Abstracts of the October issue - Vol. 36, No. 286 October 2002

1. A Quality Assurance Approach for Land Subsidence Interpolation - Miao-Hsiang Peng and Tian-Yuan Shih

Land subsidence in southwest Taiwan is mainly caused by ground-water withdrawal and a monitoring network of benchmarks has been established to observe this subsidence. Using results from differential leveling, the magnitudes of land subsidence from 1992 to 1994 were calculated for 50 benchmarks. The calculated maximum magnitude of land subsidence is 15.4 centimeters between these two years. Spatial interpolation is frequently required to provide information for assessing the distribution and extent of subsidence. In this study, geostatistics were applied to describe and characterize the spatial structure of sample data. Thus, an implementation procedure was proposed for the quality assessment of interpolation. The procedure includes geostatistical analysis, outlier detection, and comparison of different estimation techniques. The results show that the approach proposed in this study is effective to ensure the quality of interpolation.

2. A Simplified Minque Procedure for the Estimation of Variance-Covariance Components of GPS Observables - Chalermchon Satirapod, Jinling Wang, Chris Rizos

Minimum Norm Quadratic Unbiased Estimation (MINQUE) is one of the commonly used methods for the estimation of variance-covariance components. The MINQUE procedure has been successfully used to estimate the variance-covariance components of GPS observations. However, the MINQUE procedure is a big computational burden, and the requirement of having an equal number of variance-covariance components in the estimation step is a major limitation. It is therefore difficult to implement this procedure when the number of observed satellites has changed during an observation period. In this paper, a simplified MINQUE procedure is proposed in which the computational load and time are significantly reduced. The quality of the results obtained is similar to those from the rigorous procedure. Furthermore, the effect of changing the number of satellites on the computations is effectively dealt with.

3. Implications of Progressive Title Registration for Cadastral Information Production Case Study of Namibia - W. T. de Vries

Under the premise that land administration is one of the necessary components of sustainable development and better land management, this article reviews the effects of the implementation of a progressive titling approach on land administration components, such as cadastral acts and organisations, cadastral survey regulations and processes and cadastral databases. The study is largely based on the experiences of implementation of progressive titling in Namibia, where there are changes in both the legal acts governing titling as well as in cadastral survey acts and regulations. The article comes to the conclusion that the progressive titling approach as proposed for the Namibian context and its subsequent implications for cadastral information production shows that there is a need to rethink the structure and objective of cadastral surveying and a need to look for alternative models for cadastral information systems which support land administration.

4. Inverted Pseudolite Positioning and some Applications - Liwen Dai, Jinling Wang, Toshiaki Tsujii, Chris Rizos

In this paper the inverted pseudolite positioning system, comprising a ÔconstellationÕ of GPS receivers that tracks a mobile pseudolite, is discussed. Two configurations of the inverted positioning system are described. The implementation challenges for the pseudolite-based inverted positioning system, including geometry optimization, multipath mitigation and minimization of the impact of GPS receiver location errors, have been investigated. Several applications of the inverted positioning concept have been identified, including deformation monitoring and navigation services based on pseudolite installed on stratospheric airships. A static experiment was carried out using six NovAtel GPS receivers and two IntegriNautics IN200CXL pseudolite instruments, on the UNSW campus, on the 4th April 2001. The experimental setup and operational procedures are described in detail. The carrier phase measurements have been processed in an 'inverted' mode. The results indicate that the potential accuracy of 'inverted' phase-based positioning is better than 5mm. The static experiment has indicated that the two configurations for the inverted positioning are feasible in practice.

5. Testing the Precision of the Electro-Optical Distance Meter Mekometer ME 5000 on the Calibration Baseline Zagreb - N. Solaric, M. Lapaine and G. Novakovi

The paper examines the precision (accuracy) obtained with the Leica-Kern Mekometer ME 5000 distance meter on the calibration baseline Zagreb. A new method for the processing and analysing the measurements on the baseline is presented. It provides an estimate of the precision, and, with the frequency in the distance meter measured, the approximate accuracy as well. For distances up to 100 m the standard deviation of distance measurement in one direction of 0.058 mm is obtained. For distances in the range of 100 to 3000 m, applying the proposed method of data processing, the standard deviation of a measured distance (measured forward and backward, and on the basis of adjusting all measurements on the baseline) of 0.12 mm + 0.21 mm.D was obtained in 1988, and in 1996 0.07mm -0.13 mm.D + 0.37 mm D2.

