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Survey Review 48, No 351. November/December 2016

1. A new ZTD model based on permanent ground-based GNSS-ZTD data
M. Ding, W. Hu, X. Jin & L. Yu

Tropospheric delay has a major effect on the accuracy of navigation and positioning when using the Global Navigation Satellite System (GNSS). Zenith tropospheric delay (ZTD) modelling has been used to weaken the influence of the atmosphere. The work reported here focused on ZTD modelling based on real-time surface meteorological parameters, traditionally represented by the Saastamoinen model. However, Saastamoinen accuracy only reaches scale of centimetres, even to scale of centimetres when the water vapour is active, whereas the scale of ground-based GNSS-ZTD data (i.e. ZTD derived from ground GNSS data) is on the millimetre scale and is considered to be the ‘true’ value. An important direction in GNSS studies is how to make good use of ground-based GNSS-ZTD data to improve the accuracy of the Saastamoinen model. Authors studied the residuals in the Saastamoinen model using high-precision GNSS-ZTD data provided by the International GNSS Service (IGS) product and then carried out modelling based on a back propagation neural network. A new ZTD model (ISAAS) based on real-time surface meteorological parameters is proposed based on this method. The ISAAS model has good accuracy: its BIAS and root mean square error (RMSE) at the test area in Russia were -4.4 and 20.4 mm, respectively, which are lower than the results obtained using the Saastamoinen model (-10.4 and 23.3 mm, respectively). The ISAAS model can improve the ZTD prediction accuracy by more than 12.4% and therefore has important implications for precision engineering measurements in Russia.

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2. A solution to RPCs of satellite imagery with variant integration time
B. Cao, Z. Qiu, S. Zhu, W. Meng, D. Mo & F. Cao

To get a sufficient swath width and the higher resolution, most spaceborne cameras acquire the ground information by multiple time delay integration charge-coupled devices. Owing to the special imaging mechanism, TDI charge-coupled devices (CCD) is required to adjust the integration time dynamically. If the offset between two adjacent chips in the along-track direction is large enough, integration time adjustment will generate innegligible pixel offsets in different integration segments. Under this circumstance, if the PRCs are solved by traditional terrain-independent strategy, which uses the rigorous sensor model to generate evenly distributed object-image points, system errors are inevitably introduced and thus the rational polynomial coefficients (RPCs) cannot obtain the high fitting accuracy. In this paper, we derived the quantitative relationship between integration time and pixel offsets. The RPCs fitting technology based on integration time equalisation for improving the fitting accuracy was then discussed. The potential for this method to yield high fitting accuracy and the ability to keep raw object-image relations are illustrated with the experimental results obtained with four high-resolution imageries of Mapping Satellite-1 (TH-1).

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3. Outlier detection by using fault detection and isolation techniques in geodetic networks
U. M. Durdag, S. Hekimoglu & B. Erdogan

Fault detection and isolation (FDI) techniques, which are called standard parity space approach (SPSA) and optimal parity vector approach (OPVA), have been presented in literature extensively for engineering sensor systems or sensor networks. This paper demonstrates the abilities of these approaches to detect and isolate outliers in geodetic networks. The ability to detect and isolate outliers has been measured by computing the mean success rate (MSR) for some given probability of significance levels. These approaches have been applied to a levelling network and a Global Navigation Satellite System (GNSS) network. Different matrix decomposition techniques have been used as an alternative way to the Potter algorithm, which is used in SPSA and OPVA. It has been proven that the abilities of FDI techniques, i.e. the MSRs of OPVA, increase with regard to the ones of SPSA in the levelling network and the GNSS network especially if the significance level α is chosen as 0.001 by using Monte–Carlo simulation.

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4. A new quality validation of global digital elevation models freely available in China
P. Li, Z. Li, J.-P. Muller, C. Shi & J. Liu

Global Digital Elevation Models (DEMs) are widely used in the study of natural hazards and environmental change on a global scale. This paper focuses on validation of the most widely used and newly released global DEMs (SRTM v4.1, NASA SRTM v3, SRTMX and ASTER GDEM v2) in China. Authors use independent and precise ground GPS observations to assess their absolute accuracies. The SRTMX DEM performs best with a height RMSE of 9.7 m, while the RMSE of the ASTER GDEM2 is slightly better than that of the SRTM v4.1, and SRTM v3 in these regions have the largest RMSE of 16.6 m. However, systematic negative bias still exists in all the global DEMs. Results of the raster-based comparisons between the DEMs are dependent on the knowledge of vegetation type, density and structure to a large extent as well as accurate co-registration. Slope comparisons exhibit a hierarchical slope difference of about 2° between the SRTMX DEM, ASTER GDEM2 and SRTM C-band DEM (v4.1 and v3). This paper provides the first direct evidence and measurement of the product quality of SRTMX and SRTM v3 DEM in China and also offers a benchmark for the future evaluation of following global DEM products.

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5. A mixed weighted least squares and weighted total least squares adjustment method and its geodetic applications
Y. Zhou & X. Fang

A mixed weighted least squares (WLS) and weighted total least squares (WTLS) (mixed WLS–WTLS) method is presented for an errors-in-variables (EIV) model with some fixed columns in the design matrix. The numerical computational scheme and an approximate accuracy assessment method are also provided. It is extended from the mixed Least squares (LS)–Total least squares (TLS) method to deal with the case that the random columns are corrupted by heteroscedastic correlated noises. The mixed WLS–WTLS method can improve the computational efficiency compared with the existing WTLS methods without loss of accuracy, particularly when the fixed columns are far more than random ones. The Bursa transformation and parallel lines fitting examples are carried out to demonstrate the performance of the proposed algorithm. Since the mixed WLS–WTLS problem includes both the WLS and the WTLS problem, it will have a more wide range of applications.

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6. Distributed texture-based land cover classification algorithm using hidden Markov model for multispectral data
S. Jenicka & A. Suruliandi

Land cover classification is a vital application area in the satellite image processing domain. Texture is a useful feature in land cover classification. In this paper, we propose a distributed texture-based land cover classification algorithm using Hidden Markov Model (HMM). Here, HMM is used for texture-based classification of remotely sensed images. Furthermore, to enhance the performance, data-intensive remotely sensed image is segmented and distributed into parallel sessions. Experiments were conducted on IRS P6 LISS-IV data, and the results were evaluated based on the confusion matrix, classification accuracy, and Kappa statistics. These results indicate that the proposed algorithm achieves a classification accuracy of 88.75%.

