Gnss-assisted trigonometric leveling and valley crossing leveling

Nowadays, the determination of point elevations is one of the essential areas of surveying engineering in both engineering applications and scientific studies. Point elevations are commonly determined using geometric leveling, trigonometric leveling, and GNSS leveling techniques, each of which has its own advantages and limitations. Among these methods, geometric leveling is the most widely applied technique; however, it becomes difficult and time-consuming to implement, particularly in wide-span and deep valleys as well as in river crossings. Owing to recent technological developments, high-precision Total Stations capable of accurate angle and distance measurements, together with GNSS technology, have brought trigonometric leveling back into focus as a potential alternative. In this study, the applicability of GNSS-supported trigonometric leveling as an alternative to geometric leveling is investigated. For this purpose, a test area consisting of three points with different inter-point distances was established, and height differences obtained using GNSS-supported trigonometric leveling were compared with those derived from geometric leveling. The results indicate that, for trigonometric leveling carried out using a Total Station, the maximum error was -4.86 cm, the minimum error was -0.5 cm, and the mean absolute error was -2.49 cm. In contrast, for GNSS-supported trigonometric leveling based on baseline lengths obtained from GNSS solutions, the maximum error was -4.92 cm, the minimum error was -0.4 cm, and the mean absolute error was -2.52 cm. Comparative analyses of the A–B, B–C, and A–C lines demonstrate that the level of agreement with geometric leveling depends on line length. While the short B–C line (approximately 100 m) exhibited a high level of agreement, the medium-length A–C line (approximately 1400 m) also showed high consistency with geometric leveling, whereas the long A–B line (approximately 1500 m) produced results with acceptable accuracy.