Impact of Perspective Distortion on the Accuracy of Digital Level Measurements: Experimental and Modeling Insights

Accurate geodetic leveling is critical for monitoring structural deformations and ensuring engineering safety. Digital levels have improved the efficiency and precision of such measurements; however, their accuracy can be influenced by geometric factors, particularly the rotation of bar-coded leveling rods. This study investigates the impact of rod rotation on measurement accuracy using the Sokkia SDL30 digital level. Two experimental setups were implemented: (1) rotating the rod at fixed distances and (2) moving the level along radial arcs with static rods. Measurements were conducted at distances of 2, 4, 6, and 8 meters, with readings taken at incremental rotation angles of up to ±75°.

The results revealed a nonlinear relationship between rod rotation and reading errors, with cubic polynomial models providing the most accurate approximations (R² = 0.79–0.97). Errors increased sharply at shorter distances (2–4 m) due to stronger perspective distortions, while at longer distances (6–8 m), the error trends became asymmetric, indicating complex interactions between projection geometry and the internal image-processing algorithms of the digital level.

The study identifies a 4-meter distance as optimal for calibration and modeling, with minimal distortion observed at rotation angles below 60°. These findings support the development of adaptive correction algorithms based on rod orientation and distance, improving the reliability of high-precision leveling under field conditions. The results are valuable for both practitioners seeking to optimize field procedures and manufacturers aiming to enhance internal compensation algorithms in digital leveling instruments.