Abstracts of the October issue - Vol. 37, No. 290 October 2003

1. A New Height Reference Network in Taiwan - Ming Yang, Kwo-Hwa Chen and Shyang-Wen Shiao

The island of Taiwan is located in an active tectonic zone on the boundary of the Eurasian and Philippine Sea plates. Due to the continuous mountain building process in association with the collision of the two plates, it is very important for Taiwan to periodically re-survey the island so as to maintain the intrinsic accuracy requirement of its vertical reference network. The existing height network was created in 1979 by means of the spirit levelling technique with theoretical surface gravity quantities derived from the Geodetic Reference System 1967 (GRS67) normal gravity field. Because of the lack of use of actual gravity measurements in its creation, the existing network has been found to suffer from severe systematic errors in the central mountainous areas.
In this paper, we present the design and implementation of a new national vertical datum in Taiwan, Taiwan Vertical Datum 2001 (TWVD2001). The new datum was developed by optimally combining geodetic levelling and surface gravity observations collected at 1010 newly established benchmarks within a network of 2200-km first-order levelling lines. The data analyses and adjustment computation were based on geopotential numbers. Both orthometric and normal heights were computed for the new vertical reference network.

2. Fast and Accurate Determination of Astronomical and Azimuth using a Total Station and GPS Receiver - D. D. Balodimos, R. Korakitis, E. Lambrou and G. Pantazis

This work reports the development of a system for fast and accurate determination of astronomical latitude, longitude and azimuth. The system consists of a high-precision total station, with the appropriate software for automatic registration of the measured elements, connected to a GPS receiver through which accurate UTC timing is provided. This system allows the acquisition of a large amount of data during the tracking of selected stars around their meridian transit. After the appropriate processing of the data, an accuracy of 0.01 arc sec in latitude and longitude and 0.02 arc sec in azimuth may be achieved for the determination of the astronomical coordinates and azimuth.The developed system compares favourably to older classical ones, due to its compactness and the accuracy obtained within a short period of time. Thus, combined with GPS receivers for the geodetic coordinates determination, it can easily be used for the determination of the deviation of the vertical and eventually of the geoid separation N.

3. OSGM02: A New Model for Converting GPS-derived Heights to Local Height Datums in Great Britain and Ireland - J. C. Iliffe, M. Ziebart, and P. A. Cross R. Forsberg, G. Strykowski and C. C. Tscherning

The background to the recent computation of a new vertical datum model for the British Isles (OSGM02) is described. After giving a brief description of the computational techniques and the data sets used for the derivation of the gravimetric geoid, the paper focuses on the fitting of this surface to the GPS and levelling networks in the various regions of the British Isles in such a way that it can be used in conjunction with GPS to form a replacement for the existing system of bench marks. The error sources induced in this procedure are discussed, and the theoretical basis given for the fitting procedure. Results for each major region (Great Britain, Ireland, and Northern Ireland) as well as the various independent island datums are described. The problems to be expected when working between datums are discussed.

4. GPS Compatible Positioning in Ireland (Part 1) - M.J.Cory 1, I.C.Greenway 2 and C.J. Hill 3

The paper describes the justification, realisation and implications of a change of coordinate reference system for Ireland. It includes consideration of the science and the practicalities of the change, for both data providers and users. The development of a new coordinate reference system for Ireland has profound and positive implications for usability and accuracy of surveys in the future, but introduces significant transition issues which must be dealt with carefully.

5. What is the Reliability of Conventional Outlier Detection and Robust Estimation in Trilateration Networks? - M. Berber and S. Hekimoglu

There are two fundamental approaches to determine outliers; these are, the Conventional Outlier Detection Test Procedures (e.g., data-snooping of Baarda, ?-test of Pope etc.) and Robust Estimation Methods.
As is known, the Least Squares Estimation (LSE) method is very sensitive to outliers and it spreads the corrupt influence of the outliers upon the good observations. Therefore the Baarda and Pope test methods derived from the LSE are thought of as unsuccessful methods on outlier detection. It is asserted that in case of more than one outlier, these Conventional Outlier Detection Test Procedures become inefficient. In this situation, Robust Estimation Methods are proposed for application. In this study these possibilities are investigated in trilateration networks structured artificially.

