Vol. 37, No. 294 October 2004

1. Azimuth determinations using an adapted Wild GAK1 (an alternative approach)

A.Wetherelt and P.Hunt

This paper describes a fully automated adaptation to the Wild GAK1 gyro which has been developed at the Camborne School of Mines (CSM): it includes an electronic ‘eye’ attachment to the GAK1 gyro instrument, specifically designed to resolve the problems associated with manual observations and the recording of gyro tape oscillation data. An account of the entire automated system is given comprising: a description of the electronic eye; its structure and operation, the means by which the time data is captured and recorded. It is not claimed that the accuracy of results obtained by the use of this modified Wild GAK1 method are in any way superior to those obtained from modern Gyromat instruments but throughout, the emphasis is on the presentation of an automatic system which is simple to operate, accurate, reliable and comparatively inexpensive. This paper further describes a method of azimuth determination where the computation of azimuth is undertaken without the use of tape zero. The consistency of azimuths determined using this hybrid method is compared with the more conventional method.

2. On some improvements in the geodetic framework of Trinidad and Tobago

J. Saleh, K. Edwards, J. Barbaste, S. Balkaransingh, D. Grant, J. C. Weber and T. Leong

Geodetic Services was contracted by the Lands and Surveys Division and the Ministry of Energy of Trinidad and Tobago to adjust the recent precise national GPS network on the International Terrestrial Reference Frame, compute optimal transformation parameters between the six horizontal datums used in this region and compute a precise geoid for the country. This paper summarizes the work done on this project, including a related academic research on regional tectonic deformation, and suggests some further geodetic improvements.

3. Accuracy of measurements made with a CYRAX 2500 laser scanner against surfaces of known colour

J. Clark and S. Robson

Several commercial manufacturers produce laser scanning systems capable of measuring the surfaces of objects to precisions of the order of a few millimetres at ranges of between 2 and 200 metres. Experience on a number of projects has demonstrated significant variations in the quality of point cloud data as a function of object surface reflectivity.
This paper investigates the performance of a Cyrax 2500 laser scanner in making measurements to a variety of surfaces of specified colour characteristics under laboratory conditions. From the data obtained it is evident that significant systematic range discrepancies exist which can be broadly correlated against the colour of each surface with respect to the wavelength of the laser used. Over the distances investigated a high correlation between the point data quality measure returned by the scanner and the range discrepancy was observed, offering the possibility of applying a correction to the data produced by a Cyrax 2500 scanner. Such a correction, which is demonstrated to be applicable for diffusely reflecting surfaces, can be carried out with data available to the end user in order to significantly improve scanner accuracy.

4. Capacity building in Land Administration- A conceptual approach

S Enemark and I Williamson

Capacity building is increasingly seen as a key component of land administration projects in developing and countries in transition undertaken by the international development banks and individual country development assistance agencies. However, the capacity building concept is often used within a narrow meaning such as focusing on staff development through formal education and training programmes to meet the lack of qualified personnel in a project in the short term. This article argues that capacity building measures should be addressed in the wider context of developing institutional infrastructures for implementing land policies in a sustainable way.
Where a project is established to create land administration infrastructures in developing or transition countries, it is critical that capacity building is a mainstream component, not as an add-on, which is often the case. In fact such projects should be dealt with as capacity building projects in themselves.
The article introduces a conceptual analytical framework that provides some guidance when dealing with capacity building for land administration in support of a broader land policy agenda.

5. INDEX for Volume 37, Numbers 287 – 294, January 2003 – October 2004
As each volume covers two years of issues this completes 74 years of continuous publication. Volumes 1 to 3 contained a total of 22 issues and subsequently each volume was of 8 issues each. Thus it will be seen that issue 300 is due to be published in April 2006. In the 74 years to date there have been just 6 Editors.

Vol. 37, No. 293 July 2004

1. OSTN02: A new definitive transformation from GPS derived coordinates to national grid coordinates in Great Britain

M. Greaves

The computation of the definitive OSTN02™ transformation is described. A background is given on the horizontal datums in use in Great Britain and on the meaning of a “definitive transformation”. The choice of transformation model for OSTN02 is then discussed followed by a detailed account of the data collection, transformation computation and testing. The procedure of building the final transformation data set and delivering it to users is then described. Compared to the previous transformation (OSTN97), OSTN02 contains a substantial increase in stations whose ETRS89 coordinates result from direct occupation with GPS. Testing indicates that OSTN02 has a 97.8% accuracy of 0.2 m. A new transformation data file has been made available to users.

