The goal of this project is to develop, prototype, and experimentally validate a new Differential Global Navigation Satellite System (DGNSS) capable of providing sub-centimeter positioning accuracy for quasi-static scientific, survey, and structural health monitoring application. The main feature of the proposed DGNSS solution is that it leverages publically available GNSS reference data from existing NOAAs Continuously Operational Reference Stations (CORS). Customized GNSS reference receiver networks or subscription services are not needed. Advanced filtering algorithms and error modeling techniques are developed to provide reliable and economical sub-centimeter accuracy for a variety of static and quasi-static scientific and commercial application. In Phase-II, TruNav will develop and implement new algorithms to make the system more robust to data outages, erroneous data, and even measurement faults. Positioning accuracy in kinematic applications will also be improved using advanced modeling and estimation techniques.