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Volume 41, No. 313 July 2009 1. Orientation and alignment of the 5th century BC tunnel
of Eupalinus at Samos (Greece) In circa 530BC an about 1000m long tunnel was opened in Samos Island, Greece, as part of an aqueduct; this was the first tunnel ever excavated from both portals using strict surveying techniques. Despite the details studies, there are some questions concerning the techniques used by Eupalinus, the chief engineer. One of these questions is the selection of the specific path for the tunnel, a selection which appears at a first view rather awkward, for it leads to a longer tunnel and a longer aqueduct. Our investigation revealed that Eupalinus selection was constrained by two factors, one geotechnical and another geodetic. Eupalinus had first to avoid an area of weak rocks making unsafe, if not impossible the excavation, and second, to take advantage of a small valley, the only existing in rocks suitable for the excavation, and define a baseline of the maximum possible length, necessary for the accurate alignment of the excavation from the two portals. This proves that Eupalinus had an excellent understanding of what we can describe as a practical theory of errors and of measurements.
2. Integrated adjustment of Chinese’ GPS control
network. Since the beginning of the nineteen nineties, China has established six nationwide GPS networks by corresponding campaigns for different objectives. With the support of the international GPS service (IGS) network and advanced data processing strategies, an accurate and unified national GPS control network with more than 2500 stations integrating the 6 existing GPS networks has been established, which is called “National 2000’ GPS Control Network”. In the integrating adjustment of the nationwide GPS networks, some systematic model parameters were introduced into the adjustment functional model, in order to control the influences of systematic errors of the sub networks; the variance component estimation technique is used for adjusting the a priori precision of the different GPS networks and different observation sessions; the error detection and deleting technique is used in the data pre-processing of sub networks and observation sessions for resisting the effects of outlying observations; and a bifactor robust estimation theory is applied for controlling the influences of the outliers of the correlated baselines on the last coordinate parameters. It is shown that the average standard deviation for the horizontal component is smaller than 1.0cm, for the vertical component is smaller than 2.0cm, and for the three dimensional (3-D) position of geocentre coordinates is smaller than 3.0cm. The exterior checking accuracy for the 3-D position is averagely better than 0.9cm.
3. Error Correction Models and Their Effects on GPS Precise
Point Positioning Along with improvements in International GPS Services (IGS) products
with regard to GPS satellite orbit and clock errors, the Precise
Point Positioning (PPP) technique has been developed in recent years.
Compared with conventional GPS relative positioning mode, the PPP
technique does not require the presence of a nearby reference station,
which makes it more attractive than other techniques for some applications.
However, to achieve centimetre-level positioning accuracy, all GPS
errors have to be modelled carefully and removed from measurements.
Some errors that have not been seriously considered in a relative
positioning mode have to be treated now. This paper analyzes the
effects of the earth tide, satellite antenna offset, and phase wind-up
corrections on the accuracy of the PPP technique. Similar to relative
positioning mode, we can also combine measurements from different
satellites and different epochs to reduce errors in measurement
in the PPP data processing. The positioning accuracies with different
combinations of GPS phase observables are also presented in the
paper.
The patches of the rice paddies are generally positioned by a traditional surveying method such as Plane Table and Total Station in Korea. This study has been undertaken to check whether TLS (Terrestrial Laser Scanner) could meet the accuracy standard, compare TLS survey data with those one of the new modern survey technologies such as digital aerial photogrammetry and RTK GPS. As a result, it is shown that terrestrial laser scanning and 3D stereo plot of digital aerial photogrammetry technology could meet a positional accuracy standard with artificial target. The extraction of ridges of rice paddies is, however, difficult due to the limitation of the tone colour identification and the noise of digital aerial image, and low density of the point clouds in TLS scanning. It is therefore expected that more researches into the sophisticated algorithms for the natural boundary extraction and the noise removal in digital aerial image are required.
5. Surveying: a profession facing a global crisis? The surveying profession, in different parts of the world, report a range of major problems, including low student numbers, closure of surveying courses, an aging teaching profession, inadequate job opportunities in some locations, and an insufficient supply of graduates to fill the vacancies in others. There are challenges of new technologies within both education content and delivery and the risks associated with non-specialist data uses. Overarching these problems appears to be the lack of any clear international recognition of a 21st century definition of the profession of “surveying” and thus a failure to promote, at a global level, a clear, coherent “surveying” message to both clients and to the broader public. Indeed, there is evidence that some skills that are recognized and valued as being part of the surveying profession in some countries are not considered in the same light in others. This paper examines these issues, concluding that the global surveying profession is indeed lacking a clear, coherent message and that the mounting issues, if not addressed quickly, have the potential to affect severely the development of the profession and to assume crisis proportions.
