Abstracts of the October issue - Vol 36 No 282 October 2001

1. Geo-Information Systems for Decision Makers - Clarissa Fourie and Oriando Nino-Fluck

The notion of a Stakeholders' Forum was discussed at a United Nations Economic Commission for Africa Ad Hoc Expert Group Meeting held in November, 1998. Such a Forum should be set up to develop the Land Information Management system of Member States, because there have been few success stories in regard to GIS/LIS systems in Africa, and decision makers often have had to make decisions based on little or no information. The paper discusses who should sit on such a Stakeholders' Forum, its functions in relation to the creation and maintenance of a country's LIM system, its structure, and its role in undertaking a Users' Requirement Analysis. Some of the outcomes from such a Forum should be an LIM system that primarily serves decision makers, facilitates decentralization, participatory land use planning and network connectivity (institutional and technical) and develops an integrated information and mapping system.

2. Cost Recovery for Land Administration - Ir P van der Molen

Cost recovery is a concept that is easily misunderstood. However, in many countries government policies are changing in such a way that land administration is no longer considered as a natural public good. As a consequence "user pays" philosophies increasingly gain support; these require a well prepared business strategy for land administration organizations. This article aims to clarify the concepts of 'costs', 'revenues' and 'cost recovery', leading to recommendations as to how such a strategy might be implemented. This will be done in the context of two main financial systems: the government budgeting system and the cost-benefit system. Some other relevant matters will be addressed: level of services, government policy on free availability of government information, and cost flexibility when the market suffers from recession. Finally, some recommendations are given to troubled directors general.

3. The Effect of Old Geodetic Data on Deformation Analysis - A M Agatza-Balodimou and C Mitsakaki

A common geodetic approach makes use of old coordinates referring to a fictitious mid-epoch and compares them with new ones derived by GPS methods in order to evaluate displacement fields in crustal deformation studies. It is investigated whether this approach provides reliable estimations of the displacement field.

4. GPS Single Point Positioning with SA off: How accurate can we get? - Chalermchon Satirapod, Chris Rizos and Jinling Wang

The announcement by U.S. President Bill Clinton to turn off 'Selective Availability' at midnight (Washington DC time) 1 May 2000 caught everyone by surprise. This decision to stop degrading the accuracy of the Global Positioning System's (GPS) Standard Positioning Service (SPS) will have a significant impact on users all over the world. One important outcome for the geomatics community is that the substantial improvement to GPS Single Point Positioning (SPP) results could make it an attractive alternative to the Differential GPS (DGPS) mode of positioning. In this paper some results from different SPP processing strategies are presented, and the accuracy improvement in the case of averaged static solutions is discussed. Finally, the paper speculates on the attainable SPP accuracy using single-frequency GPS receivers when the ionospheric activity is less intense in the future.

5. Ambiguity Online Estimation by Combining Dual-Frequency Phase and Carrier Smoothed Code Measurements: Performance on Short Baselines - Dingfa Huang, Xiaoli Ding and Yongqi Chen

For both static and kinematic relative positioning with GPS, the success of baseline resolution depends closely on the reliable fixing of integer ambiguities of carrier phase measurements. Low noise code correlated dual-frequency GPS receivers offer accurate pseudo-range measurements on both carrier frequencies. With the help of a combination of code and carrier phase measurements, wide-lane ambiguities can be easily determined and used for the improvement of ambiguity resolutions on both L1 and L2 frequencies. A carrier smoothing technique is utilized to eliminate the noise of code measurements. Baselines ranging from 1.5 km to 48 km are used to test the proposed method.

6. The Delay Mismodelling due to Pointing Error in Precise Space to Earth Geodetic Observations - Ioannis M Ifadis

To predict the zenith, hydrostatic, wet or total atmospheric delay, we normally use only surface meteorological parameters. If we wish to scale the zenith delay to directions other than zenith we use known mapping functions, which use one or more basic parameters and the elevation of the radio source over the horizon. In this report we show that if, in any mapping function, the true elevation of the radio source is used then the resulting delay for the certain radio source is incorrect. The resulting delay is underestimated and the value of the error depends on the radio source elevation angle and height over the earth's surface. It is shown that this height and a modified elevation angle have to be considered and perhaps be modelled or included in the delay estimation procedure either in developing any mapping function or later in predicting the delay.

7. A Land Uplift Map of Fennoscandia - Jan S Danielsen

Data from GPS, tide-gauges, levelling and sea level marks have been used to determine apparent land uplift rates in Fennoscandia using least squares collocation and a method called "geometric filter". Reliable values for the whole region have been obtained.

