Email: Peter Collier
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Survey Review 43, No 323. October 2011
One of the impacts caused of the 24 December 2004 earthquake and tsunami in Aceh is the loss of several ten of thousands of land parcel boundary marks. Many land parcels were also inundated by seawater. The disaster caused damages not only to parcel marks and property rights but also to the land administration system in general. Land parcel reconstruction is very important as a solid foundation for reconstruction work, spatial planning, compensation, and long-term economic development; and also for social justice and ensuring long-term social stability. This paper describes the technical and non-technical aspects of post-tsunami land parcel reconstruction in Aceh in particular, and land administration system reconstruction in general. Some examples of the reconstruction results obtained by utilizing GPS and terrestrial surveys are also shown.
2. Microwave path survey using differential GPS
A microwave path survey is critical before any wireless communication infrastructure can be put into place. It is on the basis of this that the line of sight possibility between any pair of stations is established. This survey can also be used to determine whether there is sufficient space available on existing telecommunication towers, where additional telecommunication facilities can be hosted. This study has demonstrated that differential GPS techniques can successfully be used in microwave path surveys within the framework of telegeoinformatics. The adopted methodology simulated a levelling circuit for the defined observation network. This resulted in an acceptable misclosure of 0.039m which was distributed among the various stations in proportion to the relative length of each link. Natural and man-made obstacles (critical points) along the various telecommunication links were also determined.
This article describes a remote-controlled GPS monitoring system using GPS multi-antenna new method and General Packet Radio Service (GPRS) wireless data communication. The system has been conducted for monitoring the steep slope movement at Xiaowan hydropower station on the Lancang River in China. A dedicated electronic switching device was developed to connect the GPS receiver with the antennas, significantly reducing the required hardware investment. The slope dynamic model and observation model have then been established to estimate the slope displacements and the rate of displacements using Kalman filter, and the results show that the system has excellent performances and produces measurement accuracy of approximately 2-3 mm in horizontal direction over a 24-hour period. The slope movements have been analyzed, which are in good agreement with the studies using conventional monitoring methods.
The aim of this research was to develop the best strategy for the mitigation
of the tropospheric delays in processing of precise local GPS networks.
With the requirement of sub-centimetre accuracy and the availability of
precise IGS products, one of the ultimate accuracy limiting factors in
GPS positioning is the tropospheric delay. This is especially true for
the accuracy of the height component. In many precise GPS applications,
e.g. ground deformation and displacement analyses, volcano monitoring,
the vertical accuracy is of crucial importance.
5. Deformation monitoring in historic buildings: a case study
Deformation monitoring in heritage buildings is an essential task for conservation and restoration studies. A vast variety of techniques can be applied assuming that a three-dimensional modelization is required: GPS (Global Positioning System) measurement, photogrammetry, laser scanning, SAR (Synthetic Aperture Radar) interferometry, terrestrial surveying. They are reviewed for their possible application to a specific heritage building where deformation monitoring has to be performed under severe conditions regarding the lack of intervisibility and the requirement of extremely high accuracy. Finally high precision terrestrial surveying techniques, some of which may be considered as obsolete today, emerged as the most appropriate solution under the conditions. Results show significant displacements for particular points that agree with some suspected structural weaknesses.
Land policy in micro-states and the land administration that underpins it is often devised within a legacy framework inherited from a colonial past. Independence has allowed self-determination of the future political direction yet the range, legal framework, institutional structure and administration systems tend to mirror those of ex-colonial powers. Do land policies, administration systems and processes developed to serve large heavily populated countries scale down to serve the requirements of micro-states? The evidence suggests not: many land administration systems in the Caribbean face difficulties due to poor records, unclear title, exploitation of state lands, incomplete or ongoing land reform programmes, irregular or illegal settlement and non-enforced planning regulations. Land matters are typically the responsibility of several government departments and agencies responsible for land titling and registration, cadastral surveying of property interests, physical planning, taxation and financial regulation. Although planning is regarded as a land administration function, organisational responsibility usually rests with local rather than central government in large countries, but in micro-states local government may be politically weak, under-resourced or even non-existent. Using a case study approach this paper explores how planning functions are organised in the Caribbean state of St Vincent & the Grenadines in relation to land administration as a whole and compares the arrangement with other independent micro-states in the region.
The least squares method is a statistical tool for the estimation of unknown parameters. All the results which are derived from the method of least squares are deteriorated when outliers are present in the observation data. Therefore, outliers have to be detected and eliminated by using statistical tests or robust methods. For this purpose, norm minimization, which is a robust method, can be used in geodetic networks. In this paper, the formulation of norm minimization for correlated observations is presented. The method is applied to a simulated GPS network. The performances of the least squares method and norm minimization are compared in the cases of observations with or without outliers. Our example shows that norm minimization is a more successful method than the least squares method for outlier detection and the obtained coordinates are more reasonable and reliable than those from the least squares when some observations are burdened with blunders.