6. Buchberger Algorithm applied to Planar Lateration and Intersection Problems - Joseph L. Awange

The Buchberger algorithm which is incorporated in algebraic software of MAPLE and MATHEMATICA is here used to derive expressions relating the known coordinates of planar stations and the observables to the unknown planar coordinates of a station for planar lateration and intersection problems. In the case of lateration, the coordinates of the unknown station are expressed as quadratic equations in terms of the measured distances to the known station and the coordinates of these known stations respectively. For intersection, the coordinates of the unknown stations are expressed in terms of the measured directions and the coordinates of the known stations. These expressions can easily be programmed in laptops or programmable calculators and thus making it feasible for any practitioner with these computing devices to obtain directly planar coordinates once the distances or directions have been measured.

Abstracts from the previous issue - Vol. 37, No. 289 July 2003

1. Applications of Augmented Reality: Utility Companies - A. J. Evans, G. W. Roberts, A. H. Dodson, S. Cooper, R. Hollands, B. Denby, M. Turner and D. Owen

The use of Augmented Reality (AR) in an unprepared environment is a considerable challenge in the field of virtual environments. Solutions require high accuracy data and precise positioning of the user and their relation to the hardware to ensure correct registration between reality and the data to be augmented. Research at the University of Nottingham has utilised the highest accuracy Real Time Kinematic (RTK) GPS positioning and digital compass; giving heading, pitch and roll information to position and orientate the user in relation to a 3d data model. Precise positioning and orientation ensure that the registration of the 3d model and the real world objects is accurate which then allows the visualisation of sub surface information related to features visible to the user. The system has been tested with an existing water network database held by Yorkshire Water. The background to the technology and the use of an AR system, results and conclusions of these field trials are presented in this paper.

2. Dispute Resolution for Customary Lands: some Lessons from Fiji - Keresi R. Fonmanu, Lisa Ting and Ian P. Williamson

Customary land tenure involves a complex and detailed array of tenure rights which are often difficult to reconcile with western systems of land tenure. Land disputes arising from customary land tenure are costly, time consuming and often hinder the operation of governments, land administrators, developers, investors, proprietors and land users. These disputes may be the result of the customary system or the result of the tensions of a dual tenure system. This paper discusses the experience of Fiji in addressing disputes involving customary land and proposes a framework for resolving disputes in customary land.

3. Discussion on Standard and Robust Kalman Filters, using Post-Earthquake data set of 17 August 1999, Izmit Earthquake - U. Dogan, S. Ergintav, H. Demirel

We discuss on the performances of standard and robust Kalman filters to estimate the post-seismic deformation field produced by the 17 August 1999 Izmit, Turkey, earthquake. The data set covers a subset of the Marmara Continuous GPS (Global Positioning System) Network (MAGNET) and other available survey stations in the region. The results of the models suggest that the standard Kalman filter estimate is not optimal due to serious bias that occurs between epochs. The bias, however, can be detected and removed using a robust Kalman filter.

4. GPS Phase measure Cycle-slip detecting and GPS Base-line Resolution based on Wavelet Transform - Yongliang Xiong , Dingfa Huang and C.K. Shum

The errors in GPS measurement generally consist of systematic errors (such as clock bias, ionosphere, troposphere effects etc.), random errors (such as measuring error) and outliers. Systematic errors can be canceled by differencing techniques or by adding parameters into the equation system. Outliers may be detected by adding parameters or by statistical methods such as expectation shifting or variance inflating. Because wavelet analysis has many good natures both in the time domain and in the frequency domain, as can automatically zoom in or out with different scales (frequencies), the arbitrary details of a signal can be observed and analyzed by the aid of wavelet analysis. Based on the above features, wavelet analysis is reputed as "a mathematical microscope". The paper presents a wavelet based outlier detecting and filtering algorithm. GPS phase observables are decomposed into different components by wavelet transform. The content at scale 1 mainly consists of high frequency components including cycle-slips or outliers. Because the amount of cycle-slips is zoomed in by wavelet transform at the original location, so the locations of cycle slips are easily detected after wavelet transform. Based on the properties of outliers, cycle slips and random noises under wavelet transform, a so-called á trous reconstruction algorithm is selected. The noises in double difference phase observables are filtrated by removing some components from scale-1and reconstructing original signal. Then an algorithm for GPS base-line resolution using phase double difference based on wavelet filtering is put forward in this paper. By using the proposed algorithm, the ambiguity searching space is reduced, and the validation of fixed ambiguities is improved as well. The efficiency for the proposed algorithm is approved by three examples.

