Improving your OPUS results:

Follow these guidelines to improve the quality of your OPUS solution:

• Observe longer: A longer session provides OPUS a better opportunity to accurately fix ambiguities and mitigate multipath error. The figure below shows the correlation between session duration and accuracy. Please note: this figure is a result of a published regional study, and the performance of OPUS may be slightly better or worse in your geographic location. For details on this regional study, see Gillins, D.T., Kerr, D., and Weaver, B. (2019). "Evaluation of the Online Positioning User Service for Processing Static GPS Surveys: OPUS-Projects, OPUS-S, OPUS-Net, and OPUS-RS," ASCE Journal of Surveying Engineering, 145(3): 05019002.

• Observe again: A second independent observation which yields a similar solution is an easy way to increase confidence in your results. To maximize independence between observations:
  • Use a different observer
  • Use different equipment
  • Observe on a different day, at a different time of day


• Wait a day before submitting your file: OPUS will use the best CORS and orbits available at the time you upload your data. While most CORS are archived within 30-minutes past the hour, some aren't available until the next day. If you process your data in less than 24 hours after collection, OPUS will use Ultra-Rapid orbits. Rapid orbits, available at 17:00 UTC the next day, will offer a slight improvement in your accuracy. Final orbits, available weeks later, offer only slight benefit to solutions in areas with usable CORS nearby.

What does a quality solution look like?

The most accurate OPUS solutions have the following characteristics:

• Orbits used are precise or rapid
• Over 90% of observations are used
• Over 50% of ambiguities are fixed
• The correct antenna type and ARP height are entered
• For OPUS-S:
  • Overall RMS is less than 3 cm
  • Peak-to-peak errors are less than 5 cm
• For OPUS-RS: the solution contains no warning messages

Please note: OPUS-RS may perform poorly or fail during periods of high ionospheric disturbance or during the passage of a strong weather front. In general, it is best to avoid collecting GPS data during these events. To avoid collecting data during a geomagnetic storm, see NOAA's Space Weather Prediction Center, which issues geomagnetic storm alerts.