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Vol. 40, No. 309. July 2008

1. Test of simulated pseudolite measurements applied to GPS and multi-pseudolite integrated positioning

C. C. Chang, P. C. Lou and P. J. Ke

The near-ground operation of a GPS-like signal transmitter, the pseudolite (PL), is expected to provide extra-measurements and improve the GPS positioning accuracy and availability. Based on the true measurements received from one PL instrument during the field trial, the multi-session combined technique and the self-session duplicated technique were proposed and tested for PL data simulation. The results demonstrate that the self-session duplicated technique can effectively provide the simulated PL measurements for any appropriate number and adequate configuration of so-called virtual PL (VPL) sites. The GPS+PL+3VPL observations were practically integrated to compute for a baseline solution. The results prove that baseline precision can be significantly improved by approximately 50% and 30% on the horizontal and vertical components, respectively, compared with those using only GPS data. When VPL sites are simulated to have the minus elevation angles, the vertical positioning errors can be further reduced to achieve a consistent precision in all three-dimensional coordinates. This preliminary study has shown good performance of using simulated PL measurements for integrated GPS and multi-pseudolite positioning.


2. Examination and comparison of mobile GIS technology for real time geo-data Acquisition in the field

F. Döner and T. Yomralioglu

Scientific studies associated with land require large amount of data. The data is often collected during field studies with the use of pencil and paper based method. The method is labour-intensive and susceptible to recording and georeferencing errors during transcription. Recent advances in mobile computing, positioning and software now make it possible to bring field and office activities into a collaborative environment, thereby minimizing human errors and time delays. This paper assesses the use of Mobile Geographic Information Systems (MGIS) as an appropriate tool for geo-data acquisition applications. Firstly the computing, positioning, software and communication technology behind the system is presented. A Mobile Geographic Information System developed for field data acquisition based on the combination of Geographic Information Systems (GIS) and Global Positioning System (GPS) is described. Finally, the system is tested in two field studies to examine its effectiveness compared to traditional methods in terms of accuracy, cost and project completion time. The field studies demonstrate the noticeable gains in efficiency and cost saving achieved with the use of the MGIS technology. Results of the field studies verify that MGIS is very useful for georeferenced data acquisition applications.


3. Recent vertical crustal movements of a part of the Balkan Peninsula derived from levelling data

M. Vulic and D. Blagojevic

The historical levelling data of the epoch of 1950-1960 were used along with the levelling data of the epoch of 1970-1973 for the derivation of the vertical velocity field on the territory of the Republic of Serbia. The methodology was based on the construction of a kinematic network and least squares adjustment and aimed at obtaining the vertical velocities of representative benchmarks. Being the first attempt of this kind for the area under investigation, no further interpretation of the result is given, apart from a couple of remarks concerning the correlation between the gradient surface and the general geophysical features.


4. Reflectorless total station self-calibration

D. D. Lichti and J. Lampard

A method for reflectorless total station self-calibration of face left and face right observations in a network is proposed. The mathematical models for the observation equations augmented with systematic error terms are presented. The method is demonstrated on three datasets captured with two reflectorless total station instruments: a Trimble 5603 DR200+ and a Leica TCRA 1103+. The results show improvement of up to 71% in the RMS of estimated residuals as a result of self-calibration. Furthermore, most of the error model parameters can be estimated with sub-millimetre or sub-second precision. Statistically significant differences between some calibration parameters from two Leica datasets were found, but closer analysis shows that these are of no metric consequence. Incidence angle is demonstrated to be a significant factor in distance precision, as has been reported elsewhere for terrestrial laser scanners. Comparison of the results with those from independent component testing shows that the self-calibration method is superior for determining angular error parameters. A close agreement of 1.1 mm was achieved between the additive constant estimates from self-calibration and baseline calibration methods for the Leica instrument. The additive constant estimates for the Trimble instrument differed considerably, which is likely due to the observed non-linear behaviour of the distance meter at close range.