6. Comparison of Different Algorithms to Transform Geocentric to Geodetic Coordinates - Alireza Amiri Seemkooei

The conversion from geocentric to geodetic coordinates is among of the most important tasks in computational geodesy. This conversion is oftesn complicated and time consuming. In order to deal with the large quantities of points, it is important to select the fastest possible algorithm without compromising the accuracy. From the numerical standpoint, the available conversion algorithms have to be solved either iteratively, through a linearization, or using an algebraic equation of forth degree. In this paper, five iterative algorithms and one closed form solution for transformation from geocentric to geodetic coordinates are compared for numerical efficiency. It is concluded that the simple iteration method implemented in Bowring's algorithm executes faster than the others. Only one iteration is sufficient to produce coordinates accurate to the comparable level of 0.3.10-16 rad., which exceeds the requirements of any practical application.

Abstracts of the July issue - Vol. 36, No. 285 July 2002

1. Evaluation of Ultra-High Degree Geopotential Models in Australia - K. Zhang, R. Deakin, N. Talbot and N. Edwards

Recent development of ultra-high and high degree Earth geopotential model (EGM) opens new avenues to determine the Earth gravity field through spectral techniques to a very high accuracy and resolution. However, due to data availability, quality and type, the performance of these new EGMs varies accordingly. Therefore, the performance of any new model remains to be validated in regional or local scale. The ultra-high degree tailored model (GPM98C) developed by Wenzel is evaluated using GPS/levelling derived geometric geoid, the new Australian gravimetric geoid, land and marine gravity anomalies and satellite altimetry derived gravity information. This is of particularly importance since the gravity field of Australia is unusual due to its long geological history. Results show that, compared with EGM96, Wenzel's model presents detrimental effects over Australia, particularly over Tasmania, coastal and major geological interest areas. Therefore, it is highly desirable to develop a new high degree and resolution Australian geopotential model using regional heterogeneous data. Some closely related issues are discussed and recommendations for further development of an ultra-high Australian Geopotential model are given.

2. Wicked Problems, Soft Systems and Cadastral Systems in Periods of Uncertainty - Michael Barry and Clarissa Fourie

There have been a number of problems when cadastral systems, or elements of cadastral systems such as titling programmes, have been used in property formalisation programmes in developing countries. This is often not so much a fault with the technical systems that make up the cadastral system but the fact that the situations in which cadastral systems are used can be categorised as 'wicked'. In these situations, conventional project management techniques are unlikely to succeed as it is extremely difficult to identify a specific problem with clear objectives to be addressed. The situation is often too complex to break it up into sets of small projects. The soft systems methodology, using systems thinking and systems concepts, provides a process and a structure for incremental improvements to such situations. Ideally, such methods should involve all the stakeholders in a continual cycle of learning. However, the local dynamics may prevent this. Drawing on a case study of a South African informal settlement, the paper describes some of the problems that occur in applying cadastral systems in uncertain situations. The notion of wicked problems and the soft systems methodology are then described. Finally, the rationale for using the soft systems methodology is argued by drawing on research into the effectiveness of the cadastral system in South Africa.

3. Study of the Deformation of Koyna Dam using the Global Positioning System - Ankur Manake and Madhav N. Kulkarni

Large engineering structures such as dams, though essential for development, are also a potential hazard, causing loss of human lives and property, in case of their failure under excessive deformations. Hence, monitoring dam deformations has assumed great importance worldwide. Classical geodetic techniques, and more recently, the revolutionary space geodetic technique: Global Positioning System (GPS), are valuable tools for generating important input data to monitor such deformations. A project for crustal dynamic studies in the Koyna Region in Maharashtra, India, using GPS, has been taken up, which also includes the deformation studies for Koyna Dam. A GPS network has been established for this purpose, and observed in two sessions viz. December 2000 and May 2001. The study results indicate a definite correlation between the change in reservoir water level and the deformation of the dam. The results obtained using the conventional methods are found in close agreement with the GPS-derived results, thus proving GPS to be an effective tool for dam deformation studies.

