How to set reference latitude and longitude value for gps sensor

Hi, I am using gps sensor with polaris ranger model. But when I am doing gps->getLatitude and gps->getLongitude , it is giving me 0 value because of which gazebo x y coordinates are also coming wrong. Hence, I thought to set its reference latitude and longitude value. Could anyone please suggest how to set reference or default lat lon value? Any help would highly be appreciated. Thanks! sdf is: ..... 110.05.0 5.0 5.049.379.3