Survey Review 43, 323 October 2011
1. Analysis of Web-Based GNSS Post-Processing Services for Static
and Kinematic Positioning using Short Data Spans
In this paper the use of some of the currently available web-based online engines for the processing of static and kinematic data from a single dual-frequency receiver is evaluated. The study focuses on using these processing services for the determination of the coordinates of temporary control stations from a few hours of observations in the static mode, and in positioning in the kinematic mode, such as in hydrographic mapping, checking as-built utilities and Geographic Information Systems (GIS) data collection. The different services are briefly presented and compared. The static testing was performed using the AUSPOS and CSRS-PPP services. The results show that precision at mm to cm level can be achieved from the former and within a decimetre from the latter. Kinematic testing using the CSRS-PPP service was performed. Its positioning results were compared with independent differential processing of the same data. The impact of varying the data length on the achieved precision is investigated and the resulting positioning error levels are quantified. In general, the precision varies from a few cm to a few decimetres, and it generally improves with longer observation periods. The CSRS-PPP smoothing performance is also evaluated when breaks of satellite visibility take place and compared with the case of good visibility. Some recommendations are given to surveyors interested in using this type of processing service.
This paper cartographically analyses the map of the Amazon River prepared by La Condamine (1744) and in particular its positional quality with the aid of modern digital cartography. For the region, the chart was the main basis for the Treaty of Madrid (1750), which served as a support for defining the borders in South America between Portugal and Spain. The map shows a band in the equatorial region, from the Pacific to the Atlantic, including the plateau in which the famous arc of meridian in Peru was measured and a detailed course of this big river, from Jaén Bracamoros to Belém do Pará. The La Condamine’s main objective was to create the best and most accurate map of the Amazonas, and it was praised as such, but as shown in this paper, this praise should be tempered with some criticism. The analysis considers some cartographic and historical aspects, with emphasis on the analysis of the accuracy of geographical coordinates (latitude and longitude), examines the consequences of the error in longitude around 3°, at the mouth of the Napo River, which contaminated the entire map. The mistake was accepted as a fact and facilitated the adoption of the Treaty on the part of Spain.
School mapping consists of the building of geospatial databases of educational, demographic and socioeconomic data for educational institutions in order to support educational planning and decision making. Such databases contain data such as the geographic location of schools, the numbers of existing schools of different levels in the public and private sectors, their capacities, physical condition and facilities, enrolment and the number of teachers and their attributes. Also often included are data on related natural features and infrastructure such as rivers, roads, economic and administrative centers, medical facilities, religious facilities, etc. This paper describes the Kenyan School Mapping Project, whose objective was to collect such data for all Kenyan learning institutions and to integrate them in a GIS database that could be queried to provide useful information for educational planners, other professional users and average citizens. Results show that at the time of the project, there were nearly 73000 learning institutions in Kenya, ranging from early childhood schools to universities; useful information products on important educational indicators such as schools distribution, enrolments, pupil-teacher ratios and gender parity indices have also been generated from GIS analysis of the data. These results have demonstrated the utility of the database for its stated purpose and therefore shown the project to be a useful model that can be emulated by other developing countries.
Various mathematical models are available to predict the accuracy of GPS static positioning. Among them, one kind deals with GPS baselines ranging from 30 to 300 km while the other one is used to perform the prediction over baselines from 300 to 3000 km. In this study, we combined the two models into one to predict the accuracy of GPS static positioning from a unified model. The results from the new model agree with the results derived from the previous models in a few mm level.
This paper deals with the effects of the Athens earthquake of 7 September 1999 on the bearing elements of the main construction of the “Peace and Friendship” Stadium (SEF from its name in Greek Stadio Erinis & Filias) in Neo Faliro, situated about 10 km from the city centre. The kinematic behaviour of the bearing frame of the main construction of the Stadium was monitored using geodetic methodology, for a long time (1986 to 1998) before the strong seismic shocks in September 1999. The survey of the concrete bearing elements of the Stadium is presented, a year after (2000) the earthquake, in order to detect the structure’s response. Through this monitoring it was found that the concrete roof of the Stadium had moved. The vector of the displacement of the roof’s centre is estimated and its direction (azimuth) is related with the earthquake’s epicentre.
This paper presents an investigation towards developing a better understanding of the Kalman filtration process by adding an updating equation to the covariance of the random vector process noise in the main algorithm of Kalman. This updating equation results from the theoretical proof of the relationship between Unified Least Square Technique and the Kalman algorithm. Two numerical examples are used to illustrate the effect of the new step added to Kalman algorithm. In the first example, statistical analysis is applied on the original observations. No outliers were detected in the original observations. Three solutions were applied on the data. First, Kalman Filtration without updating the covariance of random vector process noise. Second, Kalman filtration with updating equation is added to the algorithm. Third, Recursive least square technique is used. In the second numerical example, original observations were collected from GPS observations to determine the deformation of two towers supporting a Tianjin Yong Highway cable – stayed bridge in China. Original observations were suffering from outliers. Using the same previous strategy to estimate the state vector and its variance. Finally we conclude that, when the original observations suffering from outliers, Updating the equation of the covariance of the random process noise must be added to Kalman algorithm to improve the performance of filtration process and to overcome the existence of outliers. Adding the new equation improves the variance of the estimated state vector to be identical with Recursive least Square Technique.
This paper explores the effects of LiDAR data reduction on the accuracies of produced TINs and gridded DEMs. It examined to what extent a set of LiDAR (light detection and ranging) data can be reduced without sacrificing the accuracy of produced terrain model. A primary focus was on the integration of breaklines to the reduction process to assess the contribution of breaklines to improving the accuracy of terrain models in data reduction. A series of TINs and gridded DEMs were produced and assessed at reduced data density levels with and without breaklines respectively. The results showed that LiDAR data can be reduced to a certain level without significantly decreasing the accuracy of produced terrain models. When incorporating breaklines into terrain modelling, the accuracy of produced TINs and gridded DEMs decreased only slightly as data density decreased, indicating that breaklines made a significant contribution to improving the accuracy of terrain models in data reduction.
