BackAccuracy Explanation and Demonstrations for Geode GNS2 and GNS1
10 Apr 2020
The Juniper Geode GNS2 and GNS1 are accurate to within a 60 centimeters radius 95–98 percent of the time at 2DRMS, or twice the distance root mean square, when receiving sufficient signals from GPS satellites along with SBAS (such as WAAS) satellite. That means around 95–98 percent of the time the Geode offers better than 60-centimeter accuracy. The Geode is accurate to fewer than 30 centimeters RMS around 67 percent of the time. Though 2DRMS is a truer estimate of field performance for GPS devices.
The test criteria for the Hemisphere GNSS receivers (such as the OEM P206 receiver in the Geode) is provided on page 5 of the following technical manual. Evaluating the performance of the receiver is described on page 39.
Hemisphere GNSS Technical Reference Manual
For a more general explanation of GNSS (GPS) accuracy, see GNSS/GPS Accuracy Explained.
Demonstrations of the accuracy of the Geode are described at these web links and shown in the following video.
Geode vs. Arrow 100 vs. Trimble R1
Price versus accuracy: The Geode Sub-meter GPS Receiver hits the GPS sweet spot
The Geode Sub-meter GPS Receiver Put to the Test
Some recommended basic settings using our Geode Connect utility software for getting the most accuracy from your Geode are as follows.
- Antenna Mask Angle – Set this to 10 degrees to ensure that low angle near horizon data that can have a lot of signal delay isn’t included in the solution.
- Receiver Mode Settings –
- Mixed – This includes satellites that do not have a DGPS correction in the position solution. While this is useful for retaining a solution in environments with varied sky obstructions, this can reduce overall accuracy of the position solution. Set this to OFF (Unchecked)
- SBAS Ranging – This allows the receiver to use an SBAS satellite like a GPS satellite for purposes of tracking and setting the internal receiver clock. Confirm this is set to OFF, as the SBAS clock signal may not match the GPS clock signals and could induce some error.
- Tunnel – This allows the receiver to estimate a position for faster reacquisition when coming out of a tunnel. Set this to OFF to prevent the receiver from making incorrect position assumptions.
The following is some sample code from Geode Connect showing how EHE (Estimated Horizontal Error) is determined based on the NMEA RRE string data (or fallback to GST) from the Geode.
if (LatitudeErrorEstimation != null && LongitudeErrorEstimation != null)
{
return Math.Sqrt(Math.Pow(LongitudeErrorEstimation.Value, 2) + Math.Pow(LatitudeErrorEstimation.Value, 2));
}
The accuracy of the receiver may be artificially affected by variations in datum / projection / coordinate system.
