Due to all these factors and reasons, this field has received a growing attention in the last few
years. In order to be able to reach the safety of these structures, many instruments and surveying
methods have been used. However, the main aim in most of the plans developed has been the
possibility of measuring displacements in a singular number of points. The difficulty in the
measurement of these displacements is to find a spatial measurement technique that
encompasses numerous desirable properties, such as precision, reliability, low cost and easy to
use. Some of these advantages can be seen in several methods, but it is really hard to find a method comprising all of them. In the next paragraphs some of the approaches developed in this
context are reported (starting with the classical techniques and finishing with the new
technologies)