Knowledge Base

Learn how to diagnose a common issue where the device is connected, but the heading, as seen by the device, differs drastically from the GNSS heading for a Dual Antenna INS.

Common Issues:

1. The antennas are connected, but the heading of the INS starts with 0 (relative heading).
2. The INS heading differs a lot from the GNSS heading.

Solution:

The INS algorithm uses dual GNSS headings for heading correction only if the dual GNSS solution is valid. A valid solution is when the “Angles position type” is satisfying. “Angles position type” is the GNSS position type used in orientation calculation using a dual GNSS receiver. “Angles position type” is satisfying when it reaches “Integer narrow-lane ambiguity solution.”

In OPVT2A output format, the ‘Angles position type’ value is located under the byte 85; in OPVT2AHR, it is under the byte 113. If this value is less than 100, please see its description in Table 6.17 of the ICD. If “Angles position type” < 100, then “INS solution status” is good. Otherwise, it is poor. The “Angles position type” can be observed in the INS GUI (when OPVT2A or OPVT2AHR output formats are used) – please see the red ellipse on the screenshots below.

To get a valid “Angle position type,” the antennas should be installed with a clear view of the sky. Also, installing the antennas as high as possible is generally recommended. In some cases, further isolating the antennas with a grounded metal plate at least 12 cm in diameter is necessary. The plate must be connected to a mass with large capacitance, like the vehicle or vessel body, to ensure that the plate is grounded.

If possible, it is recommended to use an antenna similar to that of the Novatel Pinwheel (https://novatel.com/products/antennas/high-performance-gnss-gps-antennas/gps-702-gg-hv). These antennas are much better at multi-path performance as a grounding plate is included.

Also, it is important to shield all possible sources of RF interference, including USB 3.0, as radio interference can cause severe degradation in signal quality.

Screenshot №1:

Angle pos. type = l1_float

If the angle position type is not “Integer,” the INS algorithm does not consider the dual GNSS heading. Therefore, as you can see, the GNSS heading was 62.15 deg, but the INS heading was 349.43 deg (the GNSS solution was treated as invalid) and was computed using the AHRS algorithm.