2. Investigation of the roughness of the Australian gravity field using statistical, graphical, fractal and Fourier power spectrum techniques

Kefei Zhang and W.E. Featherstone

As one of the world’s oldest continents, Australia has experienced a complicated geological and geomorphological history. As such, the gravity field of Australia behaves differently to that reported in other countries. This paper investigates the relative roughness of three types of gravity anomaly (free-air, refined Bouguer and topographic-isostatic) using statistical and graphical comparisons, power spectrum analysis, and the Hurst fractal technique. Gravity and height profiles in the Hamersley Ranges, central Australia and the Snowy Mountains, which exhibit some extreme features, have been selected to compare these methods. The statistical comparisons are the most informative tools for measuring the relative roughness of the gravity field. Also, not one of the free-air, refined Bouguer or topographic-isostatic gravity anomaly is consistently the smoothest type in Australia, which is due to a combination of a lack of accurate topographic density information and a relatively long-wavelength topography so that the terrain correction cannot always smooth the computed gravity anomalies. It is recommended that the smoothest type of gravity anomaly in each area be used to grid gravity data prior to geoid computation.

3. An empirical method of estimation of the variance-covariance matrix in GPS network design

Marco Gatti

For a priori analysis of the precision of a GPS network, we propose an empirical method tofor estimateing the variances and covariances of components of baselines. We hypothesize that the variances are proportional to the length of the corresponding baseline components, while for the covariances are computed from values of the correlation coefficients. Both the variances and covariances are evaluated in a 3D global Cartesian co-ordinate system. The method is applied to some previously measured GPS networks and the results are compared with those obtained by the methods of zero correlation and the post-processing computations.

4. A case study on the establishment of shoreline position

A.K. Chong

In Malaysia, Mean High Water Mark (shoreline or riverbank) is a natural boundary for lands between the State and the coastal or estuary upland owners. The State may also designate lands for coastal reserve or river reserve, which may cover 20 metres upland from the shoreline or the riverbank. In the State of Sarawak, Malaysia, an Act was passed in 1958 regarding the location of the coastal reserve or river reserve. However, shoreline or riverbank was not established accurately in some disputed native customary right land claims originating from the Act. Consequently, in 1983 seven evicted landowners brought suits against the Superintendent of Lands and Surveys and the government of Sarawak seeking compensation for their lands. In this paper the author highlights the methods used by two surveyors to determine the position of the shoreline from hydrographic charts, town plans and old aerial photographs. The court case shows that knowledge in the area of measurement error analysis; accurate photogrammetric technique and image processing are highly essential in the present-day court environment in which aerial photographic evidences are required.

5. A new method for second order design of geodetic networks: aiming at high reliability

Ali Reza Amiri-Simkooei

The main design criteria for a geodetic network are precision, reliability and strength, and cost. In this paper, a new method for second order design of geodetic networks for high reliability is suggested. In this methodology, the weight of the observations are improved in such a way that the same redundancy numbers are obtained for all observations. The effectiveness of the methodology is verified with two examples.

6. Determination of the azimuth with solar observations without any particular astronomical knowledge and spherical trigonometry

L. Sinapi and A. Vassallo

Determination of astronomical Azimuth from a Fixed station A to a Trigonometrical point B, seen from A, constitutes a problem resolvable in different ways. If point B is not present, we can employ a geodetic TARGET to calculate astronomical azimuth from solar observations, and consider such azimuth as a geodetic azimuth. Using rectangular coordinates and non spherical trigonometry, the solution of the problem becomes a simple linear solution, with the employ of planes and straight lines on the space of celestial sphere.

7. Testing a multiple reference station GPS network for real-time carrier-phase-based positioning in the Marmara region, Turkey

U. Dogan, P. Alves, G. Lachapelle, and S. Ergintav

A network of multiple ground-based, continuous GPS reference stations for generating carrier-phase- based corrections can provide a higher achievable position accuracy, and increase the speed and effectiveness of carrier phase integer ambiguity resolution for precise real-time positioning in relation to the traditional single baseline approach. This method also allows for a lower number of reference stations required to cover a larger service area than the traditional single reference station approach. The focus of this paper is to investigate the multiple reference station method for generating carrier- phase-based corrections using the Marmara Continuous GPS Network, Turkey. The carrier phase measurement corrections for the coverage area are computed using the NetAdjust method, developed at the University of Calgary. Results and analysis using the regional carrier-phase corrections are compared to the single reference receiver approach to demonstrate the achievable improvement with this method. The results show 55 to 75 percent improvement in the observation domain, 40 to 60 percent improvement in the real-time position accuracy, and an 11 to 38 percent decrease in the time required to resolve L1 ambiguities. The corresponding position accuracies for a user’s receiver show as much as 58, 45, and 35 percent improvement in the latitude, longitude and height, respectively, over the single baseline approach.

