This paper presents an original method for the analysis of the geometric and optical properties of parabolic solar trough collectors using laser scanners and image processing techniques. The aim of the paper is to propose a methodology with which to automatically analyse geometric errors in the mirror and receiver, in addition to presenting an empirical assessment of one of the most important factors that determines the entire energy efficiency of solar plants, which is optical efficiency. The definition of canonical images has allowed us to characterise a set of parameters that evaluates errors on both the surface of the parabolic reflector and regarding the orientation of the receiver. In this framework, energy efficiency is established in terms of two parameters, denominated as the interception index and the concentration index. The proposed method has been tested on-site on real surfaces of parabolic solar trough collectors in an operating solar thermal plant. The results obtained are sufficiently accurate and reliable to be able to recommend that researchers and plants reproduce this method in this kind of installations. (C) 2018 Elsevier Ltd. All rights reserved.