Volume 41,
No. 313 July 2009
1. Orientation and alignment of the 5th century BC tunnel
of Eupalinus at Samos (Greece)
Stathis C. Stiros
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.
Yang Yuan-xi, Tang Ying-zhe, Chen Chuan-lu, Wang Min, Zhang
Peng, Wang Xiao-rui, Song Li-jie, Zhang Zu-sheng
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
Wu Chen, Congwei Hu, Shan Gao, Yongqi Chen and Xiaoli Ding
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.
4. Comparison of terrestrial laser scanner with digital
aerial photogrammetry for extracting ridges in the rice paddies
I. S. Lee, J. O. Lee and L. Ge
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?
J. Hannah, J. Kavanagh, R. Mahoney and F. Plimmer
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.
Jay Hyoun Kwon Jong-Ki Lee, Burkhard Schaffrin, Yun Soo Choi,
Impyeong Lee
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
G. Even-Tzur and G. Steinberg
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.
The Geoid Undulation Model is one of the foundations of the geodetic
infrastructure. It is used to connect ellipsoidal and orthometric
heights. Intensive utilization of GNSS for geodetic, surveying and
engineering applications necessitates the rapid development of an
undulation model. Today, the efforts to develop a geoid undulation
model with an accuracy level of one centimetre over an entire country
demand multiple resources. This paper suggests a method for developing
an orthometric control system with a reasonable accuracy level on
a nationwide basis by means of GNSS measurements, ellipsoidal vertical
control and an official geoid undulation model. The best available
geoid undulation model can be used as the official geoid undulation
model, regardless of its accuracy level.
Research was conducted in Israel in order to test the feasibility
of the idea of using an official geoid undulation model. Two kinds
of official models were tested, the world wide geopotential model
GPM98B and a local countrywide model computed by the Survey of Israel.
We compared the orthometric height differences obtained by GPS measurements
using the undulation model with the known orthometric differences.
This paper presents the results of these experiments. It verifies
the capability of the suggested technique to define seamless orthometric
vertical control, adequate for most geodetic and surveying purposes,
via a low-cost and fast procedure.
8. The conception of integrated survey networks composed
of modular networks and GPS vectors
T. Gargula
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.
9. A non-iterative approach to solving horizontal curves
Saiid Shebl and Saleh A. Alsaleh
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.
This paper presents a direct method to extract the unknown elements
exploiting a cubic polynomial equation which characterizes the curve
deflection angle. The least squares technique is considered in order
to facilitate the solution with fair accuracy.
Particularly, the cubic polynomial is selected as it generates an
adequate desired accuracy. If higher accuracy is aspired, higher
order polynomials, i.e. quartics, quintics,…, may be adopted.
On contrast to other methods, which adopt iteration process, the
presented method is direct, non-iterative, accurate, and easy to
handle values of deflection angle, delta, ranging from 0 to pi without
imposing any derivatives.
The major benefits of the proposed method are illustrated as: firstly
it is direct method which may easily be executed using the pocket
calculator with high accuracy, and secondly, it avoids the uncertainty
of the convergence due to the lack of pre-estimation of the initial
value of deflection angle and number of iteration trials required
when iteration solution is considered.
The applicability and accuracy of the presented method is justified
through a numerical application. Using the same values of L and
T, it has been found that the percent of error for the previous
methods in five digits values vary from 0 to 0.00133% for delta
and 0.00084 % to 0.00252 % for R. The proposed method gives an error
of 0.00533 % for delta and 0.00644 % for R. The effect of such errors
in roadway geometry design is negligible.
Volume 41, No. 312 April 2009
1. Teaching field Surveying to final-year university students:
an example from Western Australia
W. E. Featherstone and G. P. Galvin
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.
2.Geodetic control on Barbados, West Indies
K. Miller, M. St. Clair, B. Hart, A. McClean, P. Sydney, G.
Hutchinson, A. Clarke and A. Gopee
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.
3. The GNSS ambiguity ratio-test revisited: a better way
of using it.
P.J.G. Teunissen and S. Verhagen
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.
In this contribution we study the properties and the underlying
concepts of the ratio-test. We discuss some misconceptions of the
ratio-test and in particular show that the ratio-test is not a test
for testing the correctness of the integer least-squares solution.
We also show that the common usage of the ratio-test with a fixed
critical value has shortcomings. Instead, the fixed failure rate
approach is recommended. This approach is part of the more general
theory of integer aperture estimation, and enables that the failure
rate does not exceed a user-defined value. Results of the fixed
failure-rate ratio-test and its improved performance are illustrated
with a number of examples.
4. Reducing GPS carrier phase errors with EMD-wavelet for
precise static positioning
Jian Wang, Jinling Wang and Craig Roberts
In this paper, a new EMD-Wavelet based model is used to reduce carrier
phase errors for precise static GPS positioning. The EMD is a new
signal processing method for analysing non-linear time series, which
decomposes a time series into a finite and often small number of
Intrinsic Mode Functions (IMFs). The decomposition procedure is
adaptive and data-driven. The IMFs are stationary which are more
suitable for wavelet analysis. The merits of both the EMD and Wavelets
are combined to produce an improved EMD-Wavelet systematic error
extraction model. Thereafter, a method of the GPS baseline calculation
based on the EMD-Wavelet systematic error mitigation model is suggested.
The experimental results show that the proposed scheme dramatically
improves the reliability of ambiguity resolution with a larger F-ratio
and W-ratio index after systematic error elimination.
5. Direct determination of local coordinates from GPS without
transformation
H. S. Kutoglu
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
D. Ugur Sanli and Cetin Engin
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.
8. Some notes and numerical comparisons on gravity anomalies
interpolation
A. Martín, A.B. Anquela, J. Padín and S. Baselga
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.
This paper describes the method of using the local linear correlation
with height as a parameter inside the interpolation for these last
gravity anomalies, forming a one-step interpolation procedure.
Numerical values are also obtained and compared for the interpolation
of different gravity anomalies. These gravity anomalies are: free-air,
refined Bouguer and Faye anomalies, reduced free-air, reduced refined
Bouguer and reduced Faye anomalies (using the recent EIGEN-CG03C
global geopotential model to degree 360) and residual free-air gravity
anomalies.
The area studied is located in the Valencia Region (Eastern Spain).
The analysis of the results is based on the actual error derived
from the interpolated value at a number of control points by comparison
with their actual observed values (absolute error).
The main conclusion reached is that all type of gravity anomalies
and methods used for interpolation give the same results.
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.
4. Comparison of four geodetic network densification solutions
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.
5. Using land readjustment method as an effective urban land development
tool in Turkey
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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