GPS-derived geoid using artificial neural network and least squares collocation

The geoidal undulations are needed for determining the orthometric heights from the Global Positioning System GPS-derived ellipsoidal heights. There ore several methods for geoidal undulation determination. The paper presents a method employing the Artificial Neural Network (ANN) approximation together with the Least Squares Collocation (LSC). The surface obtained by the ANN approximation is used as a trend surface in the least squares collocation. In numerical examples four surfaces were compared: the global geopotential model (EGM96), the European gravimetric quasigeoid 1997 (EGG97), the surface approximated with minimum curvature splines in tension algorithm and the ANN surface approximation. The effectiveness of the ANN surface approximation depends on the number of control points. If the number of well-distributed control points is sufficiently large, the results are better than those obtained by the minimum curvature algorithm and comparable to those obtained by the EGG97 model

Streaming GNSS data via internet using Ntrip protocol

The article presents a means of GNSS data transfer\ud via internet by using the Ntrip protocol. Ntrip is used\ud for streaming data in the standard RTCM form, but it\ud also supports any other data form. The basic elements\ud and the basis of Ntrip operation are presented. Use of\ud Ntrip is related to mobile internet, especially to packet\ud data transfer GPRS. The article discusses the use of\ud Ntrip and GPRS data transfer from user’s perspective\ud in the Slovenian GNSS network SIGNAL

Determination of deflection of the vertical from geoid heights

The geoid model represents part of the national coordinate system. It can be used for the purpose of GNSS-levelling, but the use of geoid heights also improves incorporation of terrestrial observations into the state coordinate system. In GNSS levelling tasks, geoid heights are obtained from the geoid model, but with terrestrial observations the deflection of the vertical is also needed. Determination of geoid heights from the geoid model is a simple engineering task; however, determination of deflection of the vertical is not so common in geodetic practice. The purpose of this paper is to present the local method of establishing the deflections of vertical with the help of a plane, which is calculated on the basis of interpolated geoid heights. The coefficients of the plane give the deflection of the vertical in the point of gravity. This means that, given a known geoid, we can calculate the deflection of the vertical at any point in the region of Slovenia. Comparison of calculated deflections with the measured deflections was performed in order to estimate the accuracy of the proposed procedure. The procedure was tested in the geodetic network with four points

Analiysis of GNSS-RTK instruments testing on the ISO 17123-8

GNSS-instruments (Global Navigation Satellite System) are the standard field surveying equipment (in addition to tachymeter and levels) for geodetic network establishment and detail surveying. As in the case of other geodetic instruments, it is essential to pre-analyse GNSS-receiver quality parameters, obtained from laboratory calibration and/or field testing of the specific instrument and/or measuring method. Thus, the relevance of the results, as indicated by manufacturer, is obtained that may explain the suitability of a specific GNSS-instrument for field measurements. In 2007, the International Organization of Standardization (ISO), Technical Committee 172, Subcommittee 6 (ISO/TC 172/SC6), presented a comprehensive GNSS field testing procedures for real time measurements, based on statistical evaluation and verification of the manufacturer's hardware and firmware. The test can be performed anywhere on the field assuming that the test area includes minimal potential influences to GNSS measurements. At the same time, a test does not require any additional processing software, because the test data evaluation is based on elementary statistics. This paper presents the theoretical basis of GNSS instrument testing in accordance with the ISO 17123-8 guidelines and further examination of specific measurements on the selected site

Ionosperic refraction modeling for better autonomous GNSS code positioning: in preparation of solar cycle 24.\ud

This paper describes GNSS-processing optimisation\ud for better autonomous single-point positioning using\ud single frequency code receivers. GNSS processing\ud improvement is carried out in terms of near-real time\ud ionosphere delay modelling, which will be crucial\ud during the upcoming 24th maximum solar cycle. The\ud main scope of this article is to examine how sudden\ud changes in the ionosphere, caused by events on the\ud Sun, affect autonomous single-point positioning in\ud simple navigation tasks. Further, the specific method\ud of ionosphere delay modelling from actual twofrequency\ud receivers, acquiring carrier phase and code\ud observations, is shown. The modelled value of the\ud ionospheric refraction, which is given in GNSS path\ud delay, is further used in point positioning from singlefrequency\ud code instruments. In addition, we show\ud the advantage of GNSS permanent stations that can\ud supply a wide range of users with better ionosphere\ud data in near real time. From actual experiments, the\ud magnitude of the ionospheric impact on each specific\ud 3D position component is shown and further improved\ud using modelled ionosphere delay values. Finally, we\ud show how to improve GNSS position determination\ud from simple single- or two-frequency GNSS code or\ud carrier-phase receivers in differential GNSS method.\ud This study was conducted for preparations for the\ud upcoming solar cycle maximum, expected to be held\ud in May 2013