In countries where on the tectonic plate movements, one of the distorting
effects due to plate movements occurs on national geodetic networks. As
a result of distorting effects geodetic networks lose their homogenous
characteristics, and discrepancies increase particularly around active
fault lines. Furthermore, these fault lines form distinctive borders on
the network, and two sides of fault line become apart from each other
in line with the plate movements.
Innovations in land administration are currently primarily looked at from either a legal, a technical or agricultural point of view. This article reviews the role of ‘discretionary space’ in land administration innovations. This is a concept from public administration sciences, referring to the degree of freedom that both strategic managers and operational professionals in land administration often maintain to make decisions based on their personal judgment. The article reviews this discretionary space for 3 cases in Africa: the legal land reform in Uganda, the flexible land tenure in Namibia and the organic land law in Rwanda. The cases represent 3 different historical paths of land innovation in which the discretionary space within the respective public sector organisations developed. Vignettes, being a combination of factual and anecdotal descriptions, of these cases provide the analytical basis for a comparison. From the comparison we conclude that zooming in on the issue of discretionary space of land administration organisations provides added value to the discourse of land administration innovation in Africa.
This article describes the procedure of obtaining variance component estimates with the Minimum Norm Quadratic Unbiased Estimator (MINQUE). Using the examples of simulated measurements, variance components are estimated in geodetic two-dimensional network models. The efficiency of the estimators was tested using simulated data in three different structures of variance component models. Additive, group and mixed models were analyzed using distance and direction measurements, and the efficiency of the estimator was analyzed in all three cases, focusing in particular on the impact of various ratios of the initial variance components and geodetic network characteristics on the variance components estimation.
11. Smooth piecewise algebraic approximation as applied to large-scale
2D scattered geodetic data fitting
We have developed an efficient method, Smooth Piecewise Algebraic Approximation
(hereafter SPAA), to automatically compute a smooth approximation of large-scale
functional scattered 2D observation points and tilt between them. The
area of study is divided into patches and piecewise algebraic surfaces
are fitted to the data. When the surfaces are approximated, a set of constraints
is imposed in such a way that the resulting function is continuous only
in the zero and first derivatives everywhere in the region, which results
in a very short computation time. In other word, the surfaces are fitted
simultaneously, using the constraints as set-conditions which the parameters
of the surfaces must also satisfy. This method does not require a triangulation
or quadrangulation of the data points and as such, it is very well suited
for extremely large datasets.
12 Analysis of the precision in free station establishment by
The coordinates and orientation of a total station can be determined by using common points, i.e. points surveyed both by total station and RTK (Real Time Kinematics) GPS. In this paper we use a trial and error method to analyse how the number and distribution of common points affects the precision of the total station establishment. It was found that a reasonable number of common points is 10 – 30, and that these should be distributed around the total station on a half circle. The radius of the half circle does not significantly affect precision of horizontal and vertical positions; it affects only orientation precision. Therefore we suggest locating most of the common points close to the total station and a few of them at longer distance.
The selection of the optimal GPS baselines can be performed by solving the geodetic second-order design (SOD) problem. In this paper, the particle swarm optimisation (PSO) algorithm, a stochastic global optimisation method, has been employed for the selection of the optimal GPS baselines to be measured in the field that will meet the postulated criterion matrix at a reasonable cost. PSO, which is an iterative-heuristic search algorithm in swarm intelligence, emulates collective behavior of bird flocking, fish schooling or bee swarming, to converge to the global optimum. The fundamentals of the algorithm are given. Then, the efficiency and the applicability of the algorithm are demonstrated with an example of GPS network. Our example shows that the PSO is practical because it does not produce negative or greater than maximum achievable weights of available instruments; it is effective because it yields networks that meet the optimisation criteria; and it is reliable because it converges to the global optimum of an objective function. It is also suitable for non-linear matrix functions that very often encountered in geodetic network optimisation.
In geodetic networks, probable failures in the outlier detection arise not only due to ability of outlier detection methods, but also due to the weakness in the configuration of the networks. The purpose of this paper is to detect this weakness by cross-checking the observations for existing geodetic networks or at design stage. To do it, we introduced the median equations derived from the condition equations among the observations, considering a certain number of outliers to be detected in the network in advance. Firstly the proposed method is applied on a leveling network. Then to apply the new method on all kinds of geodetic networks, a general algorithm has been developed. By using this approach, we can find the controllable or non-controllable observations in view of detecting outliers in an existing network. Thus, the results of the outlier detection methods are confirmed. Moreover, at the design stage of geodetic networks, one can decide whether the network is designed reliably prior to fieldworks. If the network configuration is found to be weak at some part, then it can be improved by adding required observation(s) to the surveying plan.
Survey Review 43, No 322. September 2011
1. Overview of the development of surveying and mapping in China
Since the founding of the People's Republic of China, Surveying and Mapping (S&M) has made a series of remarkable achievements through continuous innovation and development. China has become a very influential nation in S&M, with the standards for S&M regulation and policy having been improved, the fundamental geo-information resource increasingly enriched, the geomatics industry in the ascendant, the hi-tech innovation capacity enhanced, and the service and support capacity expanded in scope and depth.