8. Semi-automatic determination of the parallelism of the rollers in the aluminium factory TLM-Sibenik

N.Solaric, Z.Versic, Barkovic

The paper describes the semi-automatic determination of the parallelism of rollers in factory engine rooms by means of an electronic theodolite Kern E2 (0.5 arc sec) and notebook computers. A priori standard deviations in determining the parallelism of rollers have been carried out with the theodolite from 2 to 15 m away from the 1 m to 4 m long rollers and the standard deviation of distance measurement from 1 mm to 5 mm. Apart from that, it has been established that the optimum distances between the theodolite and the roller are as follows:
- approximately 2 m, if the distances are measured with a standard deviation of 1 mm, and
- approximately 4 m, if the distances are measured with a standard deviation of 5 mm.
In the aluminium factory TLM in Sibenik (Croatia), the precision obtained in determining the parallelism of rollers amounts to 0.03 mm/m in real factory conditions, and the method has shown to be very practical.

Vol.37, No. 292 April 2004

1. Improving positioning accuracy during kinematic DGPS outage periods using SINS/DGPS integration and SINS data denoising.

S. Nassar, A. Noureldin and N. El-Sheimy

In the standard integration of a Differential Global Positioning System (DGPS) and a Strapdown Inertial Navigation System (SINS), the DGPS provides position information while the SINS provides attitude information. In addition, the DGPS measurements are used to estimate the inertial sensors systematic errors and the SINS is used to detect and correct GPS cycle slips. In case of GPS signal blockages, the SINS is used instead for positioning as a stand-alone system until the GPS signals are available again. To obtain accurate positions during DGPS outages, near real-time (or post-mission) techniques should be applied, where these techniques are known as bridging algorithms. In such algorithms, new and improved positions of the outage periods are estimated. In this paper, two different bridging methods are used namely: backward smoothing and parametric modeling. An SINS/DGPS data collected with a van has been used in the analysis. The results show that both bridging algorithms reduce the SINS positional errors for DGPS outages of 75 to 100 seconds with an average of 1.35 m to an RMSE of 19 cm in case of backward smoothing and 10 cm in case of parametric modeling. To separate between the actual motion dynamics and other disturbing vibrations, a de-noising of the SINS raw data is required. Therefore, a de-noising of the van SINS data has been applied using a wavelet decomposition technique to eliminate or minimize the effect of sensor noise and other high frequency disturbances (such as engine vibrations). An analysis of the SINS sensor kinematic raw data in the frequency domain shows clearly that the majority of the van motion dynamics are contained in the low frequency portion of the spectrum (below 3.0 Hz). Consequently, several levels of wavelet decomposition can be performed without losing any motion information. The application of both bridging methods after the SINS data de-noising reduces the positional RMSE to 11 cm and 7.7 cm using backward smoothing and parametric modeling, respectively.

2. Sensor fusion and integration using an adapted Kalman filter approach for modern navigation systems

G. Retscher and E. Mok

Modern navigation systems require the integration of different sensors that are either employed as primary navigation method (e.g. dead reckoning in car navigation) to provide position information at regular time intervals (e.g. satellite based positioning for providing a start position and regular absolute position updates) as well as additional backup sensors. In most common systems, however, sensors are mainly employed in a stand-alone mode and no integrated position determination is performed. In our study, a new sensor fusion model based on an adapted Kalman filter has been developed to obtain an optimal estimate from the measurements of all available sensors. The concept for the integration and combined position determination has been employed for the combination of observations of GPS, wireless or mobile phone location services (MPLS) and dead reckoning (DR) sensors employed in vehicle navigation systems. In the following, it has been used for pedestrian navigation and guidance. The results of simulation studies are presented in the paper. The concept can also be extended to vehicle navigation in dense high-rise urban environments, where positioning problems due to blockage of GPS signals could be solved either by DR prediction or updating with MPLS for higher positioning accuracy is expected to be achieved using the 3G network, and the combination of the two.

