jgg     2009 29 (2):  1-3    ISSN: 0412-1961  CN: 21-1139/TG PROGRESS IN GNSS AND ITS INFLUENCE ON NAVIGATION AND POSITIONING Chen Junyong 1,2) 1)State Bureau of Surveying & Mapping, Beijing 1008302)Wuhan University, Wuhan 430079 Received: 1900-01-01  Revised: 1900-01-01  Online: null Supporting info null