4. The use of the Two-Dimensional Spherical FFT for Quasi-Geoid Modelling in South Africa - Ameer Amod and Charles L Merry

Quasi-geoids for the south western Cape, a coastal province of South Africa, and the Gauteng area, in the north-east of South Africa, have been computed by the application of the two-dimensional (2D) spherical fast Fourier transform (SFFT) to MolodenskyÕs formula. The gravimetric quasi-geoids for the south western Cape and Gauteng were computed on a grid resolution of one arc-minute. Validation of the gravimetric quasi-geoid models with GPS/levelling-derived geometric quasi-geoids via a simple planar transformation resulted in a root mean square (RMS) discrepancy of about 4cm for the south western Cape area and about 1.3cm for area of Gauteng. The quasi-geoids have also been evaluated using the 2D planar FFT and 2D multi-band SFFT and our results confirm the suitability of using a 2D SFFTÕs for geoid/quasi-geoid computation in mid-latitude regions.

5. Combined GPS/GLONASS Precise Positioning for Long Range Baselines - Guorong Hu and Weihong Cui

Combined GPS/GLONASS can increase the accuracy and reliability of positioning especially in some applications those with many impediments. Due to influenced by the atmosphere delay, the commonly used methods for short range baselines data processing cannot be implemented in long range baselines. In this paper, a new data processing strategy for long range baselines is proposed which uses the properties of some combination observations of combined GPS/GLONASS and reduces the influence of ionosphere delay. Numerical results show that the repeatability of long range baselines may come to the order of 10-8 and combined GPS/GLONASS increases the precision of GPS-only positioning which will benefit to monitor crust deformation and research on geodynamics.

6. Groebner basis solution of planar resection problem - Joseph L. Awange

The three nonlinear planar resection equations are usually solved analytically by first solving for the unknown orientation in the horizontal plane in a three-step procedure. The first step is the elimination step, the second step is the division step and the third step is once again elimination step. Once the unknown orientation parameter in the horizontal plane has been determined, it is substituted back in any of the two of the initial nonlinear equations to obtain the position of the unknown observing station. By making use of the Groebner basis technique, whose computing engine is the B. Buchberger algorithm, we obtain in a single step three direct relationships between the unknown planar resection, the coordinates of the three known target points and the horizontal direction observations being made from the unknown observing station to the three known target points whose coordinates are known. These three direct relationships allow a faster computation of the unknowns and an easy implementation of the algorithm in laptops and programmable scientific calculators being carried by surveyors, engineers and architectures to the field. The Groebner basis approach thus avoids the forward and backward steps of the classical analytical procedure.

7. Accuracy of First Order Levelling in Greece - A. Antonopoulos and I. Takos

The aim of the present paper is to investigate the accuracy of levelling along the lines of the First Order Levelling Network of Greece as deduced from the misclosures of its loops. Actual standard deviation of the standardized circuit misclosures significantly larger than 1 reveals correlation of the individual height differences between consecutive bench marks along a given levelling line accompanied by various other systematic effects. Correlation also exists between forward and backward levelling runs. The detection of correlations neither leads to their source nor eliminates them. However, especially for a high degree of correlation, the investigation of their causes, and their inclusion in the network adjustment may be helpful for the analysis and an improvement of the results.

8. On Robust Datum Definition - Jarir Saleh

This paper suggests a simple way for the automatic robustification of datum definition in the adjustment of free geodetic networks. In the absence of regional crustal deformations, this method leads to accurately estimated coordinates even when several reference coordinates are unreliable. If regional crustal motions are present, experience shows that the method can be used as a quick exploratory technique that uncovers all unreliable and inaccurate reference points without any iterative testing. An example is presented to demonstrate the second case. The 1901-03 triangulation network of Trinidad, which is believed to be bisected by a major geologic fault that forms part of the boundary zone between the Caribbean and the South American tectonic plates, is adjusted on the ITRF96.