3. Terrestrial laser scanners with a narrow field of view: the effect on 3D resection solutions

S. J. Gordon and D. D. Lichti

Three-dimensional (3D) resection is used to locate an unknown, occupied station in object space, given observations to three or more known, unoccupied targets. Considering the emerging technology of terrestrial laser scanning, 3D resection may be used to determine the position and orientation of a scanner head in a project coordinate system. Some scanner manufacturers have equipped their instruments with facilities to position and orient the scanner over a known point thus permitting all data collected from that location to be directly georeferenced. As a result, resection is not necessary but is optional. However, due to the hardware design path that other scanner manufacturers have pursued, their systems do not have these facilities. These laser scanning systems must use the process of 3D resection to locate the scanner in object space. Furthermore, these scanners (at the time of writing in October 2002) also possess a relatively narrow field of view (angular-wise, 40º in the vertical and 40º in the horizontal). Consequently, this restricts the placement of control targets relied upon for resection. This paper describes an investigation into the effect of control geometry on resection solutions and how errors from computed resection parameters are manifested in georeferenced scan data and measurements derived from these data. Results using simulated and real data show that the positional accuracy may be considerably worse than the (manufacturer) advertised point accuracies.

4. Improving wellbore surveying accuracy of horizontal wells by utilising a dual-axis gyro system

A. Noureldin, D. Irvine-Halliday, H. Tabler and M. P. Mintchev

Measurement-while-drilling (MWD) surveying systems utilizing fiber optic gyroscopes (FOGs) have been suggested as a replacement for the present magnetic surveying techniques in order to avoid the imperfections associated with magnetic monitoring devices. A gyroscopic surveying methodology incorporating a single FOG with its sensitive axis along the central axis of the drill pipe and three mutually orthogonal single-axis accelerometers was suggested to survey horizontal wells. This method suffered from some limitations and an increase in the surveying errors at certain orientations. This article aims at overcoming these limitations by suggesting a dual FOG system using an additional FOG with its sensitive axis normal to the central axis of the drill pipe. The proposed dual FOG system has been tested using a custom designed experimental setup that can simulate several orientations similar to those experienced by the bottom hole assembly downhole. The results showed significant improvement in the accuracy of the surveying parameters with no specific limitations. This study suggests that gyroscopic surveying utilizing a dual FOG system can be a reliable solution for MWD surveying of horizontal wells.

5. Preliminary Results of GPS Studies for the January 2001 Gujarat Earthquake

Madhav N. Kulkarni, S. Likhar, V. S. Tomar, P. Pillai

The Global Positioning System (GPS) provides a valuable tool to monitor crustal deformations, and thereby aids in understanding the complex earthquake mechanisms. After the tragic earthquake that struck the Gujarat region of western India on 26th January 2001, immediate GPS observations were carried out in the area by the GPS team of Indian Institute of Technology Bombay (IITB), for estimating the post-earthquake deformations. Repeat observations of the GPS network were completed in February 2002. The aim was not only to understand the post-earthquake crustal deformation pattern, but also to establish precise GPS control for monitoring crustal dynamics in this earthquake-affected region in the future. The data has been processed and analyzed using scientific GPS data processing software: Bernese and GAMIT. The preliminary results from the analysis of the data from these two epochs, and future plan of work, are presented here. An extensive GPS network is being established in India under the ‘National GPS for Geodynamics Programme’ by Government of India. A brief overview of this programme is also provided.

Vol. 37, No. 291 January 2004

1. Evidence of a north-south trend between AUSGeoid98 and the Australian height datum in Southwest Australia

W E Featherstone

The AUSGeoid98 gravimetric geoid model has been compared with 48 GPS-levelling points at a 50 km spacing across part of the southwest of Western Australia. This is arguably the best subset of GPS-derived ellipsoidal heights in Australia with an internally estimated precision of +/-9 mm. The sprit-levelled heights were tied to the Australian Height Datum (AHD) using class C techniques [12mm-root-km allowable misclose]. The comparisons show that AUSGeoid98 gives a GPS height transformation to the AHD with a precision of ~±13 cm, which is less than reported earlier (c.+/-36 cm) for a nationwide dataset. A clear north-south trend of c.0.81 mm/km [ppm] is also evident in the differences; of which approximately one-third is attributable to a north-south error in the AHD induced by dominant north-south sea surface topography effects at the nearby fixed tide gauges. After removal of this north-south trend, the standard deviation of the differences reduces to c.5 cm.

