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Survey Review 53, No 376. January/February 2021

1. Urban land speculation; failure of land market
B. S. Gemeda, B. Girma Abebe & F. Eckardt

This article is intended to examine the nature of urban expansion and development from a land speculation and urban sprawl perspective. Survey and case study approach were used to achieve this aim. As urban territory extends into adjacent periurban areas, speculators keep their land out of the current market so that developers of land and buildings must bypass it and home buyers should travel further distance to buy new lands and houses. This extra distance creates additional costs by increasing the cost of development, operation and travel. The finding of this article concludes that the speculators who held their land out off the market and received an average land value increase of about $230 per m2 each year generated extra social costs which they did not pay about $1,810 per m2 each year.

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2. Derivation of rigorously-conformal 7-parameter 3D geodetic datum transformations
A. C. Ruffhead

This paper proposes a new method of deriving rigorously-conformal 7-parameter 3D coordinate transformations between geodetic datums. The problem of linearisation is reduced by distance analysis which provides an estimate of scale-change. The resulting 6-parameter transformation is linearised to enable an initial least-squares estimate of the rotation parameters. The 6-parameter transformation is then re-linearised to obtain a least-squares estimate of the corrections to the rotations. The validity of the scale-change estimate can be tested and is verified in almost all cases. The exception is transformations covering very small areas where short distances maximise the impact of measurement errors in the control data. Even there, the method can be adapted to optimise the transformation. The method can also be used to obtain pseudo-optimal conformal transformations that provide a closest fit to published Bursa-Wolf transformations.

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3. GPS + Galileo + QZSS + BDS tightly combined single-epoch single-frequency RTK positioning
Shaolin Zhu, Dongjie Yue, Jian Chen & Zhiqiang Liu

The multi-GNSS fusion makes positioning more reliable and accurate. Considering the signal difference of different systems, GPS + Galileo + QZSS + BDS tightly combined double-difference model (TCDDM), including function and stochastic model, is proposed. The proposed model fully utilizes the overlapping frequency signals of various systems, and thus to enhance positioning model when DISBs are known beforehand. The observations of 3 ultra-short (1~10 m) and 3 short (4~10 km) baselines were processed by self-programming software, and the single-epoch single-frequency RTK performance using different system-combined models was evaluated by ambiguity-fixed correctness rate (ACR) and positioning accuracy. It demonstrated that three- and four-system TCDDM were superior to their corresponding loosely combined double-difference model (LCDDM) for ACR and positioning accuracy especially at high cut-off elevation. Moreover, four-system TCDDM had the best RTK performance obtaining average ACRs of 100% and 97.6% even at 25° cut-off elevation for ultra-short and short baseline, respectively.

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4. Single point positioning using full and fractional pseudorange measurements from GPS and BDS
Sihao Zhao, Xiaowei Cui & Mingquan Lu

In conventional global navigation satellite system (GNSS) receivers, full pseudorange measurements are usually required to complete a single point position fix, which takes longer time than obtaining fractional pseudorange measurements. In order to shorten the time to first fix and improve the position accuracy during cold or warm start of a dual-constellation GNSS receiver, we propose a positioning algorithm using at least four full pseudorange measurements from one constellation and fractional measurements from either or both constellations. Theoretical rapid position results can be obtained with an identical accuracy to that of the conventional method using full measurements. Tests with simulated and real Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) data validate the performance of the proposed approach.

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5. Determination of the under water position of objects by reflectorless total stations
Štefan Rákay, Slavomír Labant & Karol Bartoš

When surveying through a water surface, a distortion of several centimetres caused by the refraction and the change in the velocity of the electromagnetic waves can be observed. Therefore, neither the position nor the height of an underwater point (object), which can be seen from above the water surface, is correctly measured. The authors want to point out the magnitude of geometric errors when measuring to points under water as well as the computation of correct under water positions of points from measurement through a water layer. A practical experiment was performed for a water depth of 0.16 m.