Abstracts of the April issue - Vol 36 No 284 April 2002

1. Development of an Event-Reporting Intelligent Vehicle Navigation System for Areas with Urban Canyons - Esmond Mok , Günther Retscher and Lawrence Lau

Common vehicle navigation systems employ mostly GPS satellite positioning to track the vehicle's position and velocity. The tracked position can be dynamically shown on a digital map or automatic route guidance can be performed. So-called "Intelligent GPS Vehicle Navigation Systems", simply speaking, are extensions of common GPS vehicle navigation systems. It can be said, that they are GPS vehicle positioning systems with embedded intelligence. From the authors' point of view, an intelligent system should be able to detect the changes of the real-world situation and to give an appropriate response to the changes. Therefore, an Intelligent GPS Navigation System should have all the basic functionality of a common GPS navigation system, and be able to detect and react to the conditions that are of concern of the driver or the vehicle manager. To achieve this, an intelligent GPS navigation system should be integrated with different types of sensors and communication devices that are able to monitor and perform event reporting to the vehicle's real-word situation. Hence, event reporting is an essential component of an Intelligent Vehicle Navigation System (IVNS). With regard to the navigation part of the system, it is essential that the vehicle's trajectory can be continuously tracked to provide necessary guidance for the driver. However, for GPS-alone systems a reliable position determination in urban canyons may not always be possible, therefore it is necessary to investigate the integration of other vehicle tracking devices and methods.

After the discussion of the potential applications of an event reporting IVNS, a more detailed description of a prototype system will be given. Such a system is being developed in a research project at the Department of Land Surveying and Geo-informatics of the Hong Kong Polytechnic University. Finally, field test results of the prototype IVNS conducted in Hong Kong are presented and the integration of wireless location services for positioning and a new GPS-alone position tracking method for urban canyons are briefly discussed.

2. A new Algorithm for Point-in-Polygon Test - M.G. D'Urso and P. Russo

An original point-in-polygon test, based upon an electric analogy, is illustrated. It enhances an analogous procedure, previously developed by the first author [5], by almost halving the computer time required to numerically perform the test. The result is obtained by proving an addition formula for the inverse tangent function that corrects the one which can be usually found in mathematical handbooks. Further, the equivalence of the proposed method with the sum of angles method is shown.

3. Impact of a Large Earthquake on a GPS Network. The Case of the 1999 Chi-Chi, Taiwan Earthquake - L.C. Kuo, S.B. Yu, Y.J. Hsu, C.S. Hou, Y.H. Lee, C.S. Tsai, and C.S. Chen

On 20 September 1999, Taiwan was hit by the largest inland earthquake (Mw=7.6) in the last century, resulting in an 80-kilometre thrust rupture almost directly along the existing Chelungpu fault. Here, we estimated the coordinates of the GPS stations by using the annual epoch-observed and permanent continuously-recorded GPS data covering the 1992-1999 period. Taking into account the effects of secular motion and post-deformation, we calculated the corrected coseismic displacements. Relatively large coseismic displacements of 8-9 m in the horizontal and vertical components were found in the northern part of the fault. Stations on the hanging wall shifted horizontally 2-9 m in the NW direction and decreased in magnitude from west to east. On the other hand, displacements on the footwall were less than 2 m in the SE direction but increased from west to east. The size of the zone overlapping the hanging wall and the footwall showed a decrease of 796 ppm in 494 km2. This is in direct contrast to areas near the fault which increased in size from 13 to 237 ppm. Significant postseismic deformations were also observed in data from the existing 44 permanent stations and 7 temporary stations. Additionally, large postseismic deformations of 10-20 cm were found at stations SUNM, I007 and YUSN within 10 months.

