R. Habel, A. Neilsson, M. Wimmer:
"Level-of-Detail and Streaming Optimized Irradiance Normal Mapping";
in: "GPU Pro 2", Association of Symbolic Logic, A K Peters, Ltd., 2011, ISBN: 978-1568817187, 143 - 158.
http://publik.tuwien.ac.at/files/PubDat_200772.pdf