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7. The relation between structured cultural heritages and condominium towards 3D cadastre
Y. E. Çoruhlu, O. Demir, O. Yıldız & M. Çete

In this study, structured cultural heritages were investigated mainly in the light of three-dimensional (3D) cadastre and secondarily e-governance in the name of handing them down safely to future generations. The aim of the study is to give examples of cultural assets/heritages, 3D cadastre, condominium for realising 3D cadastre both legally and technically, and expectations of 3D cadastre, e-governance in Turkey, land management implementations and what the situation for normal buildings is and also what should be done for immovable cultural heritages. Some cultural assets to be protected have been utilised as both trade centres and tourism centres from the past to the present. These buildings, which were generally built in Ottoman times, have been used or occupied owing to repairs and restoration projects in Turkey. The registration of immovable cultural assets, which are immovable properties that are accepted and registered as cultural heritages on the land registry as 3D land objects is extremely important for providing information about drawing projects with details, floors, structural types, the number of independent units, and common areas and documents about building(s) and parcels. The registration status of the hans known as Bedesten, Taşhan, and Gönhan in Trabzon in the Çarşı District owned by fused foundations will be examined in terms of ownership in this study. Deficiencies for these hans’ constructions on 3D registration will be detected by analysing the current registration situation. The way this type of real estate is required to be legally registered from land to completed building will be presented. This study will be completed with suggested solutions in 3D and e-governmental terms at least for immovable cultural heritages. For example; if the italic ‘no’ in the table at the end of the study is transferred into ‘yes’, cultural assets can be known and managed and sustained and also handed down to the future generation not only for Turkish people but also for tourists and all mankind.

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8. Alternative methods for teaching cadastre and remote sensing
F. Manzano-Agugliaro, M. Castro-García, A. M. Pérez-Romero, A. García-Cruz, N. Novas & E. Salmerón-Manzano

Cadastre is essential for the sustainable development of modern society. As well, mapping and surveying is one of the most important tasks for surveyors worldwide in order to maintain the Cadastre. This article summarises a recent study conducted by the authors on overall student assessment of learning Cadastre and Remote Sensing. The goal is to highlight which teaching method has better success rate for students. This paper studies the academic outcomes for a total of 286 students divided into two optional courses of Cadastre at higher education for eight academic years. They are analysed through three different educational modalities: face-to-face (FTF), blended and online for one course, and FTF and online for another. In order to deepen the analysis, a model using classification trees (Classification and regression trees, CART) was created. It has been observed that the blended modality is the one that offers worst results in terms of success rate. If we compare exclusively the FTF method to the online one, we can conclude that the latter shows better results in all respects, improving the success rate and increasing the percentage of students who obtain highest marks.

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Survey Review 48, No 350. September/October 2016

1. LIDAR-based roadway and roadside modelling for sight distance studies
M. Castro, S. Lopez-Cuervo, M. Paréns-González & C. de Santos-Berbel

Sight distance is a key aspect of road design and operation because of its relationship to traffic safety. The most realistic procedures for calculating the section of roadway visibility to the driver require the use of digital elevation models (DEM), which represent both the roadway itself and the features along the roadside. In this study, the influence of different types of DEM, an essential asset in sight distance analysis, is evaluated. Digital terrain models (DTMs), which represent the bare ground surface, and digital surface models (DSMs) that also consider elements above the terrain have been utilised. Both are high-resolution models obtained through airborne Light Detection and Ranging (LIDAR) or terrestrial vehicle (Mobile Mapping System, MMS). In addition, this study shows the influence of roadside vegetation on sight distance, revealing the underlying difficulties and suggesting possible solutions for sight distance studies when using these models.

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2. Conflict and post-conflict land administration – the case of Kosovo
D. Todorovski, J. Zevenbergen & P. van der Molen

Land and its administration are always negatively affected during conflicts and in post-conflict periods. If land and its administration are neglected or not properly addressed after the end of a conflict, they can be a cause for a renewed armed conflict and an obstacle in the rebuilding of a post-conflict society. This paper aims at identifying interventions in land administration that occur in conflicts and post-conflict contexts and relate them to the characteristics of post-conflict societies. A case study is conducted in Kosovo, where with the support of the international community developments in the land administration sector were evident. A strong relation is recognised between interventions in land administration and the characteristics of post-conflict societies. In this regard, it is revealed that strengthening the institutions in the land sector, which obviously occurred in the case of Kosovo, had a positive impact on the institutional weaknesses of a post-conflict society. In addition, interventions in housing and property rights and land administration are identified as elements that contributed to solving the prevailing social and economic problems. Addressing specific land issues in the peace agreement document and the availability of a land dispute resolution mechanism supported settling disputes over land and reduced conflict tensions; these interventions supported the overall security situation. This paper concludes that interventions in land administration indeed facilitated the rebuilding of post-conflict Kosovo.

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3. Use of the gyrotheodolite in underground networks of long high-speed railway tunnels
J. Velasco-Gómez, J. F. Prieto, I. Molina, T. Herrero, J. Fábrega & E. Pérez-Martín

The quality of geodetic networks for guiding Tunnel Boring Machines (TBMs) inside long tunnels depends largely on the correct use of a gyroscope. These networks are based on a series of control points at the tunnel entrance, and link each station by means of survey observations as they advance along the tunnel. Once, the networks are used to guide the TBM, they are no longer checked again. It is necessary to perform high accuracy astronomical observations to stars in order to determine the gyrotheodolite constant. Since astronomical observations cannot be made inside tunnels, geodetic azimuths have to be used for the computations. However, these azimuths cannot theoretically be compared with the astronomical azimuths obtained by the gyrotheodolite. An alternative is to compute the instrument constant using the values of the deviation of the vertical derived from a geoid model. That is the approach used in this work where a methodology for the design of underground networks in long tunnels is also presented. This procedure has been implemented during the construction of the Guadarrama and Pajares high-speed railway tunnels (Spain).

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4. Recovery of cadastral boundaries with GNSS equipment
A. Cina, A. M. Manzino & G. Manzino

The purpose of this work is to propose a new redefinition of cadastral boundaries using GNSS equipment and cadastral maps. These maps are the ‘original’ maps of the Italian Land Cadastre, the first cartographic support built directly from measures carried out by technicians during implantation of the Italian land cadastre. They are called ‘originali di impianto’ – ‘originals of implantation’ or ‘implant maps’. As such, these maps are valuable and are kept with great care. Recently, the Italian cadastre has carried out an accurate digitisation of these maps in a raster format at a high resolution. In this work, the authors propose the use of these digital maps for the recovery of cadastral boundary. The original cadastral map, one of the primary sources relied upon in defining legal boundaries, generally uses the Bessel ellipsoid localised in Genova and the Cassini-Soldner projection; the GNSS equipment, on the other hand, uses the geocentric ellipsoid with global or continental realisations. After an RTK positioning, the receivers usually provide the cartographic coordinates in a Gauss projection. However, our study deals with the problem of using different projections and reference systems within the limits of a map. In this context, the transition between systems and projections can be made through a conformal transformation with deformations slighter than graphical errors in the map. The difficulty of finding identifiable points in both reference systems is partially solved through a new way of carrying out the redefinition of boundaries by exploiting geometric information.

