jgg     2013 33 (5):  25-28    ISSN: 0412-1961  CN: 21-1139/TG CHOICE AND ACCURACY ANALYSIS OF OPTIMAL EARTH GRAVITY  FIELD MODEL IN GUANGDONG REGION Surveying and Mapping Institute Lands and Resource Department of Guangdong Province, Guangzhou 510500 Received: 2013-05-21  Revised: null  Online: 2013-10-13 Supporting info