5. Reduction of Heave, Pitch and Roll effects in Hydrographic Surveying - Reha Metin Alkan

A hydrographic survey vessels show three-dimensional movements due to environmental effects, such as wind, current, other vessel wakes, etc. As a result of this, the vessel will experience Pitch, Roll and heave. These motions (if ignored) cause errors in depth and in the positioning of the sounding. The magnitude of the errors can reach up to even meters depending on the marine environment conditions, vessel size, vessel characteristics, and especially wave height. However, accurate and reliable depth and position data are needed in bathymetric charts prepared for shallow water navigation, dredging, various engineering applications, harbour manoeuvres, and maximizing cargo capacity safely. Therefore, compensation of vessel motion is necessary for several applications. The goal of this study is to determine and reduce the heave, Pitch and Roll effects in hydrographic surveying realized by a single narrow beam system. As a result of this study, heave, Pitch and Roll corrections are calculated and applied to the relevant data.

6. GPS Coordinate Transformation Parameters for Jamaica - Glendon G. Newsome and Bruce R. Harvey

The Surveying and Mapping community now has the benefit of real-time 3-dimensional coordinates at the centimetre level, through the Global Positioning System (GPS). The reference frame, World Geodetic System of 1984 (WGS84), within which a user ascertains these coordinates is essentially geocentric. In Jamaica all coordinate data and mapping are based on a non-geocentric coordinate system known as the Jamaican Datum of 1969 (JAD69), which like many others around the world was realized by making basic assumptions about the geoid-ellipsoid separation at the origin. WGS84 coordinates are therefore not compatible with the JAD69. This paper presents the results of work carried out to define the relationship between the two coordinate systems, through three types of transformation parameters, namely Block Shifts, Molodensky and Seven Parameter Similarity. Three of the forty-two primary control stations together with a Continuously Operating Reference Station (CORS), previously tied to the island network, forms a fiducial network at which WGS84 coordinates were determined. The two coordinate data sets for the four fiducial stations were used to solve the parameters. Tests were carried out on nine points with coordinates known in both systems. The results indicate that the Block Shift and Molodensky values transforms WGS84 coordinates to JAD69, accurate to ±1-2m and the seven parameter similarity values produce JAD69 coordinates accurate to ±0.5m or better. Arguments are put forward to suggest why coordinate transformation is an interim solution and that the development of a Geocentric Datum is preferred for Jamaica.

7. Implementing Seismic Moho depths in Geoid - Hussein Abd-Elmotaal

The paper studies the effect of implementing seismically estimated Moho depths in gravimetric geoid computation, instead of assuming an isostatic hypothesis to create the compensating masses, within the well-known remove-restore technique of geoid computation. Three different techniques were applied when using the seismic Moho depths in the geoid computation. In the first technique, a constant density contrast between the lower crust and the upper mantle for all topographic elements has been assumed. In the second technique, variable density contrast computed as a function of the seismic Moho depth has been assumed. In the third technique, variable density contrast computed as a function of the topographic height has been assumed. A comparison with a geoid computed using the commonly used Airy-Heiskanen isostatic model has been made. For all cases, a gravimetric geoid has been computed for a test area by applying Stokes’ integral in the frequency domain using the 1D-FFT technique. All geoids are scaled (fitted) to the geoid derived from GPS and levelling. A broad comparison between all geoids is carried out. The results show that using the seismic Moho depths with variable density contrast between the lower crust and upper mantle computed as a function of the seismic Moho depth improves the accuracy of the computed geoid.