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5. Models for positional accuracy assessment of linear features: 2D and 3D cases
P. Gil de la Vega, F. J. Ariza-López & A. T. Mozas-Calvache

Traditionally, the uncertainty models for segments and lines and positional accuracy assessment methods based on lines have worked with 2D elements. But the increasing availability of 3D data leads us to conjecture the need to adapt existing models and methods for this type of data. This paper gathers for the first time in a single paper the uncertainty models for segments and lines and positional accuracy assessment methods based on lines, incorporating the 3D case. Thus, this paper is intended as a reference document for those readers who are interested in this field.

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6. Strain estimation using ordinary Kriging interpolation
Y. Ghiasi & V. Nafisi

The ordinary kriging interpolation method is adopted to estimate the 2-D strain tensor elements. The results are then compared with those of the linear and spline interpolation methods. The ordinary kriging method is implemented on 12 GPS permanent stations in South California, collected during 2006 to 2012. By employing these time series, the coordinate changes in the UTM coordinate system can be obtained and the strain tensor elements at these 12 stations can be estimated by means of finite difference method. Interpolation of the strain tensor elements over the study area through these three methods (kriging, spline and linear) indicates that the ordinary kriging results, on average are 70% better than those of the spline and linear interpolation methods.

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7. Real-time cycle-slip detection and repair for BeiDou triple-frequency undifferenced observations
Y.-F. Yao, J.-X. Gao, J. Wang, H. Hu & Z.-K. Li

A new method of real-time cycle-slip detection and repair for BeiDou navigation satellite system (BDS) triple-frequency undifferenced observations is proposed. The method, which is based on code–phase and geometry-free phase combinations, composes linearly independent combination observations to uniquely determine the cycle-slip of original frequency phase observations in two independent steps. First, two extra-wide lane (EWL) code–phase combinations are utilised to determine the EWL combination cycle-slips. The sum of the carrier phase combination coefficients is zero. Second, the geometry-free phase combination with a non-zero sum of combination coefficients composes linearly independent combination observations with two code–phase combinations. Ionospheric delay variance systematic deviation is corrected with several previous carrier-phase observations without cycle-slip, which seriously affect the accuracy of the geometry-free phase combination observations. The BDS triple-frequency carrier-phase and code observations of different satellite types at 30 s sampling interval, which involve increased active ionospheric conditions in 1 day, are utilised to test the method. Results show that the proposed method can efficiently detect and accurately repair any cycle-slip combinations in real-time for different satellite types under active ionospheric conditions. No erroneous and leakage judgments are observed in the test.

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8. The SMITSWAM method of datum transformations consisting of Standard Molodensky in two stages with applied misclosures
A. C. Ruffhead

For three-parameter datum transformations to be applied rigorously, geodetic coordinates on the first ellipsoid need to be converted to Cartesian coordinates before application of the shifts, then converted to geodetic coordinates on the second ellipsoid. The Standard Molodensky method of datum transformation is more direct but is inexact. It also fails to reproduce the original coordinates when applied forward and back. However, this paper shows a pattern of proportionality between the misclosures and the errors in the forward approximations. This gives rise to a new method of computing the transformations, best described as “Standard Molodensky in two stages with applied misclosures” (SMITSWAM). The method is shown to be more than 1600 times more accurate than Standard Molodensky, coming close to the accuracy of the rigorous approach. SMITSWAM is also shown to be around 48% faster than the traditional form of the rigorous method which uses iteration.

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Survey Review 48, No 349. July/August 2016

1. Optimal cycle slip detection and correction with reliability
Z. Wang, X. Wang, S. Ji & W. Chen

Cycle slip detection and correction is very important for high-precision positioning with GNSS. In past research, a lot of work has been done on this subject, especially for current dual-frequency GPS (the global positioning system). However, few have been done about the reliability. Similarly to ambiguity resolution, reliability is important to cycle slip detection and correction. In this research work, methods on how to assess and ensure the reliability of cycle slip detection and correction are proposed.

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2. An improved algorithm of image registration based on least squares adjustment
C. Zhou, J. Zhu, D. Fan & J. Zhou

Image registration is one of the most critical steps in super-resolution (SR) image reconstruction. Correspondingly, it is of considerable importance to improve the accuracy of image registration. Here, we report a novel least squares adjustment theory to significantly improve the image registration algorithm, which combines both the advantages of Vandewalle algorithm and Keren algorithm. Compared with traditional Vandewalle algorithm, Keren algorithm and Li algorithm, the experimental results show that the registration parameters exhibit the highest accuracy in our improved algorithm. Meanwhile, the runtime of the improved algorithm is much faster than that of Keren algorithm and Li algorithm, and the peak signal-to-noise ratio (PSNR) value of the reconstructed image is 1·5 dB higher than that of Vandewalle algorithm and Keren algorithm.

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3. Assessment of orthoimage and DEM derived from ZY-3 stereo image in Northeastern China
Y. Dong, W. Chen, H. Chang, Y. Zhang, R. Feng & L. Meng

ZiYuan-3 (ZY-3, meaning Resource-3) is China's first civilian multispectral satellite with high-resolution stereo mapping capability. The along-track stereo images of ZY-3 allow the generation of digital elevation models (DEMs) for various mapping applications. This article evaluated the precision of the derived stereo DEM and orthoimages of ZY-3 data for a test site in Northeastern China. Pixel offset and GPS survey data were used to evaluate the image products. Orthoimages were derived by incorporating rational polynomial coefficients (RPCs) of the satellite orbits and the reference DEMs, including the Advanced Spaceborne Thermal Emission and Reflection Radiomete (ASTER) global digital elevation model (GDEM) and ZY-3 stereo elevation model. The generations of orthoimages were categorised into four approaches depending on the RPCs, control points and/or reference DEMs used. When only the ASTER GDEM was used, the derived orthoimages of the forward and backward viewing sensors showed clear pixel offsets against the GPS check points (CKPs). For example, the offsets of the orthoimage derived using forward-looking image were 13·58 and 26·50 m, in x (easting) and y (northing) directions, respectively. These results also indicated that the pixel offset vectors between the forward and backward orthoimages was systematic which was caused by the error in the RPCs. The second and third approaches were to generate the ZY-3 stereo DEMs first, with and without the use of ground control points (GCPs), and then used the stereo DEMs to generate the orthoimages of the forward and backward looking images. The forth approach used both GCPs and ASTER GDEM to generate the orthoimages. The results showed the use of four GCPs in the process improved the accuracy of the orthoimages. Therefore, ZY-3 can deliver the DEM and orthoimage products to meet the accuracy requirement of the national 1 : 50 000 mapping with four well distributed GCPs.