In some applications of GPS kinematic orientation and attitude determination, the length and pitch of the baseline can be measured by other means. Methods of single epoch single frequency ambiguity resolution with these constraints have been proposed. This paper analyzes the influence of the accuracy of the length and pitch to ambiguity resolution, and several examples are given to test Ambiguity Resolution (AR) performance of different length and pitch weight strategies. The analysis and the test results show that only proper weight of the baseline length and pitch can improve the performance of ambiguity resolution. Finally, a best weight strategy is given and a two-day long data set is used to test the method. The results show that the AR success rate is correlated to the number of satellites and the accuracy of the given pitch. The AR success rate is more than 95% and AR wrong rate is less than 0.005% if the error of pitch is less than 1.0 degree.
This paper puts forward a new concept of Inter-Satellite Observations (ISOs). ISOs can be classified into inside-layer (ILOs) and cross-layer observations (CLOs). ILOs denote inter-satellite two-way ranging observations (TWROs). CLOs denote the observations between satellites of different orbit heights, such as MEO-GEO and MEO-IGSO. GEO and IGSO observations can be obtained through MEO-borne receivers as designed in low-orbit satellites. Using integrated adjustment of satellite-ground observations (SGOs) and ISOs, satellite geometry can be strengthened and orbit accuracy is significantly improved. Upon the above thought, orbit determination simulations are performed in three scenarios (using SGOs, using SGOs and CLOs, and using SGOs and TWROs) according to the satellite constellation of the Chinese COMPASS satellite navigation system. The orbit results are assessed by position dilution of precision (PDOP), three-dimensional RMS of the estimated orbits and the simulated reference orbits. The results show that, using only one-day SGOs from 7 regional stations in China, three-dimensional RMS of GEOs, IGSOs and MEOs are respectively reduced from 6.7 m, 1.3 m and 7.9 m to 0.7 m, 0.8 m and 1.3m when CLOs with beam angle of 42 degrees are added; Orbit accuracies are better than 20cm when TWROs with beam angle of 45 degrees and 30cm amplitude period term systematic error are added.
A new PPP algorithm based on uncombined dual-frequency GPS code and phase observables is presented. The algorithms different from traditional ones in which the ionosphere-free code and phase observables are formed. The Line Of Sight (LOS) ionospheric delays are taken as estimate parameters by introducing the constraints of between-epoch temporal behaviour of ionosphere. This alternative approach has the advantage of avoiding adverse effect of amplified multipath and measurement errors existing in the combined observations. A further study of the performance of the proposed algorithm was conducted by comparing with the traditional ones in different case studies. The results show that kinematic positioning accuracy of several centimetres to decimetres is achieved, with an improvement of 6%-30% compared to traditional PPP algorithms, especially in the upper component; the accuracy of receive clock corrections and ZTDs estimation can be better improved to ~ 0.1ns and ~4mm respectively, which demonstrates the feasibility and effectiveness of this new algorithm.
This paper introduces the Wide Area Real-Time Differential GPS Prototype System on the basis of the PANDA software platform which is independently developed by Wuhan University. The system is a suite of algorithmic, infrastructure elements to enable the processing, distribution and archiving of Real-Time and Near Real-time GNSS data and results. Currently, it adopts observation data from nearly 100 real-time stations, including IGS global stations and regional stations of China, to continuously estimate real-time satellite clock offset second by second and to provide a Global Ionospheric Map product updated every 5 minutes. 1 HZ corrections to the GPS spacecraft position and clock to Broadcast Ephemeris and grid VTEC with 30 sec’ interval are provided to users through a wireless communication network. In this research, real-time orbit and clock product, as well as single frequency and double frequency point positioning accuracy are investigated. Results of tests show the SISRE of real-time orbit and clock by the system is about 5cm; real-time double frequency positioning RMS are respectively better than 10cm and 20cm in the horizontal and vertical direction; single frequency positioning RMS(3D) is better than 1m.
Attention has recently been paid to the algorithm for determining the orbit of navigation satellites autonomously through inter-satellite observation. Through the analyses of the structure of the normal equation for the parameter estimation when using inter-satellite distance observations only, three singular values in the normal equation are found which are significantly smaller than the others. The normal equation is therefore ill-conditioned. If the appropriate measures are not used, this ill-conditioned situation would seriously affect the accuracy and stability of the orbit determination. Based on the discussion of the concrete causes of ill-conditioning, the fitting method by selection of the parameter weights is imported, and the algorithm of adding constraints based on the a priori information of some parameters of the satellites is proposed. The necessary number and type of parameters to be constrained are investigated in detail. How to set the regularization matrix and the regularization parameter are also discussed. Through comparison between the results of different schemes, an optimized scheme is proposed.
Some constraints exist in the kinematic state parameters used for integrated navigation; if these are taken into account, the accuracy of positioning and navigation can be improved. The abnormal disturbances of the kinematic model are controlled in an integrated Kalman filter by introducing adaptive factors. Adaptive Kalman filters with constraints with respect to both a unified adaptive factor and multi adaptive factors are derived based on the generalized maximum likelihood Lagrangian condition. The adaptive factors are constructed from the discrepancies of states and predicted residuals. The approximate estimator of the adaptively constrained Kalman filter with multi adaptive factors is realized by considering that the measurement vectors are independent, and that the predicted state vectors of the kinematic model are also independent. If the constraints between the parameters of the state vector of various sensors are neglected, then the individual state estimates of adaptive Kalman filtering are obtained. The approximate estimator with unified adaptive factor is also given which is very simple to calculate. It is shown by a simulated example, that the precision of the state estimates provided by the adaptively constrained Kalman filter is better than those provided by the unconstrained adaptive Kalman filter or constrained Kalman filter.
