The quality of determining the point position with GNSS is influenced by several factors; one of them is a tropospheric refraction, which represents the delay of the GNSS signal in the troposphere. To remove the influence, a number of tropospheric refractive models have been developed. Their main problem is modeling the content of the water vapor in the atmosphere, since it changes constantly in time and space. In the lowest layer of the troposphere, water vapor can condense into the fog. The aim of the graduation thesis is to determine whether this meteorological phenomenon significantly affects the quality of the relative positioning with GNSS. For this purpose, we analyzed 10-day observations of GNSS from three constantly operating stations located in the Ljubljana basin, where fog often occurs, using the Leica Infinity program. The final result was the coordinates of two new points, which were determined by the radial processing. The influence of the fog was estimated basing on the comparison of the calculated coordinate differences for each point. The results show that the fog presence does not significantly affect the quality of the relative positioning with GNSS.