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4. Constructing a seamless digital cadastral database using colonial cadastral maps and VHR imagery – an Indian perspective
A. Sengupta, C. Lemmen, W. Devos, D. Bandyopadhyay & A. van der Veen

A Land Administration System (LAS) with its cadastral component is the infrastructure that facilitates the implementation of land policies to attain sustainable development. Therefore, the availability of a digital, up-to-date and easily accessible cadastral database has become a primary requirement for undertaking efficient land administration and/or spatial planning decisions for any country. In this paper, the authors demonstrate a method for constructing a seamless digital cadastral database (DCDB) based on colonial cadastral maps using Geographic Information System (GIS) and image interpretation techniques for an area of about 326 km2. Geo-Eye1 (pan-sharpened) data were used for this purpose in combination with limited on-site survey. The proposed approach could be considered as an alternative to a complete cadastral resurvey. It is important to mention here that the quality of these colonial maps is quite high and can be proven as a basis for spatial planning. A cadastral resurvey may be required in the future where there is an urgent need for higher accuracy, but the approach would be time consuming and potentially bring unrest in villages and urban neighbourhoods. Hence, an alternative is, therefore, to respect the contents of the existing maps and records combined with a quality upgrade: make the existing records and maps up-to-date as a basis for a spatial planning.

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5. A point-based methodology for the automatic positional accuracy assessment of geospatial databases
J. J. Ruiz-Lendínez, F. J. Ariza-López & M. A. Ureña-Cámara

This paper is based on our earlier paper (Ruiz-Lendínez et al., 2013) of this work and its new contribution is to develop a point-based methodology for the automatic assessment of positional and geometric components of spatial data. The starting point for our approach is the set of homologous polygons obtained according to the methodology developed in Ruiz-Lendínez et al. (2013). From these pairs of polygons, we first have identified and computed homologous points using a metric for comparing polygonal shapes defined by Arkin et al. (1991) and then we have applied a point-based standard developed for assessing the positional accuracy of spatial data. Specifically, we have employed the National Standard Spatial Data Accuracy (NSSDA) standard. The results obtained demonstrate the viability of this point-based evaluation and its potential compared to traditional methods.

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6. Weighted total least squares applied to mixed observation model
A. R. Amiri-Simkooei, S. Mortazavi & J. Asgari

This contribution presents the weighted total least squares (WTLS) formulation for a mixed errors-in-variables (EIV) model, generally consisting of two erroneous coefficient matrices and two erroneous observation vectors. The formulation is conceptually simple because it is formulated based on the standard least squares theory. It is also flexible because the existing body of knowledge of the least squares theory can directly be generalised to the mixed EIV model. For example, without any derivation, estimate for the variance factor of unit weight and a first approximation for the covariance matrix of the unknown parameters can directly be provided. Further, the constrained WTLS, variance component estimation and the theory of reliability and data snooping can easily be established to the mixed EIV model. The mixed WTLS formulation is also attractive because it can simply handle the two special cases of EIV models: the conditioned EIV model and the parametric EIV model. The WTLS formulation has been applied to three examples. The first two examples are simulated ones, the results of which are shown to be identical to those obtained by the non-linear Gauss-Helmert method. Further, the covariance matrix of the WTLS estimates is shown to closely approximate that obtained through a large number of simulations. The third is a real example of which two object points are photographed by three terrestrial cameras. Three scenarios are employed to show the efficiency of the proposed formulation on this last example.

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7. A comparative analysis of measurement noise and multipath for four constellations: GPS, BeiDou, GLONASS and Galileo
Changsheng Cai, Chang He, Rock Santerre, Lin Pan, Xianqiang Cui & Jianjun Zhu

With the rapid development of BeiDou system (BDS) and steady progress of Galileo system, the current GNSS (Global Navigation Satellite System) constellations consist of GPS, GLONASS, BeiDou and Galileo. The real signals from the four constellations have been available, which allows us to analyse and compare their measurement noises and multipath effects. In this study, a zero-baseline test is conducted using two ‘Trimble NetR9’ receivers to assess and compare the noises and multipath of measurements on multiple frequencies from the four satellite systems. The zero-baseline double difference approach is utilised to analyse the receiver noises. The code multipath combination and triple-frequency carrier phase combination approaches are exploited to analyse a comprehensive effect of the multipath and noises on the code and carrier phase measurements, respectively. Based on the analysis of the zero-baseline dataset, the results indicate that the code measurement noise levels range from 5 to 25 cm while the carrier phase noise levels vary within 0.9–1.5 mm for different frequencies and constellations. The code multipath and noise (CMN) level for GLONASS is the largest with a root mean square (RMS) value of 39 cm on both G1 and G2 frequencies whereas the Galileo code measurements exhibit a smallest level on the E5 frequency with a RMS value of only 10 cm. The RMS of the carrier phase multipath and noises (PMN) ranges from 1.3 to 2.6 mm for BeiDou and Galileo satellites. By contrast, the triple-frequency carrier phase combinations from the GPS Block IIF satellites demonstrate a much larger RMS value of 5.6 mm owing to an effect of inter-frequency clock biases.

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8. An adaptive stochastic model for GPS observations and its performance in precise point positioning
J. Z. Zheng & F. Guo

In this paper, the stochastic characteristics of Global Positioning System (GPS) pseudo-range noise as influenced by several factors such as receiver type, frequency, and ionosphere environment are analysed. The results indicate that the noise level of GPS observations is significantly affected by these factors. Moreover, the noise level is so mutable that it cannot be generalised and described by a uniform empirical model. Even for the same satellite, the noise level of observations may fluctuate sharply in both spatial and temporal resolution. To establish a reasonable stochastic model, a recursive sliding window method for estimating pseudo-range noise in real time is introduced. The effectiveness of the proposed method is verified by specific computational examples.

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9. The contribution of laser scanning technology in the estimation of ancient Greek monuments' deformations
G. D. Georgopoulos, E. C. Telioni & A. Tsontzou

Terrestrial laser scanning technology is nowadays more and more used for the documentation of cultural heritage monuments. The thorough exploitation of the main advantage of terrestrial laser scanners (TLS) that is the acquisition of extremely dense discrete points in a relatively small time period leads to detailed 3D representation of the monument, overcoming possible difficulties such as limited accessibility. Most often, this 3D representation is used for the monument's documentation as well as for virtual tours in, out or around it. This detailed documentation can be used for one more purpose: the estimation of the deformation that its elements have experienced through the centuries and, following, the monument's restoration, provided that, its' initial, constructional geometry is known. In this paper, research towards this goal is presented, dealing with the estimation of the deformations of a column of the ancient temple of Zeus in Nemea Greece using TLS technology. This column is standing erect since the temple's construction in 330 BC and it has been subject to serious deformations because of various causes.

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Survey Review 48, No 348. May/June 2016

1. Generalised total least squares solution based on pseudo-observation method
C. Hu, Y. Chen & W. D. Zhu

In the generalised total least squares (GTLS) problem, observations can be perturbed by random errors that are dependently, inconsistently and normally distributed with a non-zero mean, and the coefficient matrix can hold any structure. In this contribution, a set of formulae for GTLS adjustment is derived using a pseudo-observation method. Based on the derived results, an iterative algorithm (algorithm 1) only for the estimation of parameters and a two-loop iterative algorithm (algorithm 2) for the estimation of parameters and variance factors are developed. Moreover, the derivative of a vector is introduced to deal with the structured TLS problem. A straight line fitting and a simulated 2D affine transformation experiment are performed to verify the applicability of the developed algorithms. The results show that algorithm1 can be used to simultaneously handle the structured coefficient matrix, correlated error and non-zero expectation problem, while algorithm 2 can be utilised to manage the variance component estimation problem with the non-zero expectation assumption. Under the identical statistical assumptions, the suggested algorithm can achieve the same results as the solutions of Schaffrin (2008), Shen (2011), Fang (2013)and Amiri-Simkooei (2013).