In this paper, the crustal horizontal velocity fields of the Weihe Basin and the Xi’an area are determined using high-precision GPS campaign measurements, which in turn provide constraints to calculate tectonic stress fields. A finite element dynamic model is employed for the Weihe Basin and an elastic block model for the Xi'an area. It is suggested that the ground fissures in the Weihe Basin are shaped by active faults under the effect of a NW-SE regional tension stress field. Fault motion is the fundamental factor influencing the ground fissures and controls their directions and distribution, though the excessive extraction of underground water might be another major factor that accelerates the development of ground fissures. It is believed the results obtained in this study can provide important information for the prevention of basin ground fissure disasters and aid urban construction.
This paper presents an error model based on the theory of information entropy for describing positional uncertainty of line segments in Geographical Information System. The model is independent of confident level. In this model, an error entropy band is established by using information entropy of marginal probability distribution of errors along the direction perpendicular to the line segment. Based on that, an average error entropy band is drawn by using average information entropy of marginal probability distribution of the whole line segment. Further, a generic error entropy band is extended from the entropy error ellipse, which is derived from the error entropy band. These three error entropy bands provide a more complete and objective measure for the errors of line segments, since the entropy-based error bands are determined according to different entropy criteria. Practical examples in this paper show that these three error bands are suitable measurement indices for positional uncertainty of line segments.
Survey Review 43, No 321. July 2011
Nowadays an important problem in combining geospatial data from different sources is that they rarely align. In this paper we present an approach for vector-image conflation and develop an algorithm which detects road intersections from both datasets as control points by using image texture characterization. With this technique, we first train the system on a small area of the orthoimagery to learn the road texture distribution, then we can obtain its segmentation according to its texture, and finally the system locates road intersection points. The last step is to align vector data and images by using different techniques.
To date, the accuracy of static GPS positioning has been documented well. However, we have not yet encountered detailed evaluations for Rapid Static GPS. Considering this fact, in this paper the accuracy of Rapid Static GPS was investigated. BERNESE 5.0 was used to process the GPS data. GPS data was obtained from the archives of Scripps Orbit and Permanent Array Center (SOPAC). The results indicate that the accuracy of Rapid Static GPS depends on the inter-station height difference. As known from previous studies, a large inter-station height difference has a significant effect on GPS positioning accuracy, and this study modelled the effect with error equations. Empirical formulae are derived based on previously developed least squares (LS) functional models to predict the accuracy of GPS Rapid Static Positioning, and then an attempt is made to predict GPS baseline errors for the Koyulhisar landslide, in Central Turkey. The RMS of the solutions agrees with the predicted accuracy values at around the 1 cm level.
Local engineering precision networks are cur¬rently used to monitor
the displacements of large dams, with safety con¬trol purposes. These
one, two or three-dimensional networks are local, because they are tied
to local re¬fe¬ren¬ce frames, and they are precision networks,
because they aim at millimetric, or even sub¬¬millimetric, ac¬cu¬ra¬cy.
The most important obstacles to such an accuracy are the instrumental
and environmental systematic errors. The atmospheric re¬frac¬tion,
which causes curvature of the path of the electromagnetic waves and changes
its propagation velocity, is the major source of sys¬te¬ma¬tic
errors. Effective measurement quality control strategies are of utmost
importance to gua¬ran¬tee the quality of the results (displacements).
The paper presents a quality control strategy supported by ran¬dom
quadratic forms that result from the decomposition of the Mahalanobis
squared norm of the re¬si¬duals vector. The strategy is compared
to the well known data-snooping method with regard to the quality con¬trol
and parameter estimation performances.
4. Tidal line surveying and Ordnance Survey mapping for coastal
Understanding and predicting coastal change and associated sea level rise are crucial issues in coastal planning and management. Any data which increase the understanding of the long term behaviour of the natural environment are particularly important. Tidal lines, as indicated on Ordnance Survey maps, have been used and have the potential for the geomorphological analysis of changes in beach width and possibly as indicators of sea level rise and beach erosion. Tidal lines represent clearly resurveyed, temporally and spatially transient features which predate aerial photography as a potential source of evidence of coastal change. However, any use of these features requires an understanding of the reliability, repeatability and practicality of trying to map an ambiguous feature in the field. This research principally deals with tidal line definition, data capture and the practice of the ground survey mapping of tidal lines on the Ordnance Survey maps of England and Wales from 1868 until the 1960s.
Various studies have shown that alpine ecosystems in the Tibetan Plateau are very sensitive to climate change and they are facing degradation. However, such studies are regional and either use coarse resolution satellite imagery as a monitoring tool or rely upon secondary data. Traditional digital image classification methods normally can’t meet specific needs of extracting land cover categories from satellite images. This paper aims to map land use/land cover (LULC) particularly the predominant rangeland vegetation in the Lhasa River Basin by applying an accurate expert system classification (ESC). Landsat ETM+ satellite imageries taken in 2000 and other digital datasets were used. To show the advantages of ESC, the results were compared with the results of maximum likelihood classification (MLC) system. The ESC resulted in a classified map with a significant higher accuracy (84.31%) than maximum likelihood classification (74.31%). This demonstrated the successful application of ESC in the Lhasa River basin and, most importantly, three rangeland vegetation categories were extracted with acceptable accuracy. Furthermore, the results showed an effectively used of the two classifications in extracting LULC categories in zone above 4200m than in zone below 4200m, due to the relatively homogeneous landscapes. It is suggested that data of improved spatial and spectral resolution and more correct, complete and relevant expert knowledge could potentially improve the accuracy of ECS. Compared with the MLC, the ESC requires more time to extract and tune the knowledge in order to create rule bases. This drawback can be reduced by developing an automatic and reproducible system to extract knowledge from the data layers to a specific landscape in the future work.