8. Back to Basics (24) Least Squares, Statistics and all that - N Atkinson and A L Allan

This is the eleventh and last of a series of articles presenting some thoughts about Least Squares, Statistics, Quality Control and other related matters, which may be of interest to students, or practitioners new to the particular applications described. The treatment is deliberately elementary and the examples are simplified so that the various concepts can be developed with clarity. Now and then, the editor will enter a word of caution in the text, where he feels that the treatment has been oversimplified or for other reasons. As in previous articles, the topic is presented as a dialogue between this practising surveyor Nigel Atkinson and a retired academic Arthur Allan. The editor encourages comments as the series unfolds.

Abstracts of the July issue - Vol 36 No 281 July 2001

1. Land Administration and Cadastral Trends: The Impact of the Changing Humankind-Land Relationship and Major Global Drivers: the NZ Experience - Lisa Ting and Ian Williamson

The aim of this paper is to discuss some of the current forces of change on the humankind/land relationship and why an increasingly integrated approach to land administration and management is imperative. An overview of the past forces of change on land administration is discussed to demonstrate the dynamic nature of the humankind/land relationship. Particular attention is given to major global drivers such as sustainable development, globalization, economic reform and the information technology revolution. The potential impact of these current forces (particularly sustainable development), on the institutional, legal, political and technological frameworks of a nation, is discussed. New Zealand, which has undergone considerable economic and legislative reforms since the mid-1980s, is used as an illustration of trends and the imperative for a more integrated approach to land administration across those frameworks.

2. Eighteen Yards and Nine Metres - Ludvik Pfeifer

This article presents the descriptions and definitive equivalent lengths in international metres of eighteen different yards and nine different metres which are (or once were) of significance to geodesy, or which remain today of general historical interest. A concise historical account of the origin of the international metre, compiled from various authoritative sources, is also given.

3. The Performance of GPS Standard Positioning Service without selective availability - Tian-Yuan Shih, Hong-Yang Shih and Ming Yang

The accuracy of the Standard Positioning Service of GPS has greatly improved after the termination of Selective Availability. Based on GPS observations from permanent GPS-fixed stations, the actual accuracy of GPS without SA is analyzed. For Station NCTU, the local geodetic coordinates are computed with the C/A code pseudo-ranges, and then transformed into a local grid system with Trans-Mercator projection. From 77984 single epoch observations collected in twenty-nine days, the 95% accuracy is found to be /E: 17.6544m, /N: 11.8236m, /H: 31.8018m. For five selected UNAVCO stations, the axes of error ellipsoid are computed.

4. Statistical features of a linear model and their application on Data Processing - Fengxiang Jin, Michel Mayoud and Jean-Pierre Quesnel

Based on ideas of spatial vector, the geometrical descriptions and statistical features of GM (Gauss-Markov) model was analyzed carefully. From the geometric description of the model, some statistics of hypothesis testing in different cases were established on consideration of their statistical relations and features. A pithy and direct method, for people to go deep into and flexibly use the model, has been developed in the paper. Some statistics for data hypothesis testing has been also presented.

5. Back to Basics (23) Least Squares, Statistics and all that - N Atkinson and A L Allan

This is the tenth of a series of articles presenting some thoughts about Least Squares, Statistics, Quality Control and other related matters, which may be of interest to students, or practitioners new to the particular applications described. The treatment is deliberately elementary and the examples are simplified so that the various concepts can be developed with clarity. Now and then, the editor will enter a word of caution in the text, where he feels that the treatment has been oversimplified or for other reasons. As in previous articles, the topic is presented as a dialogue between this practising surveyor Nigel Atkinson and a retired academic Arthur Allan. The editor encourages comments as the series unfolds.

Abstracts of the April issue - Vol 36 No 280 April 2001

1. A Review of Geoid models over the British Isles: Progress and Proposals - W E Featherstone and J G Olliver

The history of published geoid determination for the British Isles over the last fifty years is reviewed. This includes global geopotential models, tailored geopotential models, British gravimetric geoid models, and European gravimetric geoid models that cover the British Isles. Proposals are made for a collaborative venture to produce a new geoid model using the most recent data and computational techniques.

