Evaluation of the Online Positioning User Service for Processing Static GPS Surveys: OPUS-Projects, OPUS-S, OPUS-Net, and OPUS-RS

The National Geodetic Survey has developed four versions of the online positioning user service (OPUS) for postprocessing dual-frequency, static global positioning system (GPS) data. Each version was designed for a different application and outputs coordinates at a mark to varying accuracy. To compare the accuracy of these four versions, 88 10-h-duration GPS data files collected on 18 marks in Oregon were processed in OPUS-Projects, producing horizontal coordinates and ellipsoid heights at these marks with an estimated network accuracy of less than 0.5 and 1.3 cm at 95% confidence, respectively. Then, these data files were windowed into sessions ranging from 20 min to 10 h in duration. The windowed files were processed in OPUS-static (OPUS-S), OPUS-Net, and OPUS-rapid static (OPUS-RS), and the resulting coordinates at each mark were compared with the coordinates from OPUS-Projects. At a session duration of 2 h, OPUS-RS was found to be more accurate than both OPUS-S and OPUS-Net. For sessions less than 2 h, OPUS-RS frequently produced poor solutions with error messages. At a session duration of 4 h, OPUS-S and OPUS-Net produced coordinates with both horizontal and ellipsoid height errors less than 3 cm at 95% confidence.