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2. Developing the information infrastructure based on LADM – the case of Poland
K. J. Góźdź & P. J. M. van Oosterom

In this paper, the possibilities of developing the national information infrastructure by applying the Land Administration Domain Model (LADM) are discussed. Confirmation of the legitimacy of using the LADM within the (Spatial) Information Infrastructure (SII) context is illustrated with the case of Poland. Creating the information infrastructure is an immense challenge because its components are usually dispersed among various institutions responsible for their maintenance and dissemination. Co-existing spatial and non-spatial components of the information infrastructure require their proper integration. Moreover, the interdisciplinary nature of the SII results in combining objects from physical and legal world in one computer environment. The process of standardisation is the first step to refine land administration system and to make it more understandable and transparent for involved parties. The LADM, being officially adopted as an international standard ISO 19152, gives a basis for building national profiles and supports creating the European information infrastructure, enabling communication based on common terminology. This paper provides a brief overview of the current land information system in Poland emphasising the main issues in creating the national information infrastructure. Then, the general concept of the country profile for Poland with the adaptation of the LADM is described. With respect to the users’ expectations and requirements, the conceptual model is extended to information being outside the scope of LADM. As a final point, several technical aspects of implementing the complemented LADM country profile are explored. The results indicate that effective functioning of the information infrastructure requires proper integration of data, proceeded by analysing the contents of existing data sets, indicating key registers and defining a linkage system between them.

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3. A new robust filtering for a GPS/SINS loosely coupled integration system
Q. Zhang, S. Stephenson, X. Meng, S. B. Zhang & Y. J. Wang

Integrated global positioning system (GPS)/strap-down inertial navigation system (SINS) systems are widely used for positioning and attitude determination applications. Kalman filtering is the most common method to combine both sensors. A standard Kalman filter (SKF) relies on the correct definition of the measurement and process models and cannot handle measurements with outliers. The H∞ filter can achieve better robustness performance based on minimising the worst-case estimation error. Different to other adaptive KFs, the H∞ filter controls its robustness by a restriction parameter γ. The γ parameter is usually set and fixed by experience. In this paper, an adaptive strategy to gain a time-varying γ is proposed. The construction of the time-varying parameter is based on a two-segment function of an approximate ratio of the traces of the calculated predicted residual's covariance and the theoretical covariance. The test results indicate that the proposed filtering can achieve the expected robustness performance and efficiency more comprehensively when compared with other filtering methods.

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4. Barycentre method for solving distance equations
X. Shuqiang, Y. Yuanxi & D. Yamin

When iteratively solving the distance equations, the Newton's method has quadratic convergence but it requires the second-order derivatives. The Gauss–Newton's method needs no information about the second-order derivatives but it may fail without the line search strategy. A simple method called barycentre method is proposed to locally solving the distance equations without the Hessian matrix, the matrix inversion and the line search strategy. The geometrical meaning of the non-linear least-squares solution of the distance equations is revealed that it is the barycentre of a particle system composed of the observational weights at the endpoints of observed distance vectors. By the geometrical meaning of the non-linear least squares, the authors structure an iterative equation to solve the distance equation, and then the convergence and the computational complexity of the method proposed is discussed. It shows that the barycentre method is a conservatively steepest decent method to guarantee the convergence and this method has good performances for solving well-conditioned problems. Ultimately, the method proposed is applied to well-condition and ill-posed positioning equations and the main results are verified.

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5. Evaluating the use of GPS heights in water conservation applications
A. F. Elaksher, A. Fernald & F. Kapoko

Accurate water level elevations are imperative for water resource management. This paper presents the outcomes of a research study using GPS in measuring water level heights. The authors observed the water elevations of several wells, United States Geological Survey (USGS) gauges and acequia points at three different locations in North–Central New Mexico, USA. Different rapid static and static observation sessions were collected independently and adjusted using the nearby reference control stations. The authors used two different sets of receivers: four Topcon Hiper Lite+ and two Leica GPS1200 The authors were able to examine several network configurations with different continuously operating reference station (CORS) stations. Our findings were analogous to empirically expected errors and showed insignificant differences among the heights obtained from rapid static and static sessions at a 95% confidence level. The authors also compared the results with National Geodetic Survey online positioning users service (NGS OPUS) solutions and confirmed the accuracy of our measurements. As independent measurement technique, we measured the height differences among several of these points with conventional levelling surveys. Our GPS measurements provided small disagreements with height differences obtained with the terrestrial surveys, after the GPS heights were reduced to their orthometric correspondences. Based on these findings, current rapid static GPS positioning methodologies are capable of providing equivalent accuracies as those obtained by static GPS and ground surveying techniques.

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6. An effective toolkit for the interpolation and gross error detection of GPS time series
X. Wang, Y. Cheng, S. Wu & K. Zhang

As data gaps and gross errors inevitably exist in GPS time series, robust detection and interpolation procedures are needed to obtain a uniform time series for various geospatial studies and applications. The use of traditional methods for this purpose is usually based on some improper assumptions, which are not derived based on the real properties of the data. Moreover, different interpolation methods may need to be investigated for interpolation for various gaps with different types and amount of missing data. These make the interpolation for missing data not easy. To address the issue of mentioned above, in this study, a data-analysis method named singular spectrum analysis (SSA) for missing data is assessed for reconstructing a reliable model from unevenly sampled time series without the need for any a priori knowledge of the time series data. In this method, the interpolation and detection of gross errors are carried out in one go along with the reliable reconstructed model. Both simulation data and real GPS data testing results showed that this was an efficient method for interpolation and gross error detection.

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7. Application of Monte Carlo method to statistical testing in deformation analysis based on robust M-estimation
K. Nowel

In deformation analysis of geodetic control networks, it is important to know whether the estimated displacement value of a given point is the effect of displacement or only the effect of random measurement errors. The F-test of statistical significance is used to answer this question. This test is applied both in conventional deformation analysis (CDA) based on least square (LS) estimation and in deformation analysis based on robust M-estimation. Unfortunately, the F-test is strongly flawed in the latter case. As a consequence, its results are significantly different here than assumed/expected. This paper analyses how flawed the F-test is and proposes a new solution. First, the algorithm of the global and local F-tests was derived. It was then demonstrated that for deformation analysis based on robust M-estimation, this algorithm has theoretical flaws. Next, it was shown how these problems can be solved numerically. The basis of the solutions proposed involves the use of stochastic simulations and, more specifically, the Monte Carlo (MC) method. Moreover, it was noted that other statistical test problems which also occur in deformation analysis based on robust M-estimation can be solved using present-day computers. The numerical approach can be a good support here in the selection of the proper significance level as well as in the correct performance of the test sensitivity analysis. All theoretical discussions were verified on an example simulated control network.

