This paper presents a novel methodology to find out canting errors in the facets, i.e. mirror modules, of heliostats. An optimization procedure is established to fit simulated heliostat flux distributions to those captured on a white target. On the basis of a convolution-projection optical model, a deterministic algorithm - named DIRECT - has been successfully implemented, reaching correlation coefficients up to 95.8%. In this instance, the procedure has been applied to a THEMIS heliostat presenting canting errors of its, faceted modules. From the optimization results, the heliostat modules were accordingly readjusted. And the heliostat optical quality has been significantly increased, validating the proposed methodology. (C) 2017 Elsevier Ltd. All rights reserved.