience of Ecuador, based on the analysis of the qualitative data collected in a field study in Quito. The results point to a significant policy trap in the housing and lending schemes. Internal psychological barriers experienced by vulnerable communities also reduce the effectiveness of government programmes. The housing inequalities can also be linked to defective urban planning practices in the past, and the emerging trend of fragmentation. Based on the findings, it is recommended that successful solutions would be specifically targeted to the households in extreme poverty, and guided by the principles of participatory design, appreciating the needs of these communities. An effective approach would integrate the strategies on urban planning, infrastructure, public service provision and urban labour markets.

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6. Terrestrial self-contained navigation system based on a novel laser Doppler velocimeter
C. Gao, G. Wei & X. W. Long

In order to improve the accuracy and manoeuvrability of terrestrial self-contained navigation system, an idea of building an integrated navigation system using a novel laser Doppler velocimeter together with an inertial navigation system is proposed. The structure and performance of the split reuse-type structure of the laser Doppler velocimeter are expounded, and the integrated technology of marching initial alignment and real-time errors compensation are also discussed in detail. The static inertial alignment of the inertial navigation system can be skipped over and the position error of navigation has been decreased from 1180 m in 2 h to 6 m in 2 h. The experiment results show that the strapdown inertial navigation system/laser Doppler velocimeter integrated navigation system can work effectively without parking and the high-accuracy self-contained navigation can be achieved.

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7. Adaptive slope filtering for airborne Light Detection and Ranging data in urban areas based on region growing rule
Y. B. Yang, N. N. Zhang & X. L. Li

Automatic ground filtering for Light Detection and Ranging data is a critical process for the creation of Digital Terrain Models. Several methods have been developed for filtering Light Detection and Ranging data and some improvements have been made but the problem has not been fully solved for the complicated landscape types and abrupt surfaces. In this paper, the region growing algorithm is introduced into the slope-based algorithm. A probabilistic function is introduced and the index of probability is used to further eliminate the pseudo ground points. A comprehensive test of the performance on nine study sites is conducted and compared with the results of seven other published methods based on the Kappa coefficients and the total errors. Overall, the slope-based and region growing algorithm performs the best in urban areas compared with other filtering methods published in terms of average Kappa value and total errors. The slope-based and region growing algorithm is adaptive to the thresholds of the slope and the filtering window, two commonly required parameters. The complexity of terrain does not significantly influence the performance of the slope-based and region growing algorithm, which allows it to be adopted in different terrains for urban areas.

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8. Food security, land use and land surveyors
P. van der Molen

One of the measures to provide food security for the 9.5 billion people who are estimated to live on earth in 2050 is growth of agricultural production and productivity. Yield analyses reveal that all continents have potential for growth, in particular Africa. Land expansion is still possible, and land management and land administration should contribute to efficient land use and security of tenure. Much agricultural land is not well managed and unrecorded, obstructing realising the potential for growth. As land surveyors are responsible for these issues, at least in a multi-disciplinary environment, they can contribute substantially. However, further expertise on agriculturally focussed land management, knowledge of multiform land and water rights, innovative recording methods and geospatial technologies must be acquired.

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Survey Review 49, No 352. January/February 2017

1. Multiple linear regression with correlated explanatory variables and responses
B. Li, M. Wang & Y. Yang

Different from the traditional linear regression model that captures only the errors of dependent variables (responses), this contribution presents a new multiple linear regression model where, besides the errors of responses, the errors of explanatory variables and their correlations with response errors are rigorously taken into account. The new regression model is typically a non-linear errors-in-variables (EIV) model, which is referred to as the error-affected and correlated linear regression (ECLR) in this paper. Considering the fact that only part of elements in design matrix A of the regression model are random, the authors express error matrix EA of A as a function of EX consists of all non-zero random errors. Then, the authors can easily formulate the stochastic model without the effect of non-random elements in A. An iterative solution is derived based on the Euler–Lagrange minimisation problem for ECLR. The authors further show that ECLR is very general and some of the existing linear regression methods, the ordinary least squares (OLS), the total least squares (TLS) and the weighted total least squares (WTLS), are the special cases. The experiments show that the ECLR method generally has a better performance than the OLS, TLS and WTLS methods in terms of the difference between the solution and the true values when the explanatory variables and responses are significantly correlated.

