1.1.1 Traditional geodetic methods for studying landslide processes
The use of traditional theodolite and total station measurements can achieve millimeter-scale errors when determining point coordinates (Savvaidis, 2003). Generally, a relative coordinate system is used for the survey which creates a problem when comparing such data with geo-referenced data sources. It is therefore necessary to recalculate the position of the field points to allow plotting these into the global coordinate system by specific position of the reference points (Gupta & Shukla, 2018).
The advantage of this surveying method is its high accuracy. The disadvantage is that the surveys take a long time; therefore, a limited number of points located in accessible places are selected. The development of TLS, UAVs, allowing to take large amounts of data in a short time, precisely and in detail describing the surveyed surface, makes the classical topographic survey an outdated approach (Barbarella & Fiani, 2013).
A limited control of processes operating within the landslides and the displaced ground masses are the most significant disadvantages of traditional approaches. None of these methods provides comprehensive information on quantitative characteristics and mechanism of erosion processes on slopes. Thus, the most effective methods for studying inaccessible slopes with landslides are the repeated morphological surveys with accurate referencing of multi-temporal data.