Qingtang Jiang Biorthogonal Wavelets with Six-fold axial Symmetry for Hexagonal Data and Triangle Surface Multiresolution Processing. 773-812 2011 9 Int. J. Wavelets Multiresolution Inf. Process. 5 https://doi.org/10.1142/S0219691311004316 db/journals/ijwmip/ijwmip9.html#Jiang11