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6. Global gravity models and the Ghanaian Vertical Datum: challenges of a proper definition
C. I. Kelly, S. A. Andam-Akorful, C. M. Hancock, P. B. Laari & J. Ayer

This paper analyzes errors in satellite gravity and GPS/trigonometric benchmarks (BMs) in relation to defining the Ghanaian Vertical Datum (GhVD). Results indicate that synthesized gravity introduce approximately 5 mm of error to corrected heights. However, large errors in BMs render them unsuitable for applications, including properly defining the GhVD. Overall, normal-orthometric corrections were of the order of a few millimetres, with comparatively larger Helmert orthometric and normal corrections. Accordingly, the most suitable heights for the GhVD are the normal-orthometric heights, with the geopotential of the Helmert orthometric heights, 62636861.534±2.27 m2 s−2, suggested as the potential of the GhVD.

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7. Application of baseline constraint Kalman filter to BeiDou precise point positioning
Xiaoguo Guan, Hongzhou Chai, Guorui Xiao, Chunhe Liu & Mingchen Shi

This paper proposes a baseline constrained PPP method to enhance the performance. The approach is based on constrained Kalman filter, and applied to BeiDou PPP in static, pseudo-kinematic, real kinematic modes. Both zero baseline and short baseline constrained PPP are verified in static mode, while a marine geodesy environment is designed to evaluate the performance in kinematic mode. The experiment results show that, compared to the PPP without constraint, the baseline constrained PPP can significantly improve the positional accuracy. Furthermore, the accuracy of baseline constrained static PPP can reach centimetre level, while the kinematic PPP can reach decimetre level.

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8. Evaluating success factors in the land readjustment applications: a case study of Trabzon Province, Turkey
H. E. Colak & T. Memisoglu

Land Readjustment plans (LR) provide tools for taking control of land development and construction, while organising social, cultural and technical infrastructure. In Turkey, LR applications, Pursuant to Law No. 3194, enable the creation of regular planned urban developments. The success of LR applications involves a comprehensive knowledge about the rules and relationships of the legal and community aspects of society. In this context, LR applications must be addressed and analysed by considering the success factors. In this study, LR application process was analysed to determine a set of quantitative factors in the Trabzon Province in Turkey. Cadastral and LR plans were reviewed to determine the success factors. By determining the quantitative factors: the correct regulation limits, an appropriate change in position of the parcel, the accuracy of the Development Readjustment Share account, the correctness of Public Partnership Share interruptions and the construction of the appropriate parcels, the success of LR applications were tested for pilot sites and comparisons were made with graphics.

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9. The determination of the true geometrical form of Great Ephesus theater, Turkey by using field surveys
Ozan Arslan & Orhan Kurt

The current deals with the determination of the ‘true’ geometrical shape of the Great theatre of Ephesus, which is the largest theatre in Asia Minor. To detect the geometrical form of the theatre a precise point dataset was created using terrestrial measurements performed directly on the theatre site. The well-known ellipse and circle fitting algorithms were presented for detecting the precise geometrical shape of the amphitheatre rings. The study reveals that ellipse geometry fits well to the theatre arcs that is amphitheatre rings are generally elliptical in shape. The precise metric values of the parameters of the geometrical shape were computed to characterise theatre features.

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10. Variations of precipitable water vapor using GNSS CORS in Thailand
Chokchai Trakolkul & Chalermchon Satirapod

This research aims to analyze variation in a time series of Precipitable Water Vapor (PWV time series) using data at 11 widely-distributed Continuously Operating Reference Stations (CORS) in Thailand. In this paper, the PWV time series is estimated based on data from 2007 to 2015, used to monitor trends and seasonal variations. Significant annual variations of PWV are found at all GNSS stations, with amplitude from 6 to 19 kg/m2. The variations between the annual amplitudes of PWV in the South and near the ocean coasts are generally smaller than in the inland regions. The phase shift of annual PWV variation is about −0.43 (around July, rainy season). The comparison of PWV and 24-hour cumulative rainfall data showed that the rainy season (running from around mid-May to the end of October) exhibits the slightest swing, and the highest average amount of PWV. These results are consistent with the 24-hour cumulative rainfall data.

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