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8. A digital panorama mapping system with soft-IMU technology: experience with a Chinese low-cost mobile mapping system
Z. Xu, L. Li, Z. Xiang & C. Long

Mobile mapping systems (MMSs) provide capability for direct geo-referencing, and rapid and convenient acquisition of geographic data elements. Combining global positioning system/inertial measurement unit/distance measurement indicator (GPS/IMU/DMI) data is one of the most attractive methodologies for such systems. Inertial measurement unit data give attitude information, but the equipment is expensive and faces technological blockade by foreign companies. To overcome this limitation, the current paper explores a soft-IMU technique based on panorama vision, which can acquire more information from the environment because of its wide instantaneous field of view (IFOV) compared with traditional cameras. The proposed soft-IMU technology automatically extracts and tracks image registration points (IRPs) in panorama data, and corrects paths using correction points. The development history of the mobile mapping system, the software and hardware configuration of our prototype digital panorama mapping DPM™ products, the system calibration model principle and object measurement are described. Finally, it is demonstrated that the system precision meets the demands of daily data acquisition in field experimental studies.

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Survey Review 48, No 347. March/April 2016

1. Real time monitoring ground motion using GPS with real time corrections
R. Tu, L. Wang & Z. Liu

The high rate GPS velocity determination technology which is based on the broadcast ephemeris and epoch differenced model can retrieve displacement of ground motion with the precision of a few centimetres to decimetres in real time. Moreover, the precision of the recovered displacement can be improved if the un-modelled errors such as broadcast ephemeris residuals, atmospheric residuals, multipath effects and high frequency noise are tackled more accurately. In this paper, we propose a method to improve the precision of the recovered displacement by appropriately making use of reference station corrections. For the reference stations, the coordinates are highly constrained to extract the error corrections that are to be broadcast via a communication link to the rover. After correcting the rover’s observations, some errors such as ephemeris residuals and atmospheric residuals are effectively eliminated or at least reduced. This improves the accuracy of the observations and thus enhances the reliability of the velocity estimation. The displacement can be recovered by integrating the estimated velocity after de-trending using a linear trend that is caused by the un-corrected residuals. The series of validation results in the experiment have shown that the displacement of the simulated motion can be real time recovered with a precision of 1–2 cm, and is thus applicable for real time monitoring of the ground motion.

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2. Geodetic and fibre optic measurements of a full-scale bi-axial compressional test
S. Lackner, W. Lienhart, G. Supp & R. Marte

Earth filled dams are commonly used as flood prevention dams and for hydroelectric power plants. Their stability is critical for an uninterrupted operation and a reliable protection from catastrophic incidents. During the operation, dams are subjected to lateral loading by hydrostatic pressure. In order to predict the deformation behaviour the material parameters have to be known accurately. Therefore, Graz University of Technology carried out a series of life-size experiments to determine the material parameters of an earth filled dam. Controlled vertical load was applied in these experiments and the resulting deformations were measured with geodetic and fibre optic methods. Single points on the slope were continuously tracked with robotic total stations. In addition, the whole dam surface was monitored using a scanning total station. Finally, relative movements between points on the dam were measured with fibre optic sensors based on fibre Bragg gratings. The achievable measurement precision and the relation between acting load and resulting deformation is investigated in detail for every measurement technique. The authors show in their evaluation that absolute deformations can reliably be detected with the geodetic methods. However, individual loading steps cannot be resolved because of the limited precision of the geodetic measurements. Our results demonstrate that the sensitivity of the monitoring system can be significantly increased with the fibre optic sensors and the scanning data also contribute to assess the stability of the experiment set-up.

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3. Impact of coseismic deformation fields with different time scales on finite fault modelling in 2010 California Baja Earthquake
J. Niu, C. Xu, Q. Fan & Z. Yin

In this study, the static coseismic deformations with different time scales in the target event are extracted from the long term and short term solutions of continuous GPS and the epoch-by-epoch solution of high rate GPS respectively. The mean discrepancies among these deformations are less than 1 cm. The earthquake source parameters are inverted in the layered inhomogeneous half-space under the static dislocation theory from the static coseismic displacements with different time scales. It can be concluded that the time scale of the static coseismic displacement shows a relatively small impact on the source parameters in this moderate earthquake. The disturbances on the fault slips are less than 20 cm, and less than 0·1 on the moment magnitudes. As the time scale grows, the postseismic deformation in the static coseismic displacement from the short term solution increases, which indicates that apparent early postseismic displacements exist on the day after the termination of the earthquake.

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4. Determination and testing of strain parameters in landslide region of Koyulhisar, Turkey
F. Poyraz

Koyulhisar in Turkey is in danger of landslides, and to determine the risk of landslides in this area, many projects and studies are currently being conducted. Between 2007 and 2008, global navigation satellite system measurements were made, providing data on seasonal effects. The displacements, and also the forces behind these displacements, need to be studied. These forces may be determined using various methods. One method is the determination of strain parameters. With regard to the maximum and minimum principal strain parameters obtained (λ1 = 56·3433 μs, λ2 = −35·4642 μs) from the city centre measurements, there is statistically significant stress accumulation in the Koyulhisar region. Furthermore, for the compression and contraction directions obtained in the city centre, compression was obtained in the north–south direction and contraction movement was obtained in the east–west direction. These movement directions show that the tectonic movements in the region have an effect on the landslide.

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5. Registration of foundation properties – cultural asset on behalf of their own fused foundations
Y. E. Çoruhlu

The Convention Concerning the Protection of the World Cultural and Natural Heritage for protecting cultural assets and handing them down to future generations was adopted in 1972 by United Nations Educational, Scientific and Cultural Organization (UNESCO). This convention was adopted by Turkey in 1983. This regulation has a noteworthy principle, which states that the cultural assets are not only the properties of the countries in which they are located in but also of mankind. The regulation stipulates national/international protection of cultural assets and handing them down to future generations. For this purpose, law 2863 was enacted in 1983. In Turkey, there are 96 000 registered cultural assets, 19 825 of which are managed by the General Directorate of Foundations (GDF). The GDF conducts restoration of cultural assets and handing them down to future generations in a very efficient way. Today, there are more than 40 000 fused (mazbut in Turkish) foundations and around 80 000 foundation properties in Turkey, 19 825 of which are foundation cultural assets. It became possible to increase the number of these foundation cultural assets by article 30 of Foundations Law 5737, which came into force in 2008. In other words, this article allows properties, which were first built by foundations, registered as cultural assets, and came into the possession of the Treasury, Municipality, Special Administration or Village Legal Entities to be registered at fused foundations. The aim of this study was to reveal reregistration process of properties, which are protected by national and international legislation and registered as cultural assets, in order to protect, utilise and improve them in the name of the foundations. In this study, the subject will be explored by describing the process steps, providing workflow diagrams using current applications, and giving examples from original documents.

