F. Flin, J.-B. Brzoska, B. Lesaffre, C. Coleou, and P. Lamboley, “COMPUTATION OF NORMAL VECTORS OF DISCRETE 3D OBJECTS: APPLICATION TO NATURAL SNOW IMAGES FROM X-RAY TOMOGRAPHY”, Image Anal Stereol, vol. 20, no. 3, pp. 187–191, May 2011, doi: 10.5566/ias.v20.p187-191.