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2. Adaptive time-variant adjustment for the positioning errors of a mobile mapping platform in GNSS-hostile areas
J. Han & C. Lo

A mobile mapping system (MMS) utilizes global navigation satellite system (GNSS) and inertial navigation system (INS) techniques and thus makes possible a direct geo-referencing solution everywhere along its surveyed path. It is capable of acquiring a vast amount of spatial information in an efficient manner and is adopted in a wide variety of applications. However, when the GNSS signal is obstructed, its positioning solution can only rely on the INS observables, which acquire significant and cumulative errors over time. In this study, an adaptive time-variant adjustment model is proposed to compensate for the MMS positioning error in a GNSS-hostile area using ground calibration points. Based on the results from a case study, it illustrates that the positioning error of a mobile mapping platform in an urban area for a long time could reach a level of several metres because of GNSS signal obstructions. However, this error can be properly modelled and significantly reduced to a centimetre-level when the proposed approach is applied. Consequently, both the efficiency and reliability of the MMS applications in a GNSS hostile environment can be further guaranteed.

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3. Empirical comparison of the Geodetic Coordinate Transformation Models: a case study of Croatia
Matej Varga, Marijan Grgić & Tomislav Bašić

This paper presents empirical research on coordinate transformation models that enable coordinate transformations between the historical astro-geodetic datums and datums related to the European Terrestrial Reference System (ETRS), through a case study of the Republic of Croatia. Thirteen models were investigated for the transformation from the historical Croatian State Coordinate System (HDKS) to the Croatian Terrestrial Reference System (HTRS96): Molodensky 3 and 5 parameter (standard and abridged) conformal transformation models, 7 parameter transformation models (Bursa-Wolf and Molodensky-Badekas model), Affine transformation models (8, 9, 12 parameter), Multiple Regression Equation approach, and several transformation models that include extending of the aforementioned 7 parameter and 8, 9, 12 parameter Affine transformation models with distortion modelling. Most of the models were investigated for the first time over the Croatian territory. Analysis of transformation models performance was conducted using an independent data set of reliable geodetic points. The study provides mutual comparison of the models and their comparison with the official Croatian transformation model called T7D. Furthermore, the most appropriate transformation model(s) were defined regarding the required accuracy and the available resources for the coordinate transformation models implementation. In addition, the paper provides a brief theoretical background and equations of each transformation model and summarises the bibliography on the research topic.

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4. A comprehensive evaluation of GNSS- and CORS-based positioning and terrestrial surveying for cadastral surveys
R. Cuneyt Erenoglu

Many Global Positioning System/Global Navigation Satellite System (GPS/GNSS) methods are applied to the cadastral survey after the rapid development of satellite-based positioning. These methods are reported to give efficiency, speed and economy compared to the conventional ones. In this study, it is aimed to comprehensively evaluate the most commonly used GPS/GNSS methods for cadastral survey. Furthermore, a median based comparison strategy was developed for the distribution of the results. The research results showed the difference of a few centimeters between the coordinates obtained from the terrestrial and the GPS/GNSS techniques. Furthermore, the developed robust criteria verified the compatibility of the results. It is clear that the GPS/GNSS based methods achieve high accurate output in real time and are well-matched with surveying standards in Turkey. In addition, the robust criteria appear to be a fast, effective and objective method to compare the results, especially for the height component.