4. Robustified L8- Norm Estimation - Peng Junhuan and Xie Zhiying

The paper suggests the modification accumulation function and constructs L8-norm estimation algorithm based on this function. It can overcome the numerical overflowing of the original L8-norm estimation algorithm and solve the function model with multi-parameters. Further the robustified L8-norm estimation algorithm with resistance is derived

5. The Evolution of a Well-known Seismic Area in Northern Greece after a Large Earthquake - G. Asteriadis and H. Schwan

In 1996 new measurements of a trigonometric network installed in 1979 in the seismically active area of the lake Volvi, in northern Greece near Thessaloniki, were performed with the use of GPS technology. An analysis of the data set of the 1996 measurements gave us the displacement field of the 11 stations of this network. The most dominant feature of this field is an expanding trend in north-south direction. This trend there is in this field since 1979 when the first measurements of this network were done. This means that since 1979 the rocks of this area are subjected to a force tensile in the north-south direction. This is in agreement with the foults geometry of this area, since the known faults there have a general direction from east to west.

6. Transformation between GPS Coordinates and Local Plane UTM Coordinates using the EXCEL Spreadsheet - T. G. Gacoki and F. W. O. Aduol

A procedure for obtaining plane UTM grid coordinates from GPS coordinates based on WGS84 reference system by use of Excel spreadsheet is outlined. The geographical coordinates obtained from GPS observations are transformed to the local reference system by use of a seven-parameter transformation. The local geographical coordinates are then transformed to plane UTM grid coordinates. Thereafter, the reverse computation is also performed to act as a check, i.e. transformation from grid coordinates to geographical coordinates.

7. Evaluation Practice on Airborne GPS Data Quality - Liu Jiyu

Since July 1,1991 the GPS signals transmitted by each satellite have been activated by the Selective Availability (SA) techniques that mean unauthorized users can only acquire 120m-accuracy of real-time positions. To match air photogrammetric engineering we have developed successfully an airborne GPS kinematic carrier phase measurement technique, with new software based on the Kalman filter processing for pseudorange/double difference data of carrier phase measurements, and can complete the ambiguity resolution On The Fly (OTF) on the carrier phase measurements, defining as DDKIN software. DDKIN was used to solve precisely for seven dimension state parameters of 10 types of aircraft making over 200 flights between 1994 and 2000. It is known from the analysis using 103 ground geodetic controls with millimetre accuracy, that the coordinate accuracies of Trimble 4000SST receiver installed in the aircraft have achieved 7.9 cm for 2D positions and 18.1 cm for heights above the ground. This paper discusses only three evaluations: kinematic figuration check, flight velocity evaluation and dual initialization evaluation.

Abstracts of the January issue - Vol 36 No 283 January 2002

1. GPS Multipath Change Detection in Permanent GPS Stations - L.Ge, S. Han and C.Rizos

We have proposed a technique based on an adaptive filter using the least-mean-square algorithm for detection of multipath change in permanent, continuously operating GPS (CGPS) stations. We have tested the technique on some experimental data, indicating that the multipath change smaller than the receiver noise level will go undetected. We have also conducted further tests with some CGPS data from the Japanese GEONET when there was a snowfall. The results show that when there is a change in the antenna environment it will indeed be detected in both the pseudo-range and carrier phase data. This technique provides an easy-to-implement, quality assurance tool for CGPS antenna environmental sensing after events such as typhoons, cyclones, snowfalls, volcano eruptions, earthquakes, etc. Other possible applications include the monitoring of slope stability and ground subsidence.

2. Land-based Integrated Systems for Mapping and GIS Applications - C.M.Ellum and N.El-Sheimy

An emerging solution to the problems faced in modern data collection campaigns is the integration of various navigation and remote sensing technologies together on a common land-based platform. These land-based Mobile Mapping Systems (MMS) are capable of providing fast, efficient, cost-effective, and complete data collection. Their development has been motivated by a desire to overcome the problems with alternative methods of spatial data collection. These alternative methods include point-wise GPS and traditional terrestrial surveying - which are ill suited for rapid or dense data collection - and aerial photogrammetric surveys - which do not provide complete coverage. Land-based MMS share none of these disadvantages, while still being capable of providing similar object space accuracies.