5. Adaptively robust filter with multi adaptive factors

Yuanxi Yang and Xianqiang Cui

An adaptively robust filter with multi adaptive factors is proposed, based on the principles of adaptive Kalman filter and bifactor robust estimation for correlated observations. The estimator of the adaptive filter with multi adaptive factors is derived. The corresponding adaptive factors for the components of the position vector and velocity vector are set up based on the discrepancy of the predicted state from the kinematic model and the estimated state from the measurements. The adaptively robust filter with multi adaptive factors is more flexible in controlling the disturbing effects of the state components compared to the adaptively robust filters with unified adaptive factor and classified adaptive factors. The existing problems of the adaptive filter with multi adaptive factors are analyzed. An actual GPS dada set of an aircraft is calculated and analyzed with four schemes. It is shown by the actual calculation that the results of the adaptive filter with multi adaptive factors are slightly superior to those of the adaptive filter with unified adaptive factor. However, the new adaptively robust filter cannot be applied when the number of measurements at some epochs is smaller than the number of state parameters. It is proposed that the adaptively robust filter with multi adaptive factors and that with unified adaptive factor could be integrated in practical applications.


6. Local ionospheric modeling of GPS code and carrier phase observations

H. Nahavandchi and A. Soltanpour

A limiting factor for successful ambiguity resolution in precise GPS positioning is the existence of un-modelled ionospheric errors in both the carrier phase and the pseudorange measurements. In this study, the ionospheric delay is modelled using a four-parameter polynomial utilizing dual frequency observations in the region of study in southern Iran. Thereafter, the corrected and non-corrected observations for ionospheric delay are compared with the ionospheric-free solution of the same observations. Two baselines (15 km and 72 km) are used for this comparison. An improvement of 0.22 ppm and 0.07 ppm is achieved, respectively, for the two baselines. Further, the ionospheric delay is modelled using two other methods, i.e. the Klobuchar and divergence models. The divergence model uses single frequency observations. The improvement of the results is restricted as the noise level in code observations is high. An improvement of 0.15 ppm for the 72 km baseline and no improvement for the 15 km baseline are observed using the divergence model. The Klobuchar model corrects 50%-60% of the ionospheric errors in this study.


7. Do reciprocal vertical angles have a role in Geomatics?

A. L. Johnson

Height differences are now seldom measured by observing “Reciprocal Vertical Angles”, and the method is generally considered to have been superseded by digital levels and GPS. This paper argues that the technique may still have an important part to play in verifying the results obtained from GPS, and is also considerably more accurate than may generally be supposed.

8. Determination of optimum residual gravity anomalies for mineral exploration: a least squares collocation approach

T. O. Idowu, P. C. Nwilo, F. A. Fajemirokun and C. U. Ezeigbo

Analysis of gravity anomalies, measured on the earth’s surface, can reveal information on sub-surface structures of the earth. The first step in this analysis is to extract residual gravity anomalies (needed for mineral exploration) from the observed gravity anomalies. Currently, a classical least squares technique is used to achieve this aim. However, this technique does not produce optimum results because it assumes that the observed gravity anomalies used for the computation of residual gravity anomalies are error free, whereas, all observed quantities are affected by random errors. In this study, an attempt was made to extract the residual gravity anomalies from the observed gravity anomalies using a least squares collocation technique. The least squares collocation technique was considered to be a better alternative because its formulation takes the presence of random errors of observations in the observed quantities into consideration and makes provision for filtering out the errors from the observed quantities while predicting the needed signals at the required number of points.


9. Scaling of EDM calibration baselines by GPS and controlling of EDM parameters

C. Ïnal, Ï.Sanlioglu, C.Ö.Yigit

The calibration values of electromagnetic distance measurements, which have been given by their own firms, can lose their currency in time. So, the EDMs must be controlled in the particular time intervals. The EDM controls have been usually made in the EDM calibration baselines, which are constituted for this aim. Zero addition, scale coefficient and phase difference measurement function constitute the measurement function as a result of control done. The EDM calibration baseline must be scaled to determine the scale coefficient. Not only high accuracy instruments as Kern Mekometer 3000 but also GPS can be used for scaling. In this study, it has been investigated that possibility of scaling of EDM calibration baseline by using GPS and the scaled EDM calibration baseline, and the calibration parameters of Sokkisha SET2, Topcon GTS701, Topcon GTS 229 and Sokkia Power SET 2000 electronic tacheometers have also been estimated.


