Online Positioning User Service
OPUS Upload | What is OPUS-S | Using OPUS-S | Faqs OPUS-S | Recent Solutions | What is OPUS-RS | Using OPUS-RS | Faqs OPUS-RS | Privacy Policy | OPUS Policies | Contact OPUS

Using OPUS-RS

Using OPUS-RS is similar to using regular OPUS. Almost all the guidelines for using regular OPUS apply. In particular, the sections describing the e-mail address, valid data file formats, the antenna type, and the antenna height are unchanged.

The options offered for OPUS-RS are the same as those offered for regular OPUS, except that the OPUS-RS user may select up to six reference stations.

The data file submitted to OPUS-RS may contain as little as 15 minutes of data. The maximum accepted is 4 hours of data.

There will be some data sets that will not be processed by OPUS-RS, even though they can be processed by regular OPUS. Some reasons for this are:

• OPUS-RS will not select reference stations more than 250 km from the users station (this can be overridden by user-selected stations).
• OPUS-RS applies more stingent quality control tests to the data sets from candidate reference stations. OPUS-RS requires that no more than 10% of the data during the time span of interest be missing from a reference station data set.
• OPUS-RS requires that all four observation types (L1,L2, P1 (or C1), and P2) be present at each epoch used.

The OPUS-RS Solution Report is similar to that produced by regular OPUS. The differences are:

• The software used will be some version of the rsgps program, rather than the pages program.
• The number of fixed ambiguities is not reported, since all ambiguities are always fixed by rsgps. Instead, the quality indicators from the network and rover mode solutions are reported in this part of the report.
• The overall RMS in meters is replaced with a unitless Normalized RMS. The RSGPS program uses four different observation types (L1,L2, P1 (or C1), and P2), and assigns different weights to each. See the documentation for the RSGPS program for an explanation of the weighting scheme.
• The numbers reported after the coordinates are not the peak-to-peak errors reported for regular OPUS, but are estimates of the standard deviations of the coordinates. See OPUS-RS Statistics for an explanation of the numbers.
• The number of reference stations used may be as large as six.

What to Look for.

Examine all warning messages. Warning messages are issued for:

• Quality indicators that are suspiciously low
• Normalized RMS that is suspiciously high.
• Coordinate standard deviations that are suspiciously high.

What is the accuracy of the result?

In the absense of any warning messages, the best estimates of the accuracies of the coordinates are the standard deviations reported by the single baseline analysis. Experiments at NGS indicate that the actual error is less than these estimated accuracies more than 95 percent of the time, See OPUS-RS Statistics.

What to look out for.

Since RSGPS uses the DD ionospheric delays at the reference stations to interpolate to the delays at the rover, it may not work during periods of high ionospheric disturbance. In fact, it is best to avoid performing any GPS survey during geomagnetic stgorms that cause large and variable ionospheric refraction. Geomagnetic storm alerts are issued by NOAA's Space Environment Center (http://www.sec.noaa.gov), so that the surveyor may avoid collecting data during these unusual events.

Similarly, RSGPS performs a simple geographic interpolation to predict the tropospheric delay at the rover station. Under normal conditions this works well. However, it may not work well during the passage of a strong weather front, and these situations should be avoided.

How to get a more accurate result.

Using a longer data set, such as 20 minutes, 30 minutes, or even an hour or more, will usually yield a more accurate solution.

As with regular OPUS, if you submit your data very soon after it was collected, it is possible that a predicted, rather than precise post-fit, orbit will be used to obtain your solution. The orbit source is indicated on your Solution Report. If a predicted (Ultra-Rapid) orbit was used, you may wish to resubmit your data set at a later time when a more accurate orbit is available.

Please read through each of the OPUS Help Links. It is important that you understand how to correctly submit your data and how to interpret your results. An OPUS email button is provided for any inquiries or comments that you may have.

In spite of our efforts to test OPUS-RS as thoroughly as practical, new problems will almost certainly occur. Please contact NGS with any problems you believe you see and they will be addressed as quickly as possible.

OPUS-RS, like regular OPUS, is intended for use in the conterminous U.S. and most territories. It is NGS policy to not publish geodetic coordinates outside the U.S. without the agreement of the affected countries.
See Areas Covered.