jgg     2014 34 (1):  72-77    ISSN: 0412-1961  CN: 21-1139/TG FREE STATION ESTABLISHMENT WITH HIGH PRECISION IMS  BASED ON VARIANCE COMPONENT ESTIMATION College of Surveying and Geo-informatics, Tongji University, Shanghai 200092 Received: 2013-07-11  Revised: null  Online: 2014-01-23 Supporting info