PPP method for static GNSS survey

This paper presents Precise Point Positioning (PPP),\ud a method of GPS observation processing from a single\ud receiver that provides coordinates of the highest quality.\ud The requirements for high quality results are an exact\ud mathematical model, high quality GPS biases modelling,\ud and high quality IGS products. On the basis of monthly\ud GPS observations from a permanent station GRAZ in\ud Graz, Austria, we will demonstrate that PPP method is\ud able to determine stations position with the accuracy and\ud precision of a centimetre in the ITRF global coordinate\ud frame. Because of high precision transformation between\ud ITRF and ETRS89, the PPP method can also be used\ud in Slovenia to determine high precision positions in the\ud national coordinate reference system of Slovenia (D96/TM),\ud as it is based on ETRS89

Quality analysis of the sphere parameters determination in terrestrial laser scanning

A point cloud is the result of laser scanning; in the case of\ud terrestrial laser scanning, the point cloud is composed of points\ud scanned from one or more positions. To register these points\ud into one point cloud, so-called tie points are needed; these\ud may be object points (natural targets) or selected stabilized\ud targets (artificial targets). Spherical targets are often used as\ud artificial targets; these must have their centre coordinates and\ud radius determined. The centre coordinates of a sphere are\ud calculated on the basis of scanned points on the spheres’ surface.\ud This paper presents two procedures for determining the best\ud reflection region on the sphere to determine its parameters, and\ud the procedure for determining the optimal distance between\ud the scanner and sphere.The best reflection area on the sphere\ud is determined in two ways. The first is based on minimizing\ud the difference between sphere radii when, in the adjustment\ud process, the radius of the sphere is treated as a known and\ud unknown quantity. The second is based on the standard\ud deviation of the sphere’s centre coordinates at the independent\ud determinations of sphere parameters from randomly chosen\ud scanned points on the sphere surface. For each of the spheres,\ud the best ratio between the laser beam footprint area and the\ud target surface area is calculated for the optimal combination\ud of scanning distance and region. For the best combination\ud of scanning distance and region, we chose the one with the\ud smallest standard deviation of the sphere centre coordinates

Realisation of geodesy in geotechnics

This paper deals with surveying activities in order to define the displacement of the Earth's crust, local displacements of the Earth's surface, and the displacement and deformation of constructed buildings. The determinations of horizontal movements in the terrestrial network, in the terrestrial altitude network and in the GNSS network are dealt with at two levels of accuracy. Geotechnical surveying activities are explained in the paper and demonstrated in the table. The paper Geodesy in geotechnics, published in Geodetski vestnik 54(1), and this paper present an integral whole

Geodesy in Geotechnics\ud

Geodetic methods are one of the possible means of determining the stability of geotechnical objects. The determination of the displacements of the geotechnical objects is specific due to the size and the expected displacements. The expected size of the displacement determines the necessary precision of the displacement determination, whereas the size of the object determines the method of the geodetic measurement. We choose either the terrestrical or the GNSS methods. There is no relevant legal framework for geotechnical measurements. For this reason, we present the characteristics of the single methods and suggest general recommendations regarding the implementation of the geodetic procedures when monitoring the displacements of the geotechnical objects. The recommendations are intended for geotechnical engineers planning the geotechnical objects and the operators of geodetic measurements and investors. The recommendations the facilitate supervision of the geotechnical projects

Statistical Properties of Strain and Rotation Tensors in Geodetic Network

This article deals with the characteristics of deformation of a body or a figure represented by discrete points of geodetic network. In each point of geodetic network kinematic quantities are considered normal strain, shear strain, and rotation. They are computed from strain and rotation tensors represented by displacement gradient matrix on the basis of known point displacement vector. Deformation analysis requires the appropriate treatment of kinematic quantities. Thus statistical properties of each quantity in a single point of geodetic network have to be known. Empirical results have shown that statistical properties are strongly related to the orientation in single point and local geometry of the geodetic network. Based on the known probability distribution of kinematic quantities the confidence areas for each quantity in a certain point can be defined. Based on this we can carry out appropriate statistical testing and decide whether the deformation of network in each point is statistically significant or not. On the other hand, we are able to ascertain the quality of the geometry of the geodetic network. The known characteristics of the probability distributions of two strain parameters and rotation in each point can serve as useful tools in the procedures of optimizing the geometry of the geodetic networks