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Current Abstracts
Past Abstracts

Email: Peter Collier


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Survey Review 50, No 358. January/February 2018

1. A new approach to calculate the land fragmentation indicators taking into account the adjacent plots
J. Janus, M. Mika, P. Leń, M. Siejka & J. Taszakowski

Land fragmentation is a phenomenon which constitutes one of the biggest obstacles to profitable agricultural production. Measurable estimation of this phenomenon is possible by a number of known indicators, based on the surface area of parcels in the given area, their location in space and belonging to individual farms. This method of calculation of the indicators is inaccurate due to the phenomenon of neighbourhood of plots which belong to the same owners. For the purposes of calculating the ratios of actual fragmentation of land, these parcels should be treated as one complex. The article presents a proposal for the adjustment of existing methods of determination of the fragmentation of land indicators, taking into account these phenomena. The object of the research covered area of the voivodeship of Malopolska located in the southern part of Poland. Developed by the authors, method of calculation of land fragmentation indicators, based on complexes of land belonging to the same owners (complexes of plots aggregation), gives very good results in the evaluation of the intensity of the land fragmentation. Obtained in this way, indicator’s land fragmentation represents the real situation on the ground.

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2. Surface area calculation for DEM-based terrain model
S. Xue, Y. Dang, J. Liu, J. Mi, C. Dong, Y. Cheng, X. Wang & J. Wan

The surface area calculation is meaningful for a variety of space-filling phenomena, for example the packing of plants or animals within an area of land. An integral method for calculating the landscape surface area is proposed by considering the curvature of terrain and the measurement errors in Digital Elevation Model (DEM) data. Applying the least squares method, with the DEM data we estimate the first-order and second-order derivatives of the terrain surface to reduce the influence from the DEM data errors. It shows that the first-order derivatives estimated are statistically independent to the second-order derivatives estimated when using a symmetrical configuration composed of a series of DEM points. The surface area within a polygonal region is obtained by partitioning the polygonal region into a series of squares, rectangles and triangles. The proposed method is compared with the triangle-based methods and the results show that the proposed method is more robust.

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3. Informal economies, state finances and surveyors
P. van der Molen

All countries host informal economies, sometimes even exceeding the size of the formal economy. Living in the informal economy means for citizens that they and their activities are invisible for the government. Governments miss information about which people live in their country and what economically happens. They miss relevant data to develop policies, to monitor implementation and to levy taxes for generating budget. This hampers good governance and state building. This paper analyses the problem, and argues that when surveyors would expand their capacity for administration of land to other recordable subjects and objects, they can contribute to a solution.

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4. Height biases of SRTM DEM related to EGM96: from a global perspective to regional practice
A. Üstün, R. A. Abbak & E. Zeray Öztürk

It is investigated to what extent EGM96 affects the accuracy of digital elevation model (DEM) produced from the shuttle radar topography mission (SRTM). Global and regional analysis of EGM96 compared with EGM2008 indicate that locally there are large differences distorting to the accuracy level of SRTM DEM. In the absolute sense, the overall geoid differences throughout 1x1 arc-degree tiles reach −5 m in the northeast and 2–3 m in the southern parts of Turkey. A numerical investigation over the test profiles of 200–700 km length running at various directions proves that a possible vertical datum change from EGM96 to EGM2008 yields systematically more accurate height information with an improvement of up to 2.5 m. A GPS-levelling traverse of about 900 km length points out some key patterns of this recovery. Consequently, a correction for the present version of SRTM DEM should be considered in critical implementations of Earth sciences like geoid or water flow modelling, especially for areas where EGM96 shows weak performance.

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5. Maintenance of the state survey in the Republic of Montenegro
R. Đurović, I. R. Aleksić & R. Mihajlović

The paper provides an overview of the maintenance of the state survey, as the foundation for the development of the geodetic infrastructure, real estate cadastre, mapping and the National Spatial Data Infrastructure (NSDI) in the Republic of Montenegro. A proper understanding of the problems that emerge in the maintenance of the real estate cadastre requires familiarity with its background, i.e. the conditions under which it emerged. Particular attention is focused on geodetic reference networks, as the foundation upon which the cadastral databases were established and have subsequently been maintained, with analysis of their occurrence and current state included.