Vol. 40, No. 308. April 2008

1. Mapping impervious surface areas from GIS planimetric data
W.T. Pang, H.S. Fok, and H. Bâki Iz

Urban Impervious surface is a characteristic of urban development. Knowledge about the impervious surface area is an essential component of planning decisions at metropolitan areas around the world. This paper demonstrates the use of available GIS planimetric information in the production of an impervious surface area map of Hong Kong. Hong Kong is one of the most populous cities in the world where there is a continuous need for new buildings, roads and other infrastructure. Hong Kong’s calculated impervious surface area constitutes 18 % of the total surface area of the Hong Kong territories, which makes the city one of the greenest of the world despite its high population. In this study potential challenges in the identification of impervious surfaces were investigated.

2. Land tenure reform in Uganda some reflections on the formalization of customary tenure
N. Batungi and H. Rüther

The paper provides an overview of the history of land tenure reform in Uganda from 1900 to 2000. Methods, which were used to formalise customary tenure in Uganda, are reviewed and the effects of the first reform, which formalised customary tenure through negotiations with local leaders are reported. The subsequent reform in which the colonial administration, relying on the power of the law, formalised customary land into freehold and leasehold without any consultations with the local population, is described. The land distribution policy enshrined in the Crown Lands (Adjudication) Rules, 1958 is related; the reactions of the indigenous people to the reforms in Uganda are highlighted; and the contribution of the independent Uganda government in the land tenure reform is discussed. The study concludes that both the negotiated and the enforced non-negotiated approaches successfully formalised customary tenure and that the negotiated approach was much better and preferable within the African context. It further concludes that the theory purporting that the indigenous people were incapable of adapting to the western forms of individual ownership was a political gimmick aimed at supporting and justifying the mandatory acquisition and formalisation of customary land for exclusive use of non-Africans. Finally the study proposes criteria, which should be followed by any country wanting to formalise customary land.

3. On zero position correction of hanging tape of gyro-theodolite
Jinyun Guo, Shuyan Guo and Xin Liu

Detailed theoretical analysis of the working characteristics of the hanging tape torque and the computation of zero position correction in the orientation observation with the gyro-theodolite are made in the paper. The practical data prove that the conclusion is right.

4. Re-alignment of a guyed tower
G. C. Mulaku, P.C. M. Wakoli and J. B.K. Kiema

Towers are typical structures that can be found in many urban and rural landscapes the world over. From their basic design, they are usually exposed to severe environmental loads. It is therefore prudent to carry out periodic maintenance that includes checking that they are correctly aligned. This paper describes a method that was used for the re-alignment of a guyed tower in Limuru, Kenya. Angular and distance observations, made from two observation points detected a vertical misalignment that was larger than the acceptable tolerance of An iterative re-alignment procedure was then applied, resulting in an acceptable final misalignment of

5. Transformation of 3D GPS Cartesian coordinates to ED50 using polynomial fitting by robust re-weighting technique.
Metin Soycan and Arzu Soycan

The purpose of this study is the solution of transformation problem between the GPS networks and old geodetic networks based on the national coordinate system alternatively by a 3-dimensional robust polynomial transformation (3D.R.P.T). This study focuses on and probes 3D similarity (3D.S.T), 3D polynomial transformation with least squares estimate as equal-weighted (L.S.3D.P.T), 3D polynomial transformation based on weight with the inverse of the distances of common points to the center of gravity (W.L.S.3D.P.T) and robust estimate approaches that are re-weighted and are based on iterative solution. Detailed mathematical model and solution algorithm of the proposed model is given, and it has been applied in a test area covering the city borders of Istanbul for which its results were studied and compared to other three methods.


