Online Positioning User Service (OPUS) is provided by the National Oceanic and Atmospheric Administration (NOAA). With OPUS, you may accurately determine the coordinates of a static point anywhere on the territory of the United States without real-time corrections or base station nearby.
You can use OPUS with Reach RS2 and Reach M2 only. To process data from Reach RS+, use the NRCAN CSRS-PPP service. You can learn more in the PPP guide.
In this guide, we will walk you through the following steps:
- Recording RINEX data on Reach.
- Exporting raw data from ReachView 3 to your mobile device.
- Uploading the collected file to OPUS.
- Entering the obtained base coordinates into ReachView 3.
The equipment you need to accomplish the survey:
- Reach receiver
A receiver in a standalone positioning mode finds out its position relying on the data obtained from satellites only. Along with raw data, it gets navigation messages with satellite clock offset, the ionospheric and tropospheric corrections, etc. When the corrections from the base are received, these offsets are eliminated as both receivers work in the same conditions.
OPUS allows the single receiver to achieve high-level accuracy without the use of corrections from the base station. To calculate the coordinates, OPUS uses corrections from the National Spatial Reference System (NSRS). OPUS works with software that uses data from the NOAA CORS Network for computations. This network of Continuously Operating Reference Stations (CORS) provides Global Navigation Satellite System (GNSS) data consisting of carrier phase and code range measurements in support of three-dimensional positioning, meteorology, space weather, and geophysical applications.
Thereby, the Single receiver might determine its position with a centimeter-level accuracy using only its own raw data and precise ephemerides and clock offsets provided by an NSRS.
The coordinates are the average of three independent, single-baseline solutions, each computed by double-differenced carrier-phase measurements from one of three nearby CORSs.
OPUS service uses dual-frequency GPS data for solution computation and supports the Static mode only. The Static data is required to be recorded on the stationary receiver.
There are 2 ways you can process the data in OPUS:
- Static (for data that are 2 to 48 hours in duration)
- Rapid-Static (for data that are 15 minutes to 2 hours in duration)
The Static and Rapid-Static methods use different processing software and provide pretty similar horizontal accuracy. Rapid-Static processing has more strict requirements for data quality in comparison with the Static approach. Moreover, Rapid-Static processing is available only for some regions1.
This guide will show you how to process raw data from Reach RS2 using the Static method.
You can learn more about NOAA's OPUS service on their official site.
Place a Reach device precisely above the marked point on the tripod and level it. Learn more about placing Reach receiver in this guide.
To record logs for OPUS, follow the steps below:
Go to the Logging screen in ReachView 3.
Tap Settings in the Raw data section.
Select the RINEX format in the Raw data section.
If you do not know which version of RINEX you need, we recommend using RINEX 3.03. While recording in RINEX format, you can record the UBX file as a backup.
Select the preset for OPUS.
Enter the measured height to the bottom of the receiver.
Fill in the point's name in the Marker name field.
You can start recording automatically when your receiver is turned on. Check the corresponding field in the settings.
Enable log recording by tapping Start recording.
Stop log recording by tapping the End recording button.
You may log the data for up to 24 hours, depending on the accuracy required.
Once you finish the survey, don't forget to toggle off raw data recording in the Logging tab.
After you finish raw data logging, you may download RINEX data from Reach to your mobile device.
- In ReachView 3, go to the Logging tab.
- Tap on the Download button to export the file.
- Go to the NOAA's OPUS site.
- Click on the Choose file button and browse for observation data (raw*.NNO).
EML_REACH_RS2 NONEin the Antenna field.
- Type a pole height in the Antenna Height box.
- Enter your email address.
- Click on the Upload to Static button.
OPUS will send the file with the solution to your email address.
After you get the solution report, it might be useful to check how accurate the results are.
In the solution report, you will get the name of the used reference frame, the XYZ and LLH coordinates of the point, and accuracy estimation in meters. Additionally, you can check these fields: OBS USED, FIXED AMB, OVERALL RMS.
The most accurate OPUS solutions have the following characteristics:
- Over 90% of observations are used
- Over 50% of ambiguities are fixed
- Overall RMS is less than 3 cm
If you need the acquired coordinates to use them as the base position for RTK/PPK, you can now enter the base coordinated into the ReachView 3 app.
- In ReachView 3, go to the Base mode tab.
- Tap Configure.
- Set the Coordinates entry method to Manual.
- Enter the coordinates and specify the antenna height.
If you experience any difficulties during the processing or want to discuss the workflow, start a thread at the Emlid community forum.
1: About OPUS: NOAA’s National Geodatic Survey site. URL: https://www.ngs.noaa.gov/OPUS/about.jsp