2. The Shuckburgh Scale - Ludvik Pfeifer

Airy stated unequivocally that the dimensions of his Figure of the Earth, better known as the Airy 1830 ellipsoid, were given in "feet of the Shuckburgh standard", further interpreted as feet of the first yard of the Shuckburgh scale. Because relation to the international metre was ill-defined, approximate metric equivalents have been used, e.g., by the geodetic datum of Great Britain. This article presents a definitive determination of thermal expansion of the Shuckburgh scale and of the length of its first yard.

3. Modelling GLONASS Measurements for Precise positioning - Jinling Wang, Mike P Stewart and Maria Tsakiri

GLONASS, a satellite based navigation system similar to GPS, has a great potential for precise positioning. However, unlike GPS, GLONASS satellites transmit signals at different frequencies, which results in complexity in processing GLONASS carrier phase measurements. The standard double-difference procedure used in precise GPS positioning cannot be used in precise GLONASS positioning. In this paper, a mathematical proof for this problem is given. The five existing modelling methods are then theoretically reviewed. A zero baseline data set is processed using these methods to show their performances. The paper concludes with a comparison of these modelling methods.

4. Some Numerical Prediction Methods for the Wind Speed in the Sea based on ERS-1 Scatterometer Wind Data - Yuanxi Yang

Three functional models, polynomial, autoregression and autoregressive moving average models, are fitted and compared in fitting and predicting the sea wind speeds based on the ERS-1 radar altimeters. The robust maximum likelihood theory is introduced in fitting the functional models. To purify the satellite scan data for the sea winds and construct the data sets with equivalent intervals, we deleted the data which responds to the ice and land, then using the retained pure sea data sets to fit a simple polynomial and interpolate the sea data that was deleted. By many trial computations, we find that the autoregressive moving average model is not only more complex but also less accurate than the autoregression model in our data sample. The robust autoregression model has not only the best inner precision, but also the most accurate prediction. The accuracy is very little changed with the increase of the distance between the measurement points and the predicted points.

5. A New Method for Adjustment of the Level: Adjustment in Triples - I A Harley

Surveyors are familiar with the principle of reversal: for example, in checking a straightedge or a setsquare and in routine observing strategies to eliminate instrumental errors. An extension of this idea, which may be used in the production of optical flats, allows testing for 'perfect' flatness when the surfaces are manufactured in triples. The paper describes a technique which allows 'perfect' adjustment when levels are compared in triples.

6. Carrier Phase Surveying with Garmin Handheld GPS Receivers - C J Hill, T Moore and M Dumville

GRINGO (GPS RINEX Generator) is a program which has been developed at the Institute of Engineering Surveying and Space Geodesy (IESSG) at the University of Nottingham, to record the pseudorange and carrier phase data from 12-channel Garmin handheld GPS receivers, in standard RINEX (Receiver INdependent EXchange) format. It offers owners of these receivers the possibility of post-processing to an accuracy of approximately 5 m (with pseudoranges) or a few cm (with carrier phase), without having to invest in separate DGPS receiving equipment or expensive survey-grade receivers. They retain the benefits of an inexpensive receiver with a user-friendly interface and powerful navigation features, but gain the possibility of improved accuracy if needed.
A number of experiments have been carried out to assess the accuracy of positioning with Garmin raw measurement data.
This paper presents the results of experiments.

7. An Historic Braced Quadrilateral. Jotting - J G Olliver

Wherever I happen to be in the world, a small triangle on the map triggers an uncontrollable conditioned response - a trig point! I have go there! And so it happened on a recent holiday in the Sierra Nevada. My eye lighted on the name Mulhacén, adjacent to that symbol. The altitude figure of 3483 metres (11 421 feet) gave some pause - it is the highest point in mainland Spain - but in my surveying days I had climbed almost to that height in Tanganyika and Kenya. But more than the height challenge, there was a romantic association attached to the name Mulhacén. Anyone who has turned the pages of Jordan's Handbuch der Vermessungskunde will recognise the diagram showing the vertices of the famous braced quadrilateral constituting the first geodetic connection of Spain to Algeria, or more significantly, Europe to Africa.

8. Back to Basics (22) Least Squares, Statistics and All That - N Atkinson and A L Allan

This is the ninth of a series of articles presenting some thoughts about Least Squares, Statistics, Quality Control and other related matters, which may be of interest to students, or practitioners new to the particular applications described. The treatment is deliberately elementary and the examples are simplified so that the various concepts can be developed with clarity. Now and then, the editor will enter a word of caution in the text, where he feels that the treatment has been oversimplified or for other reasons. As in previous articles, the topic is presented as a dialogue between this practising surveyor Nigel Atkinson and a retired academic Arthur Allan. The editor encourages comments as the series unfolds.

