[1] ZOU X Y, SUN Q, CHEN J B, et al. A north-finder algorithm and its signal processing[J]. Transactions of Beijing Institute of Technology, 2004, 24(9): 804-807.
[2] WETHERELT A, HUNT P. Underground azimuth determinations using an adapted wild GAK1[C]//FIG XXII International Congress. Washington, D. C, USA: 2002: 4-15.