6. A strict transformation from Cartesian to geodetic coordinates

L E Sjöberg

An algorithm is derived to transform Cartesian coordinates to geodetic coordinates by employing ellipsoidal coordinates in an intermediate step. The algorithm is comparatively simple and stable in all steps for any point in space outside a geocentric sphere of an approximate radius of 43 km.

7. Astronomical azimuth determination by the hour angle of Polaris using ordinary total stations
E. Lambrou and G. Pantazis

The determination of the astronomical azimuth of a line is not a difficult task for surveyors any more. The aim of this paper is to analyze the theoretical details and errors in order to propose the use of ordinary total stations, for an easy, efficient and accurate determination of the astronomical azimuth of a line by the hour angle method via Polaris sightings. As many modern total stations have a built – in quartz clock they can register automatically the UTC time as well as the angle measurements (horizontal and zenith) of each observation. The total fieldwork time needed is about 10 minutes and the accuracy that may be achieved is about +/- 2 arc seconds. This procedure will be proven to be easier than the determination of the geodetic azimuth of the same line. The calculation is independent and the result is free of the errors that the coordinates of a survey mark may contain, because they are not used. However good positional data is required from other sources. Astronomical azimuths are an alternative solution for the surveyors in order to check or orient their field surveys and arbitrary networks independent of the GPS system.

8. The effect of different tropospheric models on precise point positioning in kinematic mode
A. B. O. Jensen and O. Ovstedal

Precise Point Positioning, based on undifferenced dual frequency GPS carrier phase observations, is a relatively new data processing technique for high accuracy kinematic GPS applications. No reference station data is necessary making the technique applicable e.g. for airborne high accuracy GPS positioning in remote areas where the distance to the nearest GPS reference station otherwise would be hundreds of km. High accuracy kinematic GPS positioning is used, for instance, for airborne remote sensing with gravimetry, In SAR, or lidar equipment, where data is collected for various geophysical applications. In the remote areas of Greenland, Northern Canada and the Northern parts of Scandinavia airborne remote sensing is carried out by various professional groups every summer, and most of these groups would like improved and more reliable high accuracy GPS positioning algorithms.
The atmospheric effects on GPS satellite signals are significant. The dispersive effect of the ionosphere can be sufficiently addressed by the use of dual frequency observations. To mitigate the non-dispersive atmospheric effects, tropospheric a priori models are normally used. When observing for extended periods of time, additional tropospheric parameters can also be estimated as part of the adjustment process. In a differential mode and operating not too far from the reference receiver, most of the residual errors are eliminated in the differencing process. For Precise Point Positioning, however, and especially when processing shorter time spans of data in a kinematic mode, the accuracy of estimated positions heavily depends on the a priori models.
This paper investigates the use of the Saastamoinen and the UNB3 global tropospheric delay models as well as the use of tropospheric delay estimates derived from numerical weather predictions. The various tropospheric correction approaches are tested for precise point positioning, and the positioning results are evaluated by comparison with known station coordinates. With the data and test scenario used the evaluation show similar standard deviations for all three approaches, but the Saastamoinen model performs with the smallest bias when the position results are compared to the known position.
The tests are based on GPS data collected at 14 different sites in Denmark and Southern Sweden, and the numerical weather predictions available are from the HIRLAM system implemented at the Danish Meteorological Institute. The data processing is carried out using the ABSPOS software developed at the Norwegian University of Life Sciences.

9. Comparing stochastic models used in GPS precise point positioning technique
C Satirapod and M Luansang

GPS observables are normally processed using the least-squares method. In order to ensure high accuracy positioning results, both the functional model and the stochastic model must be correctly defined. In GPS Precise Point Positioning (PPP) mode, an ionosphere-free linear combination is generally used for constructing the functional mode, while post-mission information and error mitigation methods are employed to eliminate many biases. Nevertheless, some unmodelled biases still remain in the GPS observables and eventually cause errors in the coordinate results. It is, however, possible to further improve the accuracy and reliability of GPS results through an enhancement of the stochastic model. This research aims to investigate stochastic models used in the GPS PPP technique. Three different stochastic models; equal weight for all GPS observables, different weight for each GPS observable based on satellite elevation angle and different weight for each GPS observable based on the MINQUE (Minimum Norm Quadratic Unbiased Estimation) procedure, have been compared in this paper. Test results indicate that the stochastic model estimated from the MINQUE method produces the most accurate coordinate results both in horizontal and vertical components.

