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

Metode odkrivanja grobih pogreškov v geodetskih opazovanjih : Methods of Gross Error Detection in Geodetic Observations

The article describes three methods of gross error detection and their localization in geodetic surveying. The prerequisite for any gross error detection procedure is the availability of a set of redundant observations. The global model test with Data Snooping is the most commonly used method for gross error detection, however, it assumes that the a priori precision of observations is reliably known. As alternatives, the τ test and the Danish method are presented. An example of gross error detection in a plane cross-braced quadrilateral is given for all three methods

Determination of point displacements in the geodetic network

This paper describes the procedure for testing the statistical significance of point displacements in the geodetic network as the intermediate stage between the adjustment of respective epochs measurements and an in-depth deformation analysis. The cumulative distribution function of the test statistic, presenting the relation between the displacement and the displacement accuracy, is determined by simulations. On the basis of this cumulative distribution function a critical value of the test statistic for a selected significance level is determined. In the null hypothesis it is assumed that the point is stable. A comparison of the critical value to the test statistic value is made and the actual risk level for rejecting the null hypothesis is estimated. Further on, a practical example of implementing the test in a simulated network is given. The test statistic proved to be simple and applicable: The points with significant displacements were identified successfully

GPS Network Novo Mesto

Na području općine Novo Mesto obavljena su GPS mjerenja na devet točaka radi određivanja okvira veće popunjavajuće mreže na tom području. Prikazano je planiranje opažanja s većim brojem prijamnika. Težište članka je na izjednačenju mreže na Basselovom elipsoidu i Helmertovoj transformaciji dobivenih rezultata u ravninu Gauss-Krügerove projekcije.The GPS measurements for establishing a densification network Novo Mesto is being discussed. After consideration of some aspects of planning and performing GPS measurements, the focus has been put on adjustment of the network on the Bessel ellipsoid and the transformation of the results into the local two-dimensional reference frame

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