6. New affine transformation parameters for the horizontal
network of Seoul/ Korea by multivariate TLS-adjustment. The new approach of multivariate Total Least-Squares (TLS) adjustment has been applied to 33 stations of the horizontal network of Seoul/Korea in order to estimate best-fitting affine transformation parameters. The results are presented along with variances and covariances (in first order approximation), and comparisons are drawn with the standard Least-Squares (LS) approach. Although the estimates from TLS do not show practical differences with respect to LS, the fit does yield significant improvements. Furthermore, the estimates could be substantially different when the data quality drops considerably. No weights are taken into consideration at this time. 7. Using an official undulation model for orthometric height
acquisition by GNSS Since the beginning of 2006 the vertical control system in Israel
is ellipsoidal. The Survey of Israel constructs and maintains the
ellipsoidal vertical control system based on permanent Global Navigation
Satellite System (GNSS) stations. Nowadays, the vertical control
system’s objective of providing a framework upon which topographers
and engineers can base and adjust their heights is achieved more
easily by GNSS measurements. Despite this, the vertical orthometric
control system is still in use since many height data users prefer
the orthometric system. However, the characteristics of the orthometric
control system are localized. 8. The conception of integrated survey networks composed
of modular networks and GPS vectors The main feature of the modular network method is a possibility
of quick establishing the measurement network with concurrent tachymetric
measurement of situational details. The network is established on
site, without being earlier designed in any way. Sites are usually
selected in any place and treated as temporary (lost) points. This
paper puts forward a proposal to strengthen the structure of modular
networks with GPS measurements. GPS vectors can be adjusted together
with the modular network. What is obtained as result, are the coordinates
of tie (connecting) points, which are necessary for the final transformation
to the reference coordinate system. Measurement results can be adjusted
with the use of multi-group transformation. The method leads to
the solution of a system of conditional equations with unknowns.
The issue of numerical development may be related to integrated
networks considered as 2- or 3-dimensional structures. The five elements of any horizontal circular curve, which are tangent
distance, T, external distance, E, middle ordinate, M, chord length
C, and length of curve, L, can be directly determined if the radius
R and deflection angle delta are given. Practically, there are some
cases where the deflection angle delta and the radius R cannot be
measured due to the inaccessibility of the intersection point PI.
Thus, two other curve elements have to be known in order to layout
the horizontal circler curve.
Volume 41, No. 312 April 2009 1. Teaching field Surveying to final-year university students:
an example from Western Australia At Curtin University of Technology, all final-year undergraduate surveying students must take a field-to-finish survey camp as part of their degree programme. This paper outlines the six exercises now set and their educational rationale, including a novel system where a production environment is replicated by setting penalties for late submission of assignments. In addition, some deliberate ‘traps’ are set to reinforce routine checks of their observations. The approaches and philosophies used here may be of use/interest to other field-surveying educators.
Complete redevelopment of the traditional geodetic infrastructure on the island of Barbados, West Indies, took place in 1968/9 when both angles and distances were observed to provide horizontal control of high order. Observations made in 2007 at selected stations with thirteen GPS operating simultaneously to measure 377 baselines shows that integrity of the network has been retained. Seven transformation parameters are now available to convert between the local datum and WGS84 to an accuracy of 0.15 m. Accuracy of a three parameter transformation is reduced to 0.5m due to a difference of 12” in azimuth between the local datum and WGS84. In the vertical component, height data from traditional control is used with that from the GPS observations and the CARIB97 geoidal model for the region, to refine a height correction model. This is capable of reducing heights from WGS84 to the local land survey datum to an accuracy of 3 cm. Contrary to previous reports, no significant change in sea level with respect to the land survey datum is found. Analysis of data sets used previously suggests that there is more likely a misunderstanding of the reference level adopted for sea level observations. With both horizontal and vertical components of the relationship between WGS84 and the local datum now realised, the survey community can better integrate data from different sources. While some surveyors have made the transition to new technology, the density of existing control points together with the geologically stable conditions, that have preserved integrity, and clear visibility across the island imply that conditions are still suited to traditional surveying methods.
