Interpreting OPUS-Static Results Accurately

AbstractThe Online Positioning User Service (OPUS) operated by the National Geodetic Survey (NGS) has consolidated into a very attractive tool for surveyors, engineers, and the academic community to procure precise/accurate positions from global positioning system (GPS) observations. The OPUS utility continues to be improved since it was successfully launched in 2000. In general, each update results in better reliability of the precision and accuracy of OPUS solutions. However, necessary software modifications could also introduce certain biases, some significant, complicating the interpretation of OPUS results, particularly for applications that rely on high-accuracy absolute positions. This article concentrates on the interpretation of OPUS-Static solution reports primarily in relation to the transformation of reference frames and geoid models, which are two basic scientific ingredients in practical geodetic-surveying enterprises. One-year continuous GPS observations collected at a landslide site in Pue...