Barthelmes, F. (2013): Definition of functionals of the geopotential and their calculation from spherical harmonic models: theory and formulas used by the calculation service of the International Centre for Global Earth Models (ICGEM); http://icgem.gfz-potsdam.de/ICGEM/; revised Edition, (Scientific Technical Report ; 09/02), Potsdam : Deutsches GeoForschungsZentrum GFZ, 32 p.https://doi.org/10.2312/GFZ.b103-0902-26