Assessment and mitigation of the risk induced by landslide activation need an appropriate phenomenon investigation, to obtain useful information about the failure processes. The first step is the complete kinematics characterization of the landslide ground surface, evaluating the involved displacement and deformation patterns. A dense displacement field can be obtained from comparison of a series of multi-temporal observations performed by means of terrestrial laser scanning. Subsequently, the strain field can be computed starting from displacement vectors. In this paper, a modified least square technique is considered to compute the strain on the nodes of a regular grid (2D approach) or on the points of a digital terrain model (3D approach). Such a computation takes into account the displacements, their spatial distribution, as well as the measurement and modelling errors. A scale factor is introduced in order to emphasize the contributions of the experimental points on the basis of their distance from each computation point, and to recognize possible scale depending behaviours. This method has been implemented in Matlab and applied on two landslides located in the northeastern Italian Alps (Lamosano and Perarolo di Cadore). The experiments show that different kinematics can be recognized and the presence and the influence of eventual discontinuities can be revealed.