A time-variant similarity transformation model has been proposed recently for reference frame transformations across time. It has been postulated that reference frame variations only result in uniform deformations (i.e. by the same scale factor in all directions). However, this is not always the case in a deforming area. In this study, a time-variant affine transformation is proposed to accommodate possible non-uniform deformations for reference frame applications in a significantly deforming area. This model also enables the investigation of the deforming behaviour of a reference frame with physically interpretable parameters. To prove its feasibility for present day reference frame applications, numerical tests are performed on an actual data set from the continuous GPS stations in Taiwan. Results illustrate a substantial improvement in the quality of reference frame transformations when the proposed approach is implemented.
We have developed the most precise vertical displacement rate field of Taiwan Island to date from four sets of precise geodetic levelling data between 2000 and 2008. More than 4000 km of levelling lines between solidly constructed benchmarks were repeatedly surveyed by 1st-order levelling. Strict specifications for field work procedures and comprehensive corrections for systemic errors were applied to the levelling data. Furthermore, in order to account for the vertical deformations caused by four major earthquakes during the data span, coseismic offset corrections were computed and applied. The adjusted orthometric heights and vertical displacement rates of the benchmarks were obtained by least-squares estimation (LSE). The estimated standard deviations of the vertical rates are in the range of ± 0.41 mm/yr and ± 2.47 mm/yr, with a mean value of ± 1.64 mm/yr. These highly accurate results reveal that the most significant subsidence rate is observed in SW Taiwan at -109.4 mm/yr. Land uplift is widely observed in the Central Range and the Coastal Range, with the largest uplift rate of +29.4 mm/yr in SE Taiwan, at the convergence boundary of the Philippine Sea and the Eurasian plates.
The GPS observables collected at reference stations for the post-processing
type of kinematic positioning are likely to be provided by a public data
service on a routine basis with a large sampling interval of 30 seconds.
This low-rate data might lead to a non-matching observation with the rovers
recording the trajectories with a high data rate of 1 Hz or even greater.
To ensure the differential solutions achieved, GPS observables are required
to be the same data interval for the two baseline stations. A two-step
interpolation technique is proposed to work for GPS data densification
to strengthen data availability and reduce the cost of taking any supplementary
observation. A curve fitting function, with a linear correction, is applied
to interpolate both the phase and the range observables into a higher
rate data set for GPS kinematic positioning. It is found that a third
order polynomial and a linear correction can work properly to increase
the applicable data rate from 30 sec to 1 sec for kinematic positioning.
An external accuracy of 0.5 cm in plan and 2.4 cm in height is obtained
from a short baseline solution. Another medium baseline solution also
confirms that the external accuracies of 1.3 cm in plan and 7.6 cm in
height can be achieved using a 1 sec interval of interpolated observables
as opposed to raw data. A two-hour static data set is also applied to
test for the stand-alone kinematic positioning, namely the precise point
positioning (PPP). The PPP solution demonstrates that the N-S component
of the accuracy is significantly improved from 34 cm to 15 cm, when the
interpolated data is used. Based on the kinematic tests, the accuracies
of the solutions using the original data and the interpolated data are
generally in good agreement.
Survey Review 43, No 320. April 2011
1. Accuracy of 3D models derived from aerial laser scanning and
2. Tsilhqot'in Nation v British Columbia
The Tsilhqot’in case is the most recent Canadian case to contribute significantly to the jurisprudence concerning first peoples land rights. Explicit constitutional protection of Aboriginal land rights has existed in Canada since 1982. Without statutory guidance, particularly vexing issues with which the courts are grappling are firstly the concept of Aboriginal title and secondly evidentiary standards to prove such title that are both equitable and acceptable to the courts. This in turn has led the courts to reject some occidental land law concepts and embrace a sui generis approach to Aboriginal land rights and an approach to the law of evidence appropriate to Aboriginal tenure systems. To date a First Nation is yet to successfully claim Aboriginal title in Canada, and the Tsilhqot’in too were unsuccessful on first instance. However, the Tsilhqot’in judgment imparts a practical foundation for the judicial consideration of oral history and oral tradition evidence. Additionally, while the decision is not binding on cases that follow, the decision provides an indication of areas in which a claim for Aboriginal title might be successful. Moreover, whereas the idea of boundaries is a Eurocentric principle and the Tsilhqot’in have had to conform to those common law principles in order to simply make a claim; traditionally, the Tsilhqot’in society did not have any ‘metes and bounds’ boundaries but instead recognized something along the lines of social boundaries.
3. A regression study on relative GPS accuracy for different
We know that position accuracies from relative and static Global Positioning System (GPS) measurements are degraded by a variety of physical, hardware and software effects. As a result, users often take special precautions to minimise these effects and, hopefully, improve their accuracies when planning and making measurements. In this study, the effects of the baseline length (BL) and observation duration (OD) on vertical and horizontal positioning errors for relative, static GPS measurements were experimentally evaluated. In making this evaluation, 5 min to 24 hours GPS data, collected over a 15 day period, from the Southern California Integrated GPS Network (SCIGN), were analyzed. The root mean square (RMS) of the differences between the true and measured vertical (up/ellipsoidal height) and horizontal (north and east/ latitude and longitude) positions of the included stations were computed and then used to create empirical error equations dependent upon the BL and OD. Considerations for the number of satellites (SVs) and the positional dilution of precision (PDOP) were included too by necessity. With these equations, GPS users can better estimate their vertical and horizontal position accuracies based on the known BLs, desired ODs, available SVs, and predicted PDOPs when planning a project, or have an external standard of comparison when evaluating their results.