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5. Performance analysis of precise point positioning using multi-constellation GNSS: GPS, GLONASS, Galileo and BeiDou
M. Abd Rabbou & A. El-Rabbany

We developed a new GNSS PPP model, which combines the observations of GPS, GLONASS, Galileo and BeiDou satellite navigation systems for precise applications. Both undifferenced and between-satellite single-difference (BSSD) ionosphere-free GNSS PPP models are developed. The contribution of the new GNSS observations is assessed compared with the existing GPS and GPS/GLONASS PPP using three-hours GNSS static data positioning results for several GNSS stations and four consecutive days. Inter-system biases between GPS and other GNSS systems are obtained as additional unknowns in the developed PPP filter. The results indicate that both GPS and GPS/Galileo PPP present comparable positioning accuracy level, which is attributed to the limited number of Galileo satellites. The additional BeiDou observations enhances the positioning accuracy after 15 minutes by 5 cm, 4 cm and 9 cm in latitude, longitude and altitude, respectively compared with GPS only positioning accuracy. However, the BeiDou only PPP results present less accurate positioning accuracy compared with the GPS only PPP. The multi-constellation GNSS PPP enhances the positioning accuracy by 8 cm, 6 cm and 11 cm in latitude, longitude and altitude, respectively Compared with the GPS PPP results. Compared with the undifferenced PPP results, the BSSD model enhances the positioning accuracy after 15 minutes for the different GNSS constellations based PPP. The GPS/Galileo PPP positioning accuracy improves by 30%, 27% and 10% in latitude, longitude and altitude, respectively and the GPS/BeiDou PPP positioning accuracy, enhances by 17%, 22% and 15% in latitude, longitude and altitude, respectively while the multi-constellation GNSS PPP positioning accuracy improves by 22% and 15% in latitude and altitude, respectively over the undifferenced PPP technique. Additionally, the BSSD model is found to be superior with respect to the convergence times for the different GNSS combinations based PPP over the traditional undifferenced PPP model.

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6. Introduction to the GNSS geodetic infrastructure in the Gulf of Mexico Region
J. Yu & G. Wang

Global Navigation Satellite System (GNSS) technology has been frequently applied to coastal hazards studies. Some such hazards include sea-level rise, subsidence, coastal erosion, flooding and faulting. This study summarised the current GNSS geodetic infrastructure in the Gulf of Mexico (GOM) region, which consists of three fundamental components: (1) a dense Continuously Operating Reference Station (CORS) network that is open to the public, (2) a stable regional reference frame that is tied to the International GNSS Service reference frame of 2008 (IGS08) and (3) sophisticated software packages for GNSS data post-processing that are freely available to the academic community. There are over 780 CORS in the GOM region as of 2014. Approximately, 350 of those CORS have a history longer than 5 years. The long-term accumulation of continuous GNSS observations makes it possible to establish a regional reference frame for precisely and coherently delineating minor ground deformations over time and space. This study established a stable Gulf of Mexico reference frame (SGOMRF14) using GNSS data up to the end of 2014. The GIPSY-OASIS software package (V6.3) developed and maintained by the Jet Propulsion Laboratory was used to calculate daily positions in this study. GIPSY-OASIS employs the single-receiver phase ambiguity fixed precise point positioning method, which resulted in 2–3 mm horizontal and 7–8 mm vertical repeatability within the GOM region. Applications of the GOM GNSS geodetic infrastructure in monitoring plate motions, land subsidence and sea-level rise are illustrated in this paper.

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7. Visualising changing tenure relationships: the talking titler methodology, data mining and social network analysis
M. Barry & K. Asiedu

Networks of social relationships and how they evolve in relation to land interests are a fundamental attribute of land tenure systems. Individuals may be members of complex, multi-layered, changing and conflicting social networks at any particular time in changing situations. The Talking Titler relational data model (TTM), data mining and social network analysis (SNA) were used to visualise and explore rapidly changing land interests using an urbanizing customary society as the illustrative context. Land tenure relationships may change rapidly in situations where both external forces and internal agents foment conflict and social change in local politics, and elites may abuse their power to grab land. Peri-urban customary systems evolve in response to urbanization, titling programmes and land sales that put pressure on traditional customary norms. Social network analysis can facilitate visualizing complex patterns of relationships between people and how they relate to land. It may also identify new, previous, unknown and changing relationships and structures on the ground. There are practical challenges to applying the tools, but the methodology and data mining and network analysis techniques show promise as an addition to the set of tools that may be used to improve tenure security and as a scenario analysis tool.

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