Integer carrier phase ambiguity resolution is the key to fast and
high-precision global navigation satellite system (GNSS) positioning
and application. Apart from integer estimation, also acceptance
tests are part of the ambiguity resolution process. A popular acceptance
test is the so-called ratio-test. 4. Reducing GPS carrier phase errors with EMD-wavelet for
precise static positioning
Geodetic frameworks in most countries are still referenced to local horizontal geodetic datums. Therefore, GPS-determined geodetic networks have to be integrated to local (national) networks. In practice, this process is always achieved by a coordinate transformation. However, this common way has some difficulties. For avoiding these difficulties, an alternative way called DIDELOC is proposed in this study. The basis of this method is based on that the slope distances are datum free. Utilizing this property of slope distance, GPS baselines can be evaluated directly in local system by DIDELOC method. This method is successfully applied to the test data selected from the biggest hard coal basin of Turkey. The results show that the previous coordinates in the basin have experienced deformations caused by subsidence. 6. Comprehensive process-driven boundary making model: a case study of the Jordan-Israel boundary H. Srebro and M. Shoshany Surveyors had a central role in boundary-making processes from at least the 19th century. The latest technological developments in this field have further widened their involvement in the process and changed the concepts and practices implemented. The Process Model presented here incorporates the new technical means available for modern surveyors in accomplishing a more stable and sustainable boundary through a structured procedure. The roots of the traditional theory of boundary making were put down a century ago by Curzon[6], Holdich[9] and others referring mainly to the three-stage process of allocation, delimitation and demarcation. This article renews the existing model of boundary making process adding to it two additional stages: boundary documentation and boundary maintenance to build up a comprehensive approach. The direct involvement of the authors in boundary making processes between Israel and its neighboring countries facilitated assessment of the model elements and their full implementation in the Israel–Jordan Boundary making from negotiations, through demarcation in the field up to continuing bi-lateral maintenance operations. 7. Accuracy of GPS positioning over regional scales Recently, evaluation of GPS positioning accuracies has gained importance. Studies presented in this manner usually employ inter-station distances varying between 5 and 300 km. In this study, we aim to assess GPS accuracies over longer baselines (i.e. on smaller or regional scales) ranging from 300 to 3000 km. We adopted already published Least Squares functional models for accuracy assessments and investigated the effects on long baseline solutions. We used GPS data from Scripps Orbit and Permanent Array Centre (SOPAC) archives. GPS data were processed using NASA’s GIPSY OASIS II research software. Our results indicate that GPS positioning accuracies show dependency on both the observing session duration and inter-station distances over regional scales. New prediction formulas have been derived for regional scales since accuracy estimation could not be performed well with the ones that were previously derived. We also noticed that the effect of inter-station distance appears to be significant only for baselines longer than 2000 km.
The interpolation of gravity anomalies is a widely used process
by the geodetic and geophysical communities to achieve their objectives.
This interpolation is commonly made using geostatistic methods (Kriging
or least-squares prediction), over gravity anomalies uncorrelated
with height (Bouguer or residual free-air gravity anomalies). The
interpolation of free-air or Faye gravity anomalies, which are strongly
correlated with height, is usually achieved by the interpolation
of Bouguer anomalies and subsequent transformation to free-air or
Faye anomalies.
Vol. 41. No. 311 January 2009 1. International boundary surveys and demarcation in the late 19th and early 20th centuries. P. Collier Much of 19th century colonial boundary making was carried out in conferences, by diplomats who were ignorant of the geography of the areas to be delimited. In an attempt to put boundary making on a more rational footing, two British army officers, Hills and Holdich, and a politician, Curzon, made a number of recommendations. As an experienced boundary surveyor, the suggestions of Holdich should have carried the most weight. However, while the ideas of Hills, Curzon and Holdich had much to commend them, with a few notable exceptions, their ideas were rarely followed. 2. GPS-derived strain rates on an active ice shelf rift V. Janssen, R. Coleman and J.N. Bassis Ice shelves are important components of the Antarctic ice sheet due to their ice-ocean-atmosphere interface and vulnerability to global increases (or decreases) in atmospheric and oceanic temperatures. The development of rifts, which are fractures that penetrate through the entire ice shelf thickness, precede large tabular iceberg detachment and can lead to ice shelf break-up. Changes in strain rates on an active propagating rift system on the Amery Ice Shelf, East Antarctica are determined using in-situ Global Positioning System (GPS) measurements. Results for the 2002/03 Antarctic summer period (Dec-Feb) confirm previous observations that rift propagation occurs in episodic bursts separated by several days. Transverse-to-flow (i.e. parallel-to-rift) strain rates exceed longitudinal-to-flow (i.e. normal-to-rift) rates by up to a factor of 5 and maximum principal strain rates around the rift tip vary from 12 to 21 [x 10-3/yr]. A rotation in the direction of the principal strain is evident around the rift tip, indicating a change in the mechanics of rift fracture. It is demonstrated that cumulative sum analysis, obtained by differencing a pair of residual baseline time series situated approximately normal and parallel to the rift, is an effective method to detect small baseline length changes. 3. Comparison and analysis of non-linear least squares methods for 3-D coordinates transformation M. M. El-Habiby, Y. Gao, and M. G. Sideris Four different methods are evaluated by solving the Molodensky 3-D coordinate transformation problem. These methods are Steepest Descent, Trust region, Gauss Newton and Levenberg-Marquardt. Also, the problem has been solved using the traditional combined least-squares adjustment. The solutions of these methods are compared by the number of iterations required for the objective function to converge to its minimum value. Externally, the RMSE of the transformed check stations of the geodetic network (curvilinear coordinates) are compared to the RMSE obtained by transforming the same set of check stations using the transformation parameters recommended by the Egyptian Survey Authority.