10. Precise height determination using simultaneous-reciprocal trigonometric levelling
Ayhan Ceylan and Orhan Baykal

Precise levelling method has been used for the determination of precise height for many years. The application of this technique is difficult, time consuming and expensive especially in rough terrains. These difficulties have forced researchers to examine alternative methods of height determination.
As a result of modern technological developments for high-tech instruments, research of the precision trigonometric levelling has been required once again. In this study, simultaneous-reciprocal trigonometric levelling (SRTL) method is applied with different sight distances in order to determine optimum sight distances using a sample test network in Selcuk University Campus, Konya, Turkey. The results are compared with precise geometric levelling in terms of precision, cost and feasibility. SRTL method for sight distance S=200m resulted with the standard deviations of and with the production speed of 4 km/day.

 

Vol. 40, No. 307. January 2008

1. Height Transformation using regional geoids and GPS/levelling in Turkey

B Erol, S.Erol and R N Çelik

Transformation of ellipsoidal heights derived from the Global Positioning System (GPS) to orthometric heights using geoid models is investigated in the north and west parts of Turkey. Although the transformation depends on a simple relation between ellipsoidal h, orthometric H and geoid N heights, the accuracy of the resulting orthometric heights after transformation is crucial in geodetic and surveying applications. Various factors which affect this accuracy, such as measurement errors, datum inconsistencies and theoretical assumptions, are investigated in this study, while testing different methods in three test networks (Sakarya in the Northwest, Çankiri in the North and Izmir in the West). The study consists of three steps. In the first step the regional Turkey geoids TG99A, TG03 and the European gravimetric geoid EGG97 are tested comparing geoid heights derived from models and GPS/levelling at co?located benchmarks. In the second step, regional geoid models are combined with GPS/levelling using Least Squares Adjustment of height differences and corrector surface models. In this step, additionally, Variance Component Estimation (VCE) using Minimum Norm Quadratic Unbiased Estimation (MINQUE) approach is performed, in order to combine the height sets. In the last step, GPS/levelling surface type local geoids are determined and their performances are tested in transformation of GPS?heights. Finally, the resulting accuracies are compared and practical aspects of those approaches in deriving orthometric heights from GPS measurements in geodetic and surveying applications are discussed.

KEYWORDS: Ellipsoidal heights. Geoid EGG97. Geoid models. MINQUE, Variance Component Estimation.

2. Verification of accuracy of precipitable water vapour from GPS during typhoon Rusa

D. S. Song, H. S. Yun and D. H. Lee

This paper presents GPS meteorology using GPS observations obtained from the Korean permanent GPS network during a severe weather condition. Our first experimental studies in Korea were based on data collected from seventeen GPS stations and four radiosonde stations during the period of Typhoon Rusa from 31 August to 1 September 2002. The root mean square difference (RMSD) between the GPS Precipitable Water Vapour (PWV) and the radiosonde-PWV was at the 7.2 mm level. In this new study, a least square analysis was used to reduce the large RMSD and without bias, the RMSD was reduced to 5.7mm. The mean of the RMSD without consideration of Typhoon Rusa effect was 6.9 mm, whereas the RMSD of GPS-PWV with consideration of the Rusa effect was worse with 9.4 mm. The large RMSD during Typhoon Rusa was due to the change of the observation direction of the balloon based radiosonde by high wind speeds.