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6. The use of laser scanning as a method for measuring stairways following an accident
M. Eyre, P. J. Foster, K. Hallas & R. Shaw

Stairs present significant potential for harm to their users. A fall on stairs, particularly in descent, often leads to serious injury or even death. The authors have been involved in the investigation of many workplace stair accidents. Proper forensic investigation into the cause of a stair accident has often found the incident to be wholly or partly caused by poor stair design. In order to establish the relationship between the stair design and a given fall, an onsite survey has to be conducted, determining the rises and goings along with other key dimensions. The Health and Safety Laboratory (HSL), Buxton, UK, regularly undertake this type of survey using a digital inclinometer, a steel rule and a tape measure. Laser scanning is an emerging technique that is now accessible to the surveyor to complement or replace traditional approaches. The laser scanner and associated software produces a dense point survey in 3D, allowing dimensional analysis of the features. The authors used both traditional and laser scanning techniques to study the scenes of two fatal stair falls. The analysis presented allows the suitability of laser scanning for stair-fall investigation to be considered. Identification and classification of errors are needed in order to consider if the error is acceptable or can be mitigated. Laser scanners are impressive instruments providing data from which can be used to create a virtual 3D environment that can be used to reconstruct and explain an event and contributing factors. The use of both survey methods currently provides the investigator with complimentary data that allows accurate measurements to be presented in the context of the three-dimensional environment.

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7. Predicting ionospheric critical frequency of the F2 layer over Lycksele using the neural network improved by error compensation technology
D. Zheng, W. Hu & P. Li

In this contribution, according to the critical frequency of the F2 layer (foF2) from the ionosonde station and the International Reference Ionosphere 2012 (IRI2012) model [the International Radio Consultative Committee (CCIR) coefficient], a single station model (called the Fusion model) for predicting the hourly value of foF2 over Lycksele (64.69°N, 18.80°E) is developed by the back-propagation neural network (BPNN) technology compensated for the model-deviation of the IRI2012 model. The input parameters of this BPNN-based foF2 prediction model include day number (day of the year), universal time, solar zenith angle, solar cycle information, geomagnetic activity (a 3-day running mean of the 3-h planetary magnetic index Ap and Kp) and the foF2 values from the IRI2012 model; the output parameter is the model-deviation. The data sets employed in this model are obtained from the National Geophysical Data Centre and National Aeronautics and Space Administration (NASA), about 215 614 sets, which are derived during the period from January 1958 to December 1984 (1960s data is missing). The data sets from 1971 to 1984 are selected for validation instead of for training use. Prediction values from the Fusion model, the General BPNN and IRI2012 models are each compared with the observed data. The results indicate that the proposed model is superior to the other models for hourly value of foF2 prediction over Lycksele. According to the statistical analysis of average root mean square error, the proposed model offers an improvement of 19.11% over the IRI2012 model.

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8. Investigation of long-range dependencies in the stochastic part of daily GPS solutions
J. Bogusz, A. Klos, M. Figurski & M. Kujawa

The long-range dependence (LRD) of the stochastic part of GPS-derived topocentric coordinates change (North, East, Up) results with relatively high autocorrelation values with a focus on self-similarity. One of the reasons for such self-similarity in the GPS time series are noises that are commonly recognised to prevail in the form of the flicker noise model. To prove the self-similarity of the stochastic part of GPS time series we used more than 130 ASG-EUPOS (active geodetic network EUPOS) stations from an area of Poland with a 5-year span of the daily topocentric coordinate changes. The deterministic part of time series was removed by means of the least-squares (LS) method, median absolute deviation (MAD) criterion and the sequential t-test algorithm, respectively. Then the self-similarity of the residue was proved by the results of the Ljung–Box test, whose values close to zero showed the dependence of the stochastic part of the GPS time series. The residue was analysed by means of the rescaled range (R/S) method with the H (Hurst) parameter and the detrended fluctuation analysis (DFA) with the scaling exponent α. Both H and α values ranged within assumed LRD limits of 0.5 and 1. This analysis was followed by noise investigation with a maximum likelihood estimation (MLE). The white plus the power-law noise models were assumed a priori, which gave us a spectral indices κ between − 0.4 and − 1.2 for all of the time series. It proved that fractional white noise outweighs other types of noises in GPS time series. Authors found here, that the LRD methods by omitting the noise amplitude data led to an underestimation of H values and their misinterpretation. The larger the omitted amplitude is, the greater the difference between the noise characters estimated with R/S values in comparison to the reference values of κ are. Some of these differences exceed even the value of 0.6, which may result in the estimation of false noise character in GPS data thus eliciting wrong conclusions.

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9. Climate change, land use and land surveyors
P. van der Molen & D. Mitchell

Research reveals that the land sector is a major emitter of greenhouse gases. But the land sector has also potential to reduce emissions. Different from other emission sectors like energy and transport, the land sector (in particular the rural area including forests) has the potential to also remove greenhouse gases from the atmosphere through sequestration and storage. This requires land use, land use change and forestry to be managed with respect to climate change goals. Carbon storage has the potential to generate carbon credits, which according to the Kyoto Protocol are exchangeable in a market environment. But is the market secure enough? This paper aims primary at presenting the subject matter as a synthesis of extant literature. Secondary, the paper shows interfaces with the land surveyor's profession namely land management and land administration.

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Survey Review 48, No 346. January/February 2016

1. Structural integrity verification of cable stayed footbridge based on FEM analyses and geodetic surveying techniques
V. Gikas, P. Karydakis, T. Mpimis, G. Piniotis & H. Perakis

This paper presents the mathematical models developed for the design of a pedestrian, cable stayed bridge, the geodetic monitoring procedures and their detailed cross-comparisons and analyses undertaken during the phases of construction and at commissioning stage. Because of the asymmetric design, the relative flexibility of the pylons, the eccentric positioning of the central joint and the off-plane low angles of the cables, a multi-sensor, event based geodetic monitoring scheme was adopted to assess the structural integrity of the bridge. During construction, the bridge kinematics were measured along both sides of the deck and at selected points on the pylon facades using a digital level and a high accuracy total station used in metrology respectively. At a commissioning stage, a number of load test series were undertaken using conventional geodetic techniques and a tactical grade Inertial Measurement Unit (IMU). Analysis confirmed the overall mathematical modelling assumptions made for the individual stages of construction and for the completed structure. However, analysis also revealed the increased structural rigidity of the structure. This particularly applies for the torsional stiffness of the deck that exhibits low (by a factor of 0·5) rotation angles compared to those obtained from the analytical models.