Predicting the accuracy of GPS is of great interest to researchers. Today, empirical formulas that predict the GPS accuracy from local to regional scales are available for the scientific and surveying communities. Hence, it is a useful survey planning tool for field works for various geodetic applications. Research results in this area indicate that the GPS accuracy is a function of the length of the observing session over local to medium scales (i.e. between 10 and 300 km) whereas the accuracy is a function of both the session length and inter-station distance over regional scales (i.e. between 300 and 3000 km). In this study, we introduce a new constraint, i.e. the inter-station height difference that needs to be taken into account in GPS positioning accuracy studies. We use previously published least squares (LS) functional models and model the GPS accuracy taking inter-station height differences into account. Our results indicate that the accuracy of GPS is degraded in the presence of large height differences as the duration of the observing session gets shorter. This needs to be taken into account in accuracy computations. The prediction of the vertical positioning accuracy has been improved by about 20 % for 6 h sessions by combining the standard deviations predicted from regional GPS accuracy studies with the ones derived here.
Real Time Kinematic GPS System (RTK GPS) measurements like other survey measurements are not devoid of errors. The purpose of this study is to show that RTK results can seriously be degraded by obstructions such as trees and the baseline length. This paper shows the investigations of the two positioning error sources, studying their effects, and searching for methods to decrease, or possibly eliminate these two errors in order to achieve better positioning accuracies in RTK GPS. As stated above, one of the major problems is the signal attenuation which occurs when GPS signals are attenuated by shades of trees or leaves. Another problem associated with RTK positioning is the baseline length which tends to degrade the accuracy as the baseline length increases. On the other hand, this study investigates the achievable accuracy and repeatability of the RTK under different satellite configurations by using different reference points. Accuracy of spatial data is reported according to the National Standard for Spatial Data Accuracy of United States (NSSDA).
This paper aims at applying the inverse eigenvalue problem to obtain
weight optimisation for geodetic observations. Second order planning in
a geodetic network is introduced, working from the spectral point of view
and also under certain theoretical concepts. These concepts are those
capable of making the application of the inverse eigenvalue to obtain
the weight when the final network precision is specified. As an example,
the application of these concepts to a net of points with its plane coordinates
which associates weight to the variation of the observations and to the
magnitude of the measured quality to reach the desired precision. The
optimisation criteria is presented and the results are analysed and discussed.
8. Orthorectification of Quickbird ortho-ready imagery: a case
study over mountainous terrain
Geometric quality of ortho-rectified imagery is crucial for their usefulness in mapping and map updating. The use of the recently appeared very high resolution images gave cause to a debate regarding which is the best approach to geometrically correct them. This paper presents a case-study of image ortho-rectification using a QuickBird scene over an area of mountainous relief. Conclusions about ortho-rectification models are consistent with recent studies by other authors, indicating the superiority of 3D rigorous models and 3D Rational Functions (with rational polynomial coefficients supplied by the image vendor) in terms of final accuracy and number of ground control points needed. The resulting positioning errors are representative of what can be expected in an operational context by end-users such as private companies or state agencies and are well within ASPRS Class 1 requirements for the 1:5,000 scale.
Survey Review 43, No 319. January 2011
1. The NZGEOID09 model of New Zealand
The NZGeoid09 gravimetric quasigeoid model of New Zealand was computed through FFT-based Stokesian integration with a deterministically modified kernel and an iterative computation approach that accounts for offsets among New Zealand’s 13 different local vertical datums (LVDs). NZGeoid09 is an improvement over the previous NZGeoid05 due to use of the EGM2008 and DNSC08GRA models, and due to improvements to the data processing strategy. The integration parameters of degree of kernel modification L=40 and cap radius y0=2.5° were determined empirically through a comparison with 1422 GPS/levelling observations, after the LVD offsets had been removed. The precision of NZGeoid09 was assessed using the same GPS/levelling dataset, yielding an overall standard deviation of 6.2 cm. NZGeoid09 performs better than NZGeoid05 and marginally better than EGM2008, but few data are available in the Southern Alps of New Zealand to give a better evaluation.
Standard reductions to gravity readings due to Earth tides, ocean loading
and attraction, polar motion, instrumental height and air pressure variations
and loading of atmospheric masses are studied in this paper from a practical
point of view, that is, taking into account their numerical values and
their influence on gravimetric readings and relative gravimetric observations.
3. Tomas Lopez's geographic atlas of Spain in the Peninsular
War. A methodology for determining errors.
During the Peninsular War, Napoleon’s and Wellington’s armies
were aware of the lack of precision in the maps of Spain and its provinces
that appeared in Tomas Lopez’s Geographical Atlas of Spain. The
errors were due to the non-topographical surveying method he used, which
he had learned from his teacher Jean Baptiste Bourguignon D’Anville.
