jgg     2008 28 (1):  96-100    ISSN: 0412-1961  CN: 21-1139/TG GPS PRECISE POINT POSITIONING MODELS AND THEIR UTILITY ANALYSIS Wu Jiangfei 1) ; and Huang Cheng 2) 1)Institute of Surveying and Mapping, PLA Information Engineering University, Zhengzhou 4500522)Shanghai Astronomical Observatory, CAS, Shanghai 200030 Received: 1900-01-01  Revised: 1900-01-01  Online: null Supporting info null