8. Variance-Covariance perturbation analysis of a Linear Model - Fengxiang Jin, B.Merminod, H.Dupraz and P-Y.Gillieron

In this paper the perturbation influence properties of the stochastic model (variance-covariance) in linear models is discussed in detail. Some very useful formulae are established about the variance-covariance perturbation influence on the model parameter’s estimation. Then the influence properties are analyzed in different cases and illustrated by two examples. A very important fact is proved that the non-influence cases exist under some conditions. These conditions are carefully studied. The conclusions obtained are very helpful for people to well understand the function of stochastic model in the linear models, and to vividly work with them. The paper offers some very important theoretical results that should be considered for the weight function design in Robust Estimation.

Abstracts of the April issue - Vol. 37, No. 288 April 2003

1. Experiments with two different approaches to gridding terrestrial gravity anomalies and their effect on regional geoid computation - J M Goos, W E Featherstone, J F Kirby, S A Holmes

This paper compares the gridding of two types of terrestrial gravity anomaly prior to the computation of regional gravimetric geoid models over Australia. The aim is to investigate the effects of high-frequency components (by way of the terrain correction) on the resulting grid of mean gravity anomalies, and hence the geoid. The gravity anomaly types investigated comprise simple Bouguer anomalies and refined Bouguer anomalies, both computed using a constant topographic mass density. Irrespective of which anomaly type is used for gridding, the relevant additional correction terms are applied to yield an approximation of the mean Helmert anomaly. Regional gravimetric geoid models are then computed over Australia and compared with one another and with GPS-levelling points on the Australian Height Datum. This shows that the application of terrain corrections before or after gravity gridding has only a relatively small effect on the computed geoid in Australia.

2. Experimental GPS/INS/Pseudolite system for kinematic positioning - Dorota A Grejner-Brzezinska and Yudan Yi

The requirements for accuracy and reliability of kinematic positioning have dramatically increased in the past few years. Stand-alone GPS can, in general, provide high accuracy and stability over time, however, may still fail in adverse conditions (jamming, high multipath, high ionospheric activity, etc.) or in the environments with obstructions or locations with weak satellite constellation (high altitudes). One example of rather demanding positioning accuracy requirements is in mobile mapping technology that has significantly expanded its market during the last decade of the twentieth century. In order to meet the stringent accuracy requirements and to provide a continuous trajectory, the most common means of positioning used in mobile mapping is an integrated GPS/INS (inertial navigation system) system, used to provide positioning and attitude information for land-based or airborne imaging sensors. GPS contributes high accuracy and long-term stability (under no losses of lock and properly resolved ambiguities), providing means of error estimation of the INS sensors. A GPS-calibrated inertial navigation system provides reliable bridging during GPS outages and supports the ambiguity resolution after the GPS lock is reestablished. Such a system works well if GPS gaps are not too frequent and not excessively long. However, in case of navigation in urban canyons or indoor mapping, there is usually very limited or no GPS signal. Consequently, a pseudolite (PL) array may be used to supplement the satellite signal.
In this paper, an experimental GSP/INS/PL system is presented, with a special emphasis on the error spectrum and the navigation performance analysis, based on a medium-accuracy and high-reliability INS, limited GPS constellation, and varying number of pseudolites. Double difference GPS and PL phase observations are formed and used as a measurement update in the extended Kalman filter, facilitating tight integration of the navigation sensors. The simulated data and the actual test results in typical noisy environments are presented, including the geometry and the vehicle dynamics analysis, and their impact on the navigation accuracy.

3. Landslide monitoring using precise levelling observations - Mahmoud Albattah

In this paper, precise levelling observations have been used to study and to analyze the mechanical behavior of the landslide. The soil is considered as a mosaic of rigid blocks. Characteristic graphs defining its movement have been constructed from precise levelling observations. These graphs, providing inclination magnitude and azimuth of the movement of the blocks, allow us to determine the mechanical behavior of their displacement and to understand the steady-state movement of the entire area of landslide.
The Characteristic graphs constructed from precise levelling observations can reveal soil movement of very small magnitude that can not be observed with other means. This makes it the most adaptable mean to detect very small soil movements.