To map all of the Spanish provinces, Tomas Lopez divided them into circles
of three leagues in diameter (16,718 m), taking a particular town as the
centre. He asked the town’s priest to draw a map of the territory
and to complete a questionnaire that Tomas Lopez sent to him. The priest
was to return the two documents after he had completed them. Subsequently,
at his desk, Tomas Lopez used the maps and reports as well as other graphic
and written sources from various locations to make an outline of each
map. Next, he made a mosaic that served as a pattern for drawing the final
provincial map. We will see the way that this method was applied in two
concrete cases: the villages of Chavaler and Monteagudo, situated in the
Spanish province of Soria, and verify their degree of accuracy. We will
use the maps drawn by the priests in 1767, the final map of the province
which was published in 1804 by Tomás López, and a current
map of the province showing the angular and linear errors in Lopez’s
4 Updating Thai reference frame to ITRF2005 using GPS: Diversion
between ITRF2000 and 2005 in Southeast Asia
The Thai geodetic network has been regularly observed with Global Positioning System (GPS) since 1994 through several collaborative EU-ASEAN projects such as GEODYSSEA, SEAMERGES and RTSD-Delft. This geodetic network has long been served as a reference frame for Thailand. Previous realisations of the Thai coordinate reference frame were therefore tied to the global International Terrestrial Reference Frame (ITRF) at epochs 1994, 1996 and 2000. After the occurrence of the 9.2 Mw Sumatra-Andaman earthquake on the 26th December 2004, horizontal displacements were evident at different magnitudes in many surrounding countries. The geodetic network within Thailand was also significantly deformed during the earthquake at the centimetre to decimetre level. Large co-seismic horizontal displacements were observed in the southern part of Thailand, while moderate and small displacements were seen in the central and northern parts of Thailand. The Royal Thai Survey Department (RTSD) has been carrying out multiple GPS field campaigns to monitor the post-seismic displacements. This paper will analyse the GPS observations obtained from the RTSD GPS campaigns up to the end of 2008 using the Precise Point Positioning (PPP) strategy of the GIPSY-OASIS II software. It has been demonstrated that by employing the state of the art PPP technique, the users could achieve mm-level of repeatability in the horizontal components and centimetre precision in the vertical direction, for a 24-hr data span from a static site occupied by a geodetic-quality receiver. Coordinate results obtained from each campaign are then mapped to ITRF2000 and ITRF2005 using a number of well-determined global International GNSS service (IGS) sites. By comparing coordinate results between ITRF2000 and ITRF2005, it is evident that there is a significant diversion in the north component at a rate of 1.7 mm per year over Southeast Asia region. Finally, ITRF2005 coordinate results obtained from the latest RTSD GPS campaign (November 2008) will be served as a new coordinate reference frame for Thailand.
Cooke, Troughton & Simms designed a Reflecting Theodolite for use
by Major Hotine on the Arc of the 30th Meridian in Tanganyika and N Rhodesia
(now Tanzania and Zambia) in 1931-33. The origin of the design and its
evolution are described. An outline description is followed by comments
from Hotine’s unpublished field correspondence. Proposed use of
the theodolite after Hotine’s work included completion of the Arc
through Ruanda-Urundi, but it was not used again until 1954, on the Kenya-Ethiopia
boundary, and 1958, in Uganda and Kenya; it was given to the Science Museum
6 Fitting composite horizontal curves using the total least squares
The parameters of horizontal curves are sometimes missing or need to be updated using observed x and y coordinate data. The observed data for existing alignments may be obtained using global positioning systems (GPS) or extracted from digital imagery. Previous methods have addressed the case where only the circular or the transition curves are estimated. This paper presents an optimisation model for composite horizontal curves that simultaneously fits the circular curve, its transition curves and the two tangents using the total least-squares method. The objective function minimises the squared deviations between the observed and predicted values. The model can be applied to fitting single or multiple composite horizontal curves. Since the model is nonlinear and non-convex, a close initial solution is first developed and then used to obtain the global optimal solution. The model is validated and applied using actual data of a horizontal alignment. The proposed model presents an important extension to existing methods for estimating horizontal alignments and therefore should be of interest to surveying professionals.
Airborne LiDAR has become the preferred technology for digital elevation data acquisition in a wide range of applications. The vertical accuracy with respect to a specified vertical datum is the principal criterion in specifying the quality of LiDAR elevation data. The quantitative assessment of LiDAR elevation data is usually conducted by comparing high-accuracy checkpoints with elevations estimated from the LiDAR ground data. However, the collection of a sufficient number of checkpoints by field surveying is a time-consuming task. This study used survey marks to assess the vertical accuracy of LiDAR data for different land covers in a rural area and explored the performance of different methods for deriving elevations from LiDAR data corresponding to the locations of checkpoints. Normality tests using both frequency histograms and quantile-quantile plots were performed for vertical differences between the LiDAR data and the checkpoints, so the appropriate methods were used for the vertical accuracy assessment of LiDAR data for different land cover categories. The results demonstrated the suitability of using survey marks as checkpoints for the assessment of the vertical accuracy of LiDAR data.
The paper describes the methodology used for the assessment of the horizontal accuracy of digital topographic maps at a scale of 1: 50 000 produced by the Serbian Military Geographic Institute and reviews the results. The test for the horizontal accuracy compliance of a map sheet is done by comparing the planimetric coordinates of the ground points to the coordinates of the same points as determined by a horizontal check survey of higher accuracy with standard deviations equal or less than one-third of the limiting error selected for the map. In this research two standards were used and the methodology of their use is discussed in detail. Special attention was not paid to the map design but to the quality of the map assurance, using verified scientific approaches. The result obtained from this research confirmed the chosen approach and showed very good results for the digital topographic maps produced by the Serbian Military Geographic Institute. The suggested methodology may be also used for the assessment of digital topographic maps at other scales
On the Description of Coordinate Reference Systems