KEYWORDS: Precipitable water vapor, GPS, Radiosonde, Typhoon Rusa


3. Positional accuracy improvement: lessons learned from regional Victoria, Australia

S. Hope, C. Gordini and A. Kealy

Many spatial datasets in use today have been manually digitised from hard-copy maps. These datasets are typically of relatively low positional accuracy compared to the latest positioning technologies, such as those based on Global Navigation Satellite Systems (GNSS). Discrepancies between the legacy dataset and GNSS positioning solutions are becoming increasingly evident, a problem that is compounded by the growing trend to underlay such datasets with high resolution imagery. As a result, many data providers are seeking methods to update their spatial datasets.

In the example of the Victorian land parcel map base, survey-accurate data could be used to improve the positional accuracy of the existing cadastral dataset. However, since the higher accuracy data is only available in localised pockets, its integration into the map base will require rigorous methods that also enable the resultant spatial variation in the quality of the upgraded dataset to be communicated. Adjustment software based on the method of least squares is able to provide optimal positioning solutions that take into account all of the available information, including geometric constraints and the quality of the input datasets. Moreover, it provides updated quality parameters at the individual coordinate level.

A case study is presented here, demonstrating the use of such adjustment software to improve the positional accuracy of a sub-set of the Victorian cadastral database using GNSS data from an extensive survey. Initial methods to communicate the spatial variation in the quality of the updated dataset are also developed. Three separate adjustments were performed, with increasingly sophisticated data inputs. An independent ground survey was then undertaken to validate the results reported by the software. The findings indicate that the reported adjustment results are dependent upon the correctness of assumptions made in its establishment. It can be concluded that adjustment software based on the method of least squares is appropriate for positional accuracy improvement of spatial datasets only if sufficient care is given to verifying any assumptions made.

KEYWORDS: Spatial data quality. Positional accuracy improvement (PAI). Least squares adjustment. Cadastral upgrade.


4. A Toolbox for mapping and managing new interests over land

R. Bennett, J. Wallace and I. P. Williamson

The drive for sustainable development has led governments to create new interests over land. The role of cadastral and registration systems in the mapping and management of these new interests is unclear. Whilst these systems have always played an important role in the administration of land parcels and ownership, the new land interests are increasingly being mapped and managed elsewhere. As a result administrative inefficiencies and transaction complexities are growing. Existing cadastral and registration systems have the capacity to improve the situation; however, a guiding framework for their inclusion is needed. This paper introduces a framework of principles that articulate the roles of cadastres and registration systems in the management of new land interests. Importantly the framework is holistic and reflects other components essential to good land administration. These include the roles of land policy, legislation, flexible tenures, institutions, spatial data infrastructures and capacity building. The principles will systematize the management of land interests across different jurisdictions.

KEYWORDS: Cadastral Surveying. Land Administration. Land Interests. Property Rights.

5. Turkish cadastral system

O. Demir, B. Uzun and M. Çete

In Turkey, cadastral works were started after the foundation of the Republic of Turkey. These studies were carried out in such manner that ownership of the land was given to the people who were using it. Firstly, in 1924, the process was started in urban areas where one fourth of the total population of the country lived. Because of various problems including economic difficulties, technical deficiencies, personal insufficiencies, these cadastral works were only carried out in cities within the first 25 years from 1925 to 1950. Then the cadastral works were speeded up and most were carried out between 1950 and 1990. In this period, the work was achieved utilizing the available technology at that time in rural and urban areas. Today, 97% of the urban cadastral areas and 67% of the rural cadastral areas have been completed in Turkey. Generally, graphic, photogrammetric, orthogonal, and tachometric measurement methods have been used in this work. While 45% of the Turkish cadastral maps have been produced using graphic method which does not have a coordinate system, the other maps have been produced using the different measurement methods. These are also in different coordinate systems and scales. Only 7% of the whole cadastral maps are in digital format. On the other hand, because of the factors mentioned above, Turkish cadastral bases do not contain sufficient information to be converted to digital system in accordance with field. Since 1990, different methods have been used to digitize these non-digital cadastral maps. However, these attempts have failed. The main goals of this study are identifying historical background of cadastre and existing situation of its in Turkey.