4. Surveying the surveying profession - Stig Enemark

Since the late 1960s the Danish Association of Chartered Surveyors has carried out a survey of the surveying profession every 10 years starting in 1967. The changes taken place over these 30 years and especially over the last two decades are quit remarkable.
The professional profile of the Danish surveyors is a combination of technical, judicial and design areas. The profile thus is a mix of an engineer, a lawyer and an architect. The professional fields then consist of three areas: surveying and mapping, cadastre and land management, and spatial planning. Cadastral tasks are the monopoly of licensed surveyors in private practice, and the role of the private licensed surveyor has traditionally epitomised the Danish surveyor.
However, both the structure of the surveying profession and the professional profile of the Danish surveyor are turned upside down over the latest two decades.
The paper presents the concept used for surveying the surveying profession. The concept is designed for monitoring the professional profile in surveying as well as the surveying market. The key result of the survey is that “the only constant is change”. The concept is used as a strategic tool for professional development to manage this constant change. Surveying the surveying profession, this way, provides a basis for professional development, and it provides a backbone for the profession itself.

5. The Compact Method of Testing Total Stations - Alojzy Dzierzega, René Scherrer

A compact, laboratory based method is introduced that verifies the angular and distance measuring accuracy of surveying instruments. Angular measurements are carried out with collimators and distance measurements are done with or without reflectors or reflective tapes. The method has been optimized in regards to meeting stringent space and time requirements. It is suited for service workshops or institutions with limited space available.

6. Detection of Systematic Errors by Variance Components Estimation - Vahab Nafisi

Variance components estimation is a method that compute suitable weights for observations. The types of observations can be different (distance, direction, angle). Investigations show that estimations have a meaningful relation with systematic errors or blunders. In other words, if systematic errors exceed some values -that these values can be calculated using precision of observations-, then estimated components will be unreal. Using simulated data, the manner of changes of components can be evaluated. This method can complement the usual methods for detection of systematic errors and blunders.

Abstracts of the January issue - Vol. 37, No. 287 January 2003

1. A Mixed-Mode GPS Network Processing approach for Deformation Monitoring Applications - Volker Janssen and Chris Rizos

The Global Positioning System (GPS) can be utilised in a wide range of deformation monitoring applications, such as the monitoring of active volcanoes, tectonic fault lines, landslides, ground subsidence, bridges, dams, high-rise buildings, etc. During the past few years a methodology has been developed for processing data collected by GPS networks consisting of a mixed set of single-frequency and dual-frequency receivers. The strategy is to deploy a few permanent, ‘fiducial’ GPS stations with dual-frequency, geodetic-grade receivers surrounding an ‘inner’ network of low-cost, single-frequency GPS receivers. Such a configuration offers considerable flexibility and cost savings for deformation monitoring applications, which require a dense spatial coverage of GPS stations, and where it is not possible, nor appropriate, to establish permanent GPS networks using dual-frequency instrumentation.

The basis of the processing methodology is to separate the dual-frequency, ‘fiducial’ station data processing from the baseline processing involving the inner (single-frequency) receivers located in the deformation zone. The data processing for the former is carried out using a modified version of the Bernese software, to generate a file of ‘corrections’ (analogous to Wide Area DGPS correction models for the distance dependent biases - primarily due to atmospheric refraction). These ‘corrections’ are then applied to the double-differenced phase observations from the inner receivers to improve the single-frequency baseline accuracies (primarily through empirical modelling of the residual atmospheric biases that otherwise would be neglected).

This configuration has been tested by simulating such a two-stage network using data collected by part of the Southern California Integrated GPS Network (SCIGN). Six sites forming an inner network of three GPS receivers surrounded by three ‘fiducial’ GPS receivers are used in this study. All sites are equipped with dual-frequency instrumentation, however, for most of the analysis the inner sites are treated as single-frequency stations by ignoring the observations made on L2. A description of the processing strategy, together with a discussion of the results is presented.

2. Capacity Building in Land Management- Implementing Land Policy Reforms in Malawi - Stig Enemark and Rexford Ahene

There is a significant need for capacity building in the interdisciplinary area of land management, especially in developing countries and countries in transition, to deal with the complex issues of building efficient land information systems and sustainable institutional infrastructures.

