Between 1906 and 1908 Roland (Loránd) Eötvös and his colleagues Dezső Pekár and Jenő Fekete made measurements with revolutionary precision (the EPF measurement) for validating the equivalence of gravitational and inertial mass. Almost 80 years later, in 1986, Ephraim Fischbach and his colleagues reanalyzed the results of the EPF measurement and discovered a correlation between the small violations and some atomic parameter. Finally they were unable to reproduce this correlation experimentally, but there is still no valid explanation of these differences in the EPF results. Our analysis of the EPF experiment pointed to a possible bias that justifies repeating the tests under better conditions and using modern new technology. Planning and preliminary measurements started at July of 2017. Participants are from Wigner Research Centre for Physics of the Hungarian Academy of Sciences, Department of Geodesy and Surveying of Budapest University of Technology and Economics (BME), Society for the Unity of Science and Technology (SUST), and the Department of Control Engineering and Information Technology of BME in cooperation with other organizations, departments and experts. After more than one year of thoughtful preparation, in December 2018 preliminary tests have been started in a controlled and undisturbed environment of the Jánossy Underground Physics Laboratory at KFKI, 30 meters below ground level. This paper gives a brief overview of the basic physics, history, preparations and present status of the new experiments. Another good reason for repeating the EPF measurements is that 2019 – as the 100th anniversary of Eötvös’s death – is referred as “Eötvös year”.

Preparations of remeasurement of the Eötvös-Pekár-Fekete (EPF) experiment for the Weak Equivalence Principle were reported in [4]. Here we give a brief overview of the gravity field bias and try to estimate its possible effect on the EPF experiment. We report our first test results in the solar gravity field with Cu-Au and Al-Au pairs. The estimated errors were at level 2·10⁻⁹, the same accuracy that was obtained by EPF. We also found that angular positions of the balances showed good correlation with bandpass-filtered air pressure variations hence Wiener filtering may significantly reduce this correlated noise. We did not detect any deviation from the equivalence principle considering the estimated measurement error.

Ulyxes is an open source project to drive robotic total stations as well as other sensors, collect their measurements in database and finally publish the results for authorized users on the web. On special requests the results are also presented with web based maps in the background. This project is like an instant coffee: three in one (coffee, sugar and milk). The coffee and the strongest part is the research and coding. The sugar is the application of the program in industrial environment and the milk on the top is the educational usage. The software development started in 2008 connected to a monitoring task in the Hungarian Nuclear Power Plant. Since then the development has been extended from total stations to different positioning capable sensors. In 2012 the development of a new Python based object oriented framework started. The code is based on the results of some other open source projects, Python, PySerial, GNUGama, SQLite, OpenCV, etc. After connecting to the international Geo4All network in 2014, Ulyxes became a project of our Geo4All Lab. The project has its own home page (http://www.agt.bme.hu/ulyxes) and the source code is available on the GitHub portal (https://github.com/zsiki/ulyxes). The code is maintained by the colleagues at the Department of Geodesy and Surveying at the Budapest University of Technology, volunteers from all over the World are welcome. BSc and MSc students are also involved in the development and testing. More theses were connected to this project in the recent five years. In the curriculum of an MSc subject called Surveying Automation, Ulyxes is used to demonstrate automatized tasks in engineering surveying. The system has been applied for several projects during the last 10+ years. Typical applications are the load tests of bridges and other engineering structures and on the other hand Ulyxes can be used to monitor the movements of buildings in the nearby of constructional works, like metro stations, underground garage and other buildings as well. Raspberry Pi small, single board computers are used with Raspbian operating system during on-site works. The source code is divided into three parts. The first one is the Ulyxes API which is the core of the system. The second one, Ulyxes Apps is a collection of applications based upon the API. Some of them were developed by our students. The third part is the server side scripts to publish observation results through the Internet. Moreover it is also planned to implement SOS standard using IstSOS. Our Geo4All Lab maintains another open source software, called GeoEasy to process observation data in engineering and land surveying. A closer cooperation is also planned between our two open source projects. In this paper the most important features of Ulyxes will be presented with examples, an actual monitoring project in Budapest and test loads of bridges and overpasses.

The effect of the construction of the 4th subway line of Budapest (Metro4) on the potential surfaces of the gravity field has been investigated from the aspects of monitoring vertical deformation. In the study mass loss due to the excavation of the two tunnels and of the stations has been considered. Practically, the effect of the mass loss on leveling measurements was determined at a level 1m above the ground, roughly simulating common instrument heights. The indirect effect of the actual deformations of the physical surface on the leveling was not considered, so in the investigation a rigid Earth has been assumed. In the study, different arrangements of the leveling lines and of the excavations were examined, furthermore, the steepness of the leveling line and the density of the leveling points were analyzed. According to the results, under certain arrangements of the leveling line, the effect can reach the 0.05mm order of magnitude, which is equivalent to the accuracy of the precise leveling.

After more than 40 years of interruption new field observations have been made by an E-54 type torsion balance (TB)in the Csepel-island. These TB measurements were accompanied by a detailed gravimetric survey of each station with LCR gravimeters. Both vertical (VG) and horizontal (HG) gravity gradients were determined at each TB station for VG interpolation and reliability tests.Vertical gradient of gravity cannot be measured directly by the Eotvos TB. However we successfully interpolated VG differences in the network of TB measurements following the idea originally due to Haalck Reliability tests by comparing HG and VG gravimetric and TB measurements were also performed. Our recent paper discusses first results of these TB and gravimetric measurements which are scheduled to be continued in the future as well.