2. Web-based learning of spatial design and analysis concepts using simulations and visual feedback

M. R. Shortis, F. J. Leahy, C. L. Ogleby, A. Kealy and F. G. Ellis

This paper describes the process and results of the transformation of the curriculum delivery of four different areas of the syllabus of the geomatics programs at the University of Melbourne. In each case the transformation addresses the teaching and learning problems associated with spatial relationships in two or three dimensions by providing a rich resource of theory material, animations of spatial concepts and, most importantly, visualisations or simulations of real world survey problems that provide immediate feedback. The visualisations and simulations allow students to investigate the design and analysis of spatial geometry and spatial relationships at their own pace, using the feedback to reinforce their learning. The online material affords an enhancement of the learning experience for undergraduate students, both complementing and providing an alternative to the conventional teaching methods of lectures, tutorials and practice classes.

3. Sibson (natural neighbour) and non-sibsonian interpolation for digital elevation model (DEM)

Mustafa Yanalak

A new interpolation scheme called as “non-Sibsonian interpolation” based on natural neighbours is proposed in [2]. The non-Sibsonian interpolation is reviewed in details and its performance in a Galerkin method for the solution of elliptic partial differential equations is studied in [17]. The purpose of this paper is to evaluate non-Sibsonian and Sibson interpolations for height interpolation in digital elevation model (DEM). Interpolations of non-Sibsonian, Sibson (natural neighbour), nearest neighbour, weighted average, polynomial, multiquadric, minimum curvature, and linear interpolation in triangles are tested on six theoretical test surfaces. For each test surface, 150 reference points in a scattered sampling pattern and 81 interpolation points in a regular sampling pattern are derived. True surface heights of the reference and interpolation points are calculated by the surface equations. For each test surface heights of the 81 interpolation points are interpolated based on the reference points by the use of eight different interpolation methods mentioned above. The accuracy measures (standard deviation, average of errors and maximum error) of the interpolation methods are derived by differences between true and interpolated surface values.

4. GPS compatible positioning in Ireland (Part 2)

M.J.Cory , I.C.Greenway and C.J.Hill

Continued from 37, 290 p 307

5. An instantaneous ambiguity resolution procedure suitable for medium-scale GPS reference station networks

H.-Y. Chen, C. Rizos, S. Han

There is a trend for the establishment of regional-scale GPS permanent receiver networks, for a variety of applications including to support high accuracy, carrier phase-based positioning for surveying and precise navigation. When implemented in real-time, GPS users located within the region enclosed by multiple GPS reference stations can precisely position by using, for example, the 'correction terms' generated and transmitted by the reference station network. For such a configuration one of the major challenges is that the integer ambiguities have to be resolved during the real-time processing of the reference network data in order to ensure the generation of the carrier phase corrections, even when the reference receivers are many tens of kilometres apart. Due to the presence of distance dependent errors in the double-differenced data (principally the ionospheric and tropospheric delays) reliable instantaneous (single epoch) ambiguity resolution is difficult in the case of medium-scale reference networks (defined here as where the reference stations are typically in the range 50-100km apart).
In practice, the ambiguities among the reference stations can be correctly resolved during an initialization procedure, but the main challenge is to continuously resolve the new ambiguities that result when the tracked satellite experiences cycle slips, or after any long data gap, or when a new satellite rises. In this paper a three-step methodology is proposed which can be implemented in real-time. Firstly, the high correlation of the atmospheric delay between adjacent epochs is used to assist cycle-slip recovery and ambiguity resolution. Then these atmospheric biases are predicted for double-differenced observations on an epoch-by-epoch and satellite-by-satellite basis. Finally these predicted atmospheric biases are applied to an algorithm that can fix the new ambiguities after a long data gap or when a new satellite rises.
Data from a set of reference stations spaced 80 km apart were used to test the effectiveness of the algorithm. The results indicate that the proposed methodology can provide reliable integer ambiguities for reference stations spaced many tens of kilometres apart.

6. Utilising the Ordnance Survey national GPS network for digital surface modelling

A.J. Evans and D. C. Russell

High accuracy Digital Surface Models can be created quickly and efficiently using GPS survey techniques. However, survey grade GPS receivers are not renowned for their affordability. The positioning requirements of many GIS and environmental survey applications can be met with cheaper receivers, but many of the high-end requirements are not achievable unless two survey grade receivers are purchased. The advent of the National GPS network may provide a means of reducing the cost of hardware for users by the removing the requirement of two receivers. GPS data is processed using the Ordnance Survey stations as base stations for relative positioning. The results are used to create DSMs and a comparison of the outputs computed from three different stations is presented.