H.S. Fok, H. Baki Iz, and B. Schaffrin Geodetic surveying practices require the establishment of new control stations that are tied to higher order stations with known coordinates (reference control stations – fiducial stations), an activity known as densification. The coordinates of the newly established control stations are adjusted together with the coordinates of the reference control stations which are required to remain invariant along with their variance-covariance matrices (i.e. they are reproduced). In this study, we compare the performance of four different approaches that can be used to achieve this end for their optimality and sensitivity against potential systematic effects in the reference control station coordinates using a GPS network densification example.
B. Uzun In developing countries one of the urbanization issues is the provision of adequate land for new built-up areas. Therefore, it is important to implement land development plans to meet urban land needs and facilitate systematic urban development. There are different methods to realize these procedures and, worldwide, land expropriation is the most commonly used one. Compensation based procedures are mostly used to release land for urban land development applications, but this is both expensive and coercive. There needs to be a more effective way of providing land for new settlements and construction. Land readjustment (LR) is one of the land development tools used in the developing world to support urbanization requirements. It has the ability to solve land-use problems in urban areas when there is a need to redesign and create new urban settlements. In order to provide land for a continuing urban development process, LR has been implemented in Turkey. In particular, municipalities apply the method to release land for public areas such as roads, parks and play areas. This paper outlines, first, the implementation methods of urban land development plans in Turkey, and then the Turkish LR method is introduced in detail. 6. Improved Coordinate Transformation in Dubai Using a New Interpolation Approach of Coordinate Differences A. El-Mowafy, H. Fashir, and Y. Al-Marzooqi In this study, an improved coordinate transformation method between geodetic reference frames in Dubai, UAE, is investigated. In the first phase of this method, a similarity transformation is performed using a seven-parameter model between points known in the two frames involved in the transformation process. Next, the coordinate differences between the transformed coordinates and their known values in the frame into which they are transformed are computed. A database is then produced containing these coordinate differences. To transform coordinates of other points, their coordinates are initially transformed using the similarity transformation parameters estimated in the first step. Next, the coordinate corrections (as differences) at these points are interpolated using the generated database and added to the initial transformed coordinates. Instead of using the common method of double interpolation from a grid for this purpose, a new method is presented. The method directly interpolates coordinate differences at a required point from coordinate differences of the nearest three known points. These differences in the spatial domain form a triangle. Each triangle is assumed to be a surface. The coordinate difference at the required point is estimated on that surface by geometry. Results from testing show that coordinate transformation at accuracy of 2.1 cm on average was achieved in Dubai, which is better than using only the current traditional similarity transformation. Results also show that the proposed interpolation method has a very good performance. 7. Deformation monitoring by GPS at embankment dams and deformation analysis E. Gökalp and L. Tasçi Deformation measurements are very important for inspecting huge engineering structures in order to prevent disasters caused by deformation and thus protect national investment. These measurements require the use of very accurate surveying equipment. In particular, the structure of a dam and the physical effects it has on its surroundings need continuous monitoring in order to see if unexpected changes have occurred. If any change is found, remedial work can be performed to protect the structure. The Global positioning System (GPS) meets all of the requirements stated above and therefore, GPS receivers were used in this research. The main aims of this work were the examination of deformation at the crest of the dam caused by water load at different water levels and the weight of the dam. Additionally, the study was undertaken to determine whether GPS measurements could reach the accuracy requirements for dam deformation measurements. In order to monitor and examine the deformation, a monitoring network consisting of 6 reference points and 11 object points was established. Measurements were made four times over 2 years using dual frequency GPS receivers with static methods. The measurements were processed and point coordinates were determined. Then differences were calculated between periods and the differences were analyzed by iterative weighted transformation and Fredericton methods to determine the stability of the points. Finally, the results from the two methods were compared and discussed.
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