MODA: a new algorithm to compute optical depths in multidimensional hydrodynamic simulations Albino Perego, Emanuel Gafton, Rubén Cabezón, Stephan Rosswog and Matthias Liebendörfer A&A, 568 (2014) A11 Published online: 05 August 2014 DOI: 10.1051/0004-6361/201423755