Troubleshooting: “WARNING: Continuous primary GNSS position measurement rejections”

📌 Problem

Trajectory Processing that uses the Applanix GNSS Post Processing engine fails with the warning “Continuous primary GNSS position measurement rejections” in your fwdproc_Mission 1.log file.

🔍 Root Cause

This warning appears in Applanix IINPP forward processing logs (e.g., fwdproc_Mission 1.log) when the navigator rejects GNSS measurements almost continuously. It indicates a mismatch or quality issue in the GNSS/IMU integration process. This typically means the system is unable to obtain reliable GNSS data for trajectory processing.

Common Causes

1. Incorrect Lever Arm Values
   • Mismatch between physical rig and configuration (Reference → Primary GNSS lever arm).
   • Wrong sign convention or axis definition.
2. Antenna Phase Center Errors
   • Incorrect antenna type or APC model.
   • Wrong antenna height or radome settings.
3. Poor Base Station Data
   • Missing observations, cycle slips, or excessive baseline length (>15–20 km).
   • The base station coordinate may be entered incorrectly (wrong format, swapped lat/lon, or incorrect sign).
   • The base station RINEX file may lack observations during the flight period, possibly due to storage issues or data loss.
   • Bad ephemeris information from one or more satellites (e.g., GLONASS) can cause the solution to fail​.
   • Multipath, low SNR, or cycle slips due to environment (trees, structures).
4. Logging Anomalies
   • Manual start/stop, heading alignment maneuvers (HAM), or proximity mode artifacts causing anomalies.

🔍How to Diagnose

• ❗Run a QC-Only (Realtime) trajectory processing to isolate whether the problem is with the rover or base station data. This can help determine if a repeat flight or data correction is necessary​.
• Check the top of the log for:
  • Reference → Primary GNSS lever arm values.
  • Vehicle → Reference alignment angles.
• Look for preceding messages like:
  • “WL ambiguity failure”
  • “Degraded navigation”
• Inspect base RINEX quality and baseline length.
• Confirm antenna model and APC settings in POSPac Cloud.

✅ Probable Resolutions

1. Correct Lever Arm Values

• Compare log values with actual payload/APX install. 
  • Review the Reference to primary GNSS lever arm values listed in the Rover Data Summary and GNSS-Inertial Processor Configuration sections. Note those lever arm values are in meters. If the values are incorrect, you will need to fix those in the APX before you fly again. See Measuring GNSS Lever Arm Offsets in the True View 410 Hardware Users Guide.
• Use Lever Arm Offset Override in LP360 Trajectory Processing:
  • Navigate to Advanced → Lever Arm Offset Override.
  • Enter correct X, Y, Z offsets (in APX convention).

2. Validate Antenna Settings

• Ensure correct antenna type and APC model is displayed on the Base Settings page.
• Reprocess with accurate antenna parameters.

3. Improve Base Data

• Use a short, high-quality base (<15 km).
• If unavailable, consider using PP-RTX.
• Verify that your rover and base station files cover the entire flight period and are not empty or corrupted.
• Check that the base station coordinates are entered in the correct format and they Survey Nail / Reference Mark is entered using an ellipsoidal elevation.
• If using All Constellations, check for satellite issues or try processing without data from some of the constellations.

4. Handle Logging Issues

• Trim mission time window to valid intervals.
• Re-import cycles if early termination warnings appear.

✓ Quick Checklist

• [ ] Lever arm values match rig and APX convention.
• [ ] Antenna model and APC settings verified.
• [ ] Base station data quality confirmed.
• [ ] GNSS settings optimized for environment.
• [ ] IMU alignment angles correct.
• [ ] Mission log intervals validated.

📬 Need Help?

If you're still stuck, please Contact Support for assistance.