What is the difference between the PS Technique and optical levelling?
Optical levelling data can be extremely accurate in vertical direction (up to a fraction of millimetre), but errors are integrated while more and more measurements are carried out. Thus the final accuracy strongly depends on the number of benchmarks, their reciprocal distances, and very often on the logistic conditions of the surveying as well. Moreover 3-4 people are necessary for accurate optical levelling surveys. Optical levelling data are much more precise in vertical direction with respect to GPS surveys, but small horizontal displacements of the benchmarks are usually not measured. In any case, it is easy to compare PS data and optical surveying in a GIS environment, possibly supposing that target motion is merely vertical. On the other hand, whenever deformation data are not full 3D, it will not be possible a quantitative and rigorous analysis.