Capacity building in land management is not only a question of establishing a sufficient technological level or sufficient economic resources. It is mainly a question of understanding the interdisciplinary and cross-sectoral nature of land administration systems, and understanding the need for human resource development in this area. Furthermore, capacity building should ensure that the focus is on building sound institutions and good governance rather than just high-level IT-infrastructures.

This overall approach to capacity building in land management is used for implementing a new land policy reform in Malawi. The paper presents the new decentralized land policy developed as a response to the current land related problems in Malawi. The deficit in terms of qualified personnel is remarkable and calls for immediate action. An integrated curriculum is developed to provide the necessary skilled technicians and professionals for implementing the new land policy. The curriculum combines the diploma and the bachelor level and it combines the key areas of land surveying, land management and physical planning.

3. Deformation Analysis using Confidence Ellipsoids - P. Cederholm

A simple method for detecting deformations of a single point in a three-dimensional Cartesian coordinate system is presented. It is assumed that the point is surveyed with GPS. The point and its covariance matrix are estimated at two epochs. From these estimates the deformation vector and its covariance matrix is determined. A confidence ellipsoid for the deformation vector is computed from the eigenvectors and the eigenvalues of the covariance matrix. If the deformation vector penetrates the confidence ellipsoid, the deformation is significant. As the presented method is simple, it should only be used for a simplified deformation analysis. An example is given.

4. Definition of a Sphere Tangent to Four given Spheres and its Applications to GPS Positioning - A. Antonopoulos

In the present paper, the easily expressed, in analytical form, rigorous geometrical definition of a sphere tangent to four given spheres and the investigation of solutions are synoptically cited. The applications of the aforementioned definition to the determination of position in Geodesy and especially in GPS literature are highlighted; ways to predict and avoid unfavourable situations stemming from weak or even indefinite fixation of position (outages) are mentioned.

5. Measuring with Electronic Total Stations - A. Dzierzega and R. Scherrer

Since the introduction of the electronic total station, the art of measuring seems to have been relegated to the backseat. However, optimal results can still only be achieved by applying the 'Rules of the art of measuring'. These cover the various remaining sources of error in total stations, in particular electronic total stations, as well as the methods that can minimize or eliminate influences on measurements.

6. Multimedia Supported GIS Application for the Documentation of Historical Structures - C. Güney and R. N. Celik

Recent developments in technology such as Geographic Information System (GIS) and its multimedia-based applications can be very useful tools when used to research and document historical structures. This article presents a case study, which demonstrates how the research of two Ottoman fortresses from the 17th century can be documented and organised using a GIS based multimedia application. As one of the essential requirements of GIS is accurate spatial data, a primary goal of this project was to create a complete and accurate set of maps for the two Ottoman fortresses of 'Seddülbahir' and 'Kumkale' and their environs. This article demonstrates how a multimedia supported GIS can assist in the organisation of geographically oriented data and provides an efficient method of documenting historical structures.

7. Geodetic Monitoring of the Santorini (Thera) Volcano - S.C. Stiros and Aris Chasapis

Santorini (Thera) is a volcanic island complex dominated by a partly submerged caldera and famous from an eruption which buried the 3,500 years old Minoan town of Akrotiri. The volcano is active, and the last periods of its paroxysmal activity date to the 1920s, 1940s and 1950s, but in the last decades is dormant. A geodetic monitoring system aiming at an early identification of a future dilation of the caldera as a result of magma inflation was established in 1994, in the framework of an interdisciplinary project for the surveillance of this volcano.

The geodetic monitoring system consisted of a radial EDM network with a central point at the Nea Kammeni islet and 10 stations in the Thera and Therasia islands. Baseline lengths were ranging between 3.2 and 6.5km, most of the paths were >100m above the water and survey stations are selected among those of the national geodetic network.

Between June 1994 and October 2000 six epochs of baseline measurements at a centimetre-level accuracy were made using an AGA 6000 Geodimeter and sampling of meteorological conditions at baseline endpoints at the height of 2m above ground. In October 2000 a radial GPS network has been installed on the same pillars and was measured using the kinematic method. A small-scale (a few-cm level), gradual inflation of the northern part of the caldera (between Nea Kammeni and Therasia), possibly associated with magma ascent along a dike, has been inferred from EDM measurements.