As European Union member states -Latvia and Lithuania have changed their national height systems from Baltic Normal Height System 1977 to European Vertical Reference System realizations. Performing practical Global Navigation Satellite System (GNSS) measurements and obtained data mathematical processing, there is a possibility to calculate point height difference between GNSS data and data of 1 st order levelling networks. The aim of the research is to gain insight for methodology development of geodetic point height testing using GNSS measurements. To achieve the goal following tasks are set: 1) perform GNSS measurements of first order levelling network in Latvia and Lithuania; 2) do data processing to get point ellipsoidal height and compare with the point normal height; 3) detect technically feasible accuracy of geoid model for precise height measurements with GNSS method within research area. Performing GNSS measurements at the same time in the territory of Latvia and Lithuania, the experience of mutual cross-border cooperation was accumulated. The results were adjusted with academic software package Bernese and were obtained point ellipsoidal and normal heights. The height measurement accuracy using GNSS method depends on geoid model accuracy and more precise results can be obtained increasing used geoid model accuracy to 1.5 to 2 cm.
Local geodetic network is very important in harmonic development of city territory. On the base of the local geodetic network, cadastral and topographic surveying works, engineering geodetic works and executive measurements of newly built buildings and engineering networks are carried out. In the territory of Riga, the local geodetic network was started to create in 1880, and in the course of time, as the city expanded, necessity to have wider reference network emerged. In 2005, in the territory of Latvia, network of continuously working base stations LatPos was launched, which ensured completely new trends in execution of measurements and accuracy reached. One year later, base station network EUPOS-RIGA was launched in the territory of Riga. It can be regarded as consistent part of Riga local geodetic network. The purpose of the research was to state, what are differences between historically used coordinates of points of the local geodetic network, and coordinates that are determined by use of real time corrections of LatPos and EUPOS-RIGA base station network. Measurements were made in the territory of Riga in period from December 2016 until April 2017. In the framework of the research, 61 point of the local geodetic network was inspected and in 38 cases GNSS observations in RTK mode were completed. In the research, catalogues of coordinates of polygonometry points of sixties and eighties were used in order to compare what differences of coordinates existed historically. The main conclusion drawn during the research – historical points of the local geodetic network shall not be used for surveying works of any kind before improvement of them and before they comply with requirements of normative acts.
In the study, creation of 3D surface relief model in Jelgava, for southern part of the Castle Island is depicted. Information about remote sensing, its historical development, as well as directions of remote sensing, development of photogrammetry and laser scanning is summarized and analysed. Principles of work and methods of photogrammetry and laser scanning. Information about creation of surface relief model from planning of unmanned aircraft, data capture and alignment to the end product – surface relief model. Application of evaluation of data obtained. The purpose of the study – to create 3D surface relief model in Jelgava, for the southern part of the Castle Island. Tasks of the study – to consider development and improvement of photogrammetry and its processes, as well as development of laser scanning and principles of its work; to research, analyse and describe technological processes of laser scanning; to create 3D surface relief model in Jelgava, for the southern part of the Castle Island; to perform comparison of surface models obtained and describe application of laser scanning. Preparation of surface relief model is time-consuming process, which includes flight planning and preparation of end-product. End-products obtained in data processing of laser scanning have very broad usage in many sectors related to geodesy and construction.
Nowadays, various types of geodetic measuring instruments are available in surveying. When conducting a survey of a terrain, surveyor must choose a survey method that is capable of providing high precision measurements. In the surveying process, it is possible to use the following measurement methods - tachymetric survey method, positioning method and remote sensing method. Each of the methods produces data formats that can be used further for volume calculations. The paper analyses the volume differences that are obtained when using various survey methods and volume calculation programs to obtain the surface model. The use of such a tool is important for useful mineral miners, so that surveyors make qualitative surveys and obtain accurate and reliable volumes. Useful minerals miners are required to report annually on their mining volume for a specified period. The useful minerals miners shall at all times keep records of the quantities of minerals actually extracted. Regardless of the type of accounting, topographic surveying and the calculation of volumes, if mineral is extracted in mineral deposits of national importance, more than 50 000 m3, are required (Augstas detalizācijas topogrāfiskās…, 2012). High-quality and accurate topographic survey is needed to create the most realistic surface model appropriate to the terrain. It is defined that the difference between the volumes obtained from the recording of vehicle loads should not be more than 5% when comparing the result of the mineral extraction from topographic surveys (Derīgo izrakteņu ieguves…, 2012; Noteikumi par valsts…, 2018). Nowadays, various measurement methods can be used to obtain data from which a surface model can be generated, and this model can then be used for volume calculations. The surface model is a set of points where, in addition to plane coordinates (x and y), there is also altitude (z) known (Luukkonen, 2011). Each measurement method has its own different measuring instruments that can be used, each method has its own operating principles, on which the quality and accuracy of the obtained data depends.
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