KEYWORDS: Cadastral survey. Turkey. Digitisation. Land ownership.

6. A Review of surveying methods for sports and leisure

V. Kontogianni, A. Drakos, I. Haritantis and S. Stiros

Applications of modern geodetic instruments in sports and leisure-related activities are reviewed in this article. Total stations, satellite GPS receivers and laser leveling systems are used to standardize dimensions of sporting grounds, to accurately and digitally record performances in jumps and throws during games, to boost performances of athletes in rowing by recording the details of the vessel kinematics during training, to navigate yachts, boats and mountaineers, and to define heights of high-flying kites.

KEYWORDS: Sport. Electronic instruments. Sport measure recording. Track lengths.

7. Stable point research on deformation networks

H.Hakan Denli

Determination of the deformation of a geodetic network is an objective of the analysis of various geodetic deformation measurements. Deformation analysis is a step by step procedure, which in general begins with a global congruency test. If the coordinates of repeated measurement campaigns with its variance-covariance matrices and their datum are available, the question arises if congruency between different epochs exists. The analysis of the deformation field was performed in three dimensions. An alternative test procedure for detection of unstable points within the block assumed as stable beside the conventional method for congruency investigations is proposed and for both methods example solutions are given. The procedure is based on Similarity transformation. The benefit of both methods are discussed.

KEYWORDS: Similarity transformation. Deformation. Geodetic network. Unstable points.

8. Using the virtual reference stations (VRS) concept for long-range airborne GPS kinematic positioning

G.R. Hu,, O. Ovstedal, W.E. Featherstone, N. Castleden, C.J. Earls, D.A. Abbey

In this paper, the potential of long-range kinematic GPS positioning with a multiple reference station (MRS) network for airborne applications is discussed. A novel method of creating Virtual Reference Stations (VRS) is proposed for post-processed airborne GPS kinematic applications, which is called the modified semi-kinematic VRS method (MS-VRS). The purpose of the VRS is to generate data from real GPS observations made by the MRS network, resembling that of a non-existing (virtual) reference station situated close to the project area, so that the commonly used methods for short-range kinematic GPS data processing can be used to determine the position of the aircraft. During the initial phase, the VRS of the MS-VRS method refers to a fixed position according to the aircraft’s initial approximate position, and the corrections are applied according to the aircraft’s trajectory. The MS-VRS method differs from the conventional VRS method and semi-kinematic VRS method (S-VRS) in that when the aircraft’s current approximate position is more than 10 km from the initial VRS position, a new VRS is created. The MS-VRS data can be generated in RINEX format, so that it can be processed using any kinematic GPS post-processing software. Using a simulated kinematic test with static data, the MS-VRS method showed a 12.1 to 47.6 percent improvement in the three coordinate components with respect to the conventional single reference station (SRS) approach. Tests and analysis with real airborne GPS data are presented in some detail using a MRS network and flight test data in Norway. The results indicate that centimetre-level accuracy can be achieved based on the proposed MS-VRS method, which is superior to the S-VRS method, with improvements of 11.4 to 47.4 percent in terms of standard deviations of the coordinate domain.

KEYWORDS. Long Range Airborne GPS. Kinematic Positioning. Virtual Reference Stations.

9. Proposal for developing the Syrian stereographic projection

M. Habib

The conformal stereographic projection adopted by the Syrian survey authorities to represent the geodetic positions was designed for an age of paper maps according to geographical characteristics of Syria in the French mandate time (1920), which includes only the effective and cultural part of the country. Nowadays, this situation has changed since projects of land reclamation and of exploring petroleum in Al Gazira have been launched as well as modern surveying techniques such as Global Positioning System (GPS) and Geographic Information Systems (GIS) have been applied. This paper aims at overcoming the defects in the Syrian stereographic projection of the whole country by suggesting a new calculation approach and minimizing the errors in linear scale.

KEYWORDS. Conformal Mapping. Stereographic Projection. Orthographic
Projection. Conformal Sphere

 

 

 
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