Abstracts of the January issue - Vol 36 No 279 January 2001

1. An improved Tape Zero Gyro-Theodolite Calculation Technique - A Wetherelt and P Hunt

The tape zero or unknown equilibrium position of a suspended gyro has, in the past, been relatively difficult to determine accurately. Frequently, existing methods of tape zero determination have not accounted precisely for the influence of damping factors. This paper presents a new iterative method to establish estimates of the parameters for a damped oscillation model and locate its equilibrium position. Results have proved to be consistent with those obtained by more traditional methods and more reliable. Consideration is given to the possibility of applying similar techniques to the spun mode of operation of the gyro, and utilisation of automated timing.

2. The Bird Yard Parliamentary Standard - L Pfeifer

This article presents a definitive determination of the thermal expansion and length at standard temperature (62°F) of the Bird Yard (1760) Parliamentary Standard (P2), legal standard of length of the British Empire 1825-1855, destroyed in the fire of the Houses of Parliament on 16 October 1834.

3. Determination of the Hong Kong Gravimetric Geoid - Yang Zhan-ji and Chen Yong-qi

Precise determination of local geoid is of particular importance for GPS heighting. A geoid can be accurately obtained with an optimal combination of a global geo-potential model, local gravity measurements, and the topographic information. This paper uses the remove-restore technique to construct the Hong Kong gravimetric geoid. The EGM 96 geo-potential model, over 600 gravity measurements and 500m grid DTM were used. The results were compared with the geoid heights at 31 checkpoints derived from GPS/levelling data. It is shown that the constructed gravimetric geoid has an accuracy of about 20mm.

4. Adjusting Sea Level Measurements at the Port of Alexandroupolis - A M Agatze-Balodimou, A Antonopoulis and A Maratos

The reference surface of heights for the continental Hellenic area is currently defined by the mean sea level of the period 1933-1978, as estimated at the port of Pireaus. However, due to various problems having occurred there since 1981, alternative tide gauge locations in Greece have been sought in order to redefine a height reference surface according to the latest mean sea level variations. The tide gauge at the port of Alexandroupolis belongs to a permanent tidal net consisting of 20 tide gauges (major mareographs) and monitoring sea level variations in Greece. Our task is primarily to determine mean sea level height in association with a very recent time period and also a suitable measure of the precision of observations thereat. Two main models are considered according to whether variations of astronomical and meteorological nature are modelled or not modelled. Effects of time span of records and of data quality are discussed.

5. Second order design of Horizontal GPS net - Bojan Stopar

Precisions ratio of three-dimensional GPS baseline vector components, known in advance, enables the optimisation of three-dimensional GPS net with the optimisation of its horizontal part only. In a second order design of a pure GPS net some conclusions about the importance of particular GPS vectors in the net, with an assumption of uniform precision of horizontal components of GPS baseline vectors were searched for. In the second order design of a combined terrestrial and GPS net the precision of optimised GPS baseline vectors was, under the same assumption, compared with two typical types of geodetic observations in horizontal geodetic networks - distances and directions. Both cases were treated in a homogenous and isotropic horizontal GPS net.

6. Effects of Electric Power lines on the Accuracy of GPS Positioning - Abdullah S A Alsalman

A practical experiment of the potential effects of high voltage electric power lines on GPS satellite signals and hence the received GPS data was performed. In this experiment, a network of 10 stations were precisely established underneath and around 380 kV electric power lines. Then, a static GPS campaign was conducted on the network while the power was shut off. The same campaign was repeated in the next day when the power was turned on. The results of the two days were analysed and compared with each other. The results of this experiment demonstrated that there is no statistical evidence of any degradation of GPS positioning accuracy due to the high voltage electric power lines.

7. Back to Basics (21) Least Squares, Statistics and All That - N Atkinson and A L Allan

This is the eighth of a series of articles presenting some thoughts about Least Squares, Statistics, Quality Control and other related matters, which may be of interest to students, or practitioners new to the particular applications described. The treatment is deliberately elementary and the examples are simplified so that the various concepts can be developed with clarity. Now and then, the editor will enter a word of caution in the text, where he feels that the treatment has been oversimplified or for other reasons. As in previous articles, the topic is presented as a dialogue between this practising surveyor Nigel Atkinson and a retired academic Arthur Allan. The editor encourages comments as the series unfolds.