“…Some previous efforts have solved the singularity problem of SHEs of gravitational field elements (Balmino et al, 1990;Bettadpur, 1995;Casotto & Fantino, 2007;Eshagh, 2008Eshagh, , 2009Eshagh & Sjöberg, 2009;Hotine & Morrison, 1969;Ilk, 1983;Liu et al, 2010Liu et al, , 2013Petrovskaya & Vershkov, 2006, 2008Wan, 2011;Zhu et al, 2017), whereas the same problem still exists in GVs and GGTs. The reason is that the gravitational field elements are expressed by fully normalized associated Legendre function (FNALF) (Chen et al, 2006;Fantino & Casotto, 2009;Fukushima, 2012aFukushima, , 2012bHirt et al, 2010;Jekeli & Lee, 2007;Liu et al, 2012;Pail et al, 2011;Pavlis et al, 2012;Rummel et al, 2011;Wan & Yu, 2013;Šprlák & Novák, 2017), while the GVs and GGTs are expressed by Schmidt semi-normalized associated Legendre function (SNALF) (Barraclough, 1974;Benton et al, 1982;Blakely, 1995;Chambodut et al, 2005;Du et al, 2015;Hemant & Maus, 2005;Huang et al, 2011;Kim et al, 2007;Kotsiaros & Olsen, 2012;Langel, 1987;Liu et al, 2019;Malin & Pocock, 1969;Quinn et ...…”