This paper provides a brief history of land-based MMS, including a summary of nearly all systems developed up to now. It then details the development of the geo-referencing formulas used by MMS and shows how such formulas can be used to determine the accuracies of points measured by the system. The paper concludes with a closer examination of two land-based mobile mapping systems - one van-based, the other person-based. Both systems demonstrate that MMS are able to achieve absolute object-space accuracies between 10-20 cm.

3. Single Receiver Heighting using the Active Stations of the National GPS Network of Great Britain - N.T.Penna, R.M.Bingley and A.H.Dodson

Precise height determination using a single GPS receiver is now possible, following the establishment of GPS networks that include active stations with typical separations of about 100km. A method is described to determine precise heights when using a single GPS receiver and active stations of the National GPS Network of Great Britain. From the computation of the heights of 188 GPS stations distributed across the British mainland, a precision of 1.5cm was attained. This was achieved using only 4 hours of dual frequency static GPS data, but with scientific GPS processing software to mitigate systematic error effects.

4. Impact of Augmenting GPS by GLONASS on Determination of Horizontal Control Networks - Ahmed El-Mowafy

The augmentation of GPS by GLONASS measurements is investigated for improving positioning accuracy in establishing horizontal control networks. The main focus is given to the second order networks (B order). The problems of integrating measurements of the two systems and their treatment are first discussed. These include: the impact of differences in the signal structures and the existence of the receiver clock error in the GLONASS double differenced observations. A successful method for the removal of this error and for the phase ambiguity resolution is presented. In addition, several models for transformation of GLONASS satellite coordinates to the WGS-84 frame are given and their impact on the computed coordinates are quantified and analyzed. A static testing was carried out on a network consisting of six stations with leg lengths of less than 12 km. A comparison was made between using GPS data alone and using combined GPS and GLONASS data. The results showed that both approaches gave accuracy on the millimeter level in coordinate determination, and thus can be successfully used for establishing the B-order stations. However, significantly improved accuracy and faster phase ambiguity resolution was achieved when using the integrated GPS/GLONASS measurements..

5. Least Squares Adjustment through Reparameterisation - Willie Tan

Reparameterisation is a possible alternative to the usual least squares approach of fixing the network datum using minimal constraints, inner constraints or the pseudo-inverse. Since the approach estimates linear combinations of estimable parameters, it may be used when differences, and not the absolute values, are of interest.

6. Crustal Deformations from Sparce Geodetic Data - A.M.Agatza-Balodimou, P. Briole, C.Mitsakaki and K.Papazissi

During the last decade, the Higher Geodesy Laboratory of NTU and the Seismology Department of the Institut de Physique du Globe de Paris have carried out a research program concerning the evaluation of the tectonic behaviour of the Gulf of Corinth, in Greece, based on geodetic data. The area being one of the densely populated, seismically active parts of Greece, was considered suitable for monitoring deformations. Thus, a geodetic GPS control network of 193 points, spread over a broad area ( of about 10 000 km2 ) on both sides of the Gulf, was established within seven years. During this period several points were re-occupied. Thus the GPS data acquired are sparse both in space and time. In order to estimate the deformation over longer periods of time 142 of the network points were chosen to belong to the Hellenic triangulation network. In the present paper, statistically acceptable strain parameters are evaluated via a multi-epoch deformation model using GPS data alone as well as in combination with positional information from old geodetic surveys.

7. An Evaluation of some Robust Estimation Techniques in the Estimation of Geodetic Parameters - Part II - J.L.Awange and F.W.O.Aduol

In Part 1 of this study, we reported on an evaluation of the performances of four robust estimation techniques, namely: the modified residuals technique, the modified weights technique, the modified residuals-weights technique, and the iterative weighting technique. The methods were then tested on a simulated geodetic network. In this second part of the study, we carry out a further evaluation of the methods with a real geodetic network as the test network. In order that a set of gross-error contaminated observational may be available for the study, gross errors have been simulated into observational set. The results of the study largely corroborate the findings in Part I of the study.