jgg     2012 32 (2):  47-50    ISSN: 0412-1961  CN: 21-1139/TG INFLUENCE OF GEOMETRY AND NUMBER OF IGS STATION ON PRECISE ORBIT DETERMINATION OF GPS NAVIGATION CONSTELLATION Xiao Changwei 1) ; Yuan Yunbin 1) ; Sheng Chuanzhen 2) ; Wang Yongqian 1) ; and Dong Lina 1) 1)Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077; 2)Institute of Geology, China Earthquake Administration, Beijing 100029 Received: 1900-01-01  Revised: 1900-01-01  Online: null Supporting info null