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6. The use of low-cost, single-frequency GNSS receivers in mapping surveys
M. Tsakiri, A. Sioulis & G. Piniotis

The emergence of low-cost, navigation-type receivers capable to provide carrier-phase data (the so-called high-sensitivity carrier-phase positioning) has been steadily growing over the recent years. The aim of this study was to evaluate the positioning performance of a high-sensitivity receiver in a network real-time kinematic environment for mapping surveying applications. Specifically, using as rover receiver the u-blox NEO-7P module and the low-cost antenna Tallysman TW2410, sets of data were collected for the purpose of mapping surveying. The external accuracy of the obtained solutions is considered using different positioning techniques and the internal indicators of the system during real-time kinematic (RTK) positioning are assessed. The assessment indicates that in benign environments this type of receivers produce results that are comparable to RTK positioning using geodetic receivers and with a significantly lower cost.

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7. An effective QR-based reduction algorithm for the fast estimation of GNSS high-dimensional ambiguity resolution
L. Lu, W. Liu & X. Zhang

To fast estimate high-dimensional ambiguities, we propose a new lattice reduction algorithm based on QR decomposition, which achieves fast integer transformation through an iterative strategy of whole size reduction and the deep insertion of minimum basis vectors. It acquires better basis vectors for ambiguity resolution. The feasibility of the proposed algorithm is verified by comparing its performance with those of LAMBDA, LLL, the parallel Cholesky-based reduction algorithm with ascending sorting (ASCE), and a modified LLL algorithm with deep insertions (PotLLL) under three experimental scenarios. The Hermite defect and defined length ratio are used to measure the reduction quality. Both metrics verify that our proposed method acquires a good reduced basis for accelerating the ambiguity search. To evaluate the practical ambiguity resolution behaviour, we tracked the runtime of ambiguity resolution. The results show that the computational efficiency of the proposed algorithm is better than those of the comparative algorithms.

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8. Representation of the rotation parameter estimation errors in the Helmert transformation model
Q. Wang, G. Chang, T. Xu & Y. Zou

In the Helmert transformation model, the rotation is more difficult to be treated in terms of representation, estimation, and error analysis. First, two classes of representations of the rotation, i.e. the redundant class including the direction cosine matrix and the unit quaternion, and the minimum class including the rotation vector, the Gibbs vector, the modified Rodrigues parameters, and the Euler angles, are reviewed. It is concluded that in general the redundant class should be preferred as they are transcendental-function-free, singularity-free, and discontinuity-free. Second, two classes of estimation errors, i.e. the additive and the multiplicative errors, are defined and compared in detail. While the multiplicative errors are more convenient, the relationship among different representations and the relationship with their additive counterparts are also explored from first principle. It can be seen as a review paper; however, the content concerning the relationship between the additive and the multiplicative errors is believed new.

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9. Introduction to multiple regression equations in datum transformations and their reversibility
A. C. Ruffhead

This paper provides an introduction to multiple regression equations as a method of performing geodetic datum transformations. The formulae are particularly useful when there are non-linear distortions that need to be built into the transformation model. However, the equations take the form of a one-way transformation, usually a local geodetic datum to a global datum. The standard procedure for applying the equations to obtain the reverse transformation only gives approximate results relative to the original model. This paper quantifies the problem and describes three methods for computing the reverse transformation (or inverse transformation) more accurately.

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10. Comment on ‘The use of laser scanning as a method for measuring stairways following an accident’
R. Bowman, M. Roys & N. Davies

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11. Obituary: George Russell ‘Brim’ Brimacombe 5 June 1939–27 July 2017
Dr Peter Collier

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