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2. Fit-for-purpose land administration: lessons from urban and rural Ethiopia
R. M. Bennett & B. K. Alemie

Lessons for designing fit-for-purpose land administration and land management activities, where the stated purposes are poverty alleviation, food security, and good governance, are provided. Contemporary developments from urban and rural Ethiopia provide the empirical basis: data is synthesised from fieldwork and other research activities undertaken between 2011 and 2013. With its large population and important geopolitical location, Ethiopia will continue to act as a yardstick for measuring the success of the global development agenda, particularly in Eastern Africa. Observations from training sessions conducted with cadastral and urban planning experts in Addis Ababa reveal challenges and opportunities regarding capacity development for urban land administration, urban land markets, and state land management. From the city of Bahir Dar, an alternative perspective of urban land administration is provided: the presented results shed light on the varying quality of cadastral development, but also the positive and negative impacts of cadastral implementation. Meanwhile, results from Dilla Town reveal the opportunity to link cadastral development to other infrastructure development activities (e.g. road construction and upgrade). The case also reveals the ongoing tension between ensuring adequate compensation payments relating to land acquisition, whilst also delivering a broader community benefit. Outputs from exploratory design work on the potential for land consolidation in the Amhara region are also articulated. The status of cadastral development in rural areas is revealed, along with future challenges for using cadastral data in land consolidation activities. Overall, the synthesised studies expose how fit-for-purpose ideologies are increasingly informing Ethiopian cadastral design, and under what conditions these designs can support poverty alleviation, food security, and good governance.

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3. Investigating efficacy of robust M-estimation of deformation from observation differences
K. Nowel

Generalized robust M-estimation of deformation from observation differences (GREDOD) is a robust method for deformation analysis of geodetic control networks. This method has been developed based on the well known robust Iterative weighted similarity transformation (IWST) method. Hence, in the GREDOD method, as in the IWST method, the L1-norm weight function is the weight function for the displacement vector and the displacement vector components are the weight function variables. The L1-norm weight function for variables in the form of the displacement vector components is the simplest and most natural solution, but it is not known whether this is the most efficacious solution for the GREDOD method. To assess this, the current study used different robust weight functions which were tested for variables in the widely used form of the displacement vector components and for variables in the form of displacement lengths. All solutions were tested on the basis of the simulated two-epoch observations of the absolute control network of the Montsalvens dam in Switzerland. The efficacy measure for individual solutions was the mean success rate (MSR).

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4. Creation of land fund for the purpose of land management in the Republic of Serbia
J. P. Gučević, D. M. Milićević, O. P. Vasović & V. A. Djokić

This paper presents the activities carried out by the authorities of the Republic of Serbia in order to properly manage agricultural land. It is well known that land, as a scarce resource in any country, must be managed in a proper way. The government is in charge of land management, land legislation and land policies that have a major influence on land development. The Republic of Serbia is currently in transition from fully state owned land to private ownership, but this path is fraught with numerous obstacles. While the experiences of other countries may help avoid some common pitfalls, each country faces a unique set of challenges not found elsewhere. To be able to properly choose the right direction of land management, it is essential to consider multiple potential scenarios of good land stewardship. A land fund is an example of a good international practice that countries like Serbia should follow, implement and adapt in a way which reflects its national heritage and current circumstances. The real estate market is turbulent and changes over time, but it must be and remain transparent, open and without restrictions in order to assure the wellbeing of future generations and development of the country.

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5. External error modelling with combined model in terrestrial laser scanning
J. Wang, H. Kutterer & X. Fang

Terrestrial laser scanning (TLS) is a promising tool in geodetic applications. Data quality of outdoor TLS measurements is considerably limited by external errors caused by atmospheric variations and object related factors. In this study, external models related to atmospheric refraction, beam wander and incidence angle were introduced and integrated into a seven-parameter similarity transformation (7PST) model to compose a combined model. The combined model was rigorously adjusted by an iterative Gauss–Helmert (GH) model primarily to estimate external calibration parameters and transformation parameters simultaneously. In the application on a dam surface, a t-test showed that a significant external calibration parameter was the range scale, which mainly corresponded with the incidence angle model. The precision of estimated representative points was improved by approximately 50% with the proposed method. The presented models show a great potential for detecting external errors and registering multiple scans in outdoor applications.

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6. Property, human rights law and land surveyors
P. van der Molen

Land surveyors have a lot to do with property rights. This paper presents an inventory of international human rights law regarding property rights, relevant for land surveyors. It addresses the history and current status of international law and case law, and it reflects on the aspects that shape the human right to property as a controversial human right. The paper includes a consideration on related rights, such as the human right to housing and to food. The paper concludes that human rights form an important context for the land surveyor's profession and ends with describing interfaces between the human rights to property and the profession.

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7. Static GNSS precise point positioning using free online services for Africa
A. Abdallah & V. Schwieger

The GNSS precise point positioning (PPP) technique has been extensively covered in recent research. In this study, six International global navigation satellite system (GNSS) Service (IGS) stations defined by 4-digits code in Africa were selected to be processed. The stations cover different climates in Africa. HARB, SUTH and WIND stations cover the mid-latitude area and NKLG, NURK and MAL2 are located in the equatorial region. Two data sessions were selected in processing to cover the winter and summer seasons: the first session of 3 days [01–03 January 2013 (DOY: 001–003/2013)] and the second session of 3 days [01–03 July 2013 (DOY: 182–184/2013)]. This paper aims to evaluate the accuracy of static PPP coordinate solution in Africa for different convergence times using free online services: Canadian Spatial Reference System (CSRS)-PPP, Automatic Precise Point Service (APPS)-PPP and GPS Analysis and Positioning Software (GAPS)-PPP. The stations’ observation times were divided into different observation times (1, 2, 4, 8, 12, and 24 h).The PPP coordinate solution was compared to the reference solution of those stations. The investigation is continued by estimating the PPP total tropospheric zenith delay (TZD) parameters, which were obtained by the different online services. These parameters were compared to the published parameters from IGS. The comparison between the different online services shows that the CSRS-PPP provides the best solution after 4 and 8 h. The APPS-PPP and CSRS-PPP provides the same solution in millimeters level after 12 h. In the equatorial region, the PPP coordinate solution is significantly improved between 12 and 24 h. Moreover, GAPS-PPP is not recommended to be used in the equatorial stations, where it shows a high error compared to CSRS-PPP and APPS-PPP even after 24 h. The mid-latitude stations show a better PPP coordinate solution in the winter than in the summer, but the equatorial stations present a low accuracy for the two sessions. Regarding the PPP tropospheric delay estimation, an additional station (HNUS) is used in the mid-latitude area, which has a low ellipsoidal height. APPS-PPP shows the best solution in the TZD estimation. The GAPS-PPP online service shows a systemic error in estimation and a high RMS relative to the TZD values known from IGS. The ellipsoidal height for antenna indicates a negative correlation to the estimated tropospheric values, but there is no effect for the variation of the ellipsoidal height in the estimated RMS. The estimated tropospheric parameters are correlated with the PPP coordinate estimation, where the GAPS-PPP service provides the worst PPP coordinate solution and at the same time, it shows the worst accuracy for tropospheric parameters estimation. Moreover, the estimated tropospheric parameters for the mid-latitude stations in the summer season show a higher RMS than in the winter season, which matches the same sequence of the PPP coordinates. The NKLG and NURK stations present a low accuracy for the tropospheric estimation, which is matching to the